Phylogeography and epifauna of two intertidal seaweeds on the coast of South Africa
- Authors: Mmonwa, Lucas Kolobe
- Date: 2009
- Subjects: Phylogeography -- South Africa , Marine algae -- South Africa , Red algae -- South Africa , Gelidium -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5738 , http://hdl.handle.net/10962/d1005424 , Phylogeography -- South Africa , Marine algae -- South Africa , Red algae -- South Africa , Gelidium -- South Africa
- Description: Southern African biogeographic boundaries delimit the phylogeographic distribution of some coastal and estuarine invertebrates. This study investigated the impact of these boundaries on the phylogeographic distribution of two intertidal red seaweeds, Gelidium pristoides and Hypnea spicifera using the mitochondrial Cox2-3 spacer and the nuclear ITS1 regions. G. pristoides spores have short distance-dispersal, while long distance-dispersal is more likely in H. spicifera via spores and drifting fertile thallus fragments. Both markers revealed a south-western and south-eastern lineage within G. pristoides but the breaks between lineages do not coincide with any recognised biogeographic limits. The Cox2-3 spacer revealed a boundary between the two lineages at the Alexandria Coastal Dunefield (ACD) and ITS1 at the Gamtoos-Van Stadens Dunefields (GVD) which is approximately 80km west of the ACD. The minor difference between the two markers regarding location of the phylogeographic boundary is probably due to the dating differences between the two dunefields. The ACD as developed currently is superimposed on the ancient dunefields which formed during the Pleistocene, coinciding with the Cox2-3 spacer sequences divergence which dates back 500,000 - 580,000 years. The GVD formed during the Holocene (6,500 - 4,000 years ago), coinciding with the ITS1 sequences divergence which dates 4,224 - 4,928 years ago. Thus, these phylogeographic boundaries probably appeared without the influence of biogeographic boundaries, but rather due to the lack of suitable habitat in the dunefields, coupled with short dispersal-distances of the spores. Analysis of the ITS1 and Cox2-3 spacer regions in H. spicifera revealed that the species is characterized by uniform genetic structure along the coastline. This reflects the species`s potential for long range expansion as it inhabits both the intertidal and subtidal zones; and this presumably leads to high gene flow among populations. The ITS1 sequences showed minimal genetic variation of one substitution between the gametophyte and tetrasporophyte generations within H. spicifera. This suggests the predominance of asexual reproduction, which reduces gene flow and fixes alleles between generations. ANOSIM and Bray-Curtis cluster analyses showed scale-dependant variation in the abundances of epifauna (mainly amphipod, isopod, mollusc and polychaete species) on G. pristoides. At small local (within site) and large (among sites) scales, there were weak and no structure in epifaunal abundances respectively. However, at larger, biogeographic scales, samples from the same biogeographic region tended to be clustered together. Thus, there was a group containing predominantly south coast samples and a group containing east coast samples mixed with the remaining south coast samples. Such scale-dependant variation in epifaunal abundances is probably due to the effects of factors driving species richness at small local (within site) scales (e.g. wave exposure, seaweed biomass) and at larger, biogeographic scales (e.g. surface sea temperature). Moreover, at very small (individual samples) scales; there was no correlation between epifauna composition and genotype of the seaweed. Seaweed samples characterized by distinct ITS1 or Cox2-3 spacer sequences did not show any significant differences in epifaunal composition. Although the distributional pattern of the epifaunal community observed at large biogeographic scale is not clear, it seems to be associated with the biogeographic regions. However, phylogeographic distribution of Gelidium pristoides is not connected to biogeographic regions. Thus, at larger, biogeographic scales, there is no correlation between phylogeographic distribution of G. pristoides and distribution of the associated fauna
- Full Text:
- Date Issued: 2009
- Authors: Mmonwa, Lucas Kolobe
- Date: 2009
- Subjects: Phylogeography -- South Africa , Marine algae -- South Africa , Red algae -- South Africa , Gelidium -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5738 , http://hdl.handle.net/10962/d1005424 , Phylogeography -- South Africa , Marine algae -- South Africa , Red algae -- South Africa , Gelidium -- South Africa
- Description: Southern African biogeographic boundaries delimit the phylogeographic distribution of some coastal and estuarine invertebrates. This study investigated the impact of these boundaries on the phylogeographic distribution of two intertidal red seaweeds, Gelidium pristoides and Hypnea spicifera using the mitochondrial Cox2-3 spacer and the nuclear ITS1 regions. G. pristoides spores have short distance-dispersal, while long distance-dispersal is more likely in H. spicifera via spores and drifting fertile thallus fragments. Both markers revealed a south-western and south-eastern lineage within G. pristoides but the breaks between lineages do not coincide with any recognised biogeographic limits. The Cox2-3 spacer revealed a boundary between the two lineages at the Alexandria Coastal Dunefield (ACD) and ITS1 at the Gamtoos-Van Stadens Dunefields (GVD) which is approximately 80km west of the ACD. The minor difference between the two markers regarding location of the phylogeographic boundary is probably due to the dating differences between the two dunefields. The ACD as developed currently is superimposed on the ancient dunefields which formed during the Pleistocene, coinciding with the Cox2-3 spacer sequences divergence which dates back 500,000 - 580,000 years. The GVD formed during the Holocene (6,500 - 4,000 years ago), coinciding with the ITS1 sequences divergence which dates 4,224 - 4,928 years ago. Thus, these phylogeographic boundaries probably appeared without the influence of biogeographic boundaries, but rather due to the lack of suitable habitat in the dunefields, coupled with short dispersal-distances of the spores. Analysis of the ITS1 and Cox2-3 spacer regions in H. spicifera revealed that the species is characterized by uniform genetic structure along the coastline. This reflects the species`s potential for long range expansion as it inhabits both the intertidal and subtidal zones; and this presumably leads to high gene flow among populations. The ITS1 sequences showed minimal genetic variation of one substitution between the gametophyte and tetrasporophyte generations within H. spicifera. This suggests the predominance of asexual reproduction, which reduces gene flow and fixes alleles between generations. ANOSIM and Bray-Curtis cluster analyses showed scale-dependant variation in the abundances of epifauna (mainly amphipod, isopod, mollusc and polychaete species) on G. pristoides. At small local (within site) and large (among sites) scales, there were weak and no structure in epifaunal abundances respectively. However, at larger, biogeographic scales, samples from the same biogeographic region tended to be clustered together. Thus, there was a group containing predominantly south coast samples and a group containing east coast samples mixed with the remaining south coast samples. Such scale-dependant variation in epifaunal abundances is probably due to the effects of factors driving species richness at small local (within site) scales (e.g. wave exposure, seaweed biomass) and at larger, biogeographic scales (e.g. surface sea temperature). Moreover, at very small (individual samples) scales; there was no correlation between epifauna composition and genotype of the seaweed. Seaweed samples characterized by distinct ITS1 or Cox2-3 spacer sequences did not show any significant differences in epifaunal composition. Although the distributional pattern of the epifaunal community observed at large biogeographic scale is not clear, it seems to be associated with the biogeographic regions. However, phylogeographic distribution of Gelidium pristoides is not connected to biogeographic regions. Thus, at larger, biogeographic scales, there is no correlation between phylogeographic distribution of G. pristoides and distribution of the associated fauna
- Full Text:
- Date Issued: 2009
The ichthyofauna associated with Taylor's salt marsh, Kariega estuary (Eastern Cape), South Africa
- Authors: Booth, Tara Loren
- Date: 2009
- Subjects: Fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Salt marsh animals -- South Africa -- Eastern Cape , Eelgrass -- South Africa -- Eastern Cape , Gray mullets -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5710 , http://hdl.handle.net/10962/d1005396 , Fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Salt marsh animals -- South Africa -- Eastern Cape , Eelgrass -- South Africa -- Eastern Cape , Gray mullets -- South Africa -- Eastern Cape
- Description: The spatial and temporal patterns in the ichthyofaunal community composition and structure in Taylor’s salt marsh and adjacent eelgrass beds (Zostera capensis) in the Kariega Estuary, was investigated every two months between May 2006 and March 2007. Total ichthyofaunal abundances and biomass in the salt marsh ranged between 0.55 and 21.7 ind.10m-2 and between 0.03 and 1.9 g.wwt.10m⁻², respectively. There were no significant spatial patterns in the values evident (P > 0.05 in all cases) although seasonal trends were marked, with highest values consistently recorded during the warmer summer months. Investigations into the community structure showed that the ichthyofaunal community within salt marsh was composed almost exclusively of juveniles of estuarine dependant (category II) species, mainly juvenile Mugilidae (<20mm SL) that comprised up to 83% of all fish sampled. Hierarchical cluster analysis and multidimensional scaling did not identify any distinct spatial patterns in the ichthyofaunal community within the salt marsh. The absence of any spatial patterns in the community structure could be related to the absence of any significant spatial patterns in the physico-chemical (temperature, salinity and dissolved oxygen concentrations) and biological (water column and microphytobenthic algal concentrations) variables within the salt marsh (P > 0.05 in all cases). Temporal shifts in the ichthyofaunal community structure within the salt marsh were, however, evident largely reflecting the breeding cycles of individual species within the sub-region. Within the adjacent eelgrass beds, total ichthyofaunal abundances and biomass ranged between 8.4 and 49.4 ind.10m⁻² and between 2.9 and 94.5 g.wwt.10m⁻², respectively. Once again there were no distinct spatial patterns in the abundance and biomass values evident although seasonal patterns were marked. In contrast to the salt marsh, within the in the eelgrass community, there were a large number of adult individuals recorded. Again category II species, the estuarine dependent species, were numerically and gravimetrically dominant. The dominance of category II species reflects the marine dominance of Kariega Estuary. The remaining estuarine utilisation categories did not contribute significantly to abundance or standing stock totals. Hierarchical cluster analysis showed that the salt marsh and eelgrass beds represented two distinct habitats within the Kariega Estuary. Within the salt marsh, the family Mugilidae were numerically dominant contributing 83% of the total catch. Within the eelgrass beds, the sparid, Rhabdosargus holubi and representatives of the family Gobidae contributed 36.3% and 33.9% respectively to the total catch. Estuaries with a wide range of microhabitats have been demonstrated to support a more diverse ichthyofaunal community. Shallow water habitats in general are important areas for juvenile fish within estuaries. Taylor’s salt marsh provides an alternative shallow water habitat, occupied by a distinct ichthyofaunal community composition, with increased food availability and decreased predation pressure, for a wide range of fish species.
- Full Text:
- Date Issued: 2009
- Authors: Booth, Tara Loren
- Date: 2009
- Subjects: Fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Salt marsh animals -- South Africa -- Eastern Cape , Eelgrass -- South Africa -- Eastern Cape , Gray mullets -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5710 , http://hdl.handle.net/10962/d1005396 , Fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Salt marsh animals -- South Africa -- Eastern Cape , Eelgrass -- South Africa -- Eastern Cape , Gray mullets -- South Africa -- Eastern Cape
- Description: The spatial and temporal patterns in the ichthyofaunal community composition and structure in Taylor’s salt marsh and adjacent eelgrass beds (Zostera capensis) in the Kariega Estuary, was investigated every two months between May 2006 and March 2007. Total ichthyofaunal abundances and biomass in the salt marsh ranged between 0.55 and 21.7 ind.10m-2 and between 0.03 and 1.9 g.wwt.10m⁻², respectively. There were no significant spatial patterns in the values evident (P > 0.05 in all cases) although seasonal trends were marked, with highest values consistently recorded during the warmer summer months. Investigations into the community structure showed that the ichthyofaunal community within salt marsh was composed almost exclusively of juveniles of estuarine dependant (category II) species, mainly juvenile Mugilidae (<20mm SL) that comprised up to 83% of all fish sampled. Hierarchical cluster analysis and multidimensional scaling did not identify any distinct spatial patterns in the ichthyofaunal community within the salt marsh. The absence of any spatial patterns in the community structure could be related to the absence of any significant spatial patterns in the physico-chemical (temperature, salinity and dissolved oxygen concentrations) and biological (water column and microphytobenthic algal concentrations) variables within the salt marsh (P > 0.05 in all cases). Temporal shifts in the ichthyofaunal community structure within the salt marsh were, however, evident largely reflecting the breeding cycles of individual species within the sub-region. Within the adjacent eelgrass beds, total ichthyofaunal abundances and biomass ranged between 8.4 and 49.4 ind.10m⁻² and between 2.9 and 94.5 g.wwt.10m⁻², respectively. Once again there were no distinct spatial patterns in the abundance and biomass values evident although seasonal patterns were marked. In contrast to the salt marsh, within the in the eelgrass community, there were a large number of adult individuals recorded. Again category II species, the estuarine dependent species, were numerically and gravimetrically dominant. The dominance of category II species reflects the marine dominance of Kariega Estuary. The remaining estuarine utilisation categories did not contribute significantly to abundance or standing stock totals. Hierarchical cluster analysis showed that the salt marsh and eelgrass beds represented two distinct habitats within the Kariega Estuary. Within the salt marsh, the family Mugilidae were numerically dominant contributing 83% of the total catch. Within the eelgrass beds, the sparid, Rhabdosargus holubi and representatives of the family Gobidae contributed 36.3% and 33.9% respectively to the total catch. Estuaries with a wide range of microhabitats have been demonstrated to support a more diverse ichthyofaunal community. Shallow water habitats in general are important areas for juvenile fish within estuaries. Taylor’s salt marsh provides an alternative shallow water habitat, occupied by a distinct ichthyofaunal community composition, with increased food availability and decreased predation pressure, for a wide range of fish species.
- Full Text:
- Date Issued: 2009
The impact on biodiversity, and integrated control, of water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae) on the Lake Nsezi - Nseleni River system
- Authors: Jones, Roy William
- Date: 2009
- Subjects: Water hyacinth -- Control -- South Africa , Eichhornia crassipedes , Pontederiaceae , Aquatic plants -- South Africa -- Nsezi, Lake , Aquatic weeds -- South Africa -- Nsezi, Lake , Invasive plants -- South Africa -- Nsezi, Lake
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5711 , http://hdl.handle.net/10962/d1005397 , Water hyacinth -- Control -- South Africa , Eichhornia crassipedes , Pontederiaceae , Aquatic plants -- South Africa -- Nsezi, Lake , Aquatic weeds -- South Africa -- Nsezi, Lake , Invasive plants -- South Africa -- Nsezi, Lake
- Description: Water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae), a free floating aquatic plant was discovered by C. von Martius in 1823 in Brazil. It is believed to have been introduced into South Africa, as an ornamental plant, in 1908 to the Cape Province and Natal. Since its introduction, water hyacinth has spread throughout South Africa to the detriment of all aquatic systems that it has been introduced to directly or indirectly. The weed was first positively identified on the Nseleni and Mposa rivers on the Nseleni Nature Reserve which is a protected area near Richards Bay in KwaZulu- Natal in 1982 and formed a 100% cover of the river by 1983. An integrated management plan was implemented in 1995 and resulted in a reduction of the weed from a 100% cover to less than 20% cover in 5 years. The keys to success of the water hyacinth integrated management plan, presented here, were finding the source of the weed, mapping the extent of the water hyacinth infestation, identifying sources of nutrient pollution, appointing a champion to drive the programme, dividing the river into management units, consultation with interested and affected parties, judicious use of herbicides and biological control and a commitment to follow-up. This study further showed that water hyacinth on the Nseleni and Mposa river systems had a negative impact on the biodiversity of the protected area and the control of water hyacinth resulted in the recovery of the benthic invertebrate, amphibian, reptile, fish and avian fauna. The implementation of this integrated management plan was very cost-effective and serves as a model approach to the control of water hyacinth in both South Africa and the rest of the world.
- Full Text:
- Date Issued: 2009
- Authors: Jones, Roy William
- Date: 2009
- Subjects: Water hyacinth -- Control -- South Africa , Eichhornia crassipedes , Pontederiaceae , Aquatic plants -- South Africa -- Nsezi, Lake , Aquatic weeds -- South Africa -- Nsezi, Lake , Invasive plants -- South Africa -- Nsezi, Lake
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5711 , http://hdl.handle.net/10962/d1005397 , Water hyacinth -- Control -- South Africa , Eichhornia crassipedes , Pontederiaceae , Aquatic plants -- South Africa -- Nsezi, Lake , Aquatic weeds -- South Africa -- Nsezi, Lake , Invasive plants -- South Africa -- Nsezi, Lake
- Description: Water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae), a free floating aquatic plant was discovered by C. von Martius in 1823 in Brazil. It is believed to have been introduced into South Africa, as an ornamental plant, in 1908 to the Cape Province and Natal. Since its introduction, water hyacinth has spread throughout South Africa to the detriment of all aquatic systems that it has been introduced to directly or indirectly. The weed was first positively identified on the Nseleni and Mposa rivers on the Nseleni Nature Reserve which is a protected area near Richards Bay in KwaZulu- Natal in 1982 and formed a 100% cover of the river by 1983. An integrated management plan was implemented in 1995 and resulted in a reduction of the weed from a 100% cover to less than 20% cover in 5 years. The keys to success of the water hyacinth integrated management plan, presented here, were finding the source of the weed, mapping the extent of the water hyacinth infestation, identifying sources of nutrient pollution, appointing a champion to drive the programme, dividing the river into management units, consultation with interested and affected parties, judicious use of herbicides and biological control and a commitment to follow-up. This study further showed that water hyacinth on the Nseleni and Mposa river systems had a negative impact on the biodiversity of the protected area and the control of water hyacinth resulted in the recovery of the benthic invertebrate, amphibian, reptile, fish and avian fauna. The implementation of this integrated management plan was very cost-effective and serves as a model approach to the control of water hyacinth in both South Africa and the rest of the world.
- Full Text:
- Date Issued: 2009
The spatial ecology and activity patterns of leopards (Panthera pardus) in the Baviaanskloof and Greater Addo Elephant National Park (GAENP), Eastern Cape Province, South Africa
- Authors: McManus, Jeannine Stephanie
- Date: 2009
- Subjects: Leopard -- South Africa -- Eastern Cape , Leopard -- Monitoring -- South Africa -- Eastern Cape , Leopard -- Conservation -- South Africa -- Eastern Cape , Leopard -- Ecology -- South Africa -- Eastern Cape , Spatial ecology -- South Africa -- Eastern Cape , Wildlife monitoring -- South Africa -- Eastern Cape , Animal populations -- South Africa -- Eastern Cape , Wildlife conservation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5823 , http://hdl.handle.net/10962/d1007601 , Leopard -- South Africa -- Eastern Cape , Leopard -- Monitoring -- South Africa -- Eastern Cape , Leopard -- Conservation -- South Africa -- Eastern Cape , Leopard -- Ecology -- South Africa -- Eastern Cape , Spatial ecology -- South Africa -- Eastern Cape , Wildlife monitoring -- South Africa -- Eastern Cape , Animal populations -- South Africa -- Eastern Cape , Wildlife conservation -- South Africa -- Eastern Cape
- Description: The conservation of leopards in the Eastern Cape Province requires a holistic approach that considers both predator-human interactions as well as the biology of the carnivore. Numerous studies have been conducted on leopards within protected areas; however more information regarding the species is needed outside these areas to facilitate effective management of predators. The spatial ecology of the leopard (Panthera pardus) were studied in the Baviaanskloof and GAENP in the Eastern Cape. The Baviaanskloof is an extensive area of mountainous terrain (approximately 2665km²) which has a mosaic of land uses, and leopards move from conservation areas to farmland where they come into contact and conflict with farmers. This study examined the spatial ecology of leopards living on farmlands adjacent to protected land. The space utilization and activity patterns of six leopards were analysed. These animals were caught and released on farmlands in the Baviaanskloof (n=4) or translocated (n=2) when not possible to release on site. The animals were caught by means of fall-door, walk-in traps and fitted with Vectronic GPS collars that facilitated the collection of high quality GPS fixes from each animal. Data was collected using VHF and UHF telemetry to download data. An understanding of spatial requirements in areas with different land use, and the extent of overlap of space use with other leopards allow, for the first time in the region, the calculation of possible maximum population size. Analysis of range size was carried out using two methods: minimum convex polygon, and Kernel Utilization Distribution. Finally, a key predictor of space use is prey availability. I assessed the prey base using a grid of camera traps. The studied leopards revealed large range utilization with minimal overlap. The activity patterns suggest there is no preference between diurnal and nocturnal activity patterns and the population density was estimated between 0.3 - 1.3 leopards per 100km². Large home range sizes and low population densities suggest that leopards require large areas of suitable habitat, and that conservation efforts need to be extended beyond protected areas to ensure the long-term viability of leopard populations in such areas.
- Full Text:
- Date Issued: 2009
- Authors: McManus, Jeannine Stephanie
- Date: 2009
- Subjects: Leopard -- South Africa -- Eastern Cape , Leopard -- Monitoring -- South Africa -- Eastern Cape , Leopard -- Conservation -- South Africa -- Eastern Cape , Leopard -- Ecology -- South Africa -- Eastern Cape , Spatial ecology -- South Africa -- Eastern Cape , Wildlife monitoring -- South Africa -- Eastern Cape , Animal populations -- South Africa -- Eastern Cape , Wildlife conservation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5823 , http://hdl.handle.net/10962/d1007601 , Leopard -- South Africa -- Eastern Cape , Leopard -- Monitoring -- South Africa -- Eastern Cape , Leopard -- Conservation -- South Africa -- Eastern Cape , Leopard -- Ecology -- South Africa -- Eastern Cape , Spatial ecology -- South Africa -- Eastern Cape , Wildlife monitoring -- South Africa -- Eastern Cape , Animal populations -- South Africa -- Eastern Cape , Wildlife conservation -- South Africa -- Eastern Cape
- Description: The conservation of leopards in the Eastern Cape Province requires a holistic approach that considers both predator-human interactions as well as the biology of the carnivore. Numerous studies have been conducted on leopards within protected areas; however more information regarding the species is needed outside these areas to facilitate effective management of predators. The spatial ecology of the leopard (Panthera pardus) were studied in the Baviaanskloof and GAENP in the Eastern Cape. The Baviaanskloof is an extensive area of mountainous terrain (approximately 2665km²) which has a mosaic of land uses, and leopards move from conservation areas to farmland where they come into contact and conflict with farmers. This study examined the spatial ecology of leopards living on farmlands adjacent to protected land. The space utilization and activity patterns of six leopards were analysed. These animals were caught and released on farmlands in the Baviaanskloof (n=4) or translocated (n=2) when not possible to release on site. The animals were caught by means of fall-door, walk-in traps and fitted with Vectronic GPS collars that facilitated the collection of high quality GPS fixes from each animal. Data was collected using VHF and UHF telemetry to download data. An understanding of spatial requirements in areas with different land use, and the extent of overlap of space use with other leopards allow, for the first time in the region, the calculation of possible maximum population size. Analysis of range size was carried out using two methods: minimum convex polygon, and Kernel Utilization Distribution. Finally, a key predictor of space use is prey availability. I assessed the prey base using a grid of camera traps. The studied leopards revealed large range utilization with minimal overlap. The activity patterns suggest there is no preference between diurnal and nocturnal activity patterns and the population density was estimated between 0.3 - 1.3 leopards per 100km². Large home range sizes and low population densities suggest that leopards require large areas of suitable habitat, and that conservation efforts need to be extended beyond protected areas to ensure the long-term viability of leopard populations in such areas.
- Full Text:
- Date Issued: 2009
Trophodynamics of carnivorous zooplankton in the region of the subtropical convergence within the Indian sector of the Southern Ocean, with particular emphasis on chaetognaths
- Authors: Sterley, Jessica Anne
- Date: 2009
- Subjects: Zooplankton -- Antarctic Ocean , Chaetognatha , Euphausiacea , Amphipoda , Predation (Biology)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5790 , http://hdl.handle.net/10962/d1005478 , Zooplankton -- Antarctic Ocean , Chaetognatha , Euphausiacea , Amphipoda , Predation (Biology)
- Description: Trophodynamics of carnivorous zooplankton in the region of the Subtropical Convergence (STC) in the Indian sector of the Southern Ocean was investigated during austral autumn (April 2007) as part of the first cruise of the Southern Ocean Ecosystem Variability Study. Within the region of the study, the STC was well defined by the 14°C surface isotherm which separated the Agulhas Return Current and Subtropical water in the north from Sub-Antarctic waters to the south. Total average abundance (3.89 ± 5.46ind 100m-3) and biomass (0.14 ± 0.27mg Dwt 100m-3) of carnivorous zooplankton south of the front were significantly higher than the total average abundance (1.33 ± 1.81ind 100m-3) and biomass (0.03 ± 0.05mg Dwt 100m-3) north of the front (p<0.001). There were no significant correlations between the selected physico-chemical (temperature and salinity) and the biological (mesozooplankton abundance and biomass) variables and the total abundance and biomass of the carnivorous zooplankton during the investigation (p>0.05 in all cases). There was no evidence of enhanced biomass and abundance values at stations occupied in the immediate vicinity of the front. Total average carnivorous zooplankton abundance was dominated by chaetognaths (Eukrohnia hamata Möbius 1875, Sagitta gazellae Ritler-Záhony 1909 and S. zetesios Fowler 1905) and euphausiids (Nematoscelis megalops Sars 1883, Euphausia longirostris Hansen 1908 and E. spinifera Sars 1883), which contributed up to 86.58 ± 32.91% of the total counts. The total average biomass was dominated by euphausiids and amphipods (Themisto gaudichaudii Guérin-Méneville 1825, Phronima sedentaria Forsskål 1775 and Vibilia armata Bovallius 1887) which contributed up to 71.45 ± 34.85% of the total counts. In general the populations of both the euphausiids and amphipods were dominated by females while the chaetognaths were dominated by juveniles. Numerical analysis identified two major zooplankton groupings within the survey area which did not coincide with the water masses within the survey area. The SIMPER procedure of the PRIMER package indicated differences between the groups were mainly attributed to changes in the abundance of the numerically dominant species rather than the presence or absence of individual species. The absence of any significant spatial patterns in the distribution of the carnivorous zooplankton suggests that the STC did not act as a biogeographical barrier during the present study. The mean feeding rates of the chaetognaths E. hamata, S. gazellae and S. zetesios were 1.82 ± 0.85prey d-1, 3.63 ± 2.08prey d-1 and 2.18 ± 0.59prey d-1, respectively. These rates correspond to a combined predation impact equivalent to <5% of the mesozooplankton standing stock or <10% of the mesozooplankton secondary production. Mesozooplankton, comprising mainly copepods was the dominant prey in the guts of the three chaetognath species. Total predation impact of the euphausiids, chaetognaths and amphipods, estimated using published daily ration data, on the mesozooplankton standing stock and secondary production ranged from 0.01% to 1.53% and from 0.03% to 30.54%, respectively. Among the carnivorous zooplankton, chaetognaths were generally identified as the dominant predators of mesozooplankton. Low predation impact of selected carnivorous zooplankton suggested that these organisms contributed little to the vertical carbon flux within the region of investigation during the study.
- Full Text:
- Date Issued: 2009
- Authors: Sterley, Jessica Anne
- Date: 2009
- Subjects: Zooplankton -- Antarctic Ocean , Chaetognatha , Euphausiacea , Amphipoda , Predation (Biology)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5790 , http://hdl.handle.net/10962/d1005478 , Zooplankton -- Antarctic Ocean , Chaetognatha , Euphausiacea , Amphipoda , Predation (Biology)
- Description: Trophodynamics of carnivorous zooplankton in the region of the Subtropical Convergence (STC) in the Indian sector of the Southern Ocean was investigated during austral autumn (April 2007) as part of the first cruise of the Southern Ocean Ecosystem Variability Study. Within the region of the study, the STC was well defined by the 14°C surface isotherm which separated the Agulhas Return Current and Subtropical water in the north from Sub-Antarctic waters to the south. Total average abundance (3.89 ± 5.46ind 100m-3) and biomass (0.14 ± 0.27mg Dwt 100m-3) of carnivorous zooplankton south of the front were significantly higher than the total average abundance (1.33 ± 1.81ind 100m-3) and biomass (0.03 ± 0.05mg Dwt 100m-3) north of the front (p<0.001). There were no significant correlations between the selected physico-chemical (temperature and salinity) and the biological (mesozooplankton abundance and biomass) variables and the total abundance and biomass of the carnivorous zooplankton during the investigation (p>0.05 in all cases). There was no evidence of enhanced biomass and abundance values at stations occupied in the immediate vicinity of the front. Total average carnivorous zooplankton abundance was dominated by chaetognaths (Eukrohnia hamata Möbius 1875, Sagitta gazellae Ritler-Záhony 1909 and S. zetesios Fowler 1905) and euphausiids (Nematoscelis megalops Sars 1883, Euphausia longirostris Hansen 1908 and E. spinifera Sars 1883), which contributed up to 86.58 ± 32.91% of the total counts. The total average biomass was dominated by euphausiids and amphipods (Themisto gaudichaudii Guérin-Méneville 1825, Phronima sedentaria Forsskål 1775 and Vibilia armata Bovallius 1887) which contributed up to 71.45 ± 34.85% of the total counts. In general the populations of both the euphausiids and amphipods were dominated by females while the chaetognaths were dominated by juveniles. Numerical analysis identified two major zooplankton groupings within the survey area which did not coincide with the water masses within the survey area. The SIMPER procedure of the PRIMER package indicated differences between the groups were mainly attributed to changes in the abundance of the numerically dominant species rather than the presence or absence of individual species. The absence of any significant spatial patterns in the distribution of the carnivorous zooplankton suggests that the STC did not act as a biogeographical barrier during the present study. The mean feeding rates of the chaetognaths E. hamata, S. gazellae and S. zetesios were 1.82 ± 0.85prey d-1, 3.63 ± 2.08prey d-1 and 2.18 ± 0.59prey d-1, respectively. These rates correspond to a combined predation impact equivalent to <5% of the mesozooplankton standing stock or <10% of the mesozooplankton secondary production. Mesozooplankton, comprising mainly copepods was the dominant prey in the guts of the three chaetognath species. Total predation impact of the euphausiids, chaetognaths and amphipods, estimated using published daily ration data, on the mesozooplankton standing stock and secondary production ranged from 0.01% to 1.53% and from 0.03% to 30.54%, respectively. Among the carnivorous zooplankton, chaetognaths were generally identified as the dominant predators of mesozooplankton. Low predation impact of selected carnivorous zooplankton suggested that these organisms contributed little to the vertical carbon flux within the region of investigation during the study.
- Full Text:
- Date Issued: 2009
Trophodynamics of mesozooplankton in the the vicinity of the subtropical convergence in the Indian sector of the Southern Ocean
- Authors: Daly, Ryan
- Date: 2009
- Subjects: Zooplankton -- Antarctic Ocean , Phytoplankton -- Antarctic Ocean
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5791 , http://hdl.handle.net/10962/d1005479 , Zooplankton -- Antarctic Ocean , Phytoplankton -- Antarctic Ocean
- Description: The trophodynamics of the numerically dominant mesozooplankton (200-2000 m) in the vicinity of the Subtropical Convergence (STC) in the Indian sector of the Southern Ocean during austral autumn (April / May) 2007 were investigated as part of the Southern Ocean Ecosystem Variability Study. The survey consisted of six north-south transects each bisecting the STC between 38º to 43ºS and 38º to 41º45’E. In total, 48 stations situated at 30 nautical mile intervals were occupied over a period of ten days. Hydrographic data revealed a well defined surface and sub-surface expression of the STC, which appeared to meander considerably between 41ºS and 41º15’S. Surface chlorophyll-a (chla) concentrations were low, ranging between 0.08 and 0.68 mg chl-a.m-3 and were generally dominated by the picophytoplankton (<2 m) which made up 66.6% (SD±17.6) of the total pigment. Chl-a concentrations integrated over the top 150m of the water column ranged between 11.97 and 40.07 mg chl-a.m-2 and showed no significant spatial patterns (p>0.05). Total integrated mesozooplankton abundance and biomass during the study ranged between 3934.9 and 308521.4 ind.m-2 (mean = 47198.19; SD±62411.4 ind.m-2) and between 239.8 and 4614.3 mg Dwt.m-2 (mean = 1338.58; SD ±1060.5), respectively. Again, there were no significant spatial patterns in the total mesozooplankton abundance or biomass within the region of study (p>0.05). No significant correlations were found between biological (chlorophyll-a concentrations and zooplankton abundance) and physico-chemical variables (temperature and salinity) (p>0.05). The total mesozooplankton community was numerically dominated by copepods of the genera Pleuromamma, Calanus, Oncaea and Oithona. Other important representatives of the mesozooplankton community included the tunicate, Salpa thompsoni, and the pteropod, Limacina retroversa. At the 40% similarity level, numerical analysis identified five distinct mesozooplankton groupings within the survey area. Differences between the groupings were associated with changes in the relative contribution of numerically dominant species rather than the presence or absence of individual species. No groupings were associated with any specific feature of the front within the survey area. The feeding rates of the six most numerically abundant mesozooplankton species (Calanus simillimus, Limacina retroversa, Pleuromamma abdominalis, Clausocalanus breviceps, Oncaea conifera, Salpa thompsoni) accounting for on average 39% of the total mesozooplankton counts, were investigated using the gut fluorescence technique. For all species, the total gut pigment contents during the night time were significantly higher than the daytime values (p<0.05 for all species). The gut evacuation rates (k) for selected mesozooplankton ranged between 0.14 and 0.81 h-1. The ingestion rates ranged between 147.8 and 5495.4 ng(pigm)ind-1.day-1 which corresponded to a daily ration of between 2.4 and 10.9% body carbon. The combined grazing impact of the selected species on the daily phytoplankton standing stock was highly variable and ranged between 1.2 and 174.1% with an average of 27.3% (SD±38.78%) within the survey area. The highest grazing impact (>60%) was typically associated with those stations where the pteropod, L. retroversa, and the tunicate, S. thompsoni, contributed more than 5% of the total mesozooplankton counts. No significant differences were found in the grazing impact of any or all selected species situated either north, south or in the immediate vicinity of the front (p>0.05 in all cases). The lack of defined spatial patterns in the mesozooplankton abundance and community structure suggests that the STC did not act as a significant biogeographic barrier to the distribution of mesozooplankton during the study. It is presumed that the large scale mixing event caused by a storm prior to this study was responsible for the observed lack of elevated biological activity within the region of the STC.
- Full Text:
- Date Issued: 2009
- Authors: Daly, Ryan
- Date: 2009
- Subjects: Zooplankton -- Antarctic Ocean , Phytoplankton -- Antarctic Ocean
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5791 , http://hdl.handle.net/10962/d1005479 , Zooplankton -- Antarctic Ocean , Phytoplankton -- Antarctic Ocean
- Description: The trophodynamics of the numerically dominant mesozooplankton (200-2000 m) in the vicinity of the Subtropical Convergence (STC) in the Indian sector of the Southern Ocean during austral autumn (April / May) 2007 were investigated as part of the Southern Ocean Ecosystem Variability Study. The survey consisted of six north-south transects each bisecting the STC between 38º to 43ºS and 38º to 41º45’E. In total, 48 stations situated at 30 nautical mile intervals were occupied over a period of ten days. Hydrographic data revealed a well defined surface and sub-surface expression of the STC, which appeared to meander considerably between 41ºS and 41º15’S. Surface chlorophyll-a (chla) concentrations were low, ranging between 0.08 and 0.68 mg chl-a.m-3 and were generally dominated by the picophytoplankton (<2 m) which made up 66.6% (SD±17.6) of the total pigment. Chl-a concentrations integrated over the top 150m of the water column ranged between 11.97 and 40.07 mg chl-a.m-2 and showed no significant spatial patterns (p>0.05). Total integrated mesozooplankton abundance and biomass during the study ranged between 3934.9 and 308521.4 ind.m-2 (mean = 47198.19; SD±62411.4 ind.m-2) and between 239.8 and 4614.3 mg Dwt.m-2 (mean = 1338.58; SD ±1060.5), respectively. Again, there were no significant spatial patterns in the total mesozooplankton abundance or biomass within the region of study (p>0.05). No significant correlations were found between biological (chlorophyll-a concentrations and zooplankton abundance) and physico-chemical variables (temperature and salinity) (p>0.05). The total mesozooplankton community was numerically dominated by copepods of the genera Pleuromamma, Calanus, Oncaea and Oithona. Other important representatives of the mesozooplankton community included the tunicate, Salpa thompsoni, and the pteropod, Limacina retroversa. At the 40% similarity level, numerical analysis identified five distinct mesozooplankton groupings within the survey area. Differences between the groupings were associated with changes in the relative contribution of numerically dominant species rather than the presence or absence of individual species. No groupings were associated with any specific feature of the front within the survey area. The feeding rates of the six most numerically abundant mesozooplankton species (Calanus simillimus, Limacina retroversa, Pleuromamma abdominalis, Clausocalanus breviceps, Oncaea conifera, Salpa thompsoni) accounting for on average 39% of the total mesozooplankton counts, were investigated using the gut fluorescence technique. For all species, the total gut pigment contents during the night time were significantly higher than the daytime values (p<0.05 for all species). The gut evacuation rates (k) for selected mesozooplankton ranged between 0.14 and 0.81 h-1. The ingestion rates ranged between 147.8 and 5495.4 ng(pigm)ind-1.day-1 which corresponded to a daily ration of between 2.4 and 10.9% body carbon. The combined grazing impact of the selected species on the daily phytoplankton standing stock was highly variable and ranged between 1.2 and 174.1% with an average of 27.3% (SD±38.78%) within the survey area. The highest grazing impact (>60%) was typically associated with those stations where the pteropod, L. retroversa, and the tunicate, S. thompsoni, contributed more than 5% of the total mesozooplankton counts. No significant differences were found in the grazing impact of any or all selected species situated either north, south or in the immediate vicinity of the front (p>0.05 in all cases). The lack of defined spatial patterns in the mesozooplankton abundance and community structure suggests that the STC did not act as a significant biogeographic barrier to the distribution of mesozooplankton during the study. It is presumed that the large scale mixing event caused by a storm prior to this study was responsible for the observed lack of elevated biological activity within the region of the STC.
- Full Text:
- Date Issued: 2009
A stable isotope approach to trophic ecology resolving food webs in intertidal ecosystems
- Authors: Hill, Jaclyn Marie
- Date: 2008
- Subjects: Stable isotopes Food chains (Ecology) Stable isotopes in ecological research Intertidal ecology Mussels -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5771 , http://hdl.handle.net/10962/d1005459
- Description: There are broad differences in regional oceanography and primary production around the South African coast, which we might expect to give rise to major differences in trophic pathways. δ⁻¹³C and δ⁻¹⁵N isotopic ratios of suspended particulate matter (SPM), mussels, various intertidal consumers and common macroalgae along the South African coastline were explored using stable isotope analysis to investigate biogeographic and temporal variability of isotopic signatures of marine intertidal consumers and their food sources around the coast of South Africa, with a focus on evaluating the dependence of intertidal mussels on phytoplankton and macroalgal-derived organic carbon. Isotopic equilibration rates of four mussel tissues were determined through laboratory feeding experiments, which established that adductor tissue had the slowest isotopic turnover rate, and was subsequently used as an indication of overall mussel diet. Biogeographic, temporal and nearshore/offshore trends of isotopic ratios of SPM were investigated along 10km transects perpendicular to the coast and SPM exhibited overall trends of carbon depletion when moving from west to east along the coastline and from nearshore to offshore water, in both cases suggesting a shift from macrophyte detritus to a phytoplankton signature. δ⁻¹³C signatures of SPM also revealed temporal and biogeographic variation that had strong ties to local oceanography, being closely correlated to regional hydrographic features and tidal influences. Mixing models indicated filter feeders demonstrated over 50% dependence on nearshore SPM for organic carbon and it was possible to categorize them into geographic groups based on their carbon and nitrogen signatures, suggesting biogeographic shifts in resources. Biogeographic shifts in diet were also seen in some grazers. Difficulties in relating macroalgae to mussel diet led to investigations into the isotopic changes associated with macroalgal decomposition. Variation in photosynthetic fractionation, leaching and microbial mineralization are believed to have resulted from species-specific patterns of degradation. Although the strong links between carbon signatures and local oceanography indicate that stable isotope analysis is a powerful tool for the study of water mixing and coastal hydrography in relation to food-web analyses, substantial variation in fractionation of primary consumers, along with different periods of time integration between consumers and their food sources must be considered in future studies, to resolve trophic links in marine food webs successfully.
- Full Text:
- Date Issued: 2008
- Authors: Hill, Jaclyn Marie
- Date: 2008
- Subjects: Stable isotopes Food chains (Ecology) Stable isotopes in ecological research Intertidal ecology Mussels -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5771 , http://hdl.handle.net/10962/d1005459
- Description: There are broad differences in regional oceanography and primary production around the South African coast, which we might expect to give rise to major differences in trophic pathways. δ⁻¹³C and δ⁻¹⁵N isotopic ratios of suspended particulate matter (SPM), mussels, various intertidal consumers and common macroalgae along the South African coastline were explored using stable isotope analysis to investigate biogeographic and temporal variability of isotopic signatures of marine intertidal consumers and their food sources around the coast of South Africa, with a focus on evaluating the dependence of intertidal mussels on phytoplankton and macroalgal-derived organic carbon. Isotopic equilibration rates of four mussel tissues were determined through laboratory feeding experiments, which established that adductor tissue had the slowest isotopic turnover rate, and was subsequently used as an indication of overall mussel diet. Biogeographic, temporal and nearshore/offshore trends of isotopic ratios of SPM were investigated along 10km transects perpendicular to the coast and SPM exhibited overall trends of carbon depletion when moving from west to east along the coastline and from nearshore to offshore water, in both cases suggesting a shift from macrophyte detritus to a phytoplankton signature. δ⁻¹³C signatures of SPM also revealed temporal and biogeographic variation that had strong ties to local oceanography, being closely correlated to regional hydrographic features and tidal influences. Mixing models indicated filter feeders demonstrated over 50% dependence on nearshore SPM for organic carbon and it was possible to categorize them into geographic groups based on their carbon and nitrogen signatures, suggesting biogeographic shifts in resources. Biogeographic shifts in diet were also seen in some grazers. Difficulties in relating macroalgae to mussel diet led to investigations into the isotopic changes associated with macroalgal decomposition. Variation in photosynthetic fractionation, leaching and microbial mineralization are believed to have resulted from species-specific patterns of degradation. Although the strong links between carbon signatures and local oceanography indicate that stable isotope analysis is a powerful tool for the study of water mixing and coastal hydrography in relation to food-web analyses, substantial variation in fractionation of primary consumers, along with different periods of time integration between consumers and their food sources must be considered in future studies, to resolve trophic links in marine food webs successfully.
