Detecting impacts of invasive non-native sharptooth catfish, Clarias gariepinus, within invaded and non-invaded rivers.
- Kadye, Wilbert T, Booth, Anthony J
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124100 , vital:35539 , https://doi.10.1007/s10531-012-0291-5
- Description: In aquatic ecosystems, impacts by invasive introduced fish can be likened to press disturbances that persistently influence communities. This study examined invasion disturbances by determining the relationship between non-native sharptooth catfish Clarias gariepinus and aquatic macroinvertebrates in the Eastern Cape, South Africa. A Multiple Before–After Control–Impact (MBACI) experimental design was used to examine macroinvertebrate communities within two rivers: one with catfish and another one without catfish. Within the invaded river, macroinvertebrates showed little response to catfish presence, whereas predator exclusion appeared to benefit community structure. This suggests that the macroinvertebrate community within the invaded river was adapted to predation impact because of the dominance of resilient taxa, such as Hirudinea, Oligochaeta and Chironomidae that were abundant in the Impact treatment relative to the Control treatment. High macroinvertebrate diversity and richness that was observed in the Control treatment, which excluded the predator, relative to the Impact treatment suggests predator avoidance behaviour within the invaded river. By comparison, within the uninvaded river, catfish introduction into the Impact treatment plots indicated negative effects on macroinvertebrate community that was reflected by decrease in diversity, richness and biomass. A community level impact was also reflected in the multivariate analysis that indicated more variation in macroinvertebrate composition within the Impact treatment relative to the Control in the uninvaded river. Catfish impact within the uninvaded river suggests the dominance of vulnerable taxa, such as odonates that were less abundant in the Impact treatment plots after catfish introduction. From a disturbance perspective, this study revealed different macroinvertebrate responses to catfish impact, and suggests that within invaded habitats, macroinvertebrates were less responsive to catfish presence, whereas catfish introduction within uninvaded habitats demonstrated invasion impact that was shown by a decrease in the abundance of vulnerable taxa. The occurrence of non-native sharptooth catfish within many Eastern Cape rivers is a concern because of its predation impact and potential to influence trophic interrelationships, and efforts should be taken to protect uninvaded rivers, and, where possible, eradicate the invader.
- Full Text:
- Date Issued: 2012
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124100 , vital:35539 , https://doi.10.1007/s10531-012-0291-5
- Description: In aquatic ecosystems, impacts by invasive introduced fish can be likened to press disturbances that persistently influence communities. This study examined invasion disturbances by determining the relationship between non-native sharptooth catfish Clarias gariepinus and aquatic macroinvertebrates in the Eastern Cape, South Africa. A Multiple Before–After Control–Impact (MBACI) experimental design was used to examine macroinvertebrate communities within two rivers: one with catfish and another one without catfish. Within the invaded river, macroinvertebrates showed little response to catfish presence, whereas predator exclusion appeared to benefit community structure. This suggests that the macroinvertebrate community within the invaded river was adapted to predation impact because of the dominance of resilient taxa, such as Hirudinea, Oligochaeta and Chironomidae that were abundant in the Impact treatment relative to the Control treatment. High macroinvertebrate diversity and richness that was observed in the Control treatment, which excluded the predator, relative to the Impact treatment suggests predator avoidance behaviour within the invaded river. By comparison, within the uninvaded river, catfish introduction into the Impact treatment plots indicated negative effects on macroinvertebrate community that was reflected by decrease in diversity, richness and biomass. A community level impact was also reflected in the multivariate analysis that indicated more variation in macroinvertebrate composition within the Impact treatment relative to the Control in the uninvaded river. Catfish impact within the uninvaded river suggests the dominance of vulnerable taxa, such as odonates that were less abundant in the Impact treatment plots after catfish introduction. From a disturbance perspective, this study revealed different macroinvertebrate responses to catfish impact, and suggests that within invaded habitats, macroinvertebrates were less responsive to catfish presence, whereas catfish introduction within uninvaded habitats demonstrated invasion impact that was shown by a decrease in the abundance of vulnerable taxa. The occurrence of non-native sharptooth catfish within many Eastern Cape rivers is a concern because of its predation impact and potential to influence trophic interrelationships, and efforts should be taken to protect uninvaded rivers, and, where possible, eradicate the invader.
