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.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Zoology))--University of Pretoria, 2005. / Zoology and Entomology / unrestricted

As limited prey availability and persecution by humans in response to livestock predation are key conservation concerns for the Cape leopard (Martins & Martins 2006), the present study aimed to provide more information regarding their feeding habits. The first objective was to determine whether the Cape leopard was subject to a change in their prey base and how they responded to the change. This was established by comparison of their current diet in the Cederberg and Gamka Mountains, determined by using scat analysis techniques, with a previous dietary assessment (Norton et al. 1986). The second aim was to provide a preliminary assessment of the prey preference of the Cape leopard and examine the utility of camera trap surveys to determine leopard prey preference. Leopard diet in the Cederberg and Gamka Mountains consisted largely of small- (1-10 kg) and medium-sized (10-40 kg) mammals; rock hyraxes (Procavia capensis) and klipspringers (Oreotragus oreotragus) were key prey items. In terms of regional variation in leopard diet, there was a significant difference in the average weight of prey utilized in the Cederberg and Gamka Mountains. Despite the importance of prey availability of suitable size, their flexibility in terms of prey size utilization reflected their ability to switch to smaller prey to fulfil their dietary requirements, when prey is limited. The study suggested a dietary shift, with significant variation in prey species utilization in both regions. The shift did not appear to be in response to prey scarcity, but rather a reduction in key prey species, particularly the rock hyrax. The shift involved an increase in the number of species utilized, and only a very small increase in livestock predation in both areas. There was however no significant variation in prey size category utilization. This demonstrated their dietary flexibility, as well as the importance of suitable prey sizes rather than the presence of specific prey species to fulfil their dietary requirements. The camera trap survey revealed a strong correlation between the number of camera trap days and the number of photographs taken of identifiable species. Variation of this correlation between different habitats supported the notion that individual images are a better unit to determine sampling efficiency than trap days. The camera trap survey also showed that small rodent availability was underestimated by camera trap surveillance, which resulted in poor prey preference estimation. It was therefore suggested that camera trap surveys be restricted to the surveillance of larger prey species (> 1 kg). By excluding small rodents from the analysis, prey preference could be estimated for other species and prey size categories. Small- and medium-sized mammals were significantly preferred, whereas large mammals were significantly avoided by the Cape leopard.

I investigated the effect of turbidity on the foraging behaviour of juvenile Chinook salmon (Oncorhynchus tshawytscha) in the laboratory. Specifically, I examined a behavioural "tradeoff" between visual ability and "perceived" risk. I assessed visual ability by measuring the reaction distance of juvenile Chinook to planktonic Artemia prey. I found Chinook exhibited a log-linear decline in reaction distance with increasing turbidity. To determine the effects of turbidity and microhabitat on foraging rate, I conducted separate experiments for surface (Drosophila), planktonic (Artemia), and benthic (Tubifex) prey across a range of turbidity levels (0, 25, 50, 100, 200, 400, 800 mg•L⁻¹). Foraging rates were reduced at higher turbidity conditions for all three prey. However, for surface and benthic prey, foraging rates were also low in clear water; highest rates were attained at intermediate turbidity levels (50-200 mg•L⁻¹). The degree to which intermediate turbidities were associated with higher foraging rates was size-dependent. Smaller individuals (150-57 mm FL) exhibited relatively higher foraging rates in clear conditions than did larger individuals. However, planktonic foraging rates by juveniles were consistently high in clear water, regardless of fish size. In experiments manipulating light level independent of turbidity, I allowed salmon to forage under conditions which were either turbid, or clear but with light intensity correspondingly reduced. Foraging rates were similar between the two treatments for planktonic prey, but differed for benthic and surface prey. Generally, foraging rates exhibited by juvenile Chinook salmon could not be explained on the basis of visual ability alone. I suggest that young salmon also exhibited foraging behaviour consistent with their perception of risk to predation. In arena experiments, juvenile Chinook distributed themselves randomly in turbid conditions; in clear conditions they associated with the bottom. When bird and fish predator models were introduced the fish altered their spatial distribution, occupying deeper regions regardless of turbidity. However, their response in turbid conditions was less marked and lasted for a shorter time. Turbidity apparently mitigated the perceived risk of predation in juvenile Chinook. I developed a conceptual tradeoff model that predicted the general effect of turbidity on foraging behaviour. Assuming differences in either prey quality or perceived risk of predation in three microhabitats (surface, water column, bottom), the model resolved the apparent dissimilarities between planktonic and other foraging behaviours. Perceived risk of Chinook to predation was significantly different between surface and water column microhabitats. When exposed to a non-visual "fixed-risk" stimulus (sound), salmon apparently perceived less risk as turbidity increased. I conclude that in turbid waters juvenile salmon exhibit foraging behaviour in a manner consistent with a tradeoff between their visual ability and perceived risk. / Science, Faculty of / Zoology, Department of / Graduate

