Responses of stream fish assemblages to timing and extent of deforestation in Western Amazon
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Data
2018-05-04
Autores
Brejão, Gabriel Lourenço
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Universidade Estadual Paulista (Unesp)
Resumo
Os riachos da região Neotropical abrigam uma ictiofauna de pequeno porte, que frequentemente apresentam distribuições geográficas restritas e, em geral, são altamente dependentes da vegetação ripária para alimentação, abrigo e reprodução. A remoção da vegetação nativa da bacia hidrográfica está entre as modificações ambientais mais severas que afetam os ambientes aquáticos, de uma forma ainda pouco compreendida. Conhecer o histórico de desmatamento, em conjunto com a estrutura atual da paisagem, aumenta o poder das análises para avaliar os efeitos ecológicos do desmatamento. Além disso, os rumos distintos do processo de desmatamento podem afetar a composição e o funcionamento das comunidades de peixes de riachos. O rio Machado, em Rondônia, um importante tributário da bacia Amazônica, apresenta alta diversidade e endemismo, e um histórico recente de altas taxas de desmatamento e intensificação de uso do solo, que causam profundas alterações nos ambientes aquáticos. Sendo assim, o objetivo geral desta Tese foi compreender como o processo de desmatamento afeta a ictiofauna, usando a bacia do rio Machado como modelo. Para atingir esse objetivo, analisamos a relação entre a abundância das espécies de peixes com gradientes de tempo e extensão do desmatamento, para detectar quais espécies foram fortemente afetadas – positiva ou negativamente – pelo desmatamento (Capítulo 1). Conhecendo as respostas das espécies de peixes, determinamos como a composição e a estrutura da assembleia se relacionam com o tempo e a intensidade do desmatamento (Capítulo 2). E encerramos o estudo apresentando como os componentes ambientais influenciaram as taxas de substituição de espécies/atributos funcionais, considerando a idade do processo – ! desmatamento recente ou antigo (Capítulo 3). Em suma, encontramos que (1.) As populações de peixes apresentaram respostas distintas ao tempo e à extensão do desmatamento, considerando as estruturas taxonômica e funcional. As respostas negativas ocorreram em baixos níveis de desmatamento e pouco tempo após o impacto. Os limiares de resposta positivos de algumas espécies ao desmatamento extremo são tardios, não compensam a perda de taxons sensíveis e provavelmente contribuem para a homogeneização biótica. (2.) As perdas de riqueza e abundância das espécies de peixes sensíveis ocorreram sincronicamente com a perda de estrutura de hábitat, mas houve um atraso temporal no aumento dos indicadores de homogeneização de habitat e o aumento da riqueza e abundância das espécies tolerantes segue esse atraso. (3.) A substituição de espécies/atributos funcionais foi diferente do esperado pelo acaso, indicando que processos determinísticos estruturam esta assembleia de peixes. Apesar de encontrarmos alta substituição de espécies, a substituição de atributos funcionais foi menor do que a esperada pela substituição de espécies. Significa que temos comunidades taxonomicamente distintas, mas funcionalmente similares, sugerindo que a substituição de espécies ocorre principalmente entre espécies funcionalmente equivalentes. Em conclusão, ao adicionar a camada temporal para analisar os estágios iniciais das mudanças de uso do solo nesta região da Amazônia, foi possível observar a extrema sensibilidade da assembleia de peixes ao desmatamento. Ainda, é possível considerar peixes de riachos como um grupo bandeira a ser incluído em planejamentos de conservação, com o objetivo de minimizar os efeitos da perda de biodiversidade em escala regional.