- Full Text:
- Date Issued: 2012
Does the growth of structure affect our dynamical models of the Universe? The averaging, backreaction, and fitting problems in cosmology
- Clarkson, C, Ellis, G, Larena, Julien, Umeh, O
- Authors: Clarkson, C , Ellis, G , Larena, Julien , Umeh, O
- Date: 2011
- Language: English
- Type: Article
- Identifier: vital:6791 , http://hdl.handle.net/10962/d1006944
- Description: Structure occurs over a vast range of scales in the Universe. Our large-scale cosmological models are coarse-grained representations of what exists, which have much less structure than there really is. An important problem for cosmology is determining the influence the small-scale structure in the Universe has on its large-scale dynamics and observations. Is there a significant, general relativistic, backreaction effect from averaging over structure? One issue is whether the process of smoothing over structure can contribute to an acceleration term and so alter the apparent value of the cosmological constant. If this is not the case, are there other aspects of concordance cosmology that are affected by backreaction effects? Despite much progress, this 'averaging problem' is still unanswered, but it cannot be ignored in an era of precision cosmology, for instance it may affect aspects of baryon acoustic oscillation observations.
- Full Text:
- Date Issued: 2011
- Authors: Clarkson, C , Ellis, G , Larena, Julien , Umeh, O
- Date: 2011
- Language: English
- Type: Article
- Identifier: vital:6791 , http://hdl.handle.net/10962/d1006944
- Description: Structure occurs over a vast range of scales in the Universe. Our large-scale cosmological models are coarse-grained representations of what exists, which have much less structure than there really is. An important problem for cosmology is determining the influence the small-scale structure in the Universe has on its large-scale dynamics and observations. Is there a significant, general relativistic, backreaction effect from averaging over structure? One issue is whether the process of smoothing over structure can contribute to an acceleration term and so alter the apparent value of the cosmological constant. If this is not the case, are there other aspects of concordance cosmology that are affected by backreaction effects? Despite much progress, this 'averaging problem' is still unanswered, but it cannot be ignored in an era of precision cosmology, for instance it may affect aspects of baryon acoustic oscillation observations.
- Full Text:
- Date Issued: 2011
The determinants of happiness among race groups in South Africa
- Ebrahim, Amina, Botha, Ferdi, Snowball, Jeanette D
- Authors: Ebrahim, Amina , Botha, Ferdi , Snowball, Jeanette D
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68589 , vital:29291 , http://www.essa2011.org.za/fullpaper/essa2011_2182.pdf
- Description: Publisher version , Economic indicators, like GDP per capita, are commonly used as indicators of welfare. However, they have a very limited and narrow scope, excluding many potentially important welfare determinants, such as health, relative income and religion - not surprising since they were not originally designed to fill this role. There is thus growing acceptance, and use of, subjective measure of wellbeing, (called ‘happiness’ measures) both worldwide and in South Africa. Happiness economics does not propose to replace income based measure of wellbeing, but rather attempts to compliment them with broader measures, which can be important in making policy decisions that optimise societal welfare. This paper tests for differences in subjective wellbeing between race groups in South Africa, and investigates the determinants of self-rated life satisfaction (happiness) for each group. Using the 2008 National Income Dynamics Study (NIDS) data, descriptive methods (ANOVA) and an ordered probit model are applied. Results indicate that reported happiness differs substantially among race groups, with black South Africans being the least happy group despite changes since the advent of democracy in 1994. Higher levels of educational attainment increase satisfaction for the whole sample, and women are generally less happy than men (particularly black women). As found in many other studies, unemployed people have lower levels of life satisfaction than the employed, even when controlling for income and relative income. The determinants of happiness are also different for each race group: While white South Africans attached greater importance to physical health; employment status and absolute income matter greatly for black people. For coloured people and black people, positional status (as measured by relative income) is an important determinant of happiness, with religious involvement significantly contributing to the happiness of Indian people.
