Possible impacts of climate change on wetlands and its biota in the Brazilian Amazon / Possíveis impactos das mudanças climáticas em áreas úmidas e sua biota na Amazônia brasileira

Wetlands cover approximately 6% of the Earth's surface. They are frequently found at the interface between terrestrial and aquatic ecosystems and are strongly dependent on the water cycle. For this reason, wetlands are extremely vulnerable to the effects of climate change. Mangroves and floodplain ecosystems are some of the most important environments for the Amazonian population, as a source of proteins and income, and are thus the types of wetlands chosen for this review. Some of the main consequences that can be predicted from climate change for wetlands are modifications in hydrological regimes, which can cause intense droughts or inundations. A possible reduction in rainfall can cause a decrease of the areas of mangroves and floodplains, with a consequent decline in their species numbers. Conversely, an increase in rainfall would probably cause the substitution of plant species, which would not be able to survive under new conditions for a long period. An elevation in water temperature on the floodplains would cause an increase in frequency and duration of hypoxic or anoxic episodes, which might further lead to a reduction in growth rates or the reproductive success of many species. In mangroves, an increase in water temperature would influence the sea level, causing losses of these environments through coastal erosion processes. Therefore, climate change will likely cause the loss of, or reduction in, Amazonian wetlands and will challenge the adaptability of species, composition and distribution, which will probably have consequences for the human population that depend on them.(AU)

As áreas úmidas cobrem aproximadamente 6% da superfície da terra e são frequentemente encontradas na interface entre ecossistemas terrestres e aquáticos e fortemente dependentes do ciclo da água. Por esta razão são extremamente vulneráveis aos efeitos das alterações do clima. Os ecossistemas de manguezais e várzeas são muito importantes para os seres humanos da Amazônