Complex interactions involving the Cape fig, Ficus sur Forsskål, and its associated insects
- Authors: Zachariades, Costas
- Date: 1995
- Subjects: Insect-plant relationships Mutualism (Biology) Fig -- South Africa Fig wasp -- South Africa Ants Homoptera
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5655 , http://hdl.handle.net/10962/d1005338
- Description: The inadequacy of arbitrarily classifying interactions between species as antagonistic, neutral or mutualistic has become clear in recent years. Both direct and indirect interactions between species can vary between mutualism and antagonism, depending on the intrinsic and extrinsic contexts of the interaction. This study investigated the characteristics of an ant-plant-homopteran interaction in southern Africa. The polyphagous homopteran Hilda patruelis (Tettigometridae) feeds primarily on the trunk-borne fruiting branches and figs of the Cape fig tree, Ficus sur, and produces honeydew which attracts tending ants. Ten of the sixteen ant species/species groups present on F. sur tended H. patruelis, with Pheidole megacephala the most frequent attendant. Ants attracted to F. sur by H. patruelis honeydew or other liquid food sources also preyed on insects on the tree, including adults of the small agaonid fig wasps whose larvae feed on the ovules in the developing figs. One fig wasp species (Ceratosolen capensis) is also the tree's only pollinator. No benefits to H. patruelis from being tended by ants were detected, either in terms of reduced parasitism, or predation by a lycaenid caterpillar. A P. megacephala colony foraging on a F. sur tree was found to receive a high proportion of its likely energy requirements from the tree, mainly in the form of H. patruelis honeydew, during periods when it was bearing fruit. It is probable that the H. patruelis-P. megacephala interaction constitutes a direct mutualism at times, but that benefits to the homopteran are intermittent or weak. Both H. patruelis and ants benefitted from F. sur, directly or indirectly, through the provision of food (and for some ants, nesting sites). The removal of phloem sap by H. patruelis did not detectably reduce the trees' reproductive output, either in terms of pollinator or viable seed production. The indirect effects of ant and H. patruelis presence on the F. sur trees were on average positive, as ants preyed disproportionately heavily on fig wasp species parasitic on or competing with the pollinator, thus increasing pollinator production. Effects of ant presence on seed production were not investigated, but have been demonstrated as beneficial elsewhere. However, there is great varatlon both in the composition of the wasp fauna arriving to oviposit at different crops, and in ant densities per fig, on several temporal and spatial scales. This results in high variability in the effects of ants on the pollinator and, through it, the tree, from positive to zero and potentially even negative. Despite this conditionality of beneficial outcomes for the tree, the mean effect of ants on the F. sur population studied was to increase pollinator production by up to nearly 20%. This study is among the few to have demonstrated an overall benefit to a plant of having homopteran-tending ants present on it.
- Full Text:
- Date Issued: 1995
- Authors: Zachariades, Costas
- Date: 1995
- Subjects: Insect-plant relationships Mutualism (Biology) Fig -- South Africa Fig wasp -- South Africa Ants Homoptera
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5655 , http://hdl.handle.net/10962/d1005338
- Description: The inadequacy of arbitrarily classifying interactions between species as antagonistic, neutral or mutualistic has become clear in recent years. Both direct and indirect interactions between species can vary between mutualism and antagonism, depending on the intrinsic and extrinsic contexts of the interaction. This study investigated the characteristics of an ant-plant-homopteran interaction in southern Africa. The polyphagous homopteran Hilda patruelis (Tettigometridae) feeds primarily on the trunk-borne fruiting branches and figs of the Cape fig tree, Ficus sur, and produces honeydew which attracts tending ants. Ten of the sixteen ant species/species groups present on F. sur tended H. patruelis, with Pheidole megacephala the most frequent attendant. Ants attracted to F. sur by H. patruelis honeydew or other liquid food sources also preyed on insects on the tree, including adults of the small agaonid fig wasps whose larvae feed on the ovules in the developing figs. One fig wasp species (Ceratosolen capensis) is also the tree's only pollinator. No benefits to H. patruelis from being tended by ants were detected, either in terms of reduced parasitism, or predation by a lycaenid caterpillar. A P. megacephala colony foraging on a F. sur tree was found to receive a high proportion of its likely energy requirements from the tree, mainly in the form of H. patruelis honeydew, during periods when it was bearing fruit. It is probable that the H. patruelis-P. megacephala interaction constitutes a direct mutualism at times, but that benefits to the homopteran are intermittent or weak. Both H. patruelis and ants benefitted from F. sur, directly or indirectly, through the provision of food (and for some ants, nesting sites). The removal of phloem sap by H. patruelis did not detectably reduce the trees' reproductive output, either in terms of pollinator or viable seed production. The indirect effects of ant and H. patruelis presence on the F. sur trees were on average positive, as ants preyed disproportionately heavily on fig wasp species parasitic on or competing with the pollinator, thus increasing pollinator production. Effects of ant presence on seed production were not investigated, but have been demonstrated as beneficial elsewhere. However, there is great varatlon both in the composition of the wasp fauna arriving to oviposit at different crops, and in ant densities per fig, on several temporal and spatial scales. This results in high variability in the effects of ants on the pollinator and, through it, the tree, from positive to zero and potentially even negative. Despite this conditionality of beneficial outcomes for the tree, the mean effect of ants on the F. sur population studied was to increase pollinator production by up to nearly 20%. This study is among the few to have demonstrated an overall benefit to a plant of having homopteran-tending ants present on it.
- Full Text:
- Date Issued: 1995
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
Constituent processes contributing to stress induced β-carotene accumulation in Dunaliella salina
- Authors: Phillips, Lesley Gail
- Date: 1995
- Subjects: Dunaliella Carotenes Plants -- Effect of stress on
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5658 , http://hdl.handle.net/10962/d1005341
- Description: The alga Dunaliella salina possesses the unique ability to accumulate up to 14 % of it's dry weight as β-carotene in response to stress conditions. This hyper-accumulation of β-carotene has led to the commercial exploitation of this alga for the biotechnological production of this important carotenoid. In order to maximise β-carotene production, a dual-stage process which separates the distinctive growth phase from the β-carotene accumulating stress phase has recently been patented. Preliminary laboratory studies showed that although stress factors such as high salinity and nutrient limitation enhance β-carotene accumulation in D. salina (± 10 pg.cell⁻¹), high light intensity was the single most important factor contributing to the induction of β-carotene accumulation in this alga (± 20 pg.cell⁻¹). Moreover, it was demonstrated that β-carotene accumulation can be further stimulated by exposing the alga to a combination of high light intensity, salt and nutrient stresses (± 30-60 pg.cell⁻¹). The response of D. salina to stress was shown to occur in two phases. The first phase occurred within 24 hours and was characterized most importantly by higher rates of β-carotene accumulation for all the stresses investigated. In cells exposed to multiple stress factors in mass culture, the β-carotene accumulation rate was as much as 9.5 pg.cell⁻¹.day⁻¹ in the first phase compared to only 3 pg.cell·day⁻¹ in the second phase. Since the rate of β-carotene accumulation was higher within the first 24 hours after exposure to stress, the first phase was considered crucial for stress-induced β-carotene accumulation. Characterization of this phase revealed that the stress response was multifaceted. Transition of cells from the growth stage to stress conditions was characterized by the following: 1) Change in cell volume. Hypersalinity caused cell shrinkage while cells exposed to nutrient limitation and/or high light intensity caused cells to swell. Restoration of cell volume was shown to occur within 8 hours for all stresses investigated. 2) Altered photosynthesis. Inhibition of both carbon fixation and oxygen evolution was demonstrated in cells immediately after exposure to multiple stress factors. 3) Production of abscisic acid. Intracellular ABA levels increased within 6-8 hours after exposure to all stresses investigated. The rise in intracellular ABA levels coincided with an increase or return to starting cell volume. High intracellular ABA levels were however transient and within 24 hours ABA began to partition into the culture medium. 4) Change in pigment composition. Changes in xanthophyll cycle pigment content was demonstrated soon after exposure to stress conditions. In hypersalinity shocked cells, initial epoxidation of zeaxanthin to violaxanthin and subsequent de-epoxidation to zeaxanthin occurred, whereas exposure to high stress resulted in an immediate and continued decrease in the epoxidation state indicating accumulation of zeaxanthin. A rapid rate of chlorophyll depletion was also demonstrated. In addition to the above responses a rapid decrease in growth rate during this phase was also noted. An interrelationship between cell volume change, ABA production, maintenance of xanthophyll cycle operation and β-carotene accumulation therefore appeared to exist. ABA production was shown to be stoichiometrically related to changes in xanthophyll content with r² = 0.84 and slope of the curve = 0.91 being achieved for high light stressed cells. This study therefore presents strong circumstantial evidence in support of a carotenoid origin for ABA in Dunaliella. In addition, enhanced β-carotene content was achieved by the application of exogenous ABA and related compounds suggesting a role for ABA as a regulator of the overall stress response. Furthermore, zeaxanthin accumulation was shown to be positively correlated ( r²≥ 0.81) to β-carotene accumulation for all the stresses investigated. The second phase was characterized by a return to homoeostasis of the physiological processes mentioned above, indicating acclimation of the cell to prevailing conditions. This stage was characterised by continued β-carotene accumulation and a decreased epoxidation state of the xanthophyll cycle which together appeared to sustain photosynthesis, allowing this organism to tolerate stress conditions.
- Full Text:
- Date Issued: 1995
- Authors: Phillips, Lesley Gail
- Date: 1995
- Subjects: Dunaliella Carotenes Plants -- Effect of stress on
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5658 , http://hdl.handle.net/10962/d1005341
- Description: The alga Dunaliella salina possesses the unique ability to accumulate up to 14 % of it's dry weight as β-carotene in response to stress conditions. This hyper-accumulation of β-carotene has led to the commercial exploitation of this alga for the biotechnological production of this important carotenoid. In order to maximise β-carotene production, a dual-stage process which separates the distinctive growth phase from the β-carotene accumulating stress phase has recently been patented. Preliminary laboratory studies showed that although stress factors such as high salinity and nutrient limitation enhance β-carotene accumulation in D. salina (± 10 pg.cell⁻¹), high light intensity was the single most important factor contributing to the induction of β-carotene accumulation in this alga (± 20 pg.cell⁻¹). Moreover, it was demonstrated that β-carotene accumulation can be further stimulated by exposing the alga to a combination of high light intensity, salt and nutrient stresses (± 30-60 pg.cell⁻¹). The response of D. salina to stress was shown to occur in two phases. The first phase occurred within 24 hours and was characterized most importantly by higher rates of β-carotene accumulation for all the stresses investigated. In cells exposed to multiple stress factors in mass culture, the β-carotene accumulation rate was as much as 9.5 pg.cell⁻¹.day⁻¹ in the first phase compared to only 3 pg.cell·day⁻¹ in the second phase. Since the rate of β-carotene accumulation was higher within the first 24 hours after exposure to stress, the first phase was considered crucial for stress-induced β-carotene accumulation. Characterization of this phase revealed that the stress response was multifaceted. Transition of cells from the growth stage to stress conditions was characterized by the following: 1) Change in cell volume. Hypersalinity caused cell shrinkage while cells exposed to nutrient limitation and/or high light intensity caused cells to swell. Restoration of cell volume was shown to occur within 8 hours for all stresses investigated. 2) Altered photosynthesis. Inhibition of both carbon fixation and oxygen evolution was demonstrated in cells immediately after exposure to multiple stress factors. 3) Production of abscisic acid. Intracellular ABA levels increased within 6-8 hours after exposure to all stresses investigated. The rise in intracellular ABA levels coincided with an increase or return to starting cell volume. High intracellular ABA levels were however transient and within 24 hours ABA began to partition into the culture medium. 4) Change in pigment composition. Changes in xanthophyll cycle pigment content was demonstrated soon after exposure to stress conditions. In hypersalinity shocked cells, initial epoxidation of zeaxanthin to violaxanthin and subsequent de-epoxidation to zeaxanthin occurred, whereas exposure to high stress resulted in an immediate and continued decrease in the epoxidation state indicating accumulation of zeaxanthin. A rapid rate of chlorophyll depletion was also demonstrated. In addition to the above responses a rapid decrease in growth rate during this phase was also noted. An interrelationship between cell volume change, ABA production, maintenance of xanthophyll cycle operation and β-carotene accumulation therefore appeared to exist. ABA production was shown to be stoichiometrically related to changes in xanthophyll content with r² = 0.84 and slope of the curve = 0.91 being achieved for high light stressed cells. This study therefore presents strong circumstantial evidence in support of a carotenoid origin for ABA in Dunaliella. In addition, enhanced β-carotene content was achieved by the application of exogenous ABA and related compounds suggesting a role for ABA as a regulator of the overall stress response. Furthermore, zeaxanthin accumulation was shown to be positively correlated ( r²≥ 0.81) to β-carotene accumulation for all the stresses investigated. The second phase was characterized by a return to homoeostasis of the physiological processes mentioned above, indicating acclimation of the cell to prevailing conditions. This stage was characterised by continued β-carotene accumulation and a decreased epoxidation state of the xanthophyll cycle which together appeared to sustain photosynthesis, allowing this organism to tolerate stress conditions.
- Full Text:
- Date Issued: 1995
Contributions to our knowledge of the biology of Machiloides Delanyi Wygodzinsky and Ctenolepisma Longicaudata Escherich : (Hexapoda Thysanura)
- Authors: Heeg, J. (Jan)
- Date: 1963
- Subjects: Insects -- Adaptation , Insects -- Physiology , Thysanura , Apterygota
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5856 , http://hdl.handle.net/10962/d1012261 , Insects -- Adaptation , Insects -- Physiology , Thysanura , Apterygota
- Description: Among the South African Thysanura, the order Lepismatoidea has spread over the whole sub-continent, while all except one species of the order Machiloidea are confined to the discontinuous forest belt which lies below the escarpment of the inland plateau. The Machiloidea are not , however, strictly confined to the actual forests within their geographical region, some species invading regions of considerable aridity. Investigations on the ecology, water relations and orientation behaviour of a representative species of each order have been carried out. These have revealed that: (i) the physical conditions in the typical niche of the Machiloidea are extremely stable, whereas those in the habitat of the Lepismatoidea are subject to some considerable fluctuation. (ii) the Lepismatoidea are more resistant to desiccation than the Machiloidea; in both cases this resistance is due in part to physical barriers in the cuticle and partly to an active metabolic process. (iii) the Machiloidea rely on their eversible vesicles, situated on the abdominal coxosternites, for the uptake of water which cannot be drunk, such as a thin film of water or soil capillary water. (iv) the Lepismatoidea are able to absorb water from a subsaturated atmosphere. (v) the behavioural responses of both in respect of humidity, temperature, light and gravity, are such as to keep them in conditions within the range of their physiological limitations. From these results it is concluded that the Machiloidea can survive outside the shelter of forests, provided that water is readily available in some form in which it can be absorbed by the animals. The general implications of the results are such as to permit the erection of an hypothesis explaining the distribution of the Thysanura in South Africa in terms of t he availability of wate. The results also lead to speculations on the evolution of the Pterygota.