Various aspects of downstream migratory behavior of sockeye salmon fry (pncorhynchus nerka) were examined in a series of field and laboratory experiments. The field work at the Department of tie Environment (Fisheries and Marine Service) Fulton Eiver spawning channels, Babine Lake, British Columbia, was concerned with the predation by rainbow trout (Salmo gairdneri) and whitefish (Prosopium williamsoni) on sockeye fry with various kinds of prior experience. The laboratory studies focused on the effects of exposure to light on the behavior of emerging and recently emerged fry. The results showed that : (1) the number of fry moving downstream varies throughout the nightly migration period; (2) the presence cf predators modifies the movement pattern of migrating fry, such that the fry tend to move downstream over a more concentrated time period; (3) fry response to predators tends not to be predator-specific, migrating fry respond similarly to different species of predators; (4) emergent fry are not all similar in their migratory behavior, some tend to migrate rapidly (fast migrants), while others migrate at a slower rate (slow migrants); (5) generally fry with prior experience to predators displayed different migratory behavior compared to fast and slow migrants; and (6) subjecting newly-emerged fry to increasing time periods of light treatment and fry densities, alters behavior patterns. It is concluded that fry commencing downstream movement are not all similar in their migratory behavior. Begardless of the basis for the behavioral difference between fast and slow migrants, the presence of predators modifies and enhances downstream movement. Further, subjecting premigratory fry to light, alters downstream movement and behavioral interactions between fry. / Science, Faculty of / Zoology, Department of / Unknown

