Change in narrative therapy : a pragmatic hermeneutic case study
- Authors: McLean, Neville Terence
- Date: 2014
- Subjects: Narrative therapy
- Language: English
- Type: Thesis , Masters , MSocSc
- Identifier: vital:3235 , http://hdl.handle.net/10962/d1013164
- Description: The client of this case study was a twenty two year old female in her first year at university. The client had come into therapy because she had felt depressed, lonely and riddled with selfdoubt. The author used a Narrative Therapy approach with the client and was focussed on helping the client generate new meanings and stories that were more useful and empowering for the client. In this case study, the author was interested in exploring the process of change that the client underwent during the therapy process and he would rely on identifying innovative moments to track these changes. This interest informed the research question; what is the process of change in narrative therapy as tracked through the therapeutic dialogue? How does the change process in this case study track with the heuristic model of change put forward by Gonçalves and his colleagues? The author chose to use a pragmatic hermeneutic case study method in order to analyse the data and the results were organised into a coherent narrative. The data was collected from twenty two therapy sessions and these were grouped together into themes, namely a quick start, the beginning of change, thickening the innovative moments and lighting the fire. The results of this study reveal that despite being considered a good outcome case by the author, the process of change differed somewhat to that proposed by the heuristic model of change.
- Full Text:
- Date Issued: 2014
- Authors: McLean, Neville Terence
- Date: 2014
- Subjects: Narrative therapy
- Language: English
- Type: Thesis , Masters , MSocSc
- Identifier: vital:3235 , http://hdl.handle.net/10962/d1013164
- Description: The client of this case study was a twenty two year old female in her first year at university. The client had come into therapy because she had felt depressed, lonely and riddled with selfdoubt. The author used a Narrative Therapy approach with the client and was focussed on helping the client generate new meanings and stories that were more useful and empowering for the client. In this case study, the author was interested in exploring the process of change that the client underwent during the therapy process and he would rely on identifying innovative moments to track these changes. This interest informed the research question; what is the process of change in narrative therapy as tracked through the therapeutic dialogue? How does the change process in this case study track with the heuristic model of change put forward by Gonçalves and his colleagues? The author chose to use a pragmatic hermeneutic case study method in order to analyse the data and the results were organised into a coherent narrative. The data was collected from twenty two therapy sessions and these were grouped together into themes, namely a quick start, the beginning of change, thickening the innovative moments and lighting the fire. The results of this study reveal that despite being considered a good outcome case by the author, the process of change differed somewhat to that proposed by the heuristic model of change.
- Full Text:
- Date Issued: 2014
Synchronisation of breeding in populations of the brown mussel Perna perna on the South Coast of South Africa
- Authors: Ndzipa, Victoria
- Date: 2013-05-28
- Subjects: Mussels -- South Africa , Perna -- South Africa , Perna -- Breeding
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5830 , http://hdl.handle.net/10962/d1007857 , Mussels -- South Africa , Perna -- South Africa , Perna -- Breeding
- Description: The general biology and seasonality of breeding of intertidal populations of the brown mussel Perna perna in South Africa are reasonably well known, but we have little information on variability either within or among populations. Synchronous spawning offers adaptive advantages to externally breeding animals. Firstly, it enhances fertilization rates and therefore the species' reproductive fitness. Secondly, spawning can also be timed to coincide with environmental conditions conducive to larval settlement and development. In addition, synchronisation of spawning will influence the synchrony of settlement. Synchronisation of larval settlement, in turn, has implications for popUlation biology, as highly pulsed settlement is likely to lead to density-dependant mortality of recruits and uncoupling of adult/recruit densities, while poorly synchronised settlement will not. Generally, sea temperature and food availability are considered the key factors underlying the initiation and the duration of the breeding cycle of mussels. However, there are proximate local cues that trigger the proliferation, maturation and release of gametes. In this study, the hypothesis tested is that factors that control food availability affect gonad development and so influence synchrony among populations. Much of the published work on spawning is based on observations of the presence of larvae in the plankton, or on settlement. A more reliable method correlates the sequence of gonad development throughout the year with changes in length-weight relationships, using histology. This study is also designed to investigate temporal differences in the timing of the breeding cycle between sheltered and exposed sites along the south coast of South Africa by histological analysis of the reproductive tissue (the gonad) and by dry weight/shell length regreSSIOns. To do this, these two techniques were applied to six mussel populations at three III ocalities that were separated on scales of about 10-20km. Within each locality, two study sites were .dentified. One was exposed to strong wave action and one was sheltered. A few hundred meters ;eparated these sites. The first technique used length-weight regressions as an indication of mussel ~ondition. Abrupt decreases in the dry body weight of a hypothetical standard animal were taken to indicate periods of spawning. Regressions were assessed for samples of 40 mussels taken from each site at intervals of 4 weeks over 13 months. The results were analysed using a 3-way ANCOV A, with dry weight as the dependent variable, shell length as a covariate, and site, exposure and month, as independent variables. The second approach used the more reliable and detailed method of assessing the annual reproductive cycle using histological sections of the gonad. Histological sections of gonads from thirty female mussels, sampled monthly from each site, were examined in the laboratory. Each gonad was categorized into one of six arbitrary developmental stages based on ovary morphology. Synchrony in spawning was examined by comparison of gonad developmental stages of individuals within and among populations. The data were analysed by 3-way nested ANOV A with mean gonad index for each population as the dependent variable, month as an independent variable and exposure nested in site. The results obtained from both techniques showed strong synchronisation among different popUlations, regardless of the scales at which they were separated. The data also indicated good synchrony within populations and, again among populations, regardless of the degree of exposure. The results also indicated that the gonad condition varied significantly at each site, exposure level and month. However, there were significant interactions among these three factors. This means that on a broader seasonal scale the six mussel populations were reasonably synchronised, but on finer monthly scales, there were temporal differences in duration of gametogenic events. The implication is that ovary development is cued by environmental factor(s) that operate on scales of at least 7-20 km rather than more localised events that may affect food availablity either through aggregation of food (local hydrography at different localities) or food delivery to the shore (degree of wave action at different sites.) , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Authors: Ndzipa, Victoria
- Date: 2013-05-28
- Subjects: Mussels -- South Africa , Perna -- South Africa , Perna -- Breeding
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5830 , http://hdl.handle.net/10962/d1007857 , Mussels -- South Africa , Perna -- South Africa , Perna -- Breeding
- Description: The general biology and seasonality of breeding of intertidal populations of the brown mussel Perna perna in South Africa are reasonably well known, but we have little information on variability either within or among populations. Synchronous spawning offers adaptive advantages to externally breeding animals. Firstly, it enhances fertilization rates and therefore the species' reproductive fitness. Secondly, spawning can also be timed to coincide with environmental conditions conducive to larval settlement and development. In addition, synchronisation of spawning will influence the synchrony of settlement. Synchronisation of larval settlement, in turn, has implications for popUlation biology, as highly pulsed settlement is likely to lead to density-dependant mortality of recruits and uncoupling of adult/recruit densities, while poorly synchronised settlement will not. Generally, sea temperature and food availability are considered the key factors underlying the initiation and the duration of the breeding cycle of mussels. However, there are proximate local cues that trigger the proliferation, maturation and release of gametes. In this study, the hypothesis tested is that factors that control food availability affect gonad development and so influence synchrony among populations. Much of the published work on spawning is based on observations of the presence of larvae in the plankton, or on settlement. A more reliable method correlates the sequence of gonad development throughout the year with changes in length-weight relationships, using histology. This study is also designed to investigate temporal differences in the timing of the breeding cycle between sheltered and exposed sites along the south coast of South Africa by histological analysis of the reproductive tissue (the gonad) and by dry weight/shell length regreSSIOns. To do this, these two techniques were applied to six mussel populations at three III ocalities that were separated on scales of about 10-20km. Within each locality, two study sites were .dentified. One was exposed to strong wave action and one was sheltered. A few hundred meters ;eparated these sites. The first technique used length-weight regressions as an indication of mussel ~ondition. Abrupt decreases in the dry body weight of a hypothetical standard animal were taken to indicate periods of spawning. Regressions were