- Full Text:
- Date Issued: 1963
- Authors: Heeg, J. (Jan)
- Date: 1963
- Subjects: Insects -- Adaptation , Insects -- Physiology , Thysanura , Apterygota
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5856 , http://hdl.handle.net/10962/d1012261 , Insects -- Adaptation , Insects -- Physiology , Thysanura , Apterygota
- Description: Among the South African Thysanura, the order Lepismatoidea has spread over the whole sub-continent, while all except one species of the order Machiloidea are confined to the discontinuous forest belt which lies below the escarpment of the inland plateau. The Machiloidea are not , however, strictly confined to the actual forests within their geographical region, some species invading regions of considerable aridity. Investigations on the ecology, water relations and orientation behaviour of a representative species of each order have been carried out. These have revealed that: (i) the physical conditions in the typical niche of the Machiloidea are extremely stable, whereas those in the habitat of the Lepismatoidea are subject to some considerable fluctuation. (ii) the Lepismatoidea are more resistant to desiccation than the Machiloidea; in both cases this resistance is due in part to physical barriers in the cuticle and partly to an active metabolic process. (iii) the Machiloidea rely on their eversible vesicles, situated on the abdominal coxosternites, for the uptake of water which cannot be drunk, such as a thin film of water or soil capillary water. (iv) the Lepismatoidea are able to absorb water from a subsaturated atmosphere. (v) the behavioural responses of both in respect of humidity, temperature, light and gravity, are such as to keep them in conditions within the range of their physiological limitations. From these results it is concluded that the Machiloidea can survive outside the shelter of forests, provided that water is readily available in some form in which it can be absorbed by the animals. The general implications of the results are such as to permit the erection of an hypothesis explaining the distribution of the Thysanura in South Africa in terms of t he availability of wate. The results also lead to speculations on the evolution of the Pterygota.
- Full Text:
- Date Issued: 1963
Contributions to the ecology of the anomuran mud prawn Upogebia africana (Ortmann)
- Authors: Hill, Burke J
- Date: 1967
- Subjects: Decapoda , Shrimps
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5888 , http://hdl.handle.net/10962/d1013341
- Description: Estuarine ecology in South Africa has progressed in two distinct stages. The first of these was a necessary descriptive phase which documented the general distribution of estuarine animals and recorded the physical conditions within estuaries . This phase has been carried out by the Zoology Department of the University of Cape Town which has made a series of ecological surveys of southern African estuaries. These surveys have provided a vast amount of valuable information which was utilised by Day (1964.) to state some general conclusions about estuarine faunas. The most important of these conclusions is that most of the estuarine fauna is really a quiet water fauna which also occurs in sheltered non-estuarine water. The information gained in this first stage is necessarily general and it can only indicate overall trends or reveal major features of distribution. Further estuary surveys are not justified unless they deal with unique conditions. It is at this point that the second phase of estuarine ecology becomes necessary. This phase involves a detailed investigation of individual species or particular problems. The present investigation falls into this second stage of estuarine ecology and was designed to extend our knowledge of the anomuran mud prawn Upogebia africana (Ortmann). The general estuarine surveys have shown that U. africana is a common inhabitant of many estuaries and sheltered bays along the southern African coast from Langebaan on the West coast to Inhambane on the East coast. However these surveys only revealed and could not explain anomalies in its distribution such as its apparent absence from closed estuaries and from estuaries in the tropics. In addition it was not even certain whether this abundant and widespread animal should really be considered a valid species distinct from a common West Coast prawn Upogebia capensis (Krauss). It was felt that a study of an estuarine species should be based upon a sound knowledge of its distribution, population structure and habitat. Knowledge of the habitat must be gained by studies in the field to establish which facets of the environment are of importance to the species. It was decided on the basis of field observations that temperature and salinity are of prime importance: in limiting the distribution of U. africana and a detailed laboratory study was therefore made of the tolerance of U. africana to these two physical factors. The results of laboratory experiments together with field observations were finally used to interpret the ecology of the species. Most of present day knowledge of crustacean ecology has been gained from a study of European and North American animals and information about southern hemisphere species has lagged behind. It is hoped that the present study will contribute to a wider understanding of Crustacea and that it will lead to further more advanced research on South African marine and estuarine animals
- Full Text:
- Date Issued: 1967
- Authors: Hill, Burke J
- Date: 1967
- Subjects: Decapoda , Shrimps
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5888 , http://hdl.handle.net/10962/d1013341
- Description: Estuarine ecology in South Africa has progressed in two distinct stages. The first of these was a necessary descriptive phase which documented the general distribution of estuarine animals and recorded the physical conditions within estuaries . This phase has been carried out by the Zoology Department of the University of Cape Town which has made a series of ecological surveys of southern African estuaries. These surveys have provided a vast amount of valuable information which was utilised by Day (1964.) to state some general conclusions about estuarine faunas. The most important of these conclusions is that most of the estuarine fauna is really a quiet water fauna which also occurs in sheltered non-estuarine water. The information gained in this first stage is necessarily general and it can only indicate overall trends or reveal major features of distribution. Further estuary surveys are not justified unless they deal with unique conditions. It is at this point that the second phase of estuarine ecology becomes necessary. This phase involves a detailed investigation of individual species or particular problems. The present investigation falls into this second stage of estuarine ecology and was designed to extend our knowledge of the anomuran mud prawn Upogebia africana (Ortmann). The general estuarine surveys have shown that U. africana is a common inhabitant of many estuaries and sheltered bays along the southern African coast from Langebaan on the West coast to Inhambane on the East coast. However these surveys only revealed and could not explain anomalies in its distribution such as its apparent absence from closed estuaries and from estuaries in the tropics. In addition it was not even certain whether this abundant and widespread animal should really be considered a valid species distinct from a common West Coast prawn Upogebia capensis (Krauss). It was felt that a study of an estuarine species should be based upon a sound knowledge of its distribution, population structure and habitat. Knowledge of the habitat must be gained by studies in the field to establish which facets of the environment are of importance to the species. It was decided on the basis of field observations that temperature and salinity are of prime importance: in limiting the distribution of U. africana and a detailed laboratory study was therefore made of the tolerance of U. africana to these two physical factors. The results of laboratory experiments together with field observations were finally used to interpret the ecology of the species. Most of present day knowledge of crustacean ecology has been gained from a study of European and North American animals and information about southern hemisphere species has lagged behind. It is hoped that the present study will contribute to a wider understanding of Crustacea and that it will lead to further more advanced research on South African marine and estuarine animals
- Full Text:
- Date Issued: 1967
Density-dependent effects on body size, Philopatry, and dispersal in the Damaraland mole-rat (Fukomys damarensis)
- Authors: Finn, Kyle T
- Date: 2017
- Subjects: Fukomys damarensis , Fukomys damarensis -- Reproduction , Fukomys damarensis -- Growth , Rodents -- Reproduction -- South Africa -- Northern Cape , Rodents -- Growth -- South Africa -- Northern Cape , Rodent populations -- South Africa -- Northern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/50495 , vital:25993
- Description: Population density may exert changes in a variety of behavioural and physiological characters in animals. However, the effects of density-dependence and dispersal are poorly studied in subterranean rodents due to the difficulties involved in observing such effects in wild populations. Using the cooperative breeding Damaraland mole-rat (Fukomys damarensis) as a model species, the effects of population density on body size, growth rates, group size, recruitment, philopatry and dispersal were investigated at two sites (one with low density and one with high density) in the Northern Cape of South Africa. Group size, litter size and the probability of recapture were independent of population density. However, individual body size, recruitment, dispersal rate and dispersal distance were density-dependent. Individuals were significantly larger, juveniles exhibited a significantly higher growth rate, and juvenile recruitment was significantly greater when population density was low. At higher densities, significantly more individuals were lost between capture events which may be indicative of increased rates of dispersal. Mean dispersal distances in mole-rats were reduced at higher densities and increased at lower densities. While both sexes dispersed equally, males were significantly more likely to join an established colony and females created new burrow systems. In addition, four times as many single females were found when population density was low. The apparent differences in the study populations may be attributed to variable annual rainfall or food availability. The greater annual rainfall at the high-density site may provide better habitat conditions and therefore result in an increase in the population density and an increased dispersal rate due to the relaxed ecological constraints such as reduced energetic costs to burrowing. However, the larger body size found at the low-density site may indicate that the available food at that location is of better quality. This study revealed that mole-rats were able to disperse over 1km and therefore a much larger study area would be required in capture-mark-recapture studies to ensure the recapture of the majority of dispersers. Lastly, a surprising find of this study was that females may survive a solitary existence for over two years while awaiting the arrival of a mate.
- Full Text:
- Date Issued: 2017
- Authors: Finn, Kyle T
- Date: 2017
- Subjects: Fukomys damarensis , Fukomys damarensis -- Reproduction , Fukomys damarensis -- Growth , Rodents -- Reproduction -- South Africa -- Northern Cape , Rodents -- Growth -- South Africa -- Northern Cape , Rodent populations -- South Africa -- Northern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/50495 , vital:25993
- Description: Population density may exert changes in a variety of behavioural and physiological characters in animals. However, the effects of density-dependence and dispersal are poorly studied in subterranean rodents due to the difficulties involved in observing such effects in wild populations. Using the cooperative breeding Damaraland mole-rat (Fukomys damarensis) as a model species, the effects of population density on body size, growth rates, group size, recruitment, philopatry and dispersal were investigated at two sites (one with low density and one with high density) in the Northern Cape of South Africa. Group size, litter size and the probability of recapture were independent of population density. However, individual body size, recruitment, dispersal rate and dispersal distance were density-dependent. Individuals were significantly larger, juveniles exhibited a significantly higher growth rate, and juvenile recruitment was significantly greater when population density was low. At higher densities, significantly more individuals were lost between capture events which may be indicative of increased rates of dispersal. Mean dispersal distances in mole-rats were reduced at higher densities and increased at lower densities. While both sexes dispersed equally, males were significantly more likely to join an established colony and females created new burrow systems. In addition, four times as many single females were found when population density was low. The apparent differences in the study populations may be attributed to variable annual rainfall or food availability. The greater annual rainfall at the high-density site may provide better habitat conditions and therefore result in an increase in the population density and an increased dispersal rate due to the relaxed ecological constraints such as reduced energetic costs to burrowing. However, the larger body size found at the low-density site may indicate that the available food at that location is of better quality. This study revealed that mole-rats were able to disperse over 1km and therefore a much larger study area would be required in capture-mark-recapture studies to ensure the recapture of the majority of dispersers. Lastly, a surprising find of this study was that females may survive a solitary existence for over two years while awaiting the arrival of a mate.
- Full Text:
- Date Issued: 2017
Developing an attractant for monitoring fruit-feeding moths in citrus orchards
- Authors: Goddard, Mathew Keith
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/2981 , vital:20349
- Description: Fruit-piercing moths are a sporadic pest of citrus, especially in the Eastern Cape Province of South Africa, where the adults can cause significant damage in outbreak years. Currently the only way in which to successfully control fruit-feeding moths within the orchards is the use of repellent lights. However, growers confuse fruit-piercing moths with fruit-sucking moths that don‘t cause primary damage, and there is no way of monitoring which moth species are attacking the fruit in the orchards during the night. In a previous study, banana was shown to be the most attractive bait for a variety of fruit-feeding moth species. Therefore the aim of this study was to determine the population dynamics of fruit-feeding moths develop a cost-effective alternative to the use of fresh banana as a bait for fruit-piercing moths. Fresh banana was compared to nine alternative synthetic attractants, frozen banana and a control under field conditions in several orchards in the Eastern Cape Province. Once again, banana was shown to be the most attractive bait. Some 23 species of fruit-feeding moth species were sampled in the traps, but there was only two fruit-piercing species, Serrodes partita (Fabricius) (Lepidoptera: Noctuidae) and Eudocima sp. Surprisingly S. partita, which was thought to be the main pest, comprised only 6.9% of trap catches. Serrodes partita, is a sporadic pest, only becoming problematic every five to 10 years after good rainfall in the Little Karoo region that causes flushes of their larval host, wild plum, Pappea capensis (Ecklon and Zeyher). During these outbreaks, damage to fruit can range from 70 to 90% and this is especially so for soft skinned citrus. A study on the morphology of the proboscis confirmed that only two species of fruit-piercing moths were present. Trap catches over three citrus growing seasons was linked to fruit damage found within several orchards. Once again fruit-piercing moth damage was relatively low in comparison to other types of damage such as mechanical and undefined damage. There was a very weak correlation between S. partita trap catches and damage, but generally damage was recorded two to three weeks after a peak in S. partita trap catches. Climatic conditions were also recorded and compared to weekly trap catches of S. partita, and while temperature and wind direction had no influence on moth populations, precipitation in the orchards was weakly correlated with trap catches. This study has shown that in non-outbreak seasons, the main fruit-piercing moth, S. partita comprises a small percentage of fruit-feeding moths in citrus orchards, but that growers are unable to determine the difference between fruit-piercing species and the harmless fruit-sucking species. Further fresh banana remains the best method for attracting fruit-piecing moths to traps, but this is not cost effective and thus a commercially viable protocol for monitoring these species remains elusive.
- Full Text:
- Date Issued: 2016
- Authors: Goddard, Mathew Keith
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/2981 , vital:20349
- Description: Fruit-piercing moths are a sporadic pest of citrus, especially in the Eastern Cape Province of South Africa, where the adults can cause significant damage in outbreak years. Currently the only way in which to successfully control fruit-feeding moths within the orchards is the use of repellent lights. However, growers confuse fruit-piercing moths with fruit-sucking moths that don‘t cause primary damage, and there is no way of monitoring which moth species are attacking the fruit in the orchards during the night. In a previous study, banana was shown to be the most attractive bait for a variety of fruit-feeding moth species. Therefore the aim of this study was to determine the population dynamics of fruit-feeding moths develop a cost-effective alternative to the use of fresh banana as a bait for fruit-piercing moths. Fresh banana was compared to nine alternative synthetic attractants, frozen banana and a control under field conditions in several orchards in the Eastern Cape Province. Once again, banana was shown to be the most attractive bait. Some 23 species of fruit-feeding moth species were sampled in the traps, but there was only two fruit-piercing species, Serrodes partita (Fabricius) (Lepidoptera: Noctuidae) and Eudocima sp. Surprisingly S. partita, which was thought to be the main pest, comprised only 6.9% of trap catches. Serrodes partita, is a sporadic pest, only becoming problematic every five to 10 years after good rainfall in the Little Karoo region that causes flushes of their larval host, wild plum, Pappea capensis (Ecklon and Zeyher). During these outbreaks, damage to fruit can range from 70 to 90% and this is especially so for soft skinned citrus. A study on the morphology of the proboscis confirmed that only two species of fruit-piercing moths were present. Trap catches over three citrus growing seasons was linked to fruit damage found within several orchards. Once again fruit-piercing moth damage was relatively low in comparison to other types of damage such as mechanical and undefined damage. There was a very weak correlation between S. partita trap catches and damage, but generally damage was recorded two to three weeks after a peak in S. partita trap catches. Climatic conditions were also recorded and compared to weekly trap catches of S. partita, and while temperature and wind direction had no influence on moth populations, precipitation in the orchards was weakly correlated with trap catches. This study has shown that in non-outbreak seasons, the main fruit-piercing moth, S. partita comprises a small percentage of fruit-feeding moths in citrus orchards, but that growers are unable to determine the difference between fruit-piercing species and the harmless fruit-sucking species. Further fresh banana remains the best method for attracting fruit-piecing moths to traps, but this is not cost effective and thus a commercially viable protocol for monitoring these species remains elusive.
- Full Text:
- Date Issued: 2016
Development of techniques for the isolation of a granulovirus from potato tuber moth, phthorimaea operculella (Zeller)
- Authors: King, Shirley Anne
- Date: 2011
- Subjects: Potato tuberworm -- Larvae , Agricultural pests -- Biological control , Potato tuberworm , Baculoviruses
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5910 , http://hdl.handle.net/10962/d1015202
- Description: Phthorimaea operculella, commonly known as the Potato Tuber Moth, is an economically important agricultural pest worldwide. The baculovirus, Phthorimaea operculella granulovirus (PhoGV) has been considered as a means of control alternative to chemical control because of its host specificity and harmless impact on other organisms and ecosystems. An isolate of PhoGV obtained from a South African PTM population would be beneficial in the production of a biopesticide, which is not yet available. An efficient and cost-effective rearing method would be advantageous for potential commercial production. Commercial table and seed potato plantations and storage facilities located in Patensie, Bathurst, Howick and Ivanhoe were surveyed for PTM infestations. Patensie was the only site where milky discoloured larvae were found, a potential symptom of PhoGV infection. TEM analysis revealed no virus in these samples. Since no virus was found in the field-collected samples, PTM insects were collected to initiate rearing in the laboratory. PTM was raised by three different methods in the laboratory. A cost/benefit analysis, survival rate, fertility and sex ratio were recorded for each rearing method. Rearing method one was deemed unsuccessful for efficient commercial rearing, as survival percentage and fertility were low. Rearing methods two and three had high survival rates and high fertility, and were efficient and less labour intensive than rearing method one. Rearing method three was the most productive technique, but for commercial production rearing method two was considered the most manageable and efficient. The sex ratio was 1:1 for all three cultures. The cost analysis revealed that rearing methods two and three were less expensive than rearing method one because less labour was required to monitor insects. The success of rearing PTM for 19 months will enable these cultures to be up-scaled to a large production facility for mass rearing. Virus was not found in the field surveys or in laboratory cultures, therefore chemical, temperature, humidity and carbon dioxide stressors were used in an attempt to initiate a baculoviral infection. Symptoms were exhibited in larvae subjected to chemical, temperature and humidity treatments, but these were confirmed by TEM analysis not to be a result of PhoGV infection. The success of rearing PTM in the laboratory suggests that the method could be used in the commercial rearing of the insects in a large mass-rearing facility. The data obtained from induction protocols have allowed for better understanding for future induction for PhoGV and other baculoviruses in other insect species. The failure to isolate a South African PhoGV strain for developing a biopesticide against PTM has motivated further studies in obtaining a baculovirus in order for South Africa to develop a commercial product against this pest.
- Full Text:
- Date Issued: 2011
- Authors: King, Shirley Anne
- Date: 2011
- Subjects: Potato tuberworm -- Larvae , Agricultural pests -- Biological control , Potato tuberworm , Baculoviruses
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5910 , http://hdl.handle.net/10962/d1015202
- Description: Phthorimaea operculella, commonly known as the Potato Tuber Moth, is an economically important agricultural pest worldwide. The baculovirus, Phthorimaea operculella granulovirus (PhoGV) has been considered as a means of control alternative to chemical control because of its host specificity and harmless impact on other organisms and ecosystems. An isolate of PhoGV obtained from a South African PTM population would be beneficial in the production of a biopesticide, which is not yet available. An efficient and cost-effective rearing method would be advantageous for potential commercial production. Commercial table and seed potato plantations and storage facilities located in Patensie, Bathurst, Howick and Ivanhoe were surveyed for PTM infestations. Patensie was the only site where milky discoloured larvae were found, a potential symptom of PhoGV infection. TEM analysis revealed no virus in these samples. Since no virus was found in the field-collected samples, PTM insects were collected to initiate rearing in the laboratory. PTM was raised by three different methods in the laboratory. A cost/benefit analysis, survival rate, fertility and sex ratio were recorded for each rearing method. Rearing method one was deemed unsuccessful for efficient commercial rearing, as survival percentage and fertility were low. Rearing methods two and three had high survival rates and high fertility, and were efficient and less labour intensive than rearing method one. Rearing method three was the most productive technique, but for commercial production rearing method two was considered the most manageable and efficient. The sex ratio was 1:1 for all three cultures. The cost analysis revealed that rearing methods two and three were less expensive than rearing method one because less labour was required to monitor insects. The success of rearing PTM for 19 months will enable these cultures to be up-scaled to a large production facility for mass rearing. Virus was not found in the field surveys or in laboratory cultures, therefore chemical, temperature, humidity and carbon dioxide stressors were used in an attempt to initiate a baculoviral infection. Symptoms were exhibited in larvae subjected to chemical, temperature and humidity treatments, but these were confirmed by TEM analysis not to be a result of PhoGV infection. The success of rearing PTM in the laboratory suggests that the method could be used in the commercial rearing of the insects in a large mass-rearing facility. The data obtained from induction protocols have allowed for better understanding for future induction for PhoGV and other baculoviruses in other insect species. The failure to isolate a South African PhoGV strain for developing a biopesticide against PTM has motivated further studies in obtaining a baculovirus in order for South Africa to develop a commercial product against this pest.
- Full Text:
- Date Issued: 2011
Diamondback Moth, Plutella xylostella (L.), (Lepidoptera: Plutellidae ), and Other Insects of Canola, Brassica napus L., in Gauteng Province, South Africa
- Authors: Mosiane, M S
- Date: 2002
- Subjects: Plutellidae , Plutellidae -- South Africa -- Gauteng , Rape (Plant) -- South Africa -- Gauteng , Canola , Plant parasites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5937 , http://hdl.handle.net/10962/d1018250
- Description: Canola, Brassics napus L. is a relatively new crop in South Africa. Insect pests have not yet been a major problem, but the notorious brassica specialist, diamondback moth (DBM), Plutella xylostella (L.) (Plutellidae) is establishing itself as a serious pest of this crop. DBM is the most important insect pest of plants from the family Brassicaceae throughout the world. It has developed resistance to all chemical pesticides used against it in the field and to toxins of the bacterium Bacillus thuringiensis. The pest status of DBM in South Africa is lower than in other countries with similar climates. However, due to indiscriminate use of pesticides, local populations of DBM are showing signs of resistance. An initial survey has indicated that in addition to DBM, canola is also attacked by aphids, Myzus persicae (Sulzer), Brevicoryne brassicae (L.), Lipaphis e1ysimi (Kaltenbach), (Aphiade), thrips, Thrips tabaci (Lindeman) and other pests mostly brassica specialists. The study was initiated to determine the composition of the community of insects found on canola, the seasonal phenology of DBM populations in canola, and the composition, relative abundance and seasonality of its parasitoids. Monitoring of the insects was carried out at weekly intervals for three years at Rietondale and Bapsfontein in Gauteng province of South Africa. Berlese funnels have been found to be useful in extracting insects from plants, and were used to indicate the presence ofDBM larvae and other insects found on canola. Adults of DBM were monitored with synthetic pheromone traps; larval and pupal populations were monitored by scouting canola plants. Samples of larvae, pupae and parasitoid cocoons were brought into the laboratory. Parasitoids that emerged were identified and their incidence recorded. Monolepta cf bifasciata (Chrysomelidae) and Listroderes costrirostris (Schoener) (Curculionidae) were the most abundant of the coleopteran pests. (DBM) and Heliothis armigera (H.) (Noctuidae) were most abundant lepidopteran pests of Canola. There was a high proportion of first and second instar larvae as indicated by the results of the Berlese funnels as compared to visual scouting in Bapsfontein. From May to August the infestation level of DBM was high, reaching the maximum of 0.25 larvae per plant in June 1996, then declined and remained low for the rest of the season in Rietondale. From September to December for all three years of the study, the population levels Of DBM were high, reaching a maximum of 9.6larvae per plant in September 1997, and remained low from January to August in Bapsfontein. The number of adult moths per trap per week ranged from 0 to 91 in Rietondale, peaking in January 1996 and September 1997. There was no correlation between infestation levels and the pheromone trap catches. In contrast to Rietondale, there was a high correlation between pheromone trap catches and subsequent larval infestations at Bapsfontein. Although DBM infestation levels were generally low, parasitism levels often reached 100% caused by a complex of parasitoids. During the period of study, the following hymenopteran parasitoids were recorded: Cotesia plutellae (Kurdjumov) and Apanteles eriophyes (Nixon), Braconidae), both larval parasitoids, Diadegma mollipla (Holmgren) (Ichneumonidae), and Oomyzus sokolowskii (Kurdjumov) (Eulophidae), larval-pupal parasitoids, Diadromus collaris (Gravenhorst) (Ichneumonidae) pupal parasitoid, and the hyperparasitoids Mesochorus sp. (Ichneumonidae) and Pteromalus sp. (Pteromalidae). Cotesia plutellae was the most abundant parasitoid occurring throughout the year..
- Full Text:
- Date Issued: 2002
- Authors: Mosiane, M S
- Date: 2002
- Subjects: Plutellidae , Plutellidae -- South Africa -- Gauteng , Rape (Plant) -- South Africa -- Gauteng , Canola , Plant parasites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5937 , http://hdl.handle.net/10962/d1018250
- Description: Canola, Brassics napus L. is a relatively new crop in South Africa. Insect pests have not yet been a major problem, but the notorious brassica specialist, diamondback moth (DBM), Plutella xylostella (L.) (Plutellidae) is establishing itself as a serious pest of this crop. DBM is the most important insect pest of plants from the family Brassicaceae throughout the world. It has developed resistance to all chemical pesticides used against it in the field and to toxins of the bacterium Bacillus thuringiensis. The pest status of DBM in South Africa is lower than in other countries with similar climates. However, due to indiscriminate use of pesticides, local populations of DBM are showing signs of resistance. An initial survey has indicated that in addition to DBM, canola is also attacked by aphids, Myzus persicae (Sulzer), Brevicoryne brassicae (L.), Lipaphis e1ysimi (Kaltenbach), (Aphiade), thrips, Thrips tabaci (Lindeman) and other pests mostly brassica specialists. The study was initiated to determine the composition of the community of insects found on canola, the seasonal phenology of DBM populations in canola, and the composition, relative abundance and seasonality of its parasitoids. Monitoring of the insects was carried out at weekly intervals for three years at Rietondale and Bapsfontein in Gauteng province of South Africa. Berlese funnels have been found to be useful in extracting insects from plants, and were used to indicate the presence ofDBM larvae and other insects found on canola. Adults of DBM were monitored with synthetic pheromone traps; larval and pupal populations were monitored by scouting canola plants. Samples of larvae, pupae and parasitoid cocoons were brought into the laboratory. Parasitoids that emerged were identified and their incidence recorded. Monolepta cf bifasciata (Chrysomelidae) and Listroderes costrirostris (Schoener) (Curculionidae) were the most abundant of the coleopteran pests. (DBM) and Heliothis armigera (H.) (Noctuidae) were most abundant lepidopteran pests of Canola. There was a high proportion of first and second instar larvae as indicated by the results of the Berlese funnels as compared to visual scouting in Bapsfontein. From May to August the infestation level of DBM was high, reaching the maximum of 0.25 larvae per plant in June 1996, then declined and remained low for the rest of the season in Rietondale. From September to December for all three years of the study, the population levels Of DBM were high, reaching a maximum of 9.6larvae per plant in September 1997, and remained low from January to August in Bapsfontein. The number of adult moths per trap per week ranged from 0 to 91 in Rietondale, peaking in January 1996 and September 1997. There was no correlation between infestation levels and the pheromone trap catches. In contrast to Rietondale, there was a high correlation between pheromone trap catches and subsequent larval infestations at Bapsfontein. Although DBM infestation levels were generally low, parasitism levels often reached 100% caused by a complex of parasitoids. During the period of study, the following hymenopteran parasitoids were recorded: Cotesia plutellae (Kurdjumov) and Apanteles eriophyes (Nixon), Braconidae), both larval parasitoids, Diadegma mollipla (Holmgren) (Ichneumonidae), and Oomyzus sokolowskii (Kurdjumov) (Eulophidae), larval-pupal parasitoids, Diadromus collaris (Gravenhorst) (Ichneumonidae) pupal parasitoid, and the hyperparasitoids Mesochorus sp. (Ichneumonidae) and Pteromalus sp. (Pteromalidae). Cotesia plutellae was the most abundant parasitoid occurring throughout the year..