Orientador: Luís Felipe de Toledo Ramos Pereira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-24T04:49:15Z (GMT). No. of bitstreams: 1 RochaLima_AnaBeatrizCarollo_M.pdf: 4483469 bytes, checksum: 075bff58acd826eaa3ec36949ad8f85c (MD5) Previous issue date: 2013 / Resumo: A família Brachycephalidae compreende dois gêneros e 52 espécies. O gênero Brachycephalus apresenta, em sua maioria, espécies tóxicas e de coloração conspícua, enquanto o gênero Ischnocnema possui muitas espécies polimórficas e crípticas quanto a sua coloração dorsal. No primeiro capítulo foi realizado um experimento com modelos de plasticina para testar se os padrões coloridos e brilhantes do gênero Brachycephalus estão relacionados com aposematismo. Além disso, foi testada a hipótese alóctone/autóctone, que prediz que os predadores vão responder mais fortemente a um padrão autóctone do que a um alóctone, dado que eles supostamente são ingênuos ao padrão introduzido e/ou experientes quanto ao padrão autóctone. O experimento foi realizado em duas localidades de Mata Atlântica no estado de São Paulo, Brasil, onde ocorrem tanto espécies camufladas quanto conspícuas de Brachycephalidae. Foram encontradas diferenças na intensidade de ataque entre os modelos crípticos e vistosos, suportando a hipótese de que a coloração conspícua de Brachycephalus é sinal de sua toxicidade. No segundo capítulo foi investigado como fatores ambientais e espaciais afetam os padrões de coloração de espécies do complexo de Ischnocnema guentheri-henselii e I. parva, comparando populações em diferentes latitudes depositadas no acervo de quatro coleções científicas. Os diferentes padrões foram plotados em mapas e, através de análises de agrupamento, foram detectadas diferenças na proporção da frequência dos padrões nas populações situadas no limite meridional da ocorrência das espécies. A segregação de populações abaixo da latitude -24º é coincidente com variações morfológicas observadas em outras espécies, ou mesmo com limites de distribuição de espécies irmãs de anuros. Assim, é evidente que esta região caracteriza-se por forte promotora de diversificação e o clima pode ser uma das explicações para nossos resultados. Desta forma os resultados desta dissertação sugerem que a predação pode estar exercendo pressão no gênero Brachycephalus e que fatores climáticos e geológicos podem estar influenciando a coloração no gênero Ischnocnema / Abstract: Brachycephalidae family comprises two genera and 52 species. Brachycephalus genus presents mostly toxic species with conspicuous coloration, while Ischnocnema genus has many polymorphic and cryptic species as their dorsal coloration. In the first chapter we conducted an experimental essay, with plasticine frog simulacra to test if the bright colorful patterns of Brachycephalus species are related to aposematism. Furthermore, we tested the allochthonous/autochthonous hypothesis, which predicts that predators will respond strongly to an autochthonous pattern than to an allochthonous one, as they supposedly are naïve to this introduced pattern and/or experienced to the autochthonous pattern. The experiment was made in two Atlantic forest sites in the state of São Paulo, Brazil, where both cryptic and conspicuous Brachycephalidae species occur. We found differences in predation attack between cryptic and conspicuous simulacra, supporting that the conspicuous coloration of Brachycephalus is a sign of their toxicity. In the second chapter we investigated how environmental and spatial factors affect color patterns of species complex Ischnocnema guentheri-henselii and I. parva comparing populations at different latitudes deposited in four scientific collections. Different patterns were plotted on maps and, through cluster analysis, differences were detected in the ratio of the frequency of patterns in populations located in the southern limit of species occurrences. The segregation of populations below -24 º latitude coincides with morphological variations observed in other species, or even distribution limits sister species of frogs. Thus, it is clear that this region is characterized by a strong promoter of diversification and the weather can be one of the explanations for our study. Thus, the results of this dissertation suggest that predation may be exerting pressure on the Brachycephalus genus and geological and climatic factors may be influencing the coloration in the Ischnocnema genus / Mestrado / Biodiversidade Animal / Mestra em Biologia Animal

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When touched with a contact stimulus, 50% of adult Uloborus glomosus jumped from the web; 33% remained motionless; 13% moved to the edge of the web; and 4% shook the web. In a population of juveniles, 45% moved to the edge of the web; 27% jumped from the web; 24% shook the web; and 4% remained motionless. Adults with either stabilimenta or eggsac chains in their webs showed a tendency to shake their webs in the morning and move to the edge in the evening. Those without web structures jumped from their webs throughout the day. Juveniles with stabilimenta shook their webs in the afternoon; those without stabilimenta shook their webs in the evening. Adults aligned with web structures remained motionless when disturbed. Marked adults observed over the course of 4 weeks moved to the edge of the web or remained motionless when contacted in the mornings and jumped in the afternoons and evenings. During this time, the frequency of the jumping behavior increased. An adult U. glomosus jumped from its web in response to contact by a spider-hunting wasp. Other spiders tested with a contact stimulus and the combined visual and vibratory stimuli produced by a tethered wasp responded only to contact. Females tending their eggsac chains exhibited two types of defensive behaviors when either the parasitoid Arachnopteromalus dasys or spiderlings were placed on their eggsacs. They jerked their webs and swept the eggsacs with their long front legs. / Master of Science