assessed for samples of 40 mussels taken from each site at intervals of 4 weeks over 13 months. The results were analysed using a 3-way ANCOV A, with dry weight as the dependent variable, shell length as a covariate, and site, exposure and month, as independent variables. The second approach used the more reliable and detailed method of assessing the annual reproductive cycle using histological sections of the gonad. Histological sections of gonads from thirty female mussels, sampled monthly from each site, were examined in the laboratory. Each gonad was categorized into one of six arbitrary developmental stages based on ovary morphology. Synchrony in spawning was examined by comparison of gonad developmental stages of individuals within and among populations. The data were analysed by 3-way nested ANOV A with mean gonad index for each population as the dependent variable, month as an independent variable and exposure nested in site. The results obtained from both techniques showed strong synchronisation among different popUlations, regardless of the scales at which they were separated. The data also indicated good synchrony within populations and, again among populations, regardless of the degree of exposure. The results also indicated that the gonad condition varied significantly at each site, exposure level and month. However, there were significant interactions among these three factors. This means that on a broader seasonal scale the six mussel populations were reasonably synchronised, but on finer monthly scales, there were temporal differences in duration of gametogenic events. The implication is that ovary development is cued by environmental factor(s) that operate on scales of at least 7-20 km rather than more localised events that may affect food availablity either through aggregation of food (local hydrography at different localities) or food delivery to the shore (degree of wave action at different sites.) , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
The influence of Acacia Mearnsii invasion on soil properties in the Kouga Mountains, Eastern Cape, South Africa
- Van der Waal, Benjamin Cornelius Wentsel
- Authors: Van der Waal, Benjamin Cornelius Wentsel
- Date: 2010
- Subjects: Acacia mearnsii -- South Africa , Wattles (Plants) -- South Africa , Soil erosion -- South Africa -- Eastern Cape , Conservation of natural resources -- South Africa , Biological invasions -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Invasive plants -- South Africa -- Eastern Cape , Biogeography -- South Africa -- Eastern Cape , Soil management -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape , Soils -- Sodium content -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4839 , http://hdl.handle.net/10962/d1005515 , Acacia mearnsii -- South Africa , Wattles (Plants) -- South Africa , Soil erosion -- South Africa -- Eastern Cape , Conservation of natural resources -- South Africa , Biological invasions -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Invasive plants -- South Africa -- Eastern Cape , Biogeography -- South Africa -- Eastern Cape , Soil management -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape , Soils -- Sodium content -- South Africa -- Eastern Cape
- Description: The invasion of Acacia mearnsii in the Kouga catchment, Eastern Cape, South Africa, has various negative impacts on the ecosystem. These impacts include: reduced species richness, increased water use, increased nutrients and increased N cycling rates. The native shrubby fynbos vegetation has adapted to the acidic nutrient poor soils and Mediterranean climate of the Kouga Mountains. Fynbos, however, is currently being out competed by the much taller Acacia mearnsii trees, due to their competitive nature and ability to fix nitrogen, thereby enriching the soil. The invaded sections of the valley bottoms and lower hill slopes are characterised by an almost complete monoculture of Acacia mearnsii, with very few fynbos species still present. The Department of Water and Environmental Affairs sponsored Working for Water programme started clearing Acacia mearnsii in 1996 in the Kouga Mountains. Cleared sites have remained bare for long periods, indicating that soil properties are not favourable for indigenous propagule re-establishment. The aim of this research was to assess how A. mearnsii invasion and clearing affect fynbos recovery through its impact on soils. This was done by characterising vegetation and soil properties on fynbos, infested and cleared slopes. Vegetation cover for various growth forms was determined and a species list was compiled for each plot. The slope angle, surface hardness, litter cover, bare ground cover and soil depth were measured in the field, whereas water repellency, particle size and the chemical composition were measured in the laboratory. Furthermore, the plant establishment capacity of soils from fynbos, infested and cleared slopes was calculated. This was done by germinating fynbos seeds and growing fynbos plants in soils from the various slopes. The effect that invasion and clearing has on soil erosion was quantified using erosion plots on fynbos, infested and cleared slopes. The invasion and clearing of Acacia mearnsii led to an increase in soil nutrients, especially nitrogen, phosphorus, potassium, carbon and manganese. Furthermore, soils became more acidic, with increased water repellency and reduced surface hardness. The vegetation changed to a tree-dominated structure, replacing the native species. Native plant germination was relatively unaffected by invasion and clearing, with an increase in germination just after clearing. Plant growth of a native grass, Themeda triandra, and herb, Helichrysum umbraculigerum, has increased on soils from cleared slopes. This study showed that soil movement increased on slopes which are invaded and cleared of Acacia mearnsii, with erosion rates doubling on invaded slopes