- Full Text:
- Date Issued: 2002
Diet of coastal filter feeders : impact of factors operating at different scales
- Authors: Puccinelli, Eleonora
- Date: 2015
- Subjects: Benthic animals -- Ecology -- South Africa , Benthic animals -- Nutrition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5929 , http://hdl.handle.net/10962/d1017807
- Description: Benthic filter feeders have a key functional role in the dynamics of coastal food web as an intermediate trophic level and bioengineers. A wide variety of factors, operating across multiple spatial scales (e.g. hydrographic regime, human activities), can affect the composition of the water column and thus the availability of food for benthic populations. Food availability in turn affects the growth, reproductive rates and survival of benthic organisms, and consequently, can influence the functioning of the entire ecosystem. This study aims to evaluate how various environmental factors may modify the diet of intertidal filter feeders living along the South African coast. Specifically, the effects of biogeography, upwelling, urbanization and freshwater input on the dietary regimes of five species of filter feeders (two mussel and three barnacle species) were investigated using fatty acid (FA) and stable isotope (SI) analyses.Strong interspecific differences were found among the five species considered. However, all species responded to factors operating at large (100s km) and meso (10s- 100s km) scales (i.e. biogeography and upwelling respectively). The barnacles exhibit habitat segregation and showed different FA and SI signatures from each other, while the two mussel species, an invasive and native species that co-occur in the same mussel beds, had partially overlapping diets. Differences in their diets were found only using FA analysis, while their SI signatures differed on only one occasion. This highlights the importance of using the appropriate tool, and ideally combined techniques, to investigate diets.FA and SI signatures of all species considered changed among the three biographical provinces (west, south and east coasts of South Africa) exhibiting similar patterns that reflect the two oceanographic regimes that characterize the coastline: the eutrophic Benguela Current on the west coast and the oligotrophic Agulhas Current on the other two coasts. Upwelling had a significant effect on FA and SI signatures, with stronger effects on the west coast than the south coast. The results indicate that benthic filter feeders at upwelling areas consumed a mix of coastal macroalgal detritus and phytoplankton, which was probably brought onshore during downwelling events. At smaller spatialscales and using repeated sampling, the influence of upwelling on the west coast was found to be pervasive, rather than discrete, so that it may be more appropriate to categorize upwelling by referring to upwelling centres and downstream areas. SI underlined a significant effect of urbanization on the diet of filter feeders with an enrichment in the δ¹⁵N being characteristic of anthropogenic effect. Although a large number of rivers characterize the South African coast, no distinct effect of freshwater input was found for either the SI or FA signatures of the filter feeders. This contrasts with earlier work on demersal species and suggests that freshwater input does not significantly affect food availability for intertidal filter feeders, and that other factors (e.g. hydrogeography) are more important in determining the diet of these populations. These results highlight that environmental and anthropogenic factors operating at different spatial and temporal scales have a profound effect on benthic ecosystems, and that they control the relationship between primary production and primary consumers in coastal areas. Above all, this work highlights the importance of understanding the spatial and temporal scales at which different factors affect feeding regimes, and their critical role in coastal food webs.
- Full Text:
- Date Issued: 2015
- Authors: Puccinelli, Eleonora
- Date: 2015
- Subjects: Benthic animals -- Ecology -- South Africa , Benthic animals -- Nutrition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5929 , http://hdl.handle.net/10962/d1017807
- Description: Benthic filter feeders have a key functional role in the dynamics of coastal food web as an intermediate trophic level and bioengineers. A wide variety of factors, operating across multiple spatial scales (e.g. hydrographic regime, human activities), can affect the composition of the water column and thus the availability of food for benthic populations. Food availability in turn affects the growth, reproductive rates and survival of benthic organisms, and consequently, can influence the functioning of the entire ecosystem. This study aims to evaluate how various environmental factors may modify the diet of intertidal filter feeders living along the South African coast. Specifically, the effects of biogeography, upwelling, urbanization and freshwater input on the dietary regimes of five species of filter feeders (two mussel and three barnacle species) were investigated using fatty acid (FA) and stable isotope (SI) analyses.Strong interspecific differences were found among the five species considered. However, all species responded to factors operating at large (100s km) and meso (10s- 100s km) scales (i.e. biogeography and upwelling respectively). The barnacles exhibit habitat segregation and showed different FA and SI signatures from each other, while the two mussel species, an invasive and native species that co-occur in the same mussel beds, had partially overlapping diets. Differences in their diets were found only using FA analysis, while their SI signatures differed on only one occasion. This highlights the importance of using the appropriate tool, and ideally combined techniques, to investigate diets.FA and SI signatures of all species considered changed among the three biographical provinces (west, south and east coasts of South Africa) exhibiting similar patterns that reflect the two oceanographic regimes that characterize the coastline: the eutrophic Benguela Current on the west coast and the oligotrophic Agulhas Current on the other two coasts. Upwelling had a significant effect on FA and SI signatures, with stronger effects on the west coast than the south coast. The results indicate that benthic filter feeders at upwelling areas consumed a mix of coastal macroalgal detritus and phytoplankton, which was probably brought onshore during downwelling events. At smaller spatialscales and using repeated sampling, the influence of upwelling on the west coast was found to be pervasive, rather than discrete, so that it may be more appropriate to categorize upwelling by referring to upwelling centres and downstream areas. SI underlined a significant effect of urbanization on the diet of filter feeders with an enrichment in the δ¹⁵N being characteristic of anthropogenic effect. Although a large number of rivers characterize the South African coast, no distinct effect of freshwater input was found for either the SI or FA signatures of the filter feeders. This contrasts with earlier work on demersal species and suggests that freshwater input does not significantly affect food availability for intertidal filter feeders, and that other factors (e.g. hydrogeography) are more important in determining the diet of these populations. These results highlight that environmental and anthropogenic factors operating at different spatial and temporal scales have a profound effect on benthic ecosystems, and that they control the relationship between primary production and primary consumers in coastal areas. Above all, this work highlights the importance of understanding the spatial and temporal scales at which different factors affect feeding regimes, and their critical role in coastal food webs.
- Full Text:
- Date Issued: 2015
Dietary aspects of establishing a mainland-based colony of the endangered African Penguin (Spheniscus demersus) in St Francis Bay, South Africa
- Authors: Voogt, Nina Margaret
- Date: 2014
- Subjects: African penguin -- South Africa -- Cape Saint Francis , African penguin -- Food -- South Africa -- Algoa Bay , African penguin -- Habitat suitability index models -- South Africa -- Cape Saint Francis , Stable isotopes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5875 , http://hdl.handle.net/10962/d1013115
- Description: Cape St Francis, Eastern Cape, has been identified as one of four potential sites for establishing a mainland-based African penguin (Spheniscus demersus) colony. This thesis comprises three main components: a verification of a preparation method for stable isotope samples from penguin feathers; a dietary analysis of the penguins on Bird Island, Algoa Bay, though stable isotope analysis of whole blood and feathers (2012 and 2013); and an estimation of available fish surplus that could potentially support a colony of penguins at Cape St Francis. Each component contributes towards the next, all building towards answering the main research question: Will there be enough food around St Francis Bay to support a colony of penguins and sustain the already established fisheries industry within the bay? Stable isotope analysis of whole blood and feathers from breeding adults and whole blood from juveniles provided insight into the variability of African penguins’ diets at different stages in their life history. Stable isotope mixing models indicated that the predicted proportions that each prey species could potentially contribute to diet conflicted with published stomach sample data. This might arise from inaccurate trophic enrichment factors used in the model, or from systematic biases in the published stomach sampling techniques, or both. Dietary sexual dimorphism was not demonstrated by the isotope signatures of breeding penguins. Based on official catch data, the fisheries activity on the south coast, and especially around the potential colony site at St Francis, is much lower than around the west coast’s penguin colonies. The model provided a first-order estimate for fish supply around the potential colony site at St Francis both at a large coastal scale and a local small scale. At both scales the estimate indicated an ample availability of fish at current fishing levels. The model in Chapter 4 can also be applied to refining the assessments of other potential colony sites on the south coast. In conclusion, the south coast is a promising area for a new colony of penguins in terms of food availability. There is relatively low fishing activity in the area and, as suggested by the large-scale model in Chapter 4, an ample fish resource. The final chapter briefly discusses factors that need to be considered before attempting to establish a mainland-based colony of African penguins.
- Full Text:
- Date Issued: 2014
- Authors: Voogt, Nina Margaret
- Date: 2014
- Subjects: African penguin -- South Africa -- Cape Saint Francis , African penguin -- Food -- South Africa -- Algoa Bay , African penguin -- Habitat suitability index models -- South Africa -- Cape Saint Francis , Stable isotopes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5875 , http://hdl.handle.net/10962/d1013115
- Description: Cape St Francis, Eastern Cape, has been identified as one of four potential sites for establishing a mainland-based African penguin (Spheniscus demersus) colony. This thesis comprises three main components: a verification of a preparation method for stable isotope samples from penguin feathers; a dietary analysis of the penguins on Bird Island, Algoa Bay, though stable isotope analysis of whole blood and feathers (2012 and 2013); and an estimation of available fish surplus that could potentially support a colony of penguins at Cape St Francis. Each component contributes towards the next, all building towards answering the main research question: Will there be enough food around St Francis Bay to support a colony of penguins and sustain the already established fisheries industry within the bay? Stable isotope analysis of whole blood and feathers from breeding adults and whole blood from juveniles provided insight into the variability of African penguins’ diets at different stages in their life history. Stable isotope mixing models indicated that the predicted proportions that each prey species could potentially contribute to diet conflicted with published stomach sample data. This might arise from inaccurate trophic enrichment factors used in the model, or from systematic biases in the published stomach sampling techniques, or both. Dietary sexual dimorphism was not demonstrated by the isotope signatures of breeding penguins. Based on official catch data, the fisheries activity on the south coast, and especially around the potential colony site at St Francis, is much lower than around the west coast’s penguin colonies. The model provided a first-order estimate for fish supply around the potential colony site at St Francis both at a large coastal scale and a local small scale. At both scales the estimate indicated an ample availability of fish at current fishing levels. The model in Chapter 4 can also be applied to refining the assessments of other potential colony sites on the south coast. In conclusion, the south coast is a promising area for a new colony of penguins in terms of food availability. There is relatively low fishing activity in the area and, as suggested by the large-scale model in Chapter 4, an ample fish resource. The final chapter briefly discusses factors that need to be considered before attempting to establish a mainland-based colony of African penguins.
- Full Text:
- Date Issued: 2014
Direct and indirect effects of zooplanktivorous predators on the estuarine plankton community
- Authors: Wasserman, Ryan John
- Date: 2014
- Subjects: Zooplankton -- Effect of predation on , Predation (Biology) , Zooplankton -- Predators of , Copepoda
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5870 , http://hdl.handle.net/10962/d1012938
- Description: Although predation has been identified as a potentially important driver in terrestrial and freshwater ecosystems, estuarine planktonic research has focused largely on the so-called "bottom-up" drivers of community assemblages. As such, this thesis focuses on the direct and indirect effects of zooplanktivorous predators on the planktonic community in an estuarine environment. By using a suite of in situ mesocosm experiments, a number of hypotheses, pertaining to the major research themes associated with predator-prey interactions, are tested. These themes included trophic cascading, risk effects associated with predation events and the importance of predator diversity in maintaining prey communities. The first experiment assessed the significance of apex predation pressure for the planktonic community through trophic cascades. Various treatments using in situ mesocosms were established in a closed oligotrophic estuary to highlight the importance of predation in stabilising estuarine plankton abundances. Through either the removal (filtration) or addition of certain planktonic groups, varied trophic scenarios were established. The experimental treatment containing apex zooplanktivores had consequences for multiple trophic levels, exerting a stabilising pressure throughout the food web (Chapter 3). Furthermore, pyrosequencing of filtered water samples revealed that when compared to the remaining treatments, the treatment containing stable apex predatory pressure experienced limited temporal deviation-from-initial in bacterial community structure (Chapter 4). These findings are consistent with trophic cascade theory whereby predators mediate interactions at multiple lower trophic levels with consequent repercussions for diversity. To assess the non-consumptive effects of predators on prey, two experiments were conducted. Firstly, using egg numbers per clutch as a measure of potential reproductive output, the non-lethal effects of predatory pressure on reproductive success in a key planktonic copepod was investigated. In this study, the average clutch size of fecund female copepods was found to be consistently lower in the presence of predators when compared to females not exposed to predation threat (Chapter 5). The second study assessed the effects of conspecific chemical alarm cues associated with predation, on population dynamics of a copepod species. This study revealed that the copepods appear to detect the presence of chemical alarm cues associated with predation events, with repercussions for population demographics over time. Furthermore, it showed that in the absence of actual predation, copepod prey responses to alarm cues were adjusted over time, consistent with the threat sensitive predator avoidance hypothesis (Chapter 6). The final data chapter dealt with predator diversity and its implications for zooplankton community structure. By experimentally monitoring the effects of two alternate model predators on the metazoan community over time, dissimilarities in community level control emerged. Alternate key prey populations were regulated by the different model predators, highlighting the importance of predator and prey behaviour in mediating predator-prey interactions (Chapter 7). These results highlight the potential importance of predators in maintaining community dynamics in estuarine planktonic communities under certain conditions. This study represents some of the first work to address these various aspects of predator-prey dynamics within the context of planktonic estuarine ecology.
- Full Text:
- Date Issued: 2014
- Authors: Wasserman, Ryan John
- Date: 2014
- Subjects: Zooplankton -- Effect of predation on , Predation (Biology) , Zooplankton -- Predators of , Copepoda
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5870 , http://hdl.handle.net/10962/d1012938
- Description: Although predation has been identified as a potentially important driver in terrestrial and freshwater ecosystems, estuarine planktonic research has focused largely on the so-called "bottom-up" drivers of community assemblages. As such, this thesis focuses on the direct and indirect effects of zooplanktivorous predators on the planktonic community in an estuarine environment. By using a suite of in situ mesocosm experiments, a number of hypotheses, pertaining to the major research themes associated with predator-prey interactions, are tested. These themes included trophic cascading, risk effects associated with predation events and the importance of predator diversity in maintaining prey communities. The first experiment assessed the significance of apex predation pressure for the planktonic community through trophic cascades. Various treatments using in situ mesocosms were established in a closed oligotrophic estuary to highlight the importance of predation in stabilising estuarine plankton abundances. Through either the removal (filtration) or addition of certain planktonic groups, varied trophic scenarios were established. The experimental treatment containing apex zooplanktivores had consequences for multiple trophic levels, exerting a stabilising pressure throughout the food web (Chapter 3). Furthermore, pyrosequencing of filtered water samples revealed that when compared to the remaining treatments, the treatment containing stable apex predatory pressure experienced limited temporal deviation-from-initial in bacterial community structure (Chapter 4). These findings are consistent with trophic cascade theory whereby predators mediate interactions at multiple lower trophic levels with consequent repercussions for diversity. To assess the non-consumptive effects of predators on prey, two experiments were conducted. Firstly, using egg numbers per clutch as a measure of potential reproductive output, the non-lethal effects of predatory pressure on reproductive success in a key planktonic copepod was investigated. In this study, the average clutch size of fecund female copepods was found to be consistently lower in the presence of predators when compared to females not exposed to predation threat (Chapter 5). The second study assessed the effects of conspecific chemical alarm cues associated with predation, on population dynamics of a copepod species. This study revealed that the copepods appear to detect the presence of chemical alarm cues associated with predation events, with repercussions for population demographics over time. Furthermore, it showed that in the absence of actual predation, copepod prey responses to alarm cues were adjusted over time, consistent with the threat sensitive predator avoidance hypothesis (Chapter 6). The final data chapter dealt with predator diversity and its implications for zooplankton community structure. By experimentally monitoring the effects of two alternate model predators on the metazoan community over time, dissimilarities in community level control emerged. Alternate key prey populations were regulated by the different model predators, highlighting the importance of predator and prey behaviour in mediating predator-prey interactions (Chapter 7). These results highlight the potential importance of predators in maintaining community dynamics in estuarine planktonic communities under certain conditions. This study represents some of the first work to address these various aspects of predator-prey dynamics within the context of planktonic estuarine ecology.
