Cape Fold Ecoregion fish community ecology and responses to stressors
- Authors: Broom, Casey Jay
- Date: 2022-10-14
- Subjects: Cyprinidae South Africa Western Cape , Freshwater fishes South Africa Western Cape , Cyprinidae Habitat South Africa Western Cape , Food chains (Ecology) , Restoration ecology South Africa Western Cape , Riparian restoration South Africa Western Cape
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365644 , vital:65772 , DOI https://doi.org/10.21504/10962/365644
- Description: Freshwater fishes are in global decline and fish as a group are the most imperilled of all vertebrates. Freshwater systems are among the most threatened globally, largely owing to their comparatively high species and habitat diversity while occupying a minute fraction of the Earth’s surface. In South Africa, invasion by non-native fishes has had a devastating effect on freshwater systems across the country. Numerous other stressors and anthropogenic impacts continue to impact these systems, including habitat degradation, water abstraction and global change effects. In general, South African freshwater systems are under-studied and there is a lack of baseline biological and ecological studies on many freshwater fish species. The Cape Fold Ecoregion (CFE) of South Africa is a particularly vulnerable region, with many range-restricted species and highly fragmented native fish ranges following high invasion rates. Within the CFE, the Olifants-Doring River System (ODRS) is of primary concern owing to the high endemism and imperilled status of its freshwater fish species. The Rondegat River in the ODRS is of notable conservation value, as it hosts populations of important endemic CFE species. This river is unique, being the site of the first alien fish eradication programme of its kind in South Africa. Thus the Rondegat River, and in particular its imperilled cyprinid assemblage, is used here as a case study of the responses and community dynamics of recovering freshwater fish species. The members of this cyprinid assemblage are Sedercypris calidus, Pseudobarbus phlegethon and Labeobarbus seeberi. Sedercypris calidus and L. seeberi are listed by the International Union for the Conservation of Nature (IUCN) as “Near-Threatened”, while P. phlegethon is listed as “Endangered”. Understanding the dynamics and responses to understudied vulnerable fish communities in the wake of restoration efforts was the overarching goal of this thesis. The first chapter served as a review of current knowledge of the CFE, the Rondegat River, the myriad stressors that have impacted on or are projected to affect this region, and the freshwater fish species on which those stressors act. My first investigations served as an extension of the existing Rondegat River monitoring programme, making use of remote underwater video (RUV) data to assess relative abundance and habitat associations of the focal species (Chapter 2). A relatively limited spatial range of P. phlegethon was established, which was suggested to be a result of relatively highly specialised habitat requirements and sensitivity to disturbance. Sedercypris calidus was confirmed as a relatively more abundant and ubiquitous species across the length of the Rondegat River, sharing much of the lower and middle reaches with L. seeberi. I sought to use experimental trials of functional response, as a proxy for feeding performance, across representative temperatures and relevant prey types, in the spatially overlapping S. calidus and L. seeberi (Chapter 3). Labeobarbus seeberi generally outcompeted S. calidus across temperature treatments and prey types. The ecomorphology and diet of all three species were used to construct trophic profiles, which suggested that there was a high degree of feeding capacity overlap between L. seeberi and S. calidus, while P. phlegethon diverged from the other two species (Chapter 4). Gut content suggested that all three species overlapped broadly in diet. This indicated that the realised trophic niche of these species is similar, despite some morphological specialisation. I then used RUV data to investigate in-situ feeding behaviours, with the aim to disentangle the nuances of community dynamics and mechanisms of coexistence in the cyprinid assemblage (Chapter 5). I found that, despite the higher feeding performance of L. seeberi (Chapter 3) and its overlaps in diet and feeding capacity with S. calidus (Chapter 4), S. calidus is able to mitigate competitive pressures through foraging mode switching and exploitation of allochthonous food inputs. Evidence for further habitat and prey selectivity in Pseudobarbus phlegethon was gathered based on dependence on complex habitats and pool refugia for the majority of its feeding, supporting this species as a headwater specialist; alongside signals of its spatial and habitat use patterns (Chapter 2). While S. calidus and L. seeberi were found to be less habitat-specific than