- Full Text:
- Date Issued: 2010
- Authors: Van der Waal, Benjamin Cornelius Wentsel
- Date: 2010
- Subjects: Acacia mearnsii -- South Africa , Wattles (Plants) -- South Africa , Soil erosion -- South Africa -- Eastern Cape , Conservation of natural resources -- South Africa , Biological invasions -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Invasive plants -- South Africa -- Eastern Cape , Biogeography -- South Africa -- Eastern Cape , Soil management -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape , Soils -- Sodium content -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4839 , http://hdl.handle.net/10962/d1005515 , Acacia mearnsii -- South Africa , Wattles (Plants) -- South Africa , Soil erosion -- South Africa -- Eastern Cape , Conservation of natural resources -- South Africa , Biological invasions -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Invasive plants -- South Africa -- Eastern Cape , Biogeography -- South Africa -- Eastern Cape , Soil management -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape , Soils -- Sodium content -- South Africa -- Eastern Cape
- Description: The invasion of Acacia mearnsii in the Kouga catchment, Eastern Cape, South Africa, has various negative impacts on the ecosystem. These impacts include: reduced species richness, increased water use, increased nutrients and increased N cycling rates. The native shrubby fynbos vegetation has adapted to the acidic nutrient poor soils and Mediterranean climate of the Kouga Mountains. Fynbos, however, is currently being out competed by the much taller Acacia mearnsii trees, due to their competitive nature and ability to fix nitrogen, thereby enriching the soil. The invaded sections of the valley bottoms and lower hill slopes are characterised by an almost complete monoculture of Acacia mearnsii, with very few fynbos species still present. The Department of Water and Environmental Affairs sponsored Working for Water programme started clearing Acacia mearnsii in 1996 in the Kouga Mountains. Cleared sites have remained bare for long periods, indicating that soil properties are not favourable for indigenous propagule re-establishment. The aim of this research was to assess how A. mearnsii invasion and clearing affect fynbos recovery through its impact on soils. This was done by characterising vegetation and soil properties on fynbos, infested and cleared slopes. Vegetation cover for various growth forms was determined and a species list was compiled for each plot. The slope angle, surface hardness, litter cover, bare ground cover and soil depth were measured in the field, whereas water repellency, particle size and the chemical composition were measured in the laboratory. Furthermore, the plant establishment capacity of soils from fynbos, infested and cleared slopes was calculated. This was done by germinating fynbos seeds and growing fynbos plants in soils from the various slopes. The effect that invasion and clearing has on soil erosion was quantified using erosion plots on fynbos, infested and cleared slopes. The invasion and clearing of Acacia mearnsii led to an increase in soil nutrients, especially nitrogen, phosphorus, potassium, carbon and manganese. Furthermore, soils became more acidic, with increased water repellency and reduced surface hardness. The vegetation changed to a tree-dominated structure, replacing the native species. Native plant germination was relatively unaffected by invasion and clearing, with an increase in germination just after clearing. Plant growth of a native grass, Themeda triandra, and herb, Helichrysum umbraculigerum, has increased on soils from cleared slopes. This study showed that soil movement increased on slopes which are invaded and cleared of Acacia mearnsii, with erosion rates doubling on invaded slopes
- Full Text:
- Date Issued: 2010
Finite fuzzy sets, keychains and their applications
- Authors: Mahlasela, Zuko
- Date: 2009
- Subjects: Fuzzy sets , Finite groups , Lattice theory , Economics -- Mathematical models
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5406 , http://hdl.handle.net/10962/d1005220 , Fuzzy sets , Finite groups , Lattice theory , Economics -- Mathematical models
- Description: The idea of keychains, an (n+1)-tuple of non-increasing real numbers in the unit interval always including 1, naturally arises in study of finite fuzzy set theory. They are a useful concept in modeling ideas of uncertainty especially those that arise in Economics, Social Sciences, Statistics and other subjects. In this thesis we define and study some basic properties of keychains with reference to Partially Ordered Sets, Lattices, Chains and Finite Fuzzy Sets. We then examine the role of keychains and their lattice diagrams in representing uncertainties that arise in such problems as in preferential voting patterns, outcomes of competitions and in Economics - Preference Relations.
- Full Text:
- Date Issued: 2009
- Authors: Mahlasela, Zuko
- Date: 2009
- Subjects: Fuzzy sets , Finite groups , Lattice theory , Economics -- Mathematical models
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5406 , http://hdl.handle.net/10962/d1005220 , Fuzzy sets , Finite groups , Lattice theory , Economics -- Mathematical models
- Description: The idea of keychains, an (n+1)-tuple of non-increasing real numbers in the unit interval always including 1, naturally arises in study of finite fuzzy set theory. They are a useful concept in modeling ideas of uncertainty especially those that arise in Economics, Social Sciences, Statistics and other subjects. In this thesis we define and study some basic properties of keychains with reference to Partially Ordered Sets, Lattices, Chains and Finite Fuzzy Sets. We then examine the role of keychains and their lattice diagrams in representing uncertainties that arise in such problems as in preferential voting patterns, outcomes of competitions and in Economics - Preference Relations.
- Full Text:
- Date Issued: 2009
An investigation into the validity of life tables used for the calculation of personal injury damages
- Authors: Forshaw, Timothy James
- Date: 2006
- Subjects: Torts -- South Africa , Damages -- South Africa , Damages -- South Africa -- Accounting , Mortality -- Tables , Personal injuries -- South Africa
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:1077 , http://hdl.handle.net/10962/d1008371 , Torts -- South Africa , Damages -- South Africa , Damages -- South Africa -- Accounting , Mortality -- Tables , Personal injuries -- South Africa
- Description: Currently in South Africa when an individual is injured due to the acts of another they may claim damages for the losses which they may incur. These can be claimed from a variety of institutions, such as the Road Accident Fund, Workmen's compensation or an individual's private insurance. In all the afore-mentioned cases the calculation of damages are along the same lines, whereby the damages are quantified first, and thereafter reduced to reflect future possibilities that may occur. Traditionally future losses are reduced to reflect the possibility that the claimant may die at an age prior to the loss being incurred. To account for this risk awards for future losses are reduced using standard South African mortality tables. The set of tables currently being used were calculated from the 1985 South African census, and as such encapsulate the mortality of the population at that period. When the tables were calculated no reliable statistics were available for the Black population the result is that the tables currently being used do not contain a sample of the majority of the population. The thesis first examines, in detail, the calculation methods used to arrive at the value for damages to be awarded using the current set of life tables. Thereafter an analysis is conducted looking at differences between racial groups in the country and geographic locations, in order to uncover the mortality differences between groups to confirm or disprove the proposition that the exclusion of the Black population results in lower levels of mortality being reflected in the South African 1984-1986 life tables. This is accompanied by a review of mortality trenps in South African since 1986. Following from the findings of the expected increase in mortality since 1986, alternative life tables shall be used to show what impact these would have on the calculation of damages. Due to the fact that none of the alternatives return satisfactory results, structured settlements shall be reviewed to illustrate how the shortcomings of the lump sum approach can be circumvented, and altogether avoid the problems of out dated life tables being used as a basis for damage calculations. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Authors: Forshaw, Timothy James
- Date: 2006
- Subjects: Torts -- South Africa , Damages -- South Africa , Damages -- South Africa -- Accounting , Mortality -- Tables , Personal injuries -- South Africa
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:1077 , http://hdl.handle.net/10962/d1008371 , Torts -- South Africa , Damages -- South Africa , Damages -- South Africa -- Accounting , Mortality -- Tables , Personal injuries -- South Africa
- Description: Currently in South Africa when an individual is injured due to the acts of another they may claim damages for the losses which they may incur. These can be claimed from a variety of institutions, such as the Road Accident Fund, Workmen's compensation or an individual's private insurance. In all the afore-mentioned cases the calculation of damages are along the same lines, whereby the damages are quantified first, and thereafter reduced to reflect future possibilities that may occur. Traditionally future losses are reduced to reflect the possibility that the claimant may die at an age prior to the loss being incurred. To account for this risk awards for future losses are reduced using standard South African mortality tables. The set of tables currently being used were calculated from the 1985 South