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.
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- Date Issued: 2014
Teachers' perceptions of behavioural problems manifested by Grade 11 and 12 learners in three Namibian schools
- Authors: Akawa, Ester Anna Nelago
- Date: 2014
- Subjects: Education, Secondary -- Namibia School children -- Namibia -- Attitudes Learning disabilities -- Social aspects Behavior disorders in children -- Education (Secondary) -- Namibia Children with social disabilities -- Education (Secondary) -- Namibia Emotional problems of children -- Education (Secondary) -- Namibia Teachers -- Job stress -- Namibia
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1962 , http://hdl.handle.net/10962/d1010868
- Description: In Namibia today few learners with behavioural and learning problems are within special schools as most are placed within the mainstream school system. Placing these learners within the mainstream system is part of the policy of Inclusive Education (IE) because it argues that this would benefit these learners and also save resources. IE is concerned with addressing barriers to learning and behavioural problems are regarded as one of these barriers. IE argues for a series of new approaches to the diagnosis and response to learners with behavioural problems. This poses challenges for teachers in mainstream schools. Teachers are at the forefront of this situation as they are usually the first to observe and experience the behavioural problems in the schools and are expected to respond appropriately. They find this situation both challenging and problematic. This research explores a sample of teachers’ perceptions of learners’ behavioural problems. To collect in-depth information, this study followed a qualitative approach with a case study design. The data were collected through semi-structured interviews, supplemented with observation and document analysis. The study consisted of fifteen respondents: three principals, three teacher counsellors and nine teachers from the three selected schools. This study illuminates the types of behaviour that teachers encounter, the impact of these behaviours, the factors seen as contributing to these behaviours, and how teachers and the school system deal with these behaviours. In addition the study applies Bronfenbrenner’s bioecological model (1992) to explain how the behaviours manifested by Grade 11 and 12 learners, and identified as problematic by teachers, are part of an interconnected nested social system. The results from the study indicate the manifestation of behavioural problems to be common occurrences in secondary schools are evident, amongst others, through fighting, bullying, substance abuse, truancy, and disrespect of teachers and authority. The teachers pointed to the prevalence of these problems as well as the serious impact such problems have on these learners, their fellow learners, and on the teachers. The teachers identified a complex array of what they saw as contributing factors located within the school, peer groups, family and home circumstances, the local community, as well within the national education policy, the economy and society. The study points to some specific, as well as broader, lessons and opportunities for action both for those managing the education system at the national level and for schools and teachers.
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- Date Issued: 2014