- Full Text:
- Date Issued: 2011
- Authors: Ebrahim, Amina , Botha, Ferdi , Snowball, Jeanette D
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68589 , vital:29291 , http://www.essa2011.org.za/fullpaper/essa2011_2182.pdf
- Description: Publisher version , Economic indicators, like GDP per capita, are commonly used as indicators of welfare. However, they have a very limited and narrow scope, excluding many potentially important welfare determinants, such as health, relative income and religion - not surprising since they were not originally designed to fill this role. There is thus growing acceptance, and use of, subjective measure of wellbeing, (called ‘happiness’ measures) both worldwide and in South Africa. Happiness economics does not propose to replace income based measure of wellbeing, but rather attempts to compliment them with broader measures, which can be important in making policy decisions that optimise societal welfare. This paper tests for differences in subjective wellbeing between race groups in South Africa, and investigates the determinants of self-rated life satisfaction (happiness) for each group. Using the 2008 National Income Dynamics Study (NIDS) data, descriptive methods (ANOVA) and an ordered probit model are applied. Results indicate that reported happiness differs substantially among race groups, with black South Africans being the least happy group despite changes since the advent of democracy in 1994. Higher levels of educational attainment increase satisfaction for the whole sample, and women are generally less happy than men (particularly black women). As found in many other studies, unemployed people have lower levels of life satisfaction than the employed, even when controlling for income and relative income. The determinants of happiness are also different for each race group: While white South Africans attached greater importance to physical health; employment status and absolute income matter greatly for black people. For coloured people and black people, positional status (as measured by relative income) is an important determinant of happiness, with religious involvement significantly contributing to the happiness of Indian people.
- Full Text:
- Date Issued: 2011
The origin and development of the Nyl River floodplain wetland, Limpopo Province, South Africa: trunk–tributary river interactions in a dryland setting
- McCarthy, T S, Tooth, Stephen, Jacobs, Zenobia, Rowberry, Matthew D, Thompson, Mark, Brandt, Dion, Hancox, P John, Marren, Philip M, Woodborne, Stephan, Ellery, William F N
- Authors: McCarthy, T S , Tooth, Stephen , Jacobs, Zenobia , Rowberry, Matthew D , Thompson, Mark , Brandt, Dion , Hancox, P John , Marren, Philip M , Woodborne, Stephan , Ellery, William F N
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144321 , vital:38331 , DOI: 10.1080/03736245.2011.619324
- Description: The Nyl River floodplain wetland, one of South Africa's largest floodplain wetlands and a Ramsar site of international conservation importance, is located in an area of long-term and still active valley sediment accumulation. Creation of accommodation space for sedimentation has previously been attributed to tectonic controls, but new investigations reveal that a more likely cause is progradation of coarse-grained tributary fans across the narrow river valley downstream of the main area of floodplain wetland. Obstruction of trunk river flow and sediment transfer by these tributary fans has led to backponding and upstream gradient reduction and to accumulation of valley fills up to ∼35 m thick. Chronological control for the timing and rate of sediment accumulation is limited, but we hypothesise that a semi-arid to arid climate, characterised by asynchronous trunk–tributary activity that results in marked discontinuities in downstream water and sediment transfer, is likely to have been a key control. These interpretations are supported by other studies of dryland rivers globally and the findings add to our growing understanding of the controls on the origin and development of southern African wetlands, particularly by demonstrating how the combination of a particular physiography and a dryland climate can impart some distinctive geomorphological characteristics.
- Full Text:
- Date Issued: 2011
- Authors: McCarthy, T S , Tooth, Stephen , Jacobs, Zenobia , Rowberry, Matthew D , Thompson, Mark , Brandt, Dion , Hancox, P John , Marren, Philip M , Woodborne, Stephan , Ellery, William F N
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144321 , vital:38331 , DOI: 10.1080/03736245.2011.619324
- Description: The Nyl River floodplain wetland, one of South Africa's largest floodplain wetlands and a Ramsar site of international conservation importance, is located in an area of long-term and still active valley sediment accumulation. Creation of accommodation space for sedimentation has previously been attributed to tectonic controls, but new investigations reveal that a more likely cause is progradation of coarse-grained tributary fans across the narrow river valley downstream of the main area of floodplain wetland. Obstruction of trunk river flow and sediment transfer by these tributary fans has led to backponding and upstream gradient reduction and to accumulation of valley fills up to ∼35 m thick. Chronological control for the timing and rate of sediment accumulation is limited, but we hypothesise that a semi-arid to arid climate, characterised by asynchronous trunk–tributary activity that results in marked discontinuities in downstream water and sediment transfer, is likely to have been a key control. These interpretations are supported by other studies of dryland rivers globally and the findings add to our growing understanding of the controls on the origin and development of southern African wetlands, particularly by demonstrating how the combination of a particular physiography and a dryland climate can impart some distinctive geomorphological characteristics.
- Full Text:
- Date Issued: 2011
- «
- ‹
- 1
- ›
- »