The streams of the Neotropical region harbor a small-sized fish fauna, frequently with limited geographical distribution and, generally, highly dependent on riparian vegetation for feeding, shelter, and reproduction. The watershed native vegetation removal is one among several modifications, which effects on aquatic environments are not entirely understood yet. The knowledge of deforestation history along with current landscape structure enhances the power of analysis to evaluate ecological deforestation effects. Moreover, distinct ways of deforestation process might affect the fish community composition and functioning. The Machado river, in Rondônia, an important tributary of Amazon basin, exhibit high diversity and endemism and presents a recent history of high deforestation and land use intensification, which can cause profound changes in aquatic environments. Thus, the general aim of this Thesis is to comprehend how deforestation process influences the ichthyofauna. To reach this aim, we analyzed the relation between fish species abundance to environmental gradients of time and extent of deforestation, to detect which species were strongly affected – positively or negatively – by deforestation (Chapter 1). Knowing the fish species responses, we determined how fish assemblage composition and structure was related to deforestation time and intensity (Chapter 2). We end the study by presenting how the environmental components influenced the taxonomic and functional turnover rates, considering the process age – recent or old deforestation (Chapter 3). In Summary, we found that (1.) Stream fish populations present distinct responses to deforestation time and extent, regarding their taxonomic and functional structures, most negative threshold responses occurred at low levels of deforestation and soon after impact, so even in minimal change is expected to affect biodiversity ! negatively. Delayed positive threshold responses to extreme deforestation by a few species do not offset the loss of sensitive taxa and likely contribute to biotic homogenization; (2.) The sensitive fish richness and abundance lost occurred synchronically to the habitat structure loss, but there was a time-lag response for habitat homogenization indicators, and tolerant fish richness and abundance increase followed this time-lag; and (3.) Species/functional traits turnover was different than expected by chance, indicating that deterministic processes are structuring this stream fish community. Although we found a high species turnover, functional traits turnover was lower than the expected by the species turnover. It means that taxonomically dissimilar, but functionally similar, suggesting that the species turnover is occurring mainly among functionally equivalents species. In conclusion, by adding the temporal layer to analyze the initial stage of land use changes in this portion of Amazon, was possible to verify the extreme sensitivity of fish assemblages to deforestation. And there is possible to consider stream fish as a flag group to be included on conservation plannings, aiming to reduce the effects of biodiversity loss on a regional scale.
The streams of the Neotropical region harbor a small-sized fish fauna, frequently with limited geographical distribution and, generally, highly dependent on riparian vegetation for feeding, shelter, and reproduction. The watershed native vegetation removal is one among several modifications, which effects on aquatic environments are not entirely understood yet. The knowledge of deforestation history along with current landscape structure enhances the power of analysis to evaluate ecological deforestation effects. Moreover, distinct ways of deforestation process might affect the fish community composition and functioning. The Machado river, in Rondônia, an important tributary of Amazon basin, exhibit high diversity and endemism and presents a recent history of high deforestation and land use intensification, which can cause profound changes in aquatic environments. Thus, the general aim of this Thesis is to comprehend how deforestation process influences the ichthyofauna. To reach this aim, we analyzed the relation between fish species abundance to environmental gradients of time and extent of deforestation, to detect which species were strongly affected – positively or negatively – by deforestation (Chapter 1). Knowing the fish species responses, we determined how fish assemblage composition and structure was related to deforestation time and intensity (Chapter 2). We end the study by presenting how the environmental components influenced the taxonomic and functional turnover rates, considering the process age – recent or old deforestation (Chapter 3). In Summary, we found that (1.) Stream fish populations present distinct responses to deforestation time and extent, regarding their taxonomic and functional structures, most negative threshold responses occurred at low levels of deforestation and soon after impact, so even in minimal change is expected to affect biodiversity ! negatively. Delayed positive threshold responses to extreme deforestation by a few species do not offset the loss of sensitive taxa and likely contribute to biotic homogenization; (2.) The sensitive fish richness and abundance lost occurred synchronically to the habitat structure loss, but there was a time-lag response for habitat homogenization indicators, and tolerant fish richness and abundance increase followed this time-lag; and (3.) Species/functional traits turnover was different than expected by chance, indicating that deterministic processes are structuring this stream fish community. Although we found a high species turnover, functional traits turnover was lower than the expected by the species turnover. It means that taxonomically dissimilar, but functionally similar, suggesting that the species turnover is occurring mainly among functionally equivalents species. In conclusion, by adding the temporal layer to analyze the initial stage of land use changes in this portion of Amazon, was possible to verify the extreme sensitivity of fish assemblages to deforestation. And there is possible to consider stream fish as a flag group to be included on conservation plannings, aiming to reduce the effects of biodiversity loss on a regional scale.
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Código florestal brasileiro, Ponto de mudança, Limiares de diversidade, Ecomorfologia, Débito de extinção, Atributos funcionais, Dinâmica da paisagem, Atraso temporal, Bacia amazônica, Bacia do Machado, Brazil forest code, Change point, Diversity thresholds, Ecomorphology, Extinction debt, Functional traits, Landscape dynamics, Time lag, Amazon basin, Machado basin