- Full Text:
- Date Issued: 2008
Agathis bishopi (Nixon) (Hymenoptera: braconidae) its biology and usefulness as a biological control agent for false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: tortricidae), on citrus bishopi (Nixon) (Hymenoptera: braconidae) its biology and usefulness as a biological control agent for false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: tortricidae), on citrus
- Authors: Gendall, Kierryn Leigh
- Date: 2008
- Subjects: Cryptophlebia leucotreta -- Parasites , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Tortricidae , Braconidae , Citrus -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5635 , http://hdl.handle.net/10962/d1005317 , Cryptophlebia leucotreta -- Parasites , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Tortricidae , Braconidae , Citrus -- Diseases and pests
- Description: The false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), is one of the major pests of citrus in South Africa, the others being mealybug, Mediterranean fruit fly, bollworm and some mites. Due to problems such as the expense of pesticides, insects evolving pesticide resistance (Hogsette 1999), chemical residue on the skin of export fruit and the negative impact of pesticides on the environment, it became necessary to find alternative methods for pest control (Viggiani 2000). Agathis bishopi (Nixon) (Hymenoptera: Braconidae), a larval parasitoid of false codling moth known only from the Sundays River Valley area (Sishuba 2003), offers a means of control for the pest. A total of 11 389 navel oranges were collected from various orchards in the Addo/Kirkwood area, and false codling moth larvae infested 36.09% of the fruit. A single parasitoid species, A. bishopi, was reared from these larvae. In 2006 the highest parasitism rate, 11.43%, was recorded in May and in 2007, the highest parasitism rate, 13.27%, was in April. Agathis bishopi parasitizes larvae in instars 2 and 3, possibly due to the accessibility of these younger instars to the female parasitoid and possibly due to the length of the life cycle of this koinobiont. Second instar hosts yielded the highest number of parasitoids, and there was no emergence of parasitoids from fifth instar larvae. Females of A. bishopi live for 18.5 days (n = 20; S.E. = 3.1) and males for 8.25 days (n = 20; S.E. = 1.23). Females produce an average of 23 offspring in a lifetime, while female false codling moths produce about 800 eggs each. A high number of parasitoids will be required per hectare to reduce the population of false codling moth. Captive rearing of A. bishopi proved difficult due to viral and fungal contamination. Agathis bishopi has potential for use in an integrated pest management programme once the hurdle of mass-rearing has been overcome.
- Full Text:
- Date Issued: 2008
- Authors: Gendall, Kierryn Leigh
- Date: 2008
- Subjects: Cryptophlebia leucotreta -- Parasites , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Tortricidae , Braconidae , Citrus -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5635 , http://hdl.handle.net/10962/d1005317 , Cryptophlebia leucotreta -- Parasites , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Tortricidae , Braconidae , Citrus -- Diseases and pests
- Description: The false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), is one of the major pests of citrus in South Africa, the others being mealybug, Mediterranean fruit fly, bollworm and some mites. Due to problems such as the expense of pesticides, insects evolving pesticide resistance (Hogsette 1999), chemical residue on the skin of export fruit and the negative impact of pesticides on the environment, it became necessary to find alternative methods for pest control (Viggiani 2000). Agathis bishopi (Nixon) (Hymenoptera: Braconidae), a larval parasitoid of false codling moth known only from the Sundays River Valley area (Sishuba 2003), offers a means of control for the pest. A total of 11 389 navel oranges were collected from various orchards in the Addo/Kirkwood area, and false codling moth larvae infested 36.09% of the fruit. A single parasitoid species, A. bishopi, was reared from these larvae. In 2006 the highest parasitism rate, 11.43%, was recorded in May and in 2007, the highest parasitism rate, 13.27%, was in April. Agathis bishopi parasitizes larvae in instars 2 and 3, possibly due to the accessibility of these younger instars to the female parasitoid and possibly due to the length of the life cycle of this koinobiont. Second instar hosts yielded the highest number of parasitoids, and there was no emergence of parasitoids from fifth instar larvae. Females of A. bishopi live for 18.5 days (n = 20; S.E. = 3.1) and males for 8.25 days (n = 20; S.E. = 1.23). Females produce an average of 23 offspring in a lifetime, while female false codling moths produce about 800 eggs each. A high number of parasitoids will be required per hectare to reduce the population of false codling moth. Captive rearing of A. bishopi proved difficult due to viral and fungal contamination. Agathis bishopi has potential for use in an integrated pest management programme once the hurdle of mass-rearing has been overcome.
- Full Text:
- Date Issued: 2008
Aspects of the thermal ecology of six species of carcass beetles in South Africa
- Authors: Midgley, John Mark
- Date: 2008
- Subjects: Forensic entomology , Diptera -- South Africa , Beetles -- South Africa , Burying beetles , Burying beetles -- South Africa , Beetles -- Effect of temperature on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5643 , http://hdl.handle.net/10962/d1005325 , Forensic entomology , Diptera -- South Africa , Beetles -- South Africa , Burying beetles , Burying beetles -- South Africa , Beetles -- Effect of temperature on
- Description: The forensic application of entomology is well known, but it is generally a field which concentrates on Diptera. Many Coleoptera also have forensic application, but are generally neglected by forensic entomology researchers. Necrophilic Coleoptera are diverse and therefore have application in estimating Post-Mortem Interval (PMI) by community composition, but they are also valuable in estimating PMI by development. In addition, Coleoptera are more common in stored product cases. Six species of forensically important Coleoptera were studied, three from the family Dermestidae (Dermestes haemorrhoidalis, D. maculatus and D. peruvianus) and three from the family Silphidae (Silpha punctulata, Thanatophilus micans and T. mutilatus). The effect of killing method and storage time on larval length was investigated in T. micans. Coleopteran larvae were shown not to behave in the same way as dipteran larvae. In contrast to dipteran larvae, it is recommended that coleopteran larvae be killed using ethanol. A development model is presented for T. micans. This represents the first statistically robust development model for forensically important Coleoptera, and the first development model for forensically important Silphidae. The model offers a method of estimating PMI which can be used once Diptera are no longer present on a corpse. Upper lethal temperature limits for four species of carcass beetle were determined. A comparison between species shows distinct differentiation between families and species. This differentiation accounts for microhabitat differences which these species show on carcasses. Bioclimatic models for the six species showed contrasting distributions, with both widespread and localised species. These models allow forensic investigators to assess whether the absence of a species from a corpse is forensically significant, or a result of the species distributions. Moisture-related variables were shown to be more important in predicting species distributions than temperature at a regional scale. Forensic entomology standards can be adjusted based on the findings of this study. Length was again shown to be an inferior measurement of larval age. Coleopteran development has been shown to be useful, and should be given greater consideration in future work. T. micans has been shown to be capable of locating and ovipositing on carcasses promptly after death, making it a good forensic indicator. Further work is needed for the full potential of necrophilic Coleoptera to be realised.
- Full Text:
- Date Issued: 2008
- Authors: Midgley, John Mark
- Date: 2008
- Subjects: Forensic entomology , Diptera -- South Africa , Beetles -- South Africa , Burying beetles , Burying beetles -- South Africa , Beetles -- Effect of temperature on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5643 , http://hdl.handle.net/10962/d1005325 , Forensic entomology , Diptera -- South Africa , Beetles -- South Africa , Burying beetles , Burying beetles -- South Africa , Beetles -- Effect of temperature on
- Description: The forensic application of entomology is well known, but it is generally a field which concentrates on Diptera. Many Coleoptera also have forensic application, but are generally neglected by forensic entomology researchers. Necrophilic Coleoptera are diverse and therefore have application in estimating Post-Mortem Interval (PMI) by community composition, but they are also valuable in estimating PMI by development. In addition, Coleoptera are more common in stored product cases. Six species of forensically important Coleoptera were studied, three from the family Dermestidae (Dermestes haemorrhoidalis, D. maculatus and D. peruvianus) and three from the family Silphidae (Silpha punctulata, Thanatophilus micans and T. mutilatus). The effect of killing method and storage time on larval length was investigated in T. micans. Coleopteran larvae were shown not to behave in the same way as dipteran larvae. In contrast to dipteran larvae, it is recommended that coleopteran larvae be killed using ethanol. A development model is presented for T. micans. This represents the first statistically robust development model for forensically important Coleoptera, and the first development model for forensically important Silphidae. The model offers a method of estimating PMI which can be used once Diptera are no longer present on a corpse. Upper lethal temperature limits for four species of carcass beetle were determined. A comparison between species shows distinct differentiation between families and species. This differentiation accounts for microhabitat differences which these species show on carcasses. Bioclimatic models for the six species showed contrasting distributions, with both widespread and localised species. These models allow forensic investigators to assess whether the absence of a species from a corpse is forensically significant, or a result of the species distributions. Moisture-related variables were shown to be more important in predicting species distributions than temperature at a regional scale. Forensic entomology standards can be adjusted based on the findings of this study. Length was again shown to be an inferior measurement of larval age. Coleopteran development has been shown to be useful, and should be given greater consideration in future work. T. micans has been shown to be capable of locating and ovipositing on carcasses promptly after death, making it a good forensic indicator. Further work is needed for the full potential of necrophilic Coleoptera to be realised.
- Full Text:
- Date Issued: 2008
Composition and phenology of insect pests of Capsicum (Solanaceae) cultivated in the Makana District, Eastern Cape Province, South Africa
- Authors: Hepburn, Colleen
- Date: 2008
- Subjects: Insects -- South Africa -- Eastern Cape -- Composition Insects -- South Africa -- Eastern Cape -- Phenology Agricultural pests -- South Africa -- Eastern Cape Peppers -- Diseases and pests -- South Africa -- Eastern Cape Solanaceae -- Diseases and pests -- South Africa -- Eastern Cape Insect pests -- South Africa -- Eastern Cape Insect pests -- Biological control -- South Africa -- Eastern Cape Insect pests -- Control -- Methods -- South Africa -- Eastern Cape Insects -- Host plants -- South Africa -- Eastern Cape Insect-plant relationships -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5656 , http://hdl.handle.net/10962/d1005339
- Description: Capsicum baccatum var. pendulum was first grown in the Makana District in 2005. Extremely little was known about best practices for cultivation or the insects and diseases associated with the crop in this area. The study was conducted during the second year of production, November 2005 and November 2006, in an attempt to identify the composition and phenology of insects occurring on C. baccatum. In the more rural parts of the Eastern Cape, and more particularly in Grahamstown, there are very few industries. With the advent of this new agricultural venture, a processing factory has been opened in Grahamstown creating more than 600 seasonal jobs in the factory and 1000 seasonal jobs on farms for local people. This business enterprise has not only brought about the creation of jobs, but also training and skills development and empowerment, generating much-needed income in this area. An extensive literature review yielded limited information on insect pests associated with Capsicum. Data from a pilot sampling trial undertaken were statistically analyzed to establish the number of plants to be scouted per site and the most effective scouting techniques to use. Based on the data available and insects collected during the pilot sampling trial, a surveillance programme was designed. Five different types of monitoring traps were placed in each of the eight study sites. Collection of trap catches and scouting of fifteen individual plants per site was undertaken on a weekly basis over the 52-week study period. The most commonly occurring potential insect pests were African Bollworm Helicoverpa armigera (Hübner), False Codling Moth Thaumatotibia leucotreta (= Cryptophlebia leucotreta) (Meyrick), Mediterranean Fruit Fly Ceratitis capitata (Wiedemann) and several species of thrips. Population densities of these pests and their phenology on Capsicum were determined. Statistical analyses established the efficacy of the monitoring traps for each pest, tested for differences among and between study sites, calculated an estimate of the number of pods damaged and a measure of plant damage.The results show that the majority of damage caused to the Capsicum baccatum cropping system was due to Mediterranean Fruit Fly populations. It was established that, although African Bollworm and False Codling Moth were present during the study period, their numbers were negligible and only nominal damage was caused by these pests. Damage caused by thrips species was apparent but not quantifiable. Intervention strategies using an Integrated Pest Management approach, are discussed.
- Full Text:
- Date Issued: 2008
- Authors: Hepburn, Colleen
- Date: 2008
- Subjects: Insects -- South Africa -- Eastern Cape -- Composition Insects -- South Africa -- Eastern Cape -- Phenology Agricultural pests -- South Africa -- Eastern Cape Peppers -- Diseases and pests -- South Africa -- Eastern Cape Solanaceae -- Diseases and pests -- South Africa -- Eastern Cape Insect pests -- South Africa -- Eastern Cape Insect pests -- Biological control -- South Africa -- Eastern Cape Insect pests -- Control -- Methods -- South Africa -- Eastern Cape Insects -- Host plants -- South Africa -- Eastern Cape Insect-plant relationships -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5656 , http://hdl.handle.net/10962/d1005339
- Description: Capsicum baccatum var. pendulum was first grown in the Makana District in 2005. Extremely little was known about best practices for cultivation or the insects and diseases associated with the crop in this area. The study was conducted during the second year of production, November 2005 and November 2006, in an attempt to identify the composition and phenology of insects occurring on C. baccatum. In the more rural parts of the Eastern Cape, and more particularly in Grahamstown, there are very few industries. With the advent of this new agricultural venture, a processing factory has been opened in Grahamstown creating more than 600 seasonal jobs in the factory and 1000 seasonal jobs on farms for local people. This business enterprise has not only brought about the creation of jobs, but also training and skills development and empowerment, generating much-needed income in this area. An extensive literature review yielded limited information on insect pests associated with Capsicum. Data from a pilot sampling trial undertaken were statistically analyzed to establish the number of plants to be scouted per site and the most effective scouting techniques to use. Based on the data available and insects collected during the pilot sampling trial, a surveillance programme was designed. Five different types of monitoring traps were placed in each of the eight study sites. Collection of trap catches and scouting of fifteen individual plants per site was undertaken on a weekly basis over the 52-week study period. The most commonly occurring potential insect pests were African Bollworm Helicoverpa armigera (Hübner), False Codling Moth Thaumatotibia leucotreta (= Cryptophlebia leucotreta) (Meyrick), Mediterranean Fruit Fly Ceratitis capitata (Wiedemann) and several species of thrips. Population densities of these pests and their phenology on Capsicum were determined. Statistical analyses established the efficacy of the monitoring traps for each pest, tested for differences among and between study sites, calculated an estimate of the number of pods damaged and a measure of plant damage.The results show that the majority of damage caused to the Capsicum baccatum cropping system was due to Mediterranean Fruit Fly populations. It was established that, although African Bollworm and False Codling Moth were present during the study period, their numbers were negligible and only nominal damage was caused by these pests. Damage caused by thrips species was apparent but not quantifiable. Intervention strategies using an Integrated Pest Management approach, are discussed.
- Full Text:
- Date Issued: 2008
Ecological role of free-living bacteria in the microbial food web of the temporarily open/closed East Kleinemonde Estuary, South Africa
- Authors: Allan, Elizabeth Louise
- Date: 2008
- Subjects: Bacterial growth -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Microbial ecology -- South Africa -- Eastern Cape , Nutrient cycles -- South Africa -- Eastern Cape , Food chains (Ecology)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5666 , http://hdl.handle.net/10962/d1005351 , Bacterial growth -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Microbial ecology -- South Africa -- Eastern Cape , Nutrient cycles -- South Africa -- Eastern Cape , Food chains (Ecology)
- Description: The main aim of this study was to assess the “top-down” and “bottom-up” control of bacterial production in the small temporarily open/closed East Kleinemonde Estuary, situated on the south-eastern coastline of southern Africa. Spatial and temporal patterns in bacterial abundance, biomass and production and the importance of abiotic and biotic factors were investigated over the period May 2006 to April 2007. The trophic interactions between bacteria, phytoplankton, nanoflagellates (< 20 μm), microzooplankton (< 200 μm) and mesozooplankton (< 2 000 μm) were investigated during winter and summer. Bacterial abundance, biomass and production ranged between 1.00 × 10⁹ and 4.93 × 10⁹ cells 1⁻¹, 32.4 and 109 μg C 1⁻¹ and 0.01 and 1.99 μg C 1⁻¹ h⁻¹, respectively. With a few exceptions there were no spatial patterns in the values. Bacterial abundance, biomass and production, however, demonstrated a distinct temporal pattern with the lowest values consistently recorded during the winter months. Nanoflagellate and bacterial abundances were significantly correlated to one another (lower reaches: r = 0.818, p < 0.001; middle reaches: r = 0.628, p < 0.001; upper reaches: r = 0.484, p < 0.05) suggesting a strong predator-prey relationship. The frequency of visibly infected bacterial cells and the mean number of virus particles within each bacterial cell during this study demonstrated no temporal or spatial patterns and ranged from 0.5 to 6.1 % and 12.0 to 37.5 virus particles per bacterium, respectively. Viral infection and lysis was thus a constant source of bacterial mortality throughout the year. The estimated percentage of bacterial production removed by viral lysis ranged between 7.8 and 88.9% of the total which suggests that viral lysis represented a very important source of bacterial mortality during this study. The biological interactions between the selected components of the plankton community demonstrated that among the heterotrophic components of the plankton, the nanoflagellates were identified as the most important consumers of bacteria and small phytoplankton cells (< 20 μm). In the presence of microzooplankton the impact of the nanoflagellates on both the bacteria and phytoplankton was reduced, indicating that larger heterotrophs were preying upon the nanoflagellates. Mesozooplankton, however, appeared to exert the greatest impact on nanoflagellates. In the cascading experiments, the data suggest that mesozooplankton consume nanoflagellates, which resulted in a decrease in the predation impact of these organisms on the bacteria. This result is consistent with predator-prey cascades. The presence of the larger heterotrophs therefore, mediates the interactions between the primary bacterivores, the nanoflagellates, and the bacteria within the temporarily open/closed East Kleinemonde Estuary.
- Full Text:
- Date Issued: 2008
- Authors: Allan, Elizabeth Louise
- Date: 2008
- Subjects: Bacterial growth -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Microbial ecology -- South Africa -- Eastern Cape , Nutrient cycles -- South Africa -- Eastern Cape , Food chains (Ecology)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5666 , http://hdl.handle.net/10962/d1005351 , Bacterial growth -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Microbial ecology -- South Africa -- Eastern Cape , Nutrient cycles -- South Africa -- Eastern Cape , Food chains (Ecology)
- Description: The main aim of this study was to assess the “top-down” and “bottom-up” control of bacterial production in the small temporarily open/closed East Kleinemonde Estuary, situated on the south-eastern coastline of southern Africa. Spatial and temporal patterns in bacterial abundance, biomass and production and the importance of abiotic and biotic factors were investigated over the period May 2006 to April 2007. The trophic interactions between bacteria, phytoplankton, nanoflagellates (< 20 μm), microzooplankton (< 200 μm) and mesozooplankton (< 2 000 μm) were investigated during winter and summer. Bacterial abundance, biomass and production ranged between 1.00 × 10⁹ and 4.93 × 10⁹ cells 1⁻¹, 32.4 and 109 μg C 1⁻¹ and 0.01 and 1.99 μg C 1⁻¹ h⁻¹, respectively. With a few exceptions there were no spatial patterns in the values. Bacterial abundance, biomass and production, however, demonstrated a distinct temporal pattern with the lowest values consistently recorded during the winter months. Nanoflagellate and bacterial abundances were significantly correlated to one another (lower reaches: r = 0.818, p < 0.001; middle reaches: r = 0.628, p < 0.001; upper reaches: r = 0.484, p < 0.05) suggesting a strong predator-prey relationship. The frequency of visibly infected bacterial cells and the mean number of virus particles within each bacterial cell during this study demonstrated no temporal or spatial patterns and ranged from 0.5 to 6.1 % and 12.0 to 37.5 virus particles per bacterium, respectively. Viral infection and lysis was thus a constant source of bacterial mortality throughout the year. The estimated percentage of bacterial production removed by viral lysis ranged between 7.8 and 88.9% of the total which suggests that viral lysis represented a very important source of bacterial mortality during this study. The biological interactions between the selected components of the plankton community demonstrated that among the heterotrophic components of the plankton, the nanoflagellates were identified as the most important consumers of bacteria and small phytoplankton cells (< 20 μm). In the presence of microzooplankton the impact of the nanoflagellates on both the bacteria and phytoplankton was reduced, indicating that larger heterotrophs were preying upon the nanoflagellates. Mesozooplankton, however, appeared to exert the greatest impact on nanoflagellates. In the cascading experiments, the data suggest that mesozooplankton consume nanoflagellates, which resulted in a decrease in the predation impact of these organisms on the bacteria. This result is consistent with predator-prey cascades. The presence of the larger heterotrophs therefore, mediates the interactions between the primary bacterivores, the nanoflagellates, and the bacteria within the temporarily open/closed East Kleinemonde Estuary.
- Full Text:
- Date Issued: 2008
Effects of coastal topography on physiology, behaviour and genetics of indigenous (Perna perna) and invasive (Mytilus galloprovincialis) mussels
- Authors: Nicastro, Katy R
- Date: 2008
- Subjects: Mussels -- Ecology -- South Africa , Perna -- Physiology -- South Africa , Perna -- Behavior -- South Africa , Mussels -- Behavior -- Environmental factors -- South Africa , Mussels -- Habitat -- South Africa , Mytilus galloprovincialis , Mytilus galloprovincialis -- Physiology -- South Africa , Mytilus galloprovincialis -- Behavior -- South Africa , Mytilus galloprovincialis -- Genetics -- South Africa , Coastal ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5833 , http://hdl.handle.net/10962/d1008262
- Description: Organisms inhabit environments that have many dimensions, each of which can vary temporally and spatially. The spatial-temporal variations of environmental stressors and disturbances may have major but different effects on indigenous and invasive species, favouring either of them at different times and places. The invasive mussel Mytilus galloprovincialis invaded the South African coast 30 years ago and, on the south coast of South Africa, it now competes and co-exists with the indigenous Perna perna in the lower eulittoral zone (referred to here as the mussel zone) The invasive and indigenous species dominate the upper and the lower mussel zones respectively, while the two co-exist in the mid-zone. My results show that intertidal mussels experience, and respond to, spatial and temporal fluctuations of several biotic and abiotic stressors. The invasive and the indigenous species adopt different strategies when reacting to environmental factors and their physiological and behavioural responses vary in time and in different habitats as different pressures become of overriding importance. Attachment strength of both species decreased in summer and increased in winter, and was higher on the open coast than in bays for both species, showing a strong positive correlation with wave force in time and space. P. perna had significantly higher attachment strength than M. galloprovincialis but, contrary to previous studies, the difference in gonad index between the two species varied according to the habitat. In bay habitats, M. galloprovincialis had a higher maximum reproductive effort than P. perna, however, on the open coast, there was no significant difference between the two species, suggesting that for the invasive species wave action is a limiting factor not only in terms of the attachment strength but also of energy availability for reproductive tissue development. Major spawning events occurred during periods of low wave action while minor spawning coincided with periods of intense hydrodynamic stress. On the open coast, gonad index was negatively correlated with attachment strength for both species while, in bays, there was no correlation between these two factors for either. The two species also showed different behaviour. In the field, M. galloprovincialis moved significantly more than P. perna over a period of six months. The higher mobility of the invasive species was also confirmed in the laboratory where, in general, M. galloprovincialis formed clumps more readily than P. perna. Taken collectively, these results suggest that channelling more energy into attachment strength limits reproductive tissue development and that, while the indigenous species invests more in byssal production, the invasive species adopts a more dynamic strategy looking for aggregation or a safer arrangement. Higher endolithic infestation and a greater expression of heat shock proteins (Hsps) in mussel populations on the open coast than in bays indicate that this habitat is a more stressful environment not only in terms of wave action. Endolith damaged mussels had significantly lower attachment strengths and condition indices than clean mussels, probably due to the need to channel energy into shell repair. The constant shell repair and expression of Hsps typical of open coast populations are energetically demanding processes. These observations suggest that on the open coast, mussels are subjected to more severe energetic constraints than in bay habitats. Wave and sand stress fluctuated seasonally with the former having a greater effect on mussel mortality on the open coast and the latter a higher impact on bay populations. Overall, mussel mortality rates were higher on the open coast than in bays. My results show that populations on the open coast had fewer private haplotypes and less genetic endemism than those inside bays. Gene flow analysis showed the relatively stable bay habitats act as source populations with greater genetic migration rates out of bays than into them. These differences in genetic structure on scales of las of kilometers show that coastal configuration strongly affects selection, larval dispersal and haplotype diversity. Environmental gradients that are key factors in species distribution over large geographical scales can also be responsible for micro-scale distributions. My results show that M. galloprovincialis colonizes the upper mussel zone where temperature is high, but is less tolerant to this stressor and has to maintain a high expression of Hsps. This suggests that temperature is probably a limiting factor in its invasion towards the sub-tropical east coast. There are inter- and intra-specific differences in responses to the environment which highlight the efforts of M. galloprovincialis and P. perna to optimize resource utilization for survival and reproduction. Determining these differences is crucial to understanding patterns of co-existence between competing indigenous and invasive species.
- Full Text:
- Date Issued: 2008
- Authors: Nicastro, Katy R
- Date: 2008
- Subjects: Mussels -- Ecology -- South Africa , Perna -- Physiology -- South Africa , Perna -- Behavior -- South Africa , Mussels -- Behavior -- Environmental factors -- South Africa , Mussels -- Habitat -- South Africa , Mytilus galloprovincialis , Mytilus galloprovincialis -- Physiology -- South Africa , Mytilus galloprovincialis -- Behavior -- South Africa , Mytilus galloprovincialis -- Genetics -- South Africa , Coastal ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5833 , http://hdl.handle.net/10962/d1008262
- Description: Organisms inhabit environments that have many dimensions, each of which can vary temporally and spatially. The spatial-temporal variations of environmental stressors and disturbances may have major but different effects on indigenous and invasive species, favouring either of them at different times and places. The invasive mussel Mytilus galloprovincialis invaded the South African coast 30 years ago and, on the south coast of South Africa, it now competes and co-exists with the indigenous Perna perna in the lower eulittoral zone (referred to here as the mussel zone) The invasive and indigenous species dominate the upper and the lower mussel zones respectively, while the two co-exist in the mid-zone. My results show that intertidal mussels experience, and respond to, spatial and temporal fluctuations of several biotic and abiotic stressors. The invasive and the indigenous species adopt different strategies when reacting to environmental factors and their physiological and behavioural responses vary in time and in different habitats as different pressures become of overriding importance. Attachment strength of both species decreased in summer and increased in winter, and was higher on the open coast than in bays for both species, showing a strong positive correlation with wave force in time and space. P. perna had significantly higher attachment strength than M. galloprovincialis but, contrary to previous studies, the difference in gonad index between the two species varied according to the habitat. In bay habitats, M. galloprovincialis had a higher maximum reproductive effort than P. perna, however, on the open coast, there was no significant difference between the two species, suggesting that for the invasive species wave action is a limiting factor not only in terms of the attachment strength but also of energy availability for reproductive tissue development. Major spawning events occurred during periods of low wave action while minor spawning coincided with periods of intense hydrodynamic stress. On the open coast, gonad index was negatively correlated with attachment strength for both species while, in bays, there was no correlation between these two factors for either. The two species also showed different behaviour. In the field, M. galloprovincialis moved significantly more than P. perna over a period of six months. The higher mobility of the invasive species was also confirmed in the laboratory where, in general, M. galloprovincialis formed clumps more readily than P. perna. Taken collectively, these results suggest that channelling more energy into attachment strength limits reproductive tissue development and that, while the indigenous species invests more in byssal production, the invasive species adopts a more dynamic strategy looking for aggregation or a safer arrangement. Higher endolithic infestation and a greater expression of heat shock proteins (Hsps) in mussel populations on the open coast than in bays indicate that this habitat is a more stressful environment not only in terms of wave action. Endolith damaged mussels had significantly lower attachment strengths and condition indices than clean mussels, probably due to the need to channel energy into shell repair. The constant shell repair and expression of Hsps typical of open coast populations are energetically demanding processes. These observations suggest that on the open coast, mussels are subjected to more severe energetic constraints than in bay habitats. Wave and sand stress fluctuated seasonally with the former having a greater effect on mussel mortality on the open coast and the latter a higher impact on bay populations. Overall, mussel mortality rates were higher on the open coast than in bays. My results show that populations on the open coast had fewer private haplotypes and less genetic endemism than those inside bays. Gene flow analysis showed the relatively stable bay habitats act as source populations with greater genetic migration rates out of bays than into them. These differences in genetic structure on scales of las of kilometers show that coastal configuration strongly affects selection, larval dispersal and haplotype diversity. Environmental gradients that are key factors in species distribution over large geographical scales can also be responsible for micro-scale distributions. My results show that M. galloprovincialis colonizes the upper mussel zone where temperature is high, but is less tolerant to this stressor and has to maintain a high expression of Hsps. This suggests that temperature is probably a limiting factor in its invasion towards the sub-tropical east coast. There are inter- and intra-specific differences in responses to the environment which highlight the efforts of M. galloprovincialis and P. perna to optimize resource utilization for survival and reproduction. Determining these differences is crucial to understanding patterns of co-existence between competing indigenous and invasive species.