African census, and as such encapsulate the mortality of the population at that period. When the tables were calculated no reliable statistics were available for the Black population the result is that the tables currently being used do not contain a sample of the majority of the population. The thesis first examines, in detail, the calculation methods used to arrive at the value for damages to be awarded using the current set of life tables. Thereafter an analysis is conducted looking at differences between racial groups in the country and geographic locations, in order to uncover the mortality differences between groups to confirm or disprove the proposition that the exclusion of the Black population results in lower levels of mortality being reflected in the South African 1984-1986 life tables. This is accompanied by a review of mortality trenps in South African since 1986. Following from the findings of the expected increase in mortality since 1986, alternative life tables shall be used to show what impact these would have on the calculation of damages. Due to the fact that none of the alternatives return satisfactory results, structured settlements shall be reviewed to illustrate how the shortcomings of the lump sum approach can be circumvented, and altogether avoid the problems of out dated life tables being used as a basis for damage calculations. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
The structure of ant communities and their impact on soil-pupating pests in citrus orchards in the Grahamstown area of the Eastern Cape
- Authors: Bownes, Angela
- Date: 2003
- Subjects: Ants -- South Africa -- Eastern Cape , Pests -- Control -- South Africa , Homoptera -- Control -- South Africa -- Eastern Cape , Citrus -- Diseases and pests -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5775 , http://hdl.handle.net/10962/d1005463 , Ants -- South Africa -- Eastern Cape , Pests -- Control -- South Africa , Homoptera -- Control -- South Africa -- Eastern Cape , Citrus -- Diseases and pests -- South Africa -- Eastern Cape
- Description: Two ant species, Pheidole megacephala (Fabricius) and Anoplolepis custodiens (Smith) reach pest status in citrus orchards through precipitating outbreaks of homopterous pests. However, predacious ants, including these two ant species, play an important role in pest suppression in agroecosystems and are therefore beneficial to these systems. If A. custodiens and P. megacephala are important natural control agents in citrus, using ant bands to break the mutualism between the ants and the Homoptera as a method of ant control is preferable to poisoning. Ant communities were sampled by pitfall trapping in three experimental subunits of 2-, 4-, 15- and 30-year-old citrus orchards, in the Grahamstown area of the Eastern Cape. In one subunit in each orchard, populations of P. megacephala and A. custodiens were suppressed by poison applications. In a second subunit, trees were banded with trunk barriers so that ants were prevented from foraging in the trees and a third subunit served as the untreated control. Bait pupae of bollworm, false codling moth and fruit fly were planted in bait trays in all of the subunits to investigate predation on these citrus pests in the relative absence of predacious ants and where they were excluded from the trees. Pheidole megacephala dominated exclusively in all of the plots. Community composition did not change dramatically with increasing age of the trees, but species diversity and species abundance did. Rank-abundance curves showed that community diversity was highest in the 2-year-old plots and lowest in the 30-year-old plots. The Simpson and Shannon-Wiener diversity indices and their evenness measures indicated that diversity and equitability were highest in the poisoned subunits and lowest in the banded subunits. Principle component analysis revealed that the poisoned subunits were similar and distinct in species composition, that there was significant monthly variation in species composition and that community stability increases with an increase in orchard age. The presence of P. megacephala was significantly negatively correlated (rs = -0.293; p < 0.001) with pest pupal survival. Pupal survival was significantly higher for bollworm (p < 0.001), FCM (p < 0.001) and fruit fly (p < 0.001) in the poisoned subunits, than in the banded and control subunits. There was a general trend for survivorship to increase with an increase in the age of the trees. A significant difference (p < 0.001) was found between the months in which the trials were carried out. Pupal survival was significantly lower (p < 0.001) for FCM than for bollworm and fruit fly. In citrus orchards, ant communities are organised by ecological processes and interactions and are influenced by methods of ant control. Ant bands are preferable to poisoning as a method of ant control, so that beneficial species are left on the ground to prey on pests that pupate in the soil. Maintaining high ant species diversity in citrus orchards would be beneficial as predation on the pupae was more effective where ant species diversity was higher.
