História de vida de tilápias e influências para pesca e estado trófico de em lagos e reservatórios tropicais
The individual body size affects the competitive potential, consumption rates and responses in the face of mortality and resource availability. Also, changing diet with increasing body size has important consequences for the role played in food webs. Understanding how populations and communities are...
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| Formato: | doctoralThesis |
| Idioma: | por |
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| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/24950 |
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| Resumo: | The individual body size affects the competitive potential, consumption rates and responses in the face of mortality and resource availability. Also, changing diet with increasing body size has important consequences for the role played in food webs. Understanding how populations and communities are structured about size helps in management practices to control introduced species, increase the production of species commercial importance, and reintroduction or recovery of native populations. However, only recently intraspecific variations have been taken into account in competition and predation studies. In this thesis, we aim to understand the effects of size-selective predation and intraspecific competition by resources on variations in the size-structure of populations of tropical omnivorous fish, such as Nile tilapia. In the first chapter, we present empirical results that demonstrate the role of size-selective mortality by a native predator on the change in size structure of Nile tilapia in man-made lakes of Northeast Brazil. Size-selective predation on fingerlings and juveniles increases the maximum and average size of tilapias in a population by reducing intraspecific competition among tilapia juveniles. In the absence of size-selective mortality (absence of piscivorous), tilapia populations are characterized by high biomass of juveniles and adults of small body size. The second chapter presents the differentiated effects of consumers, such as tilapias, which undergo ontogenetic niche shift (planktivores when juveniles and omnivorous when adults), on the dynamics of the resources (zooplankton and phytoplankton) under a low and high concentration of nutrients for the phytoplankton. The results of this work demonstrate that the omnivore tilapia has a stabilizing role on plankton in contrast to the effect of planktivorous juveniles. In the third chapter, we use a model that describes the patterns of growth, reproduction and energetic use of tilapia throughout life according to the availability of the resource. In this chapter, we found a high variability in tilapia growth and reproduction rates and the adoption of different life-history strategies in tropical lakes, as a possible response to food availability. Finally, in the last chapter, we explored the effects of per capita food availability on the dynamics and size-structure of tilapia populations by varying resource carrying capacity and rates of mortality from predation and fishing. Our results demonstrate that predation on juveniles has a facilitating role on fishing, that is, predation increases the biomass of large adults, the target of fisheries. Dwarfism in tilapias is favored by fishing and increased biomass of the resource for tilapia adults (eutrophication), in the absence of predation. Our model corroborates the empirical results found in the first chapter of the thesis and not only reflects the life-history of the tilapia but also indicates essential processes in the population dynamics, becoming a useful tool for the species management. |
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