- Full Text:
- Date Issued: 2008
Effects of temperature on the development, behaviour and geography of blowflies in a forensic context
- Authors: Richards, Cameron Spencer
- Date: 2008
- Subjects: Blowflies Blowflies -- South Africa Diptera -- South Africa Insects -- Development Insects -- Behavior Forensic entomology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5683 , http://hdl.handle.net/10962/d1005369
- Description: The development of immature insects is commonly employed in forensic investigations to estimate time of death, or postmortem interval (PMI), of a corpse on which they are feeding. The bulk of this thesis focuses on factors influencing the accuracy of developmental data, and exploring how and why developmental data differ between studies involving the same species, and between different species. Because carrion feeding insects are ectotherms, temperature may be expected to significantly influence their behaviour, development and distribution, and the remainder of the thesis therefore focuses on the thermal biology and geographical distribution of seven forensically important blowflies. The species include Chrysomya albiceps, C. putoria, C. chloropyga, C. megacephala, C. marginalis, C. inclinata and Calliphora croceipalpis. A robust experimental design for estimating developmental models is outlined and tested. It is recommended that forensic entomologists should involve at least six constant temperatures, starting at about 7°C above the relevant developmental zero (D0) and going to about 10°C above the upper critical temperature, and a temporal sampling interval with a relative precision of about 10%. Using this design, focused experiments consistently provided the most reliable developmental data, while data pooled from different studies yielded inconsistent results. Similarly, developmental data from closely related species differed significantly, and surprisingly so did developmental data from different populations of the same species. Possible explanations for the latter lay in the different methods of data collection but only temporal sampling resolution had a direct influence on the accuracy of developmental data. Consequently, disparities in such data were primarily ascribed to genetic differences and phenotypic plasticity. Comparisons between numerous thermal thresholds of larvae, pupae and adults support this conclusion and suggest a phylogenetic component to the thermal biology of blowflies. Further comparisons were made between these temperature thresholds and the distributions of blowfly species present on two rhinoceros carcasses. These comparisons suggest that blowfly larvae with high upper lethal temperature thresholds dominate in interspecific competition in favorable thermal environments by raising maggot mass temperature above the thresholds of other carrion-feeding blowflies, through maggot-generated heat. Bioclimatic modeling using maximum entropy analysis provided a successful means of predicting whether a species is likely to occur in an area, and whether it would therefore be expected in a local carcass community. It also showed that temperature was less important than moisture in shaping the geographical distribution of African carrion blowflies. Based on these results, several recommendations are made for the practice of forensic entomology.
- Full Text:
- Date Issued: 2008
- Authors: Richards, Cameron Spencer
- Date: 2008
- Subjects: Blowflies Blowflies -- South Africa Diptera -- South Africa Insects -- Development Insects -- Behavior Forensic entomology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5683 , http://hdl.handle.net/10962/d1005369
- Description: The development of immature insects is commonly employed in forensic investigations to estimate time of death, or postmortem interval (PMI), of a corpse on which they are feeding. The bulk of this thesis focuses on factors influencing the accuracy of developmental data, and exploring how and why developmental data differ between studies involving the same species, and between different species. Because carrion feeding insects are ectotherms, temperature may be expected to significantly influence their behaviour, development and distribution, and the remainder of the thesis therefore focuses on the thermal biology and geographical distribution of seven forensically important blowflies. The species include Chrysomya albiceps, C. putoria, C. chloropyga, C. megacephala, C. marginalis, C. inclinata and Calliphora croceipalpis. A robust experimental design for estimating developmental models is outlined and tested. It is recommended that forensic entomologists should involve at least six constant temperatures, starting at about 7°C above the relevant developmental zero (D0) and going to about 10°C above the upper critical temperature, and a temporal sampling interval with a relative precision of about 10%. Using this design, focused experiments consistently provided the most reliable developmental data, while data pooled from different studies yielded inconsistent results. Similarly, developmental data from closely related species differed significantly, and surprisingly so did developmental data from different populations of the same species. Possible explanations for the latter lay in the different methods of data collection but only temporal sampling resolution had a direct influence on the accuracy of developmental data. Consequently, disparities in such data were primarily ascribed to genetic differences and phenotypic plasticity. Comparisons between numerous thermal thresholds of larvae, pupae and adults support this conclusion and suggest a phylogenetic component to the thermal biology of blowflies. Further comparisons were made between these temperature thresholds and the distributions of blowfly species present on two rhinoceros carcasses. These comparisons suggest that blowfly larvae with high upper lethal temperature thresholds dominate in interspecific competition in favorable thermal environments by raising maggot mass temperature above the thresholds of other carrion-feeding blowflies, through maggot-generated heat. Bioclimatic modeling using maximum entropy analysis provided a successful means of predicting whether a species is likely to occur in an area, and whether it would therefore be expected in a local carcass community. It also showed that temperature was less important than moisture in shaping the geographical distribution of African carrion blowflies. Based on these results, several recommendations are made for the practice of forensic entomology.
- Full Text:
- Date Issued: 2008
Queens, pseudoqueens and laying workers reproductive competition in the Cape Honeybee (Apis mellifera capensis Eschscholtz)
- Authors: Muerrle, Thomas Martin
- Date: 2008
- Subjects: Honeybee Honeybee -- Reproduction
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5750 , http://hdl.handle.net/10962/d1005437
- Description: In honeybees (Apis mellifera L.) the queen monopolises reproduction. However, especially after queen loss, workers can lay eggs, but are unable to mate. They produce haploid male offspring (drones) from unfertilised eggs via arrhenotokous parthenogenesis. In contrast, workers of the honeybee subspecies Apis mellifera capensis Eschscholtz typically produce diploid female offspring from unfertilised eggs thelytokously. After queen loss and without queen-derived brood A. m. capensis colonies can successfully requeen from worker-derived brood. This, however, is a relatively rare event in wild populations. Moreover, workerderived queens were described to be smaller, more worker-like and reproductively inferior. On the other hand, the fixation of the thelytokous trait relies mainly on sufficient numbers of viable drones produced by worker-derived queens. Small numbers of reproductively inferior worker-derived queens in A. m. capensis populations would be clearly counterintuitive. It is therefore necessary to quantify the significance of worker-dependant queen rearing pathways on the individual (queen) and on population level.Reproductive inferiority of worker-derived queens could not be confirmed on the individual (queen) level when comparing parameters indicating potential reproductive success of queen- and worker-derived queens. Queen- and worker-derived queens clearly showed a congruent range of reproductive performance. In queen rearing preference tests, increased acceptance of worker-derived female larvae was exactly counterbalanced by increased mortality, resulting in an equal number of eclosing virgin queens from an equal number of grafts in both test groups. Larval survival and successful eclosion is a prerequisite for a queen’s reproductive success. I found no difference in eclosion success for queen- and worker-derived virgin queens, indicating a similar potential for reproductive success in both queen types. Assessments of the developmental patterns of colonies headed by both queen and worker-derived queens in long-term experiments revealed no significant differences in reproductive success. Colonies headed by queen-derived queens and colonies headed by worker-derived queens could not be separated when comparing the different developmental pathways observed or from differences in worker-force. Reproductive dominance in A. m. capensis appeared tobe determined by a function of relative compositional and absolute quantitative pheromonal patterns, where individuals, which produce compositionally most queen-like blends in highest quantities, occupy top positions. Queen- and worker-derived virgin queens occupied intermediate positions between pseudoqueens and mated queens. However, no significant differences between the pheromonal status of queen- and worker-derived virgin queens were observed, suggesting a similar range of reproductive dominance for both queen types. In behavioural bioassays queen- and worker-derived virgin queens appeared to be similarly attractive to clustering workers and to drones in a drone congregation area, indicating no differences in potential reproductive success for queens from both origins for those parameters. The significant influence of the queen substance 9-ODA on attractiveness to workers and drones was confirmed. Rare requeening events from worker-derived female brood in queenless A.m. capensis do not satisfactorily explain the fixation of the thelytokous trait at a population level. I observed A. m. capensis worker ovipositing into empty artificial queen cell cups in queen-right colonies. The queen was confined behind a queen excluder grid in a separate compartment of the colony, to imitate reduced pheromonal flow, similar to swarming or superseding colonies. Eggs oviposited by workers in artificial queen cell cups were readily accepted for queen rearing and successful eclosion of viable virgin queens was observed. Consequently I suggested an alternative worker-dependant reproductive pathway in A. m. capensis, which was never described before: In swarming or superseding queenright colonies, laying workers may directly compete with the queen for reproductive success by ovipositing (instead of the queen) into natural queen cell cups. At a population level this reproductive tactic may result in large numbers of worker-derived queens of high reproductive quality in natural populations of A. m. capensis.
- Full Text:
- Date Issued: 2008
- Authors: Muerrle, Thomas Martin
- Date: 2008
- Subjects: Honeybee Honeybee -- Reproduction
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5750 , http://hdl.handle.net/10962/d1005437
- Description: In honeybees (Apis mellifera L.) the queen monopolises reproduction. However, especially after queen loss, workers can lay eggs, but are unable to mate. They produce haploid male offspring (drones) from unfertilised eggs via arrhenotokous parthenogenesis. In contrast, workers of the honeybee subspecies Apis mellifera capensis Eschscholtz typically produce diploid female offspring from unfertilised eggs thelytokously. After queen loss and without queen-derived brood A. m. capensis colonies can successfully requeen from worker-derived brood. This, however, is a relatively rare event in wild populations. Moreover, workerderived queens were described to be smaller, more worker-like and reproductively inferior. On the other hand, the fixation of the thelytokous trait relies mainly on sufficient numbers of viable drones produced by worker-derived queens. Small numbers of reproductively inferior worker-derived queens in A. m. capensis populations would be clearly counterintuitive. It is therefore necessary to quantify the significance of worker-dependant queen rearing pathways on the individual (queen) and on population level.Reproductive inferiority of worker-derived queens could not be confirmed on the individual (queen) level when comparing parameters indicating potential reproductive success of queen- and worker-derived queens. Queen- and worker-derived queens clearly showed a congruent range of reproductive performance. In queen rearing preference tests, increased acceptance of worker-derived female larvae was exactly counterbalanced by increased mortality, resulting in an equal number of eclosing virgin queens from an equal number of grafts in both test groups. Larval survival and successful eclosion is a prerequisite for a queen’s reproductive success. I found no difference in eclosion success for queen- and worker-derived virgin queens, indicating a similar potential for reproductive success in both queen types. Assessments of the developmental patterns of colonies headed by both queen and worker-derived queens in long-term experiments revealed no significant differences in reproductive success. Colonies headed by queen-derived queens and colonies headed by worker-derived queens could not be separated when comparing the different developmental pathways observed or from differences in worker-force. Reproductive dominance in A. m. capensis appeared tobe determined by a function of relative compositional and absolute quantitative pheromonal patterns, where individuals, which produce compositionally most queen-like blends in highest quantities, occupy top positions. Queen- and worker-derived virgin queens occupied intermediate positions between pseudoqueens and mated queens. However, no significant differences between the pheromonal status of queen- and worker-derived virgin queens were observed, suggesting a similar range of reproductive dominance for both queen types. In behavioural bioassays queen- and worker-derived virgin queens appeared to be similarly attractive to clustering workers and to drones in a drone congregation area, indicating no differences in potential reproductive success for queens from both origins for those parameters. The significant influence of the queen substance 9-ODA on attractiveness to workers and drones was confirmed. Rare requeening events from worker-derived female brood in queenless A.m. capensis do not satisfactorily explain the fixation of the thelytokous trait at a population level. I observed A. m. capensis worker ovipositing into empty artificial queen cell cups in queen-right colonies. The queen was confined behind a queen excluder grid in a separate compartment of the colony, to imitate reduced pheromonal flow, similar to swarming or superseding colonies. Eggs oviposited by workers in artificial queen cell cups were readily accepted for queen rearing and successful eclosion of viable virgin queens was observed. Consequently I suggested an alternative worker-dependant reproductive pathway in A. m. capensis, which was never described before: In swarming or superseding queenright colonies, laying workers may directly compete with the queen for reproductive success by ovipositing (instead of the queen) into natural queen cell cups. At a population level this reproductive tactic may result in large numbers of worker-derived queens of high reproductive quality in natural populations of A. m. capensis.
- Full Text:
- Date Issued: 2008
Spatial and temporal variations in metals in the sediment and water of selected Eastern Cape Estuaries, South Africa
- Authors: Orr, Kyla Kathleen
- Date: 2008
- Subjects: Marine sediments -- South Africa -- Eastern Cape , Metals -- South Africa -- Eastern Cape , Metals -- Environmental aspects , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuarine sediments -- South Africa -- Eastern Cape , Water quality -- South Africa -- Eastern Cape , Water pollution -- South Africa -- Eastern Cape , Environmental toxicology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5769 , http://hdl.handle.net/10962/d1005457 , Marine sediments -- South Africa -- Eastern Cape , Metals -- South Africa -- Eastern Cape , Metals -- Environmental aspects , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuarine sediments -- South Africa -- Eastern Cape , Water quality -- South Africa -- Eastern Cape , Water pollution -- South Africa -- Eastern Cape , Environmental toxicology -- South Africa -- Eastern Cape
- Description: The spatio-temporal patterns in concentrations of selected metals within the sediment (Cd, Co, Cu, Fe, Pb, Ni and Zn) and water (Cd and Pb) of three permanently open estuaries (Kariega, Kowie, Great Fish) and six temporary open-closed estuaries (Mpekweni, East Kleinemonde, West Kleinemonde, Riet, Kasouga, Boknes) were investigated. The concentrations of metals were influenced by size composition and total organic content of the sediments. Enrichment factors (EFs), using Fe as a reference element, and baseline linear regression models for metals vs. Fe were calculated to assess the extent of metal enrichment in the sediments. The mean concentrations of metals in the sediments(mg·kg⁻¹) showed ranges of 0.28 – 2.31 for Cd, 1.26 – 6.24 Co, 0.69 – 6.93 for Cu, 2119 – 14912 for Fe, 2.29 –14.01 for Ni, 4.81 – 22.20 for Pb and 5.77 – 21.75 for Zn. Mean normalized enrichment factors ranged between 0.75 – 6.19 for Cd, 0.53 – 2.71 for Co, 0.22 – 0.84 for Cu, 0.30 – 1.87 for Ni, 0.99 – 3.17 for Pb and 0.14 – 0.98 for Zn. All nine estuaries had average enrichment factors of greater than 1 for Cd. In general there was no enrichment of Cu and Zn in the sediments of any of the estuaries included in this study (EFs < 1). The Kariega, East Kleinemonde, West Kleinemonde, Riet and Great Fish Estuaries showed some degree of enrichment for Co (1 < EF < 4), Ni (1 < EF < 2) and Pb (1 < EF < 4), while the Mpekweni, Kasouga, Boknes and Kowie Estuaries were unenriched with these metals (EF < 1). Enrichment factors for Cd, Co and Pb typically followed the development gradient along the estuaries, suggesting anthropogenic enrichment. The concentrations of Cd and Pb in the water of the nine estuaries were also determined. The average concentrations of Cd and Pb in the water (μg·ℓ⁻¹) ranged between 0.05 – 3.32 and 0.75 – 34.13 respectively. On average the concentrations of Cd and Pb in the water of all the estuaries were below the South African recommended water quality guidelines for coastal marine waters. Variations in metal concentrations associated with changes in hydrology (wet vs. dry season) were determined in the water and sediment of the Kariega, East Kleinemonde and Riet Estuaries. Cobalt, Pb and Ni enrichment in the Kariega Estuary sediment was significantly higher during the dry season, and the mean concentrations of Pb and Cd in the water column were 19-fold and 66-fold higher in the dry season. The elevated concentration of metals during the dry season could be related to accumulation of diffuse pollution from human activities within the catchment area. Conversely, inflow of fresh water into the estuary had the net effect of reducing the concentration and enrichment of these metals within the Kariega Estuary due to scouring and outflow of estuarine water and sediment into the marine environment. The temporal variations in metal concentrations and enrichment factors were less pronounced in the temporary open-closed estuaries than the permanently open Kariega Estuary. The observed trend can probably be related to the low anthropogenic impact within the catchment areas of these systems, and the relatively smaller size of the catchments. Significant spatial variations existed in metal enrichment in the sediment of both the East Kleinemonde and Riet estuaries, with the highest degrees of enrichment occurring in the sediments from the marine environment and lower reaches.