- Full Text:
- Date Issued: 2003
- Authors: Bownes, Angela
- Date: 2003
- Subjects: Ants -- South Africa -- Eastern Cape , Pests -- Control -- South Africa , Homoptera -- Control -- South Africa -- Eastern Cape , Citrus -- Diseases and pests -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5775 , http://hdl.handle.net/10962/d1005463 , Ants -- South Africa -- Eastern Cape , Pests -- Control -- South Africa , Homoptera -- Control -- South Africa -- Eastern Cape , Citrus -- Diseases and pests -- South Africa -- Eastern Cape
- Description: Two ant species, Pheidole megacephala (Fabricius) and Anoplolepis custodiens (Smith) reach pest status in citrus orchards through precipitating outbreaks of homopterous pests. However, predacious ants, including these two ant species, play an important role in pest suppression in agroecosystems and are therefore beneficial to these systems. If A. custodiens and P. megacephala are important natural control agents in citrus, using ant bands to break the mutualism between the ants and the Homoptera as a method of ant control is preferable to poisoning. Ant communities were sampled by pitfall trapping in three experimental subunits of 2-, 4-, 15- and 30-year-old citrus orchards, in the Grahamstown area of the Eastern Cape. In one subunit in each orchard, populations of P. megacephala and A. custodiens were suppressed by poison applications. In a second subunit, trees were banded with trunk barriers so that ants were prevented from foraging in the trees and a third subunit served as the untreated control. Bait pupae of bollworm, false codling moth and fruit fly were planted in bait trays in all of the subunits to investigate predation on these citrus pests in the relative absence of predacious ants and where they were excluded from the trees. Pheidole megacephala dominated exclusively in all of the plots. Community composition did not change dramatically with increasing age of the trees, but species diversity and species abundance did. Rank-abundance curves showed that community diversity was highest in the 2-year-old plots and lowest in the 30-year-old plots. The Simpson and Shannon-Wiener diversity indices and their evenness measures indicated that diversity and equitability were highest in the poisoned subunits and lowest in the banded subunits. Principle component analysis revealed that the poisoned subunits were similar and distinct in species composition, that there was significant monthly variation in species composition and that community stability increases with an increase in orchard age. The presence of P. megacephala was significantly negatively correlated (rs = -0.293; p < 0.001) with pest pupal survival. Pupal survival was significantly higher for bollworm (p < 0.001), FCM (p < 0.001) and fruit fly (p < 0.001) in the poisoned subunits, than in the banded and control subunits. There was a general trend for survivorship to increase with an increase in the age of the trees. A significant difference (p < 0.001) was found between the months in which the trials were carried out. Pupal survival was significantly lower (p < 0.001) for FCM than for bollworm and fruit fly. In citrus orchards, ant communities are organised by ecological processes and interactions and are influenced by methods of ant control. Ant bands are preferable to poisoning as a method of ant control, so that beneficial species are left on the ground to prey on pests that pupate in the soil. Maintaining high ant species diversity in citrus orchards would be beneficial as predation on the pupae was more effective where ant species diversity was higher.
- Full Text:
- Date Issued: 2003
- «
- ‹
- 1
- ›
- »