P. phlegethon, caution was noted in the potential for ongoing stressors, such as habitat destruction, loss of river connectivity and global change effects, to impact on the reproductive success of these two species. Stressors affecting the habitats and sensitive invertebrate taxa upon which all three species depend continue to threaten the Rondegat system, highlighting the need to maintain ecosystem integrity through conservation interventions. There remains significant scope to maintain restoration efforts in the Rondegat River and other river systems of the CFE, through direct conservation actions, enhanced community awareness, indigenous riparian vegetation restoration and involvement of local stakeholders in various conservation-centred activities. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Authors: Broom, Casey Jay
- Date: 2022-10-14
- Subjects: Cyprinidae South Africa Western Cape , Freshwater fishes South Africa Western Cape , Cyprinidae Habitat South Africa Western Cape , Food chains (Ecology) , Restoration ecology South Africa Western Cape , Riparian restoration South Africa Western Cape
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365644 , vital:65772 , DOI https://doi.org/10.21504/10962/365644
- Description: Freshwater fishes are in global decline and fish as a group are the most imperilled of all vertebrates. Freshwater systems are among the most threatened globally, largely owing to their comparatively high species and habitat diversity while occupying a minute fraction of the Earth’s surface. In South Africa, invasion by non-native fishes has had a devastating effect on freshwater systems across the country. Numerous other stressors and anthropogenic impacts continue to impact these systems, including habitat degradation, water abstraction and global change effects. In general, South African freshwater systems are under-studied and there is a lack of baseline biological and ecological studies on many freshwater fish species. The Cape Fold Ecoregion (CFE) of South Africa is a particularly vulnerable region, with many range-restricted species and highly fragmented native fish ranges following high invasion rates. Within the CFE, the Olifants-Doring River System (ODRS) is of primary concern owing to the high endemism and imperilled status of its freshwater fish species. The Rondegat River in the ODRS is of notable conservation value, as it hosts populations of important endemic CFE species. This river is unique, being the site of the first alien fish eradication programme of its kind in South Africa. Thus the Rondegat River, and in particular its imperilled cyprinid assemblage, is used here as a case study of the responses and community dynamics of recovering freshwater fish species. The members of this cyprinid assemblage are Sedercypris calidus, Pseudobarbus phlegethon and Labeobarbus seeberi. Sedercypris calidus and L. seeberi are listed by the International Union for the Conservation of Nature (IUCN) as “Near-Threatened”, while P. phlegethon is listed as “Endangered”. Understanding the dynamics and responses to understudied vulnerable fish communities in the wake of restoration efforts was the overarching goal of this thesis. The first chapter served as a review of current knowledge of the CFE, the Rondegat River, the myriad stressors that have impacted on or are projected to affect this region, and the freshwater fish species on which those stressors act. My first investigations served as an extension of the existing Rondegat River monitoring programme, making use of remote underwater video (RUV) data to assess relative abundance and habitat associations of the focal species (Chapter 2). A relatively limited spatial range of P. phlegethon was established, which was suggested to be a result of relatively highly specialised habitat requirements and sensitivity to disturbance. Sedercypris calidus was confirmed as a relatively more abundant and ubiquitous species across the length of the Rondegat River, sharing much of the lower and middle reaches with L. seeberi. I sought to use experimental trials of functional response, as a proxy for feeding performance, across representative temperatures and relevant prey types, in the spatially overlapping S. calidus and L. seeberi (Chapter 3). Labeobarbus seeberi generally outcompeted S. calidus across temperature treatments and prey types. The ecomorphology and diet of all three species were used to construct trophic profiles, which suggested that there was a high degree of feeding capacity overlap between L. seeberi and S. calidus, while P. phlegethon diverged from the other two species (Chapter 4). Gut content suggested that all three species overlapped broadly in diet. This indicated that the realised trophic niche of these species is similar, despite some morphological specialisation. I then used RUV data to investigate in-situ feeding behaviours, with the aim to disentangle the nuances of community dynamics and mechanisms of coexistence in the cyprinid assemblage (Chapter 5). I found that, despite the higher feeding performance of L. seeberi (Chapter 3) and its overlaps in diet and feeding capacity with S. calidus (Chapter 4), S. calidus is able to mitigate competitive pressures through foraging mode switching and exploitation of allochthonous food inputs. Evidence for further habitat and prey selectivity in Pseudobarbus phlegethon was gathered based on dependence on complex habitats and pool refugia for the majority of its feeding, supporting this species as a headwater specialist; alongside signals of its spatial and habitat use patterns (Chapter 2). While S. calidus and L. seeberi were found to be less habitat-specific than P. phlegethon, caution was noted in the potential for ongoing stressors, such as habitat destruction, loss of river connectivity and global change effects, to impact on the reproductive success of these two species. Stressors affecting the habitats and sensitive invertebrate taxa upon which all three species depend continue to threaten the Rondegat system, highlighting the need to maintain ecosystem integrity through conservation interventions. There remains significant scope to maintain restoration efforts in the Rondegat River and other river systems of the CFE, through direct conservation actions, enhanced community awareness, indigenous riparian vegetation restoration and involvement of local stakeholders in various conservation-centred activities. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
Evaluating the trophic ecology and feeding habits of three divergent lineages of Sandelia bainsii (Teleostei: Anabantidae), from the Eastern Cape Rivers using stable isotope analysis
- Authors: Nkomo, Thulisile
- Date: 2022-10-14
- Subjects: Anabantidae , Trophic ecology , Food chains (Ecology) , Food web , Freshwater fishes Food , Stable isotopes
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/364984 , vital:65667
- Description: Despite supporting a disproportionately large fraction of the global biodiversity, freshwater ecosystems are ranked as the most highly threatened habitats on the planet, ahead of both terrestrial and marine ecosystems. Many regions are still characterised by limited knowledge regarding the taxonomy and ecology of freshwater fish taxa. The need for ecological information is increasingly becoming important due to the discovery of new species and unique lineages, which require conservation management. The aim of this study was thus to evaluate the trophic ecology and feeding habits of the three recently described and divergent Sandelia bainsii lineages, namely Sandelia sp. ‘bainsii Kowie’ from the Great Fish River, Sandelia sp. ‘bainsii Keiskamma’ found in the Keiskamma River, and Sandelia sp. ‘bainsii Buffalo’ confined to the Buffalo River system in the Amathole-Winterberg freshwater ecoregion in the Eastern Cape Province, South Africa. Based on the allopatric distribution and the generalist feeding habits of these lineages, this thesis postulated that these three lineages were likely to show similar trophic ecology patterns, different dietary composition and as a result would have variable trophic positioning in the different river systems. Therefore, the primary objectives were to use stable isotope analysis to (1) evaluate the food web patterns of the river systems where the three S. bainsii lineages occurred, and (2) determine dietary source contributions for the three lineages using isotope mixing models. The results revealed general variability and significant differences in the δ13C and δ¹⁵N values for the different basal resources, macroinvertebrates and fish community across the different headwater streams. Within and across the different rivers, the S. bainsii lineages exhibited variable isotopic niche sizes, which appeared to coincide with the variation in the isotopic composition of the individual communities. Furthermore, these lineages did not exhibit any discernible patterns in their interspecific interactions in different habitats. This suggests that these lineages’ isotopic niche patterns were largely influenced by spatial differences in both trophic resources and probable interactions with contraspecifics. Assessment of trophic positions of S. bainsii lineages showed that the three lineages had higher trophic positions than other co-occurring species at most sites, except in the Buffalo River. This suggest that the different lineages were generally top predators in the different river systems. Although S. ‘bainsii Buffalo’ had a lower trophic position compared to other co-occurring species, its trophic position was generally characterised by high uncertainty, indicating that this lineage was likely influenced by the occurrence of diet sources that had highly variable stable isotope values. Findings from stable isotope mixing models revealed that the diet sources varied from the dominance of either single diet source in the Fairburn and Tyume 1 River to the importance of multiple prey sources from the Lushington and Kat River system. This suggests that despite being a top predator at most sites, the diet sources for the different lineages were highly variable. The patterns observed in this study did not appear to be attributed to species divergence possibly caused by allopatric speciation, but rather differences in food web characteristics of the river systems, as well as the lineages interspecific relationships and their generalized feeding strategies. Understanding the trophic dynamics of these lineages will assist in implementing effective conservation strategies and policies dealing with narrowly distributed species that are threatened by habitat fragmentation and invasion of piscivorous fish. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Authors: Nkomo, Thulisile
- Date: 2022-10-14
- Subjects: Anabantidae , Trophic ecology , Food chains (Ecology) , Food web , Freshwater fishes Food , Stable isotopes
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/364984 , vital:65667
- Description: Despite supporting a disproportionately large fraction of the global biodiversity, freshwater ecosystems are ranked as the most highly threatened habitats on the planet, ahead of both terrestrial and marine ecosystems. Many regions are still characterised by limited knowledge regarding the taxonomy and ecology of freshwater fish taxa. The need for ecological information is increasingly becoming important due to the discovery of new species and unique lineages, which require conservation management. The aim of this study was thus to evaluate the trophic ecology and feeding habits of the three recently described and divergent Sandelia bainsii lineages, namely Sandelia sp. ‘bainsii Kowie’ from the Great Fish River, Sandelia sp. ‘bainsii Keiskamma’ found in the Keiskamma River, and Sandelia sp. ‘bainsii Buffalo’ confined to the Buffalo River system in the Amathole-Winterberg freshwater ecoregion in the Eastern Cape Province, South Africa. Based on the allopatric distribution and the generalist feeding habits of these lineages, this thesis postulated that these three lineages were likely to show similar trophic ecology patterns, different dietary composition and as a result would have variable trophic positioning in the different river systems. Therefore, the primary objectives were to use stable isotope analysis to (1) evaluate the food web patterns of the river systems where the three S. bainsii lineages occurred, and (2) determine dietary source contributions for the three lineages using isotope mixing models. The results revealed general variability and significant differences in the δ13C and δ¹⁵N values for the different basal resources, macroinvertebrates and fish community across the different headwater streams. Within and across the different rivers, the S. bainsii lineages exhibited variable isotopic niche sizes, which appeared to coincide with the variation in the isotopic composition of the individual communities. Furthermore, these lineages did not exhibit any discernible patterns in their interspecific interactions in different habitats. This suggests that these lineages’ isotopic niche patterns were largely influenced by spatial differences in both trophic resources and probable interactions with contraspecifics. Assessment of trophic positions of S. bainsii lineages showed that the three lineages had higher trophic positions than other co-occurring species at most sites, except in the Buffalo River. This suggest that the different lineages were generally top predators in the different river systems. Although S. ‘bainsii Buffalo’ had a lower trophic position compared to other co-occurring species, its trophic position was generally characterised by high uncertainty, indicating that this lineage was likely influenced by the occurrence of diet sources that had highly variable stable isotope values. Findings from stable isotope mixing models revealed that the diet sources varied from the dominance of either single diet source in the Fairburn and Tyume 1 River to the importance of multiple prey sources from the Lushington and Kat River system. This suggests that despite being a top predator at most sites, the diet sources for the different lineages were highly variable. The patterns observed in this study did not appear to be attributed to species divergence possibly caused by allopatric speciation, but rather differences in food web characteristics of the river systems, as well as the lineages interspecific relationships and their generalized feeding strategies. Understanding the trophic dynamics of these lineages will assist in implementing effective conservation strategies and policies dealing with narrowly distributed species that are threatened by habitat fragmentation and invasion of piscivorous fish. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
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