Full text
| |
| Author(s): |
Paulo Ricardo Ilha Jiquiriçá
Total Authors: 1
|
| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB) |
| Defense date: | 2015-06-29 |
| Examining board members: |
Luís César Schiesari;
Lilian Casatti;
Marcia Nunes Macedo;
Renata Guimarães Moreira Whitton;
Jansen Alfredo Sampaio Zuanon
|
| Advisor: | Luís César Schiesari |
| Abstract | |
The expansion of the Amazonian agricultural frontier possibly represents the most extensive and profound land use change in the contemporary world. Deforestation, dam construction, and numerous other pressures have serious impacts on its aquatic ecosystems, that collectively hold the greatest diversity of freshwater fish on the planet. Deforestation and dam construction cause profound changes in biotic and abiotic characteristics of stream ecosystems, including water heating and changes in the composition and structure of fish assemblages. There are many evidences that the increase in temperature negatively affect organisms body size, and warming caused by climate changes have already been associated with reductions in fish body size. However, there are no studies showing that local and regional processes of major relevance, such land use changes, can also cause the same result. With a geographic focus on the Amazonian arc of deforestation in the headwaters of the Xingu River, the objectives of this thesis were: (i) to investigate the effects of deforestation and dam construction on environmental characteristics, and on the composition and structure of fish assemblages in first order streams; and (ii) to test the hypothesis that the conversion of forests into agricultural areas is associated with stream warming and reductions in fish body size, and that this reduction in body size is a result of changes in individual growth caused by adaptation and/or phenotypic plasticity, promoted by environmental warming. In the first chapter of this thesis, we show that deforestation and the construction of dams cause changes in environmental characteristics of first-order streams that affect the habitat availability for fish. This resulted in changes in the composition and structure of assemblages, so that agricultural area streams showed higher abundance and biomass of fish that forest streams. Reservoirs had lower species richness than lotic stretches both in forested and deforested streams, suggesting that the construction of dams poses a significant threat to the conservation of fish biodiversity. In the second chapter, we combine field sampling and laboratory and field experiments to demonstrate that the conversion of forests into agricultural areas warms headwater streams and reduces fish body size through changes in individual growth rates. Warming and size reductions we observed were considerably higher than those reported in the literature for the observed and predicted effects of global warming. This is the first study as far as we know, that investigated the effects of warming caused by deforestation in fish body size. It is possible that a broad scale fish body size reduction due to warming is occurring throughout the arc of deforestation, in streams that collectively account for a large fraction of Amazonian fish biodiversity. (AU) | |
| FAPESP's process: | 11/20458-6 - Effects of land use change on the ecology of fishes in the headwaters of the Xingu River |
| Grantee: | Paulo Ricardo Ilha Jiquiriçá |
| Support Opportunities: | Scholarships in Brazil - Doctorate |