- Full Text:
- Date Issued: 2008
- Authors: Orr, Kyla Kathleen
- Date: 2008
- Subjects: Marine sediments -- South Africa -- Eastern Cape , Metals -- South Africa -- Eastern Cape , Metals -- Environmental aspects , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuarine sediments -- South Africa -- Eastern Cape , Water quality -- South Africa -- Eastern Cape , Water pollution -- South Africa -- Eastern Cape , Environmental toxicology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5769 , http://hdl.handle.net/10962/d1005457 , Marine sediments -- South Africa -- Eastern Cape , Metals -- South Africa -- Eastern Cape , Metals -- Environmental aspects , Estuaries -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Estuarine sediments -- South Africa -- Eastern Cape , Water quality -- South Africa -- Eastern Cape , Water pollution -- South Africa -- Eastern Cape , Environmental toxicology -- South Africa -- Eastern Cape
- Description: The spatio-temporal patterns in concentrations of selected metals within the sediment (Cd, Co, Cu, Fe, Pb, Ni and Zn) and water (Cd and Pb) of three permanently open estuaries (Kariega, Kowie, Great Fish) and six temporary open-closed estuaries (Mpekweni, East Kleinemonde, West Kleinemonde, Riet, Kasouga, Boknes) were investigated. The concentrations of metals were influenced by size composition and total organic content of the sediments. Enrichment factors (EFs), using Fe as a reference element, and baseline linear regression models for metals vs. Fe were calculated to assess the extent of metal enrichment in the sediments. The mean concentrations of metals in the sediments(mg·kg⁻¹) showed ranges of 0.28 – 2.31 for Cd, 1.26 – 6.24 Co, 0.69 – 6.93 for Cu, 2119 – 14912 for Fe, 2.29 –14.01 for Ni, 4.81 – 22.20 for Pb and 5.77 – 21.75 for Zn. Mean normalized enrichment factors ranged between 0.75 – 6.19 for Cd, 0.53 – 2.71 for Co, 0.22 – 0.84 for Cu, 0.30 – 1.87 for Ni, 0.99 – 3.17 for Pb and 0.14 – 0.98 for Zn. All nine estuaries had average enrichment factors of greater than 1 for Cd. In general there was no enrichment of Cu and Zn in the sediments of any of the estuaries included in this study (EFs < 1). The Kariega, East Kleinemonde, West Kleinemonde, Riet and Great Fish Estuaries showed some degree of enrichment for Co (1 < EF < 4), Ni (1 < EF < 2) and Pb (1 < EF < 4), while the Mpekweni, Kasouga, Boknes and Kowie Estuaries were unenriched with these metals (EF < 1). Enrichment factors for Cd, Co and Pb typically followed the development gradient along the estuaries, suggesting anthropogenic enrichment. The concentrations of Cd and Pb in the water of the nine estuaries were also determined. The average concentrations of Cd and Pb in the water (μg·ℓ⁻¹) ranged between 0.05 – 3.32 and 0.75 – 34.13 respectively. On average the concentrations of Cd and Pb in the water of all the estuaries were below the South African recommended water quality guidelines for coastal marine waters. Variations in metal concentrations associated with changes in hydrology (wet vs. dry season) were determined in the water and sediment of the Kariega, East Kleinemonde and Riet Estuaries. Cobalt, Pb and Ni enrichment in the Kariega Estuary sediment was significantly higher during the dry season, and the mean concentrations of Pb and Cd in the water column were 19-fold and 66-fold higher in the dry season. The elevated concentration of metals during the dry season could be related to accumulation of diffuse pollution from human activities within the catchment area. Conversely, inflow of fresh water into the estuary had the net effect of reducing the concentration and enrichment of these metals within the Kariega Estuary due to scouring and outflow of estuarine water and sediment into the marine environment. The temporal variations in metal concentrations and enrichment factors were less pronounced in the temporary open-closed estuaries than the permanently open Kariega Estuary. The observed trend can probably be related to the low anthropogenic impact within the catchment areas of these systems, and the relatively smaller size of the catchments. Significant spatial variations existed in metal enrichment in the sediment of both the East Kleinemonde and Riet estuaries, with the highest degrees of enrichment occurring in the sediments from the marine environment and lower reaches.
- Full Text:
- Date Issued: 2008
The ecology and conservation of Mackinder's eagle owls (Bubo capensis mackinderi) in central Kenya in relation to agricultural land-use and cultural attitudes
- Authors: Ogada, Darcy L
- Date: 2008
- Subjects: Cape eagle owl -- Kenya Cape eagle owl -- Habitat -- Kenya Cape eagle owl -- Breeding -- Kenya Cape eagle owl -- Nutrition -- Kenya Bubo -- Kenya Wildlife conservation -- Kenya Biodiversity conservation -- Kenya
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5668 , http://hdl.handle.net/10962/d1005353
- Description: The loss of habitat to agriculture is a worldwide problem for biodiversity conservation. One species that has seemingly been able to adapt to the conversion of forests to farmlands is Mackinder’s eagle owl (Bubo capensis mackinderi), which inhabits highland areas, but little is known of its ecology, especially outside of protected areas. This study examined the impact of agricultural practices and farmer’s attitudes on the foraging and population ecology of the Mackinder’s eagle owl in central Kenya. Owl territories were monitored monthly from June 2004- October 2006 for signs of occupancy, breeding activity, mortality and to collect data on food resources. Nest site characteristics were measured for all known nests. Because previous studies showed an affinity for rodents, small mammals were trapped monthly using mark-recapture methodology. In each territory, the type and amount of farm crops were measured each month and farmers were interviewed about their knowledge and beliefs about owls. Mackinder’s eagle owls in central Kenya lived at extremely high density 0.87 owl pairs/km². This density was high compared to other populations of Mackinder’s eagle owl and to Eurasian eagle owl (Bubo bubo) populations in Europe. Breeding success was 48% over three years and this compared well with other species of eagle owl inhabiting human-disturbed areas. All nests and roosts were located in river valleys, and all successful nest sites were located on cliffs or other inaccessible rocky terrain. Nest sites were located adjacent to farms, which provided for both open hunting and an abundance of prey. Breeding activity was concentrated after the rainy seasons and this was likely linked to prey availability after the rains. Agricultural activities generally had a positive effect on rodent populations. Small mammal trapping results revealed that rodents were over 14 times more abundant in farms than in adjacent grassland habitat. This population of Mackinder’s eagle owl had a very catholic diet and consumed mostly mammalian prey species including hares, giant rats, root rats, grooved-tooth rats and small rodents. Small rodents accounted for almost half of the owls’ diet and when their numbers increased, owls responded by consuming more of them, indicating the importance of farming activities to this population of owls. Other populations of eagle owl inhabiting human-disturbed areas had diet widths positively related to levels of habitat disturbance. This result supported optimal foraging theory that more productive environments have predators with more specialized diets, while patchy environments have generalist predators. The ecology of this population of Mackinder’s eagle owls was heavily influenced by human agricultural activities, which generally had a positive effect on their population. Farming activities changed rapidly both within and between seasons as plots were small and neighbouring farmers planted various crops at different times of the year and this was enhanced by irrigation in some areas. Year-round availability of forage within farms had a positive effect on owl prey species, some of which increased relative to the type and amount of crops found in farms. However, 57% of owl injuries and mortalities that occurred were related either directly or indirectly to human activities. Cultural prejudices against owls remain the biggest threat to this population’s long-term persistence. Farmer education was shown to play a significant role in overcoming negative beliefs about owls. Because Mackinder’s eagle owls are highly adaptable to anthropomorphic landscape changes, largely due to their adaptability as food generalists, they are one of the few top predators remaining in this highly disturbed agricultural system. However, populations within agricultural areas remain especially vulnerable to negative human attitudes towards owls due to their close association with human activities.
- Full Text:
- Date Issued: 2008
- Authors: Ogada, Darcy L
- Date: 2008
- Subjects: Cape eagle owl -- Kenya Cape eagle owl -- Habitat -- Kenya Cape eagle owl -- Breeding -- Kenya Cape eagle owl -- Nutrition -- Kenya Bubo -- Kenya Wildlife conservation -- Kenya Biodiversity conservation -- Kenya
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5668 , http://hdl.handle.net/10962/d1005353
- Description: The loss of habitat to agriculture is a worldwide problem for biodiversity conservation. One species that has seemingly been able to adapt to the conversion of forests to farmlands is Mackinder’s eagle owl (Bubo capensis mackinderi), which inhabits highland areas, but little is known of its ecology, especially outside of protected areas. This study examined the impact of agricultural practices and farmer’s attitudes on the foraging and population ecology of the Mackinder’s eagle owl in central Kenya. Owl territories were monitored monthly from June 2004- October 2006 for signs of occupancy, breeding activity, mortality and to collect data on food resources. Nest site characteristics were measured for all known nests. Because previous studies showed an affinity for rodents, small mammals were trapped monthly using mark-recapture methodology. In each territory, the type and amount of farm crops were measured each month and farmers were interviewed about their knowledge and beliefs about owls. Mackinder’s eagle owls in central Kenya lived at extremely high density 0.87 owl pairs/km². This density was high compared to other populations of Mackinder’s eagle owl and to Eurasian eagle owl (Bubo bubo) populations in Europe. Breeding success was 48% over three years and this compared well with other species of eagle owl inhabiting human-disturbed areas. All nests and roosts were located in river valleys, and all successful nest sites were located on cliffs or other inaccessible rocky terrain. Nest sites were located adjacent to farms, which provided for both open hunting and an abundance of prey. Breeding activity was concentrated after the rainy seasons and this was likely linked to prey availability after the rains. Agricultural activities generally had a positive effect on rodent populations. Small mammal trapping results revealed that rodents were over 14 times more abundant in farms than in adjacent grassland habitat. This population of Mackinder’s eagle owl had a very catholic diet and consumed mostly mammalian prey species including hares, giant rats, root rats, grooved-tooth rats and small rodents. Small rodents accounted for almost half of the owls’ diet and when their numbers increased, owls responded by consuming more of them, indicating the importance of farming activities to this population of owls. Other populations of eagle owl inhabiting human-disturbed areas had diet widths positively related to levels of habitat disturbance. This result supported optimal foraging theory that more productive environments have predators with more specialized diets, while patchy environments have generalist predators. The ecology of this population of Mackinder’s eagle owls was heavily influenced by human agricultural activities, which generally had a positive effect on their population. Farming activities changed rapidly both within and between seasons as plots were small and neighbouring farmers planted various crops at different times of the year and this was enhanced by irrigation in some areas. Year-round availability of forage within farms had a positive effect on owl prey species, some of which increased relative to the type and amount of crops found in farms. However, 57% of owl injuries and mortalities that occurred were related either directly or indirectly to human activities. Cultural prejudices against owls remain the biggest threat to this population’s long-term persistence. Farmer education was shown to play a significant role in overcoming negative beliefs about owls. Because Mackinder’s eagle owls are highly adaptable to anthropomorphic landscape changes, largely due to their adaptability as food generalists, they are one of the few top predators remaining in this highly disturbed agricultural system. However, populations within agricultural areas remain especially vulnerable to negative human attitudes towards owls due to their close association with human activities.
- Full Text:
- Date Issued: 2008
The effects of elephants at low densities and after short occupation time on the ecosystems of the Eastern Cape Province, South Africa
- Authors: Parker, Daniel Matthew
- Date: 2008
- Subjects: Elephants -- South Africa -- Eastern Cape Biotic communities -- South Africa -- Eastern Cape Animal populations -- South Africa -- Eastern Cape Plant communities -- South Africa -- Eastern Cape Mammals -- Ecology -- South Africa -- Eastern Cape Animal-plant relationships -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5678 , http://hdl.handle.net/10962/d1005363
- Description: Elephants (Loxodonta africana, Blumenbach) are recognised as keystone herbivores and ecosystem engineers in African ecosystems due to the noticeable impact they have on plant communities. This impact can influence other animal taxa and ecosystem processes, especially within enclosed systems. I investigated the effects of elephants in four vegetation types and the cascade effect on three associated taxa and two ecosystem processes at five sites with elephants and five paired sites without elephants in the Eastern Cape Province, South Africa, between April 2005 and July 2007. In grassland habitats, the physical structure of the vegetation was neither enhanced nor degraded in the presence of elephants. Within the locally important Thicket Biome, elephant browsing transformed relatively homogeneous stands of vegetation into more heterogeneous units. However, although seeds from thicket plant species were recorded in elephant dung, elephants did not promote the viability and germination success of these plants. In addition, elephant foraging on aloes caused declines in their populations. By contrast, the size of bushclumps was not reduced in the presence of elephants in bushclump savanna. The associated insect, bird and mammal communities appeared to benefit from elephant foraging in all vegetation types assessed, whereas vegetation patch dynamics and soil surface processes were neither enhanced nor degraded in the presence of elephants. I conclude that, at current densities, elephants do not (in most cases) negatively affect plant and animal communities or ecosystem processes in enclosed reserves. However, elephants have only been present at each site for a relatively short period and it is likely that their impact will be cumulative, increasing over time in these closed systems. Thus, future research along a continuum of elephant density and time since re-introduction is recommended.
- Full Text:
- Date Issued: 2008
- Authors: Parker, Daniel Matthew
- Date: 2008
- Subjects: Elephants -- South Africa -- Eastern Cape Biotic communities -- South Africa -- Eastern Cape Animal populations -- South Africa -- Eastern Cape Plant communities -- South Africa -- Eastern Cape Mammals -- Ecology -- South Africa -- Eastern Cape Animal-plant relationships -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5678 , http://hdl.handle.net/10962/d1005363
- Description: Elephants (Loxodonta africana, Blumenbach) are recognised as keystone herbivores and ecosystem engineers in African ecosystems due to the noticeable impact they have on plant communities. This impact can influence other animal taxa and ecosystem processes, especially within enclosed systems. I investigated the effects of elephants in four vegetation types and the cascade effect on three associated taxa and two ecosystem processes at five sites with elephants and five paired sites without elephants in the Eastern Cape Province, South Africa, between April 2005 and July 2007. In grassland habitats, the physical structure of the vegetation was neither enhanced nor degraded in the presence of elephants. Within the locally important Thicket Biome, elephant browsing transformed relatively homogeneous stands of vegetation into more heterogeneous units. However, although seeds from thicket plant species were recorded in elephant dung, elephants did not promote the viability and germination success of these plants. In addition, elephant foraging on aloes caused declines in their populations. By contrast, the size of bushclumps was not reduced in the presence of elephants in bushclump savanna. The associated insect, bird and mammal communities appeared to benefit from elephant foraging in all vegetation types assessed, whereas vegetation patch dynamics and soil surface processes were neither enhanced nor degraded in the presence of elephants. I conclude that, at current densities, elephants do not (in most cases) negatively affect plant and animal communities or ecosystem processes in enclosed reserves. However, elephants have only been present at each site for a relatively short period and it is likely that their impact will be cumulative, increasing over time in these closed systems. Thus, future research along a continuum of elephant density and time since re-introduction is recommended.
- Full Text:
- Date Issued: 2008
The feeding and spatial ecologies of the large carnivore guild on Kwandwe Private Game Reserve
- Authors: Bissett, Charlene
- Date: 2008
- Subjects: Wildlife conservation -- South Africa -- Eastern Cape Kwandwe Private Game Reserve Lion -- Behavior -- South Africa -- Eastern Cape Lion -- Nutrition -- South Africa -- Eastern Cape Cheetah -- Behavior -- South Africa -- Eastern Cape Cheetah -- Nutrition -- South Africa -- Eastern Cape African wild dog -- South Africa -- Eastern Cape Spatial behavior in animals Predation (Biology) Game reserves -- Management
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5802 , http://hdl.handle.net/10962/d1006195
- Description: The reintroduction of lions, cheetahs and African wild dogs to Kwandwe Private Game Reserve in the Eastern Cape Province of South Africa created the opportunity to study the biology and behaviour of these large carnivores in an enclosed system. The research focused on space utilisation and feeding ecology of the predators, using standard observational methods. Changes in the structure of the carnivore guild, and changes in the prey base that occurred during the study were used as natural experiments to examine factors affecting space use and diet. In general, the diets of the predators were similar to previous studies and prey abundance was more important than prey species size in determining prey selection. Changes in the abundance of certain prey species was matched by a dietary switch in lions from kudu to warthog and an increase in the proportion of springbok kills by the cheetahs. There was no significant difference in the proportions of prey species detected by ad hoc or continuous observations. Core areas occupied by the predators were significantly smaller than home ranges except when females were denning. Home ranges overlapped both within and between species, but there was very little overlap of core areas. An increase in the number of lion prides in the area during the study resulted in an increase in overlap of home ranges of lions and cheetahs, but did not result in a change in home range size. Space use by female cheetahs with cubs increased as the cubs grew older. The use of thicket vegetation by cheetahs decreased with an increase in the number of lion prides. Minimum Daily Energy Expenditure, energy intake and net benefit were calculated for the predators using data from continuous observations. All predators exhibited a large net benefit and the net benefit for single female cheetahs was greater than for the members of the coalition. Net benefit for the alpha pair of African wild dogs was lower than that of the pack.
- Full Text:
- Date Issued: 2008
- Authors: Bissett, Charlene
- Date: 2008
- Subjects: Wildlife conservation -- South Africa -- Eastern Cape Kwandwe Private Game Reserve Lion -- Behavior -- South Africa -- Eastern Cape Lion -- Nutrition -- South Africa -- Eastern Cape Cheetah -- Behavior -- South Africa -- Eastern Cape Cheetah -- Nutrition -- South Africa -- Eastern Cape African wild dog -- South Africa -- Eastern Cape Spatial behavior in animals Predation (Biology) Game reserves -- Management
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5802 , http://hdl.handle.net/10962/d1006195
- Description: The reintroduction of lions, cheetahs and African wild dogs to Kwandwe Private Game Reserve in the Eastern Cape Province of South Africa created the opportunity to study the biology and behaviour of these large carnivores in an enclosed system. The research focused on space utilisation and feeding ecology of the predators, using standard observational methods. Changes in the structure of the carnivore guild, and changes in the prey base that occurred during the study were used as natural experiments to examine factors affecting space use and diet. In general, the diets of the predators were similar to previous studies and prey abundance was more important than prey species size in determining prey selection. Changes in the abundance of certain prey species was matched by a dietary switch in lions from kudu to warthog and an increase in the proportion of springbok kills by the cheetahs. There was no significant difference in the proportions of prey species detected by ad hoc or continuous observations. Core areas occupied by the predators were significantly smaller than home ranges except when females were denning. Home ranges overlapped both within and between species, but there was very little overlap of core areas. An increase in the number of lion prides in the area during the study resulted in an increase in overlap of home ranges of lions and cheetahs, but did not result in a change in home range size. Space use by female cheetahs with cubs increased as the cubs grew older. The use of thicket vegetation by cheetahs decreased with an increase in the number of lion prides. Minimum Daily Energy Expenditure, energy intake and net benefit were calculated for the predators using data from continuous observations. All predators exhibited a large net benefit and the net benefit for single female cheetahs was greater than for the members of the coalition. Net benefit for the alpha pair of African wild dogs was lower than that of the pack.
- Full Text:
- Date Issued: 2008
Understanding and improving the residual efficacy of the cryptophlebia leucotreta granulovirus (Cryptogran)
- Authors: Kirkman, Wayne
- Date: 2008
- Subjects: Cryptophlebia leucotreta , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Citrus -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5794 , http://hdl.handle.net/10962/d1005482 , Cryptophlebia leucotreta , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Citrus -- Diseases and pests
- Description: False codling moth (FCM), Thaumatotibia (=Cryptophlebia) leucotreta (Meyr) (Lepidoptera: Tortricidae), is one of the most important pests on citrus. The Cryptophlebia leucotreta granulovirus (CrleGV) has been developed into a successful biological control agent, registered under the name Cryptogran, and is currently the preferred product for the control of FCM on citrus in South Africa. A prerequisite to the continued success of Cryptogran as a means of controlling false codling moth is to understand the factors affecting field persistence of the virus, and to find ways to improve it. The aim of this study was to gain a clearer understanding of the product and the abiotic and biotic factors affecting its persistence in the field, and to investigate methods to improve this persistence. The effect of UV-irradiation on the virus was determined, and various products were tested as UV protectants in laboratory bioassays. Lignin was the most effective additive, and was tested in several field trials, where it also enhanced the efficacy of Cryptogran. Laboratory trials indicated that Cryptogran is rainfast. Cryptogran applications early in the season had a longer period of residual activity than sprays applied closer to harvest. Daytime applications were less effective that evening sprays. Sprays applied coinciding with peaks in pheromone moth trap catches were more effective than those applied between peaks. Biotic factors influencing persistence were investigated. Residual efficacy was longer when treatments were applied to blocks than as single tree treatments. Attempts were made to quantify the effect of the navel end of a navel orange on the field persistence of Cryptogran. Cryptogran was shown to be compatible with many agricultural chemicals used on citrus. Economic thresholds and various cost-benefit analyses are discussed. A list of practical recommendations to growers was drawn up, and possibilities for future research are presented.
- Full Text:
- Date Issued: 2008
- Authors: Kirkman, Wayne
- Date: 2008
- Subjects: Cryptophlebia leucotreta , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Citrus -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5794 , http://hdl.handle.net/10962/d1005482 , Cryptophlebia leucotreta , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Citrus -- Diseases and pests
- Description: False codling moth (FCM), Thaumatotibia (=Cryptophlebia) leucotreta (Meyr) (Lepidoptera: Tortricidae), is one of the most important pests on citrus. The Cryptophlebia leucotreta granulovirus (CrleGV) has been developed into a successful biological control agent, registered under the name Cryptogran, and is currently the preferred product for the control of FCM on citrus in South Africa. A prerequisite to the continued success of Cryptogran as a means of controlling false codling moth is to understand the factors affecting field persistence of the virus, and to find ways to improve it. The aim of this study was to gain a clearer understanding of the product and the abiotic and biotic factors affecting its persistence in the field, and to investigate methods to improve this persistence. The effect of UV-irradiation on the virus was determined, and various products were tested as UV protectants in laboratory bioassays. Lignin was the most effective additive, and was tested in several field trials, where it also enhanced the efficacy of Cryptogran. Laboratory trials indicated that Cryptogran is rainfast. Cryptogran applications early in the season had a longer period of residual activity than sprays applied closer to harvest. Daytime applications were less effective that evening sprays. Sprays applied coinciding with peaks in pheromone moth trap catches were more effective than those applied between peaks. Biotic factors influencing persistence were investigated. Residual efficacy was longer when treatments were applied to blocks than as single tree treatments. Attempts were made to quantify the effect of the navel end of a navel orange on the field persistence of Cryptogran. Cryptogran was shown to be compatible with many agricultural chemicals used on citrus. Economic thresholds and various cost-benefit analyses are discussed. A list of practical recommendations to growers was drawn up, and possibilities for future research are presented.
- Full Text:
- Date Issued: 2008
A preliminary examination of selected biological links between four Eastern Cape estuaries and the inshore marine environment
- Authors: Vorwerk, Paul D
- Date: 2007
- Subjects: Estuaries -- South Africa -- Eastern Cape Marine fishes -- South Africa -- Eastern Cape Marine ecology -- South Africa -- Eastern Cape Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5747 , http://hdl.handle.net/10962/d1005434
- Description: The coastal transition zone (CTZ), which links the terrestrial and marine environments, has been identified as a region of high biological diversity and elevated production. Results of studies conducted in the northern hemisphere indicate that the links between estuaries and the adjacent marine environment is critical to ecological functioning within the CTZ. This study assessed the influence of selected estuaries with different hydrodynamic characteristics on the adjacent marine environment along the south-eastern coastline of southern Africa. Four estuaries were examined, including two permanently open systems, the fresh water deprived Kariega and fresh water dominated Great Fish, and two temporarily open/closed estuaries (TOCE), the Kasouga and East Kleinemonde. Results of the study indicated that outflow of estuarine water from the Great Fish Estuary contributed to a plume of less saline water being evident within the adjacent marine environment. The plume of water was associated with increased zooplankton biomass and particulate organic matter (POM) and chlorophyll-a concentrations. Adjacent to the Kariega Estuary, no evidence of fresh water outflow into the marine environment was observed. However, in the sea directly opposite the mouth of the estuary an increase in zooplankton abundance and biomass was evident. Results of numerical analyses indicated that the increase in zooplankton abundance observed adjacent to the mouth of both permanently open estuaries could not be attributed to the export of zooplankton from the estuary, but rather the accumulation of marine species within the region. The mechanisms responsible for this accumulation were not determined, but it was thought to be associated with increased food availability in the estuarine frontal zone. A similar, but less dramatic biological response was also observed in the marine environment adjacent to the two TOCEs. It is suggested that the increase in biological activity within these regions could be ascribed to seepage of estuarine or ground water through the sand bar that separates these estuaries from the sea. Results of stable carbon isotope analyses indicated that both the Great Fish and Kariega estuaries exported carbon to the nearshore marine environment. The area influenced by estuarine derived carbon was dependent on the volume of estuarine outflow to the marine environment. Adjacent to the fresh water dominated Great Fish Estuary, estuarine derived carbon was recorded up to 12km from the mouth, while adjacent to the fresh water deprived Kariega, estuarine derived carbon was only evident directly opposite the mouth. The recruitment of macrozooplankton (> 2cm) into the fresh water deprived Kariega Estuary was in the range recorded for other permanently open southern African estuaries with higher fresh water flow rates. This indicates that the mechanisms which allow estuarine dependent larvae to locate and enter estuaries are not related to fresh water inflow. In conclusion, this study has demonstrated that despite their small size relative to European and North American systems, South African permanently open and temporarily open/closed estuaries also influence biological activity within the adjacent nearshore marine environment.
- Full Text:
- Date Issued: 2007
- Authors: Vorwerk, Paul D
- Date: 2007
- Subjects: Estuaries -- South Africa -- Eastern Cape Marine fishes -- South Africa -- Eastern Cape Marine ecology -- South Africa -- Eastern Cape Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5747 , http://hdl.handle.net/10962/d1005434
- Description: The coastal transition zone (CTZ), which links the terrestrial and marine environments, has been identified as a region of high biological diversity and elevated production. Results of studies conducted in the northern hemisphere indicate that the links between estuaries and the adjacent marine environment is critical to ecological functioning within the CTZ. This study assessed the influence of selected estuaries with different hydrodynamic characteristics on the adjacent marine environment along the south-eastern coastline of southern Africa. Four estuaries were examined, including two permanently open systems, the fresh water deprived Kariega and fresh water dominated Great Fish, and two temporarily open/closed estuaries (TOCE), the Kasouga and East Kleinemonde. Results of the study indicated that outflow of estuarine water from the Great Fish Estuary contributed to a plume of less saline water being evident within the adjacent marine environment. The plume of water was associated with increased zooplankton biomass and particulate organic matter (POM) and chlorophyll-a concentrations. Adjacent to the Kariega Estuary, no evidence of fresh water outflow into the marine environment was observed. However, in the sea directly opposite the mouth of the estuary an increase in zooplankton abundance and biomass was evident. Results of numerical analyses indicated that the increase in zooplankton abundance observed adjacent to the mouth of both permanently open estuaries could not be attributed to the export of zooplankton from the estuary, but rather the accumulation of marine species within the region. The mechanisms responsible for this accumulation were not determined, but it was thought to be associated with increased food availability in the estuarine frontal zone. A similar, but less dramatic biological response was also observed in the marine environment adjacent to the two TOCEs. It is suggested that the increase in biological activity within these regions could be ascribed to seepage of estuarine or ground water through the sand bar that separates these estuaries from the sea. Results of stable carbon isotope analyses indicated that both the Great Fish and Kariega estuaries exported carbon to the nearshore marine environment. The area influenced by estuarine derived carbon was dependent on the volume of estuarine outflow to the marine environment. Adjacent to the fresh water dominated Great Fish Estuary, estuarine derived carbon was recorded up to 12km from the mouth, while adjacent to the fresh water deprived Kariega, estuarine derived carbon was only evident directly opposite the mouth. The recruitment of macrozooplankton (> 2cm) into the fresh water deprived Kariega Estuary was in the range recorded for other permanently open southern African estuaries with higher fresh water flow rates. This indicates that the mechanisms which allow estuarine dependent larvae to locate and enter estuaries are not related to fresh water inflow. In conclusion, this study has demonstrated that despite their small size relative to European and North American systems, South African permanently open and temporarily open/closed estuaries also influence biological activity within the adjacent nearshore marine environment.
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- Date Issued: 2007