- Full Text:
- Date Issued: 2014
Disentangling the role of prokaryotes in regulating export flux via suspended and sinking organic matter in the southern ocean
- Authors: Dithugoe, Choaro David
- Date: 2022-10-14
- Subjects: Microbial ecology , Bioinformatics , Biochemistry , Oceanography , Metagenomics , Carbon cycle (Biogeochemistry) , Prokaryotes
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365745 , vital:65782 , DOI https://doi.org/10.21504/10962/365745
- Description: The role of phytoplankton in regulating atmospheric carbon dioxide in the marine environment has been the subject of extensive research. We lack, however, comparative insights regarding the functional contributions of bacteria, archaea, fungi, and viruses (the microbiota) to organic matter export especially in understudied polar marine environments such as the Southern Ocean. This knowledge deficit is in part due to the high levels of microbial diversity which obscures efforts to study the relationship between diversity and ecosystem functions including their roles in the sequestration of carbon and nitrogen. Elucidating their precise contributions to organic matter export may be central to potential ecosystems feedbacks to global climate change. We examined several factors which may influence organic matter export to depth including net primary production, phytoplankton biomass, temperature, and prokaryotic functional capacity in the Southern Ocean. A Marine Snow Catcher was used to collect suspended and sinking material 10 metres below mixed layer depth at Southern Ocean Time Series (SOTS) in autumn (March-April) and in the Atlantic sector of the Southern Ocean in winter (July-August) and spring (October-November) 2019. The suspended and sinking material was used to determine the particulate organic carbon and nitrogen concentrations which were then used to calculate fluxes and export ratio ((e-ratio) - particulate organic carbon flux divided by net primary production). Additionally, genomic DNA was extracted from the suspended and sinking material and sequenced to obtain Shotgun metagenomic data which was employed to reconstruct metagenome assembled genome (MAGs) and their functional capacity using bioinformatic tools such as DRAM. Data from the Atlantic sector of the Southern Ocean, demonstrate that net primary production and temperature were inversely related to the e-ratio which is consistent with previous findings from the northern region of the Southern Ocean. Genomic functional capacity from SOTS suggested that r-strategist (organisms adapted to live in unstable environments) bacteria (e.g., Gammaproteobacteria) were prominent in the suspended pool. By contrast, the sinking particle-pool appeared to be dominated by K- strategists (organisms adapted to stable environment). The opposite was true for the archaea. This finding (i.e., bacteria) differs from a previous study in the northern region of the Southern Ocean, showing that microbes with K-strategists were more abundant in the suspended fraction. K-strategists typically degrade sinking organic matter into suspended organic matter or dissolved organic matter reducing the organic carbon export efficiency. Furthermore, Data from the Atlantic sector of the Southern Ocean revealed that seasonal temperature changes might dictate the rate of regional prokaryotic degradation across the zones. Resulting in rapid degradation at the northerly warmer regions and slow degradation further south. The data further provide evidence of chemolithoautotrophic mechanisms, with prokaryotes harbouring key pathways, required to transform dissolved inorganic carbon into complex organic forms, including recalcitrant dissolved organic carbon. Collectively, the SOTS and Atlantic sector of the Southern Ocean data suggest that shifts in prokaryotic community structure and functional capacity may regulate (either degradation or synthesis of organic matter) carbon export to depth. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Dithugoe, Choaro David
- Date: 2022-10-14
- Subjects: Microbial ecology , Bioinformatics , Biochemistry , Oceanography , Metagenomics , Carbon cycle (Biogeochemistry) , Prokaryotes
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365745 , vital:65782 , DOI https://doi.org/10.21504/10962/365745
- Description: The role of phytoplankton in regulating atmospheric carbon dioxide in the marine environment has been the subject of extensive research. We lack, however, comparative insights regarding the functional contributions of bacteria, archaea, fungi, and viruses (the microbiota) to organic matter export especially in understudied polar marine environments such as the Southern Ocean. This knowledge deficit is in part due to the high levels of microbial diversity which obscures efforts to study the relationship between diversity and ecosystem functions including their roles in the sequestration of carbon and nitrogen. Elucidating their precise contributions to organic matter export may be central to potential ecosystems feedbacks to global climate change. We examined several factors which may influence organic matter export to depth including net primary production, phytoplankton biomass, temperature, and prokaryotic functional capacity in the Southern Ocean. A Marine Snow Catcher was used to collect suspended and sinking material 10 metres below mixed layer depth at Southern Ocean Time Series (SOTS) in autumn (March-April) and in the Atlantic sector of the Southern Ocean in winter (July-August) and spring (October-November) 2019. The suspended and sinking material was used to determine the particulate organic carbon and nitrogen concentrations which were then used to calculate fluxes and export ratio ((e-ratio) - particulate organic carbon flux divided by net primary production). Additionally, genomic DNA was extracted from the suspended and sinking material and sequenced to obtain Shotgun metagenomic data which was employed to reconstruct metagenome assembled genome (MAGs) and their functional capacity using bioinformatic tools such as DRAM. Data from the Atlantic sector of the Southern Ocean, demonstrate that net primary production and temperature were inversely related to the e-ratio which is consistent with previous findings from the northern region of the Southern Ocean. Genomic functional capacity from SOTS suggested that r-strategist (organisms adapted to live in unstable environments) bacteria (e.g., Gammaproteobacteria) were prominent in the suspended pool. By contrast, the sinking particle-pool appeared to be dominated by K- strategists (organisms adapted to stable environment). The opposite was true for the archaea. This finding (i.e., bacteria) differs from a previous study in the northern region of the Southern Ocean, showing that microbes with K-strategists were more abundant in the suspended fraction. K-strategists typically degrade sinking organic matter into suspended organic matter or dissolved organic matter reducing the organic carbon export efficiency. Furthermore, Data from the Atlantic sector of the Southern Ocean revealed that seasonal temperature changes might dictate the rate of regional prokaryotic degradation across the zones. Resulting in rapid degradation at the northerly warmer regions and slow degradation further south. The data further provide evidence of chemolithoautotrophic mechanisms, with prokaryotes harbouring key pathways, required to transform dissolved inorganic carbon into complex organic forms, including recalcitrant dissolved organic carbon. Collectively, the SOTS and Atlantic sector of the Southern Ocean data suggest that shifts in prokaryotic community structure and functional capacity may regulate (either degradation or synthesis of organic matter) carbon export to depth. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
Dispersal of the cochineal insect Dactylopius Austrinus de Lotto (Homoptera : Dactylopiidae)
- Authors: Gunn, Brian Howard
- Date: 1979
- Subjects: Cochineal insect--South Africa , Cochineal insects , Biological control , Jointed cactus , South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5596 , http://hdl.handle.net/10962/d1002046
- Description: Dispersal of the cochineal insect Dactylopius austrinus De Lotto, introduced into South Africa in 1932 as a biological control agent against jointed cactus Opuntia aurantiaca Lindley, was investigated. Zimmermann et al. (l974) suggested that the apparent failure of this insect to control jointed cactus infestations is due to limited dispersal of the first instar nymphs (hereafter referred to as crawlers). Studies on crawler morphology have shown a clear sexual dimorphism in the pattern and development of filaments on the head, thorax and abdomen of male and female crawlers. This enabled differentiation between the sexes with respect to terminal velocities, behaviour and survival of crawlers which have shown that the crawlers, especially the females, are well adapted to dispersal. Long filaments on the head, thorax and abdomen of the female crawlers, that are restricted to dispersal in the crawler stage (as later instars are sessile) and a behaviour directed towards "take-off" enhance the potential for dispersal. The more sedentary males, with long filaments restricted to the abdomen, are able to disperse as winged adults. The principal factors influencing the timing of dispersal and number of crawlers blown from the host plant are wind and temperature; the latter determining the number of crawlers moving on the host plant. Dispersal is confined to the period between 06h00 and 20h00 and it was possible to correlate the pattern of crawler dispersal with wind patterns. The general equation of Taylor (1978) provided an adequate description of horizontal distribution of D.austrinus crawlers in all directions. Wind dispersal of the apterous crawlers is restricted by the low height of jointed cactus plants. Horizontal distribution is limited (generally less than 10 m) although a small proportion of crawlers carried vertically upwards by turbulence or convection currents are sufficiently hardy to survive long range displacement. It is suggested that the small size of the host plant will also reduce effective colonization as the canopy area provides a small target for the wind-blown crawlers. The limitation on dispersal due to the low height of the host plant suggested a system for artificially enhancing crawler dispersal from elevated towers in the field. Evaluation of this system confirmed that it would be practical to augment or introduce cochineal into jointed cactus infestations to enhance the biocontrol potential of this insect. This offers an alternative to chemical control, that has so far failed to control the spread of jointed cactus despite an intensive and expensive herbicide program
- Full Text:
- Date Issued: 1979
- Authors: Gunn, Brian Howard
- Date: 1979
- Subjects: Cochineal insect--South Africa , Cochineal insects , Biological control , Jointed cactus , South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5596 , http://hdl.handle.net/10962/d1002046
- Description: Dispersal of the cochineal insect Dactylopius austrinus De Lotto, introduced into South Africa in 1932 as a biological control agent against jointed cactus Opuntia aurantiaca Lindley, was investigated. Zimmermann et al. (l974) suggested that the apparent failure of this insect to control jointed cactus infestations is due to limited dispersal of the first instar nymphs (hereafter referred to as crawlers). Studies on crawler morphology have shown a clear sexual dimorphism in the pattern and development of filaments on the head, thorax and abdomen of male and female crawlers. This enabled differentiation between the sexes with respect to terminal velocities, behaviour and survival of crawlers which have shown that the crawlers, especially the females, are well adapted to dispersal. Long filaments on the head, thorax and abdomen of the female crawlers, that are restricted to dispersal in the crawler stage (as later instars are sessile) and a behaviour directed towards "take-off" enhance the potential for dispersal. The more sedentary males, with long filaments restricted to the abdomen, are able to disperse as winged adults. The principal factors influencing the timing of dispersal and number of crawlers blown from the host plant are wind and temperature; the latter determining the number of crawlers moving on the host plant. Dispersal is confined to the period between 06h00 and 20h00 and it was possible to correlate the pattern of crawler dispersal with wind patterns. The general equation of Taylor (1978) provided an adequate description of horizontal distribution of D.austrinus crawlers in all directions. Wind dispersal of the apterous crawlers is restricted by the low height of jointed cactus plants. Horizontal distribution is limited (generally less than 10 m) although a small proportion of crawlers carried vertically upwards by turbulence or convection currents are sufficiently hardy to survive long range displacement. It is suggested that the small size of the host plant will also reduce effective colonization as the canopy area provides a small target for the wind-blown crawlers. The limitation on dispersal due to the low height of the host plant suggested a system for artificially enhancing crawler dispersal from elevated towers in the field. Evaluation of this system confirmed that it would be practical to augment or introduce cochineal into jointed cactus infestations to enhance the biocontrol potential of this insect. This offers an alternative to chemical control, that has so far failed to control the spread of jointed cactus despite an intensive and expensive herbicide program
- Full Text:
- Date Issued: 1979
Dispersal, settlement and recruitment : their influence on the population dynamics of intertidal mussels
- Authors: Phillips, Tracey Elizabeth
- Date: 1995
- Subjects: Perna -- South Africa -- Eastern Cape -- Algoa bay Mytilus galloprovincialis -- South Africa -- Eastern Cape -- Algoa bay Mytilidae -- South Africa -- Eastern Cape -- Algoa bay
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5663 , http://hdl.handle.net/10962/d1005347
- Description: Recruitment of planktonic larvae into sedentary benthic populations regulates the population dynamics of marine invertebrates. The processes controlling recruitment, however, are poorly understood, and recruitment remains largely unpredictable, which complicates management of exploited shellfish resources. The mussels Perna perna, Choromytilus meridionalis and Mytilus galloprovincialis, found on the south coast of southern Africa, have planktonic larvae and sedentary adult stages. This thesis examines dispersal, settlement and early post-settlement growth and mortality, and their effect on recruitment and demography of intertidal mussel populations in the region of Algoa Bay on the south coast of southern Africa. Temporal and spatial variation in the body mass, density and size structure of mussels, the distribution of bivalve larvae on plankton grids in the nearshore zone and the distribution of a recently introduced invasive mussel, Mytilus galloprovincialis, were examined between 1989 and 1992. Furthermore, data on hourly or daily changes in wind strength and direction, air and sea surface temperatures and low and high tide levels in the study region, were obtained. There were 3-4 peaks in spawning (characterised by an abrupt decline in weight) and settlement activity annually. These peaks varied in exact timing, intensity and duration between sites and over time. However, at a site, spawning was followed by settlement 4-8 weeks later, and there was a significant (P < 0.05) direct correlation between spawning intensity prior to the appearance of a new cohort and the cohort density (settlement intensity). The stochastic spatial and temporal variation in breeding activity was superimposed on a more general pattern of a higher intensity of spawning and settlement in Algoa Bay than on the open coast, and a higher settlement intensity on coastal sandstone shores than on dune rock shores. Spawning was more frequent in winter and spring, and the probability of spawning and settlement peaked around the spring and autumn equinox, if temperature and wind conditions were suitable. Larval behaviour had little effect on their dispersal in the well-mixed nearshore region. Larvae were passively dispersed by currents, and their dispersal range and direction depended on prevailing winds and local topography. The sharp decline in density of recruit and adult M. galloprovincialis with increasing distance from the point of introduction, showed that some larvae were carried by wind generated currents over moderately long distances (-100 km). However, since most (76 %) M. galloprovincialis recruited within 4 km of the parent population, it is possible that larvae become trapped in small gullies and crevices around rocky shores, and have a limited dispersal range. This could explain the link between local patterns of spawning and settlement. The distribution and abundance of settlers on the shore was influenced by larval behaviour and the availability of settlement, substrata. Larvae preferred to settle primarily on foliose coralline algae and migrate to the adult mussel bed when they were larger (0.60-7 mm), but larvae also settled directly on adult mussels, possibly because the amount of coralline algae was limited. Both direct and secondary settlement were considered to be important in maintaining mussel populations since the rate of settlement was low(generally < 60 000.m-2). Cohort analyses showed that prior to maturity post-settlement growth (- 30 mm in 10 months) and mortality rates (60-100%) were high, but varied. When settlement intensity was low this variability uncoupled the relationship between spawning and recruitment intensity. Multiple regression analysis showed that together reproductive effort (gamete output), settlement intensity, growth and mortality prior to maturity, accounted for 76 % of the variance in recruitment into mature adult populations. The low settlement rate coupled with the short life span of mussels « 3 years), meant that populations underwent marked spatial and temporal variations in structure and abundance as settlement intensity varied, but there were consistent general differences between mussel populations on dune rock and sandstone shores in Algoa Bay and on the open coast. It was concluded from these results that, spawning intensity and post-settlement growth and mortality, rather than dispersal, regulated recruitment and the structure and abundance of intertidal P. perna and C. meridionalis populations along the south coast of southern Africa. On the basis of these results it is recommended that species with limited dispersal, variable recruitment and high natural mortality, such as P. perna, should be conserved by protecting a small part of the population in reserves, and controlling utilisation outside reserves to minimize disturbance to local brood stocks. Furthermore, since the potential for reseeding adjacent exploited areas is limited, several small reserves placed at regular intervals along the coast would be more effective than a single large reserve.
- Full Text:
- Date Issued: 1995
- Authors: Phillips, Tracey Elizabeth
- Date: 1995
- Subjects: Perna -- South Africa -- Eastern Cape -- Algoa bay Mytilus galloprovincialis -- South Africa -- Eastern Cape -- Algoa bay Mytilidae -- South Africa -- Eastern Cape -- Algoa bay
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5663 , http://hdl.handle.net/10962/d1005347
- Description: Recruitment of planktonic larvae into sedentary benthic populations regulates the population dynamics of marine invertebrates. The processes controlling recruitment, however, are poorly understood, and recruitment remains largely unpredictable, which complicates management of exploited shellfish resources. The mussels Perna perna, Choromytilus meridionalis and Mytilus galloprovincialis, found on the south coast of southern Africa, have planktonic larvae and sedentary adult stages. This thesis examines dispersal, settlement and early post-settlement growth and mortality, and their effect on recruitment and demography of intertidal mussel populations in the region of Algoa Bay on the south coast of southern Africa. Temporal and spatial variation in the body mass, density and size structure of mussels, the distribution of bivalve larvae on plankton grids in the nearshore zone and the distribution of a recently introduced invasive mussel, Mytilus galloprovincialis, were examined between 1989 and 1992. Furthermore, data on hourly or daily changes in wind strength and direction, air and sea surface temperatures and low and high tide levels in the study region, were obtained. There were 3-4 peaks in spawning (characterised by an abrupt decline in weight) and settlement activity annually. These peaks varied in exact timing, intensity and duration between sites and over time. However, at a site, spawning was followed by settlement 4-8 weeks later, and there was a significant (P < 0.05) direct correlation between spawning intensity prior to the appearance of a new cohort and the cohort density (settlement intensity). The stochastic spatial and temporal variation in breeding activity was superimposed on a more general pattern of a higher intensity of spawning and settlement in Algoa Bay than on the open coast, and a higher settlement intensity on coastal sandstone shores than on dune rock shores. Spawning was more frequent in winter and spring, and the probability of spawning and settlement peaked around the spring and autumn equinox, if temperature and wind conditions were suitable. Larval behaviour had little effect on their dispersal in the well-mixed nearshore region. Larvae were passively dispersed by currents, and their dispersal range and direction depended on prevailing winds and local topography. The sharp decline in density of recruit and adult M. galloprovincialis with increasing distance from the point of introduction, showed that some larvae were carried by wind generated currents over moderately long distances (-100 km). However, since most (76 %) M. galloprovincialis recruited within 4 km of the parent population, it is possible that larvae become trapped in small gullies and crevices around rocky shores, and have a limited dispersal range. This could explain the link between local patterns of spawning and settlement. The distribution and abundance of settlers on the shore was influenced by larval behaviour and the availability of settlement, substrata. Larvae preferred to settle primarily on foliose coralline algae and migrate to the adult mussel bed when they were larger (0.60-7 mm), but larvae also settled directly on adult mussels, possibly because the amount of coralline algae was limited. Both direct and secondary settlement were considered to be important in maintaining mussel populations since the rate of settlement was low(generally < 60 000.m-2). Cohort analyses showed that prior to maturity post-settlement growth (- 30 mm in 10 months) and mortality rates (60-100%) were high, but varied. When settlement intensity was low this variability uncoupled the relationship between spawning and recruitment intensity. Multiple regression analysis showed that together reproductive effort (gamete output), settlement intensity, growth and mortality prior to maturity, accounted for 76 % of the variance in recruitment into mature adult populations. The low settlement rate coupled with the short life span of mussels « 3 years), meant that populations underwent marked spatial and temporal variations in structure and abundance as settlement intensity varied, but there were consistent general differences between mussel populations on dune rock and sandstone shores in Algoa Bay and on the open coast. It was concluded from these results that, spawning intensity and post-settlement growth and mortality, rather than dispersal, regulated recruitment and the structure and abundance of intertidal P. perna and C. meridionalis populations along the south coast of southern Africa. On the basis of these results it is recommended that species with limited dispersal, variable recruitment and high natural mortality, such as P. perna, should be conserved by protecting a small part of the population in reserves, and controlling utilisation outside reserves to minimize disturbance to local brood stocks. Furthermore, since the potential for reseeding adjacent exploited areas is limited, several small reserves placed at regular intervals along the coast would be more effective than a single large reserve.
- Full Text:
- Date Issued: 1995
Distribution, ecological and economic impacts and competition of the invasive alien aquatic weeds (Pontederia crassipes Mart., Pistia stratiotes L., Salvinia molesta D.S. Mitch. and Azolla filiculoides Lam.) in Madagascar
- Authors: Lehavana, Adolphe
- Date: 2021-10-29
- Subjects: Pontederiaceae Madagascar , Water lettuce Madagascar , Salvinia molesta Madagascar , Azolla filiculoides Madagascar , Introduced aquatic organisms , Aquatic weeds Economic aspects , Aquatic weeds Social aspects , Aquatic weeds Geographical distribution
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191225 , vital:45072
- Description: In Madagascar, as in several countries in the world, the invasion by four aquatic weeds (Pontederia crassipes Mart. (Pontederiaceae), Pistia stratiotes L. (Araceae), Salvinia molesta D.S. Mitch Salviniaceae) and Azolla filiculoides Lam. (Azollaceae) are among the drivers of environmental and socio-economic deterioration in aquatic ecosystems. Pistia stratiotes was first recorded on the island in the 19th century, and P. crassipes from the beginning of the 20th century, while S. molesta and A. filiculoides were only documented during in the 21st century. From the 1920s, botanists such as Henri Perrier de la Bathie and Raymond Decary were already aware of the dangers caused, in particular by P. crassipes in other countries, and raised the alarm, but little attention has been paid to these species. The aim of the research conducted for this thesis was to determine the distribution, socio-economic and ecological impacts of these four invasive alien aquatic weeds in Madagascar and to make recommendations for their control. First, the distributions of these four aquatic weeds were mapped. This mapping exercise compiled data from different sources including herbarium records, online data and field visits across Madagascar. The mapping study was undertaken from August 2015 to June 2020. Except for mountainous areas above 1800 m (Tsaratanana Massif, Ankaratra Massif and Andringitra Massif) where no data were available, all of Madagascar's bioclimates were invaded by at least one of the four aquatic weeds. In total, at least one species was recorded in 18 of the 22 Regions. Pontederia crassipes was recorded in 13 Regions, S. molesta in 14 Regions, P. stratiotes in 12 Regions, and A. filiculoides in 13 Regions. Herbarium records revealed the oldest record for P. stratiotes to be 1847, 1931 for P. crassipes, 1995 for S. molesta and there were no herbarium specimens for A. filiculoides prior to the start of the current study in 2015. We now know where these four weeds occur and how abundant they are. An objective of this research was to assess the impacts of the four invasive aquatic plants on the socio-economy of the island, mainly on rice production and fishing. Between 2016 and 2019, 102 households in three regions, Soanierana Ivongo, Foulpointe and Antananarivo, were randomly selected and questioned on the impact of these weeds in their aquatic ecosystems and their livelihoods such as fishing and rice growing. Surveys revealed that the four aquatic weeds significantly threatened household activities. On the east coast of Madagascar, the invasions of these four invasive species decreased fish and freshwater shrimp production by 82%. On the high plateau of Madagascar, they reduced rice yield by 30% despite requiring an additional expense of US$ 1,107/ha for control. Although farmers surveyed only used manual control to manage these weeds, they were receptive to other control methods, including integrated control using herbicides and biological control. Another objective of this research was to determine the ecological impacts of the four weeds and specifically if freshwater ecosystem functioning would return after control. To assess the ecological impact, between February 2017 to August 2019, on Lake Antsokafina, the following abiotic and biotic factors were considered: physico-chemistry of water, succession of macrophyte community and animal diversity. With the exception of turbidity, the values of the physico-chemical parameters of the water (pH, electrical conductivity, water temperature and turbidity), were similar between the infested zone and cleared zone. A study on the invasion process of aquatic weeds showed that the plant community succession of the lake changed over time in the areas that had been cleared. The submerged species Ceratophyllum demersum was the pioneer, followed by creeping species such as Echinochloa colona and Ipomoea aquatica, before the area was recolonized by aquatic weeds. Among the aquatic weeds, S. molesta was the most aggressive, covering 92% of the area one year after the start of the experiment. For animal diversity, bird, shrimp and fish community were assessed. The cleaning of the plots in the lake allowed the resumption of fishing activity providing 50 to 200g/catch for shrimp and from 0.25 to 0.5kg/catch for fish per person per day, while no catch was obtained in the areas infested by aquatic weeds were fishermen still attempting to harvest fish/shrimp from the aquatic weed infested areas. Three species of birds, Humblot’s Heron (Ardea humbloti), the white-faced whistling duck (Dendrocygna viduata) and red-billed teal (Anas erythrorhyncha) returned once the areas had been cleared. A manipulated outdoor as descriptor for laboratory experiment was conducted to determine the level and nature of competition of four aquatic weeds species against the indigenous floating fern, Salvinia hastata Desv. (Salviniaceae), using an additive series density model. It was shown that all four invasive species outcompeted S. hastata, with P. crassipes being 24 times more dominant, followed by P. stratiotes at 12 times, S. molesta at 8 times, and finally A. filiculoides at 1.2 times more dominant. This study provided direct evidence of the biodiversity impact of these four species and thus also provided an environmental argument for their control. Based on the findings of this study, a series of recommendations was formulated to manage the invasions of alien species in Madagascar with particular attention to invasive aquatic weeds. These recommendations mainly concern the establishment of management structures and legal instruments such as the creation of a lead government agency at national level and a cross-sectorial invasive species advisory committee, which should review legislation and regulations related to invasive species. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Lehavana, Adolphe
- Date: 2021-10-29
- Subjects: Pontederiaceae Madagascar , Water lettuce Madagascar , Salvinia molesta Madagascar , Azolla filiculoides Madagascar , Introduced aquatic organisms , Aquatic weeds Economic aspects , Aquatic weeds Social aspects , Aquatic weeds Geographical distribution
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191225 , vital:45072
- Description: In Madagascar, as in several countries in the world, the invasion by four aquatic weeds (Pontederia crassipes Mart. (Pontederiaceae), Pistia stratiotes L. (Araceae), Salvinia molesta D.S. Mitch Salviniaceae) and Azolla filiculoides Lam. (Azollaceae) are among the drivers of environmental and socio-economic deterioration in aquatic ecosystems. Pistia stratiotes was first recorded on the island in the 19th century, and P. crassipes from the beginning of the 20th century, while S. molesta and A. filiculoides were only documented during in the 21st century. From the 1920s, botanists such as Henri Perrier de la Bathie and Raymond Decary were already aware of the dangers caused, in particular by P. crassipes in other countries, and raised the alarm, but little attention has been paid to these species. The aim of the research conducted for this thesis was to determine the distribution, socio-economic and ecological impacts of these four invasive alien aquatic weeds in Madagascar and to make recommendations for their control. First, the distributions of these four aquatic weeds were mapped. This mapping exercise compiled data from different sources including herbarium records, online data and field visits across Madagascar. The mapping study was undertaken from August 2015 to June 2020. Except for mountainous areas above 1800 m (Tsaratanana Massif, Ankaratra Massif and Andringitra Massif) where no data were available, all of Madagascar's bioclimates were invaded by at least one of the four aquatic weeds. In total, at least one species was recorded in 18 of the 22 Regions. Pontederia crassipes was recorded in 13 Regions, S. molesta in 14 Regions, P. stratiotes in 12 Regions, and A. filiculoides in 13 Regions. Herbarium records revealed the oldest record for P. stratiotes to be 1847, 1931 for P. crassipes, 1995 for S. molesta and there were no herbarium specimens for A. filiculoides prior to the start of the current study in 2015. We now know where these four weeds occur and how abundant they are. An objective of this research was to assess the impacts of the four invasive aquatic plants on the socio-economy of the island, mainly on rice production and fishing. Between 2016 and 2019, 102 households in three regions, Soanierana Ivongo, Foulpointe and Antananarivo, were randomly selected and questioned on the impact of these weeds in their aquatic ecosystems and their livelihoods such as fishing and rice growing. Surveys revealed that the four aquatic weeds significantly threatened household activities. On the east coast of Madagascar, the invasions of these four invasive species decreased fish and freshwater shrimp production by 82%. On the high plateau of Madagascar, they reduced rice yield by 30% despite requiring an additional expense of US$ 1,107/ha for control. Although farmers surveyed only used manual control to manage these weeds, they were receptive to other control methods, including integrated control using herbicides and biological control. Another objective of this research was to determine the ecological impacts of the four weeds and specifically if freshwater ecosystem functioning would return after control. To assess the ecological impact, between February 2017 to August 2019, on Lake Antsokafina, the following abiotic and biotic factors were considered: physico-chemistry of water, succession of macrophyte community and animal diversity. With the exception of turbidity, the values of the physico-chemical parameters of the water (pH, electrical conductivity, water temperature and turbidity), were similar between the infested zone and cleared zone. A study on the invasion process of aquatic weeds showed that the plant community succession of the lake changed over time in the areas that had been cleared. The submerged species Ceratophyllum demersum was the pioneer, followed by creeping species such as Echinochloa colona and Ipomoea aquatica, before the area was recolonized by aquatic weeds. Among the aquatic weeds, S. molesta was the most aggressive, covering 92% of the area one year after the start of the experiment. For animal diversity, bird, shrimp and fish community were assessed. The cleaning of the plots in the lake allowed the resumption of fishing activity providing 50 to 200g/catch for shrimp and from 0.25 to 0.5kg/catch for fish per person per day, while no catch was obtained in the areas infested by aquatic weeds were fishermen still attempting to harvest fish/shrimp from the aquatic weed infested areas. Three species of birds, Humblot’s Heron (Ardea humbloti), the white-faced whistling duck (Dendrocygna viduata) and red-billed teal (Anas erythrorhyncha) returned once the areas had been cleared. A manipulated outdoor as descriptor for laboratory experiment was conducted to determine the level and nature of competition of four aquatic weeds species against the indigenous floating fern, Salvinia hastata Desv. (Salviniaceae), using an additive series density model. It was shown that all four invasive species outcompeted S. hastata, with P. crassipes being 24 times more dominant, followed by P. stratiotes at 12 times, S. molesta at 8 times, and finally A. filiculoides at 1.2 times more dominant. This study provided direct evidence of the biodiversity impact of these four species and thus also provided an environmental argument for their control. Based on the findings of this study, a series of recommendations was formulated to manage the invasions of alien species in Madagascar with particular attention to invasive aquatic weeds. These recommendations mainly concern the establishment of management structures and legal instruments such as the creation of a lead government agency at national level and a cross-sectorial invasive species advisory committee, which should review legislation and regulations related to invasive species. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10-29
DNA-based identification of forensically significant beetles from Southern Africa
- Authors: Collett, Isabel Judith
- Date: 2015
- Subjects: Carrion insects , Forensic entomology , Cleridae , Dermestidae , Silphidae , Staphylinidae , Scarabaeidae , Histeridae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5923 , http://hdl.handle.net/10962/d1017801
- Description: Necrophilous insects, if correctly identified, can provide useful forensic information. Research in this area has focussed on flies and beetles remain comparatively under-studied, partly because some adult carrion beetles are difficult to identify morphologically, as are their juvenile stages, often requiring specialist expertise in both cases. Molecular taxonomy has been proposed as a solution to these problems. DNA “barcodes" are short fragments of mitochondrial cytochrome oxidase I (COI) DNA that are anticipated to delineate species. This approach is becoming increasingly popular, but has been met with varying enthusiasm from taxonomists. This thesis examines their use in identifying forensically significant beetles.The DNA barcodes of 234 specimens of 25 forensically significant southern African beetle species from seven families (Cleridae, Dermestidae, Silphidae, Staphylinidae, Scarabaeidae, Trogidae and Histeridae) were obtained. Thirty-three initial barcode amplification failures were overcome by using primers other than the standard Folmer pair, undermining the barcode concept’s hope of universal primers that would allow even non-specialists to produce barcodes. Another 150 specimens (64%) entirely failed to yield barcodes, including 18 fresh specimens of three species of Trogidae, implying another lack of universality of the barcoding protocol. The majority of the beetles clustered with confamilials on neighbour-joining and maximum likelihood trees, but 1.3% of the barcodes failed to cluster with their respective families, raising questions concerning the associating power of barcodes. The identification tools of the GenBank and BOLD on-line DNA sequence databases identified 21% of the specimens to the species level, 6% of them correctly. There was evidence of a paralogous sequence in the Cleridae that, while supporting identification now that it has been associated with a morphological identification, would hamper attempts at identification by clustering or phylogenetic analysis.Distance and haplotype network analyses of the barcodes of six widespread species showed that they are not geographically structured. Barcodes are thus unlikely to be indicators of the region of origin of a species and will not determine whether a corpse has been relocated after death. To assess whether a different mitochondrial DNA fragment might address (some of) these problems, a 2.2 kb fragment extending from the 5’ end of the COI gene to the 3’ end of the Cytochrome Oxidase II (COII) gene was analysed for nine species. It was found that, for Dermestidae, Scarabaeidae and Histeridae, higher degrees of diversity occurred downstreamof the barcode region, but the region of highest diversity in the Cleridae was in the barcode region. Thus, finding a more reliable fragment along the COI-COII region for each family may make robust and guaranteed DNA-based identification of these beetles more likely. The possibility of a forensic specimen being incorrectly or not identified based on its barcode alone exists in about 40% of cases, even with the new barcodes reported here. Forensic science sets a very high bar in assessing the performance of its techniques, and it is concluded that barcodes currently have unsettling failure rates as court-worthy evidence.
- Full Text:
- Date Issued: 2015
- Authors: Collett, Isabel Judith
- Date: 2015
- Subjects: Carrion insects , Forensic entomology , Cleridae , Dermestidae , Silphidae , Staphylinidae , Scarabaeidae , Histeridae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5923 , http://hdl.handle.net/10962/d1017801
- Description: Necrophilous insects, if correctly identified, can provide useful forensic information. Research in this area has focussed on flies and beetles remain comparatively under-studied, partly because some adult carrion beetles are difficult to identify morphologically, as are their juvenile stages, often requiring specialist expertise in both cases. Molecular taxonomy has been proposed as a solution to these problems. DNA “barcodes" are short fragments of mitochondrial cytochrome oxidase I (COI) DNA that are anticipated to delineate species. This approach is becoming increasingly popular, but has been met with varying enthusiasm from taxonomists. This thesis examines their use in identifying forensically significant beetles.The DNA barcodes of 234 specimens of 25 forensically significant southern African beetle species from seven families (Cleridae, Dermestidae, Silphidae, Staphylinidae, Scarabaeidae, Trogidae and Histeridae) were obtained. Thirty-three initial barcode amplification failures were overcome by using primers other than the standard Folmer pair, undermining the barcode concept’s hope of universal primers that would allow even non-specialists to produce barcodes. Another 150 specimens (64%) entirely failed to yield barcodes, including 18 fresh specimens of three species of Trogidae, implying another lack of universality of the barcoding protocol. The majority of the beetles clustered with confamilials on neighbour-joining and maximum likelihood trees, but 1.3% of the barcodes failed to cluster with their respective families, raising questions concerning the associating power of barcodes. The identification tools of the GenBank and BOLD on-line DNA sequence databases identified 21% of the specimens to the species level, 6% of them correctly. There was evidence of a paralogous sequence in the Cleridae that, while supporting identification now that it has been associated with a morphological identification, would hamper attempts at identification by clustering or phylogenetic analysis.Distance and haplotype network analyses of the barcodes of six widespread species showed that they are not geographically structured. Barcodes are thus unlikely to be indicators of the region of origin of a species and will not determine whether a corpse has been relocated after death. To assess whether a different mitochondrial DNA fragment might address (some of) these problems, a 2.2 kb fragment extending from the 5’ end of the COI gene to the 3’ end of the Cytochrome Oxidase II (COII) gene was analysed for nine species. It was found that, for Dermestidae, Scarabaeidae and Histeridae, higher degrees of diversity occurred downstreamof the barcode region, but the region of highest diversity in the Cleridae was in the barcode region. Thus, finding a more reliable fragment along the COI-COII region for each family may make robust and guaranteed DNA-based identification of these beetles more likely. The possibility of a forensic specimen being incorrectly or not identified based on its barcode alone exists in about 40% of cases, even with the new barcodes reported here. Forensic science sets a very high bar in assessing the performance of its techniques, and it is concluded that barcodes currently have unsettling failure rates as court-worthy evidence.
- Full Text:
- Date Issued: 2015
Drivers of macrophyte assemblages in South African freshwater systems
- Authors: Martin, Grant Douglas
- Date: 2013
- Subjects: Freshwater plants -- South Africa Aquatic weeds -- South Africa Invasive plants -- South Africa Freshwater ecology -- South Africa Biotic communities -- South Africa Maximum entropy method Lagarosiphon major -- South Africa Phytophagous insects -- South Africa Hydrellia -- South Africa Parasitoids -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5621 , http://hdl.handle.net/10962/d1004127
- Description: Potentially damaging submerged invasive freshwater macrophytes have been identified in South African freshwater systems, but have received less attention than their floating counterparts. To ascertain the changes and effects that these species may have on macrophyte ecology, an understanding of the drivers of macrophyte assemblages is essential. The aims of this thesis were to investigate select abiotic and biotic factors driving introduction, establishment and spread of submerged macrophytes in South Africa. Surveys on the status of submerged plant species in South Africa were conducted to find out the distribution and diversity of the species present, imported to, and traded in South Africa. Numerous submerged indigenous and invasive macrophyte locality records were collected during field surveys, of which many were first time records. Pet stores and aquarist trading activities were identified as potential vectors for the spread of submerged macrophytes through online surveys and personal interviews. These results highlighted the potential these species have for continuing to enter, and spread within South African water bodies. Maximum Entropy (MAXENT) is a general-purpose method used to predict or infer distributions from incomplete information, and was used here to predict areas suitable for the establishment of five of these invasive macrophytes. Many systems throughout South Africa, particularly those in the subtropical coastal regions, were found to be climatically suitable for the establishment of Elodea canadensis Michx., Egeria densa Planch., Hydrilla verticillata (L.f.) Royle (all Hydrocharitaceae), Myriophyllum spicatum L. (Haloragaceae), and Cabomba caroliniana Gray (Cabombaceae). Despite the high probability of invasion, facilitated by vectors and suitable climate, South Africa’s rich indigenous submerged aquatic flora may be preventing the establishment of these submerged invasive species. Studies on the competitive interactions between a common indigenous submerged macrophytes, Lagarosiphon major (Roxb.) (Hydrocharitaceae) and M.spicatum, an invasive native to Eurasia, were conducted to ascertain which conditions influence competitive superiority. High sediment nutrient conditions significantly increased the growth rate and competitive ability of both species, while clay sediments significantly increased the competitive ability of L. major over M. spicatum, but sandy sediments improved the competitive ability of M. spicatum. These results highlighted the dynamic changes in competition between submerged species driven by abiotic factors, but did not take into consideration the effect that herbivory, a biotic factor, could have on competition between the two species. The effect of herbivory by phytophagous insects of submerged plant species has been regarded as negligible. To find out what this effect is, multiple field surveys were undertaken throughout South Africa to find natural enemies of indigenous Lagarosiphon species with the aim of identifying such species, and quantifying their influence on plant growth dynamics. Several new phytophagous species were recorded for the first time. An ephydrid fly, Hydrellia lagarosiphon Deeming (Diptera: Ephydridae) was ascertained to be the most ubiquitous and abundant species associated with L. major in South Africa. The influence of herbivory by this fly on the competitive ability of L. major in the presence of M. spicatum was investigated using an inverse linear model, which showed that herbivory by H. lagarosiphon reduced the competitive ability of L. major by approximately five times in favour of M. spicatum. This study served to highlight the importance of herbivory as a driver of submerged aquatic plant dynamics. Current ecological theory emphasises the importance of investigating beyond plant-herbivore interactions, by including multitrophic interactions in community dynamics. Therefore, the potential of parasitism by a parasitoid wasp, Chaenusa luteostigma sp. n. Achterberg (Hymenoptera: Braconidae: Alysiinae) on H. lagarosiphon to shift the competitive interactions between the two plant species was also examined. The addition of the parasitoid reduced the effect of herbivory by the fly on L. major by half, thereby shifting the competitive balance in favour of L. major over M. spicatum. This study provides valuable insight into a selection of drivers of submerged macrophyte assemblages of South Africa. It highlights the precarious position of South African freshwater systems with regard to the potential invasion by damaging submerged invasive species. It also provides interesting insights into the effect of competition, herbivory and parasitism on the establishment and spread of species within submerged freshwater systems. Understanding the different influences could assist managers and policy makers to make validated decisions ensuring the integrity of South African freshwater systems.
- Full Text:
- Date Issued: 2013
- Authors: Martin, Grant Douglas
- Date: 2013
- Subjects: Freshwater plants -- South Africa Aquatic weeds -- South Africa Invasive plants -- South Africa Freshwater ecology -- South Africa Biotic communities -- South Africa Maximum entropy method Lagarosiphon major -- South Africa Phytophagous insects -- South Africa Hydrellia -- South Africa Parasitoids -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5621 , http://hdl.handle.net/10962/d1004127
- Description: Potentially damaging submerged invasive freshwater macrophytes have been identified in South African freshwater systems, but have received less attention than their floating counterparts. To ascertain the changes and effects that these species may have on macrophyte ecology, an understanding of the drivers of macrophyte assemblages is essential. The aims of this thesis were to investigate select abiotic and biotic factors driving introduction, establishment and spread of submerged macrophytes in South Africa. Surveys on the status of submerged plant species in South Africa were conducted to find out the distribution and diversity of the species present, imported to, and traded in South Africa. Numerous submerged indigenous and invasive macrophyte locality records were collected during field surveys, of which many were first time records. Pet stores and aquarist trading activities were identified as potential vectors for the spread of submerged macrophytes through online surveys and personal interviews. These results highlighted the potential these species have for continuing to enter, and spread within South African water bodies. Maximum Entropy (MAXENT) is a general-purpose method used to predict or infer distributions from incomplete information, and was used here to predict areas suitable for the establishment of five of these invasive macrophytes. Many systems throughout South Africa, particularly those in the subtropical coastal regions, were found to be climatically suitable for the establishment of Elodea canadensis Michx., Egeria densa Planch., Hydrilla verticillata (L.f.) Royle (all Hydrocharitaceae), Myriophyllum spicatum L. (Haloragaceae), and Cabomba caroliniana Gray (Cabombaceae). Despite the high probability of invasion, facilitated by vectors and suitable climate, South Africa’s rich indigenous submerged aquatic flora may be preventing the establishment of these submerged invasive species. Studies on the competitive interactions between a common indigenous submerged macrophytes, Lagarosiphon major (Roxb.) (Hydrocharitaceae) and M.spicatum, an invasive native to Eurasia, were conducted to ascertain which conditions influence competitive superiority. High sediment nutrient conditions significantly increased the growth rate and competitive ability of both species, while clay sediments significantly increased the competitive ability of L. major over M. spicatum, but sandy sediments improved the competitive ability of M. spicatum. These results highlighted the dynamic changes in competition between submerged species driven by abiotic factors, but did not take into consideration the effect that herbivory, a biotic factor, could have on competition between the two species. The effect of herbivory by phytophagous insects of submerged plant species has been regarded as negligible. To find out what this effect is, multiple field surveys were undertaken throughout South Africa to find natural enemies of indigenous Lagarosiphon species with the aim of identifying such species, and quantifying their influence on plant growth dynamics. Several new phytophagous species were recorded for the first time. An ephydrid fly, Hydrellia lagarosiphon Deeming (Diptera: Ephydridae) was ascertained to be the most ubiquitous and abundant species associated with L. major in South Africa. The influence of herbivory by this fly on the competitive ability of L. major in the presence of M. spicatum was investigated using an inverse linear model, which showed that herbivory by H. lagarosiphon reduced the competitive ability of L. major by approximately five times in favour of M. spicatum. This study served to highlight the importance of herbivory as a driver of submerged aquatic plant dynamics. Current ecological theory emphasises the importance of investigating beyond plant-herbivore interactions, by including multitrophic interactions in community dynamics. Therefore, the potential of parasitism by a parasitoid wasp, Chaenusa luteostigma sp. n. Achterberg (Hymenoptera: Braconidae: Alysiinae) on H. lagarosiphon to shift the competitive interactions between the two plant species was also examined. The addition of the parasitoid reduced the effect of herbivory by the fly on L. major by half, thereby shifting the competitive balance in favour of L. major over M. spicatum. This study provides valuable insight into a selection of drivers of submerged macrophyte assemblages of South Africa. It highlights the precarious position of South African freshwater systems with regard to the potential invasion by damaging submerged invasive species. It also provides interesting insights into the effect of competition, herbivory and parasitism on the establishment and spread of species within submerged freshwater systems. Understanding the different influences could assist managers and policy makers to make validated decisions ensuring the integrity of South African freshwater systems.
- Full Text:
- Date Issued: 2013
Ecological assessment of a temperate river system using biomonitoring techniques: a case study of the Bloukrans River system, South Africa
- Authors: Magadze, Tinotenda
- Date: 2020
- Subjects: Bloukrans River , Ecological assessment (Biology) -- South Africa , Stream ecology -- South Africa , Rivers -- Environmental aspects -- South Africa , Benthic animals -- Effect of human beings on -- South Africa , Water quality biological assessment -- South Africa , Diatoms -- South Africa -- Data processing
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142933 , vital:38177
- Description: Escalating pressures from growing human populations and environmental impacts increasingly imperil freshwater ecosystems. The Bloukrans River, which drains an urbanised and agricultural catchment in the Eastern Cape province of South Africa, is no exception. Detailed knowledge of the structure and function of the aquatic ecosystems is required in order to create models and matrices that predict, guide assessment and direct intervention on ecological integrity and water quality management in these systems. The main objectives of this research were to: examine the effects of urbanization on the benthic macroinvertebrate functional feeding guild structure among different stream orders; determine if benthic diatoms can be used as effective and reliable indicators of ionic composition and conductivity in different stream order categories and finally; to evaluate the applicability of the South African Diatom Index (SADI) and other indices in the Eastern Cape region of South Africa. Field studies were carried out to explore temporal patterns in community structure (macroinvertebrates and diatoms) and ecosystem function related to land-use patterns, instream habitat availability, and water quality parameters in the Bloukrans River system across four study periods: February (summer) and July (winter) 2016 and February (summer) and May/July (winter) 2018. The study was conducted along a gradient of impacts from less impacted agricultural headwaters to highly impacted urban sites located immediately downstream of the city of Makhanda. Macroinvertebrates were separated into functional feeding groups (FFGs) (i.e. collector-gatherer, collector-filterer, scraper, shredder, and predator) which were then used to assess the effects of selected physico-chemical variables and riparian zone condition on FFG organization. Collector-gatherers were the most abundant in the Bloukrans River and represented 71.3 % of the macroinvertebrate assemblages. Stream order 1species such as Nitzschia palea, Gomphonema parvulum, Tryblionella apiculata, Diploneis vulgaris and Staurosira elliptica. Multivariate analysis (Canonical correspondence analysis (CCA)) indicated that differences in diatom community assemblages were best explained by calcium, magnesium, pH, phosphate, nitrate, dissolved oxygen, sediment nitrate, conductivity and salinity. These results indicate that diatoms can be used as bioindicators for monitoring highly impacted river systems and to also further examine pollution gradients and impacts of specific/point pollution sources. In order to further test the application of diatom indices, nine sites with contrasting water quality were sampled along the length river system in February, May and July 2018. Diatom-based indices incorporated in OMNIDIA software were applied to assess the integrity of the water quality as indicated by diatom communities. For comparative purposes, several foreign indices (e.g. the trophic diatom index (TDI), the percentage pollution-tolerant valves (%PTV), biological diatom index (BDI)) and the South African Diatom Index (SADI) were used in the study. From the results, the Percentage Pollution-Tolerant Valves (%PTV) of most urban sites in the Bloukrans River was above the 20% limit indicating the presence of organic pollutants. Although the foreign diatom indices were applicable in the study, the SADI had significant correlations with most water quality variables (p < 0.05) compared to other indices such as Watanabe Index (WAT), Biological Index of Water Quality Trophic Index (BIWQ) and Trophic Index (TI)). These results support wider use of the SADI as an indicator of water quality conditions in South African river systems. Finally, the observed variations in diatom community structure and composition as a result of changes in water quality were broadly in agreement with the results of macroinvertebrate FFG structure indicating that the two biological indicators can, and should, be used as complementary techniques in the biomonitoring of rivers and streams in South Africa.
- Full Text:
- Date Issued: 2020
- Authors: Magadze, Tinotenda
- Date: 2020
- Subjects: Bloukrans River , Ecological assessment (Biology) -- South Africa , Stream ecology -- South Africa , Rivers -- Environmental aspects -- South Africa , Benthic animals -- Effect of human beings on -- South Africa , Water quality biological assessment -- South Africa , Diatoms -- South Africa -- Data processing
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142933 , vital:38177
- Description: Escalating pressures from growing human populations and environmental impacts increasingly imperil freshwater ecosystems. The Bloukrans River, which drains an urbanised and agricultural catchment in the Eastern Cape province of South Africa, is no exception. Detailed knowledge of the structure and function of the aquatic ecosystems is required in order to create models and matrices that predict, guide assessment and direct intervention on ecological integrity and water quality management in these systems. The main objectives of this research were to: examine the effects of urbanization on the benthic macroinvertebrate functional feeding guild structure among different stream orders; determine if benthic diatoms can be used as effective and reliable indicators of ionic composition and conductivity in different stream order categories and finally; to evaluate the applicability of the South African Diatom Index (SADI) and other indices in the Eastern Cape region of South Africa. Field studies were carried out to explore temporal patterns in community structure (macroinvertebrates and diatoms) and ecosystem function related to land-use patterns, instream habitat availability, and water quality parameters in the Bloukrans River system across four study periods: February (summer) and July (winter) 2016 and February (summer) and May/July (winter) 2018. The study was conducted along a gradient of impacts from less impacted agricultural headwaters to highly impacted urban sites located immediately downstream of the city of Makhanda. Macroinvertebrates were separated into functional feeding groups (FFGs) (i.e. collector-gatherer, collector-filterer, scraper, shredder, and predator) which were then used to assess the effects of selected physico-chemical variables and riparian zone condition on FFG organization. Collector-gatherers were the most abundant in the Bloukrans River and represented 71.3 % of the macroinvertebrate assemblages. Stream order 1species such as Nitzschia palea, Gomphonema parvulum, Tryblionella apiculata, Diploneis vulgaris and Staurosira elliptica. Multivariate analysis (Canonical correspondence analysis (CCA)) indicated that differences in diatom community assemblages were best explained by calcium, magnesium, pH, phosphate, nitrate, dissolved oxygen, sediment nitrate, conductivity and salinity. These results indicate that diatoms can be used as bioindicators for monitoring highly impacted river systems and to also further examine pollution gradients and impacts of specific/point pollution sources. In order to further test the application of diatom indices, nine sites with contrasting water quality were sampled along the length river system in February, May and July 2018. Diatom-based indices incorporated in OMNIDIA software were applied to assess the integrity of the water quality as indicated by diatom communities. For comparative purposes, several foreign indices (e.g. the trophic diatom index (TDI), the percentage pollution-tolerant valves (%PTV), biological diatom index (BDI)) and the South African Diatom Index (SADI) were used in the study. From the results, the Percentage Pollution-Tolerant Valves (%PTV) of most urban sites in the Bloukrans River was above the 20% limit indicating the presence of organic pollutants. Although the foreign diatom indices were applicable in the study, the SADI had significant correlations with most water quality variables (p < 0.05) compared to other indices such as Watanabe Index (WAT), Biological Index of Water Quality Trophic Index (BIWQ) and Trophic Index (TI)). These results support wider use of the SADI as an indicator of water quality conditions in South African river systems. Finally, the observed variations in diatom community structure and composition as a result of changes in water quality were broadly in agreement with the results of macroinvertebrate FFG structure indicating that the two biological indicators can, and should, be used as complementary techniques in the biomonitoring of rivers and streams in South Africa.
- Full Text:
- Date Issued: 2020
Ecological effects of impoundments in the Buffalo River, Eastern Cape, with particular reference to the distribution of blackflies (Diptera : simuliidae)
- Authors: Palmer, Robert William
- Date: 1992
- Subjects: Stream ecology -- South Africa -- Buffalo River (Eastern Cape) Dipter -- South Africa -- Buffalo River (Eastern Cape)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6028 , http://hdl.handle.net/10962/d1006157
- Description: This thesis examines the extent and intensity of the effects of impoundments on selected physical, chemical and biotic conditions in an impounded southern African river. Life-history characteristics and environmental requirements which determine the success of impoundment-outlet blackflies in southern Africa were studied. Difficulties with the identification of immature blackflies led to a search for additional diagnostic characters, the description of larvae of seven species previously unknown, and the development of new keys to the species of Simulium (larvae and pupae) in southern Africa. Distribution records for each species are presented, and their ecology is summarised. Three pairs of closely related species, which were formerly indistinguishable, can now be recognised by differences between the structure of their cephalic fan microtrichia. Monthly physical, chemical and invertebrate samples at 16 sites upstream and downstream of four impoundments in the Buffalo River, eastern Cape, were taken over a period of two years. The downstream effects of impoundments on these parameters depended on the variable examined, the position of the impoundment along the river profile, the depth from which water was released, and the quality of the inflowing water. Impoundments in the Buffalo River caused an upstream shift of the thermal and suspended organic conditions, and the distribution of blackfly species. Surface-release impoundments in the clean, upper-reaches of the river caused increases in water temperature (by as much as 8ºC) and chlorophyll a (by as much as 600%). Recovery to riverine conditions was within 2.6 to 18.4 km, depending on flow. A polluted, surface-release impoundment in the middle-reaches of the river had a slight dampening effect on river temperatures, converted the particle size spectrum of the river from small (<80 μm) to large (250-1000 μm), and improved the water quality of the downstream reaches (with the exception of nitrate concentrations, which were higher in the tailwaters compared to inflowing water). An impoundment in the lower reaches caused reductions in maximum temperature of up to 6ºC when releasing water from the surface, and up to 16ºC when releasing water from the bottom. Bottom-released water carried high concentrations (36 to 190 g m³) of small (<5 μm) and largely inorganic (86 to 93%) material.Twenty species of blackflies were found in the Buffalo River, of which 18 were distinguishable as larvae. They were divided into those which were widespread (5 taxa), those restricted to waterfalls and mountain torrents (2 taxa), those found in the foothill stony run zone (6 taxa), and rare taxa (5 taxa). Impoundments in the Buffalo River did not alter population densities of blackfly larvae, but did alter blackfly species composition, favouring five species commonly found in mid-order streams in southern Africa (s. meduseaforme, S. hargreavesi, S. nigritarse, S. adersi and s. damnosum s.l.) at the expense of upper-reach species (s. rutherfoordi, S. letabum and s. impukane). These five species are regarded as typical of impoundment-outlets, and were small, multivoltine flies whose larvae shared a generalised cephalic fan microtrichial structure, consisting of a single row of moderately differentiated microtrichia. A strong relation was found between cephalic fan microtrichial structure and larval habitats: Taxa found in fast-flowing, clear water had a more complex fan structure compared to those found in slow-flowing, turbid water. It is concluded that impoundment-induced changes to hydrodynamics and transported material (food) are important factors which have changed the distribution of blackflies in southern Africa in recent times. These changes are more severe downstream of upper-reach impoundments than middle or lower-reach impoundments.
- Full Text:
- Date Issued: 1992
- Authors: Palmer, Robert William
- Date: 1992
- Subjects: Stream ecology -- South Africa -- Buffalo River (Eastern Cape) Dipter -- South Africa -- Buffalo River (Eastern Cape)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6028 , http://hdl.handle.net/10962/d1006157
- Description: This thesis examines the extent and intensity of the effects of impoundments on selected physical, chemical and biotic conditions in an impounded southern African river. Life-history characteristics and environmental requirements which determine the success of impoundment-outlet blackflies in southern Africa were studied. Difficulties with the identification of immature blackflies led to a search for additional diagnostic characters, the description of larvae of seven species previously unknown, and the development of new keys to the species of Simulium (larvae and pupae) in southern Africa. Distribution records for each species are presented, and their ecology is summarised. Three pairs of closely related species, which were formerly indistinguishable, can now be recognised by differences between the structure of their cephalic fan microtrichia. Monthly physical, chemical and invertebrate samples at 16 sites upstream and downstream of four impoundments in the Buffalo River, eastern Cape, were taken over a period of two years. The downstream effects of impoundments on these parameters depended on the variable examined, the position of the impoundment along the river profile, the depth from which water was released, and the quality of the inflowing water. Impoundments in the Buffalo River caused an upstream shift of the thermal and suspended organic conditions, and the distribution of blackfly species. Surface-release impoundments in the clean, upper-reaches of the river caused increases in water temperature (by as much as 8ºC) and chlorophyll a (by as much as 600%). Recovery to riverine conditions was within 2.6 to 18.4 km, depending on flow. A polluted, surface-release impoundment in the middle-reaches of the river had a slight dampening effect on river temperatures, converted the particle size spectrum of the river from small (<80 μm) to large (250-1000 μm), and improved the water quality of the downstream reaches (with the exception of nitrate concentrations, which were higher in the tailwaters compared to inflowing water). An impoundment in the lower reaches caused reductions in maximum temperature of up to 6ºC when releasing water from the surface, and up to 16ºC when releasing water from the bottom. Bottom-released water carried high concentrations (36 to 190 g m³) of small (<5 μm) and largely inorganic (86 to 93%) material.Twenty species of blackflies were found in the Buffalo River, of which 18 were distinguishable as larvae. They were divided into those which were widespread (5 taxa), those restricted to waterfalls and mountain torrents (2 taxa), those found in the foothill stony run zone (6 taxa), and rare taxa (5 taxa). Impoundments in the Buffalo River did not alter population densities of blackfly larvae, but did alter blackfly species composition, favouring five species commonly found in mid-order streams in southern Africa (s. meduseaforme, S. hargreavesi, S. nigritarse, S. adersi and s. damnosum s.l.) at the expense of upper-reach species (s. rutherfoordi, S. letabum and s. impukane). These five species are regarded as typical of impoundment-outlets, and were small, multivoltine flies whose larvae shared a generalised cephalic fan microtrichial structure, consisting of a single row of moderately differentiated microtrichia. A strong relation was found between cephalic fan microtrichial structure and larval habitats: Taxa found in fast-flowing, clear water had a more complex fan structure compared to those found in slow-flowing, turbid water. It is concluded that impoundment-induced changes to hydrodynamics and transported material (food) are important factors which have changed the distribution of blackflies in southern Africa in recent times. These changes are more severe downstream of upper-reach impoundments than middle or lower-reach impoundments.
- Full Text:
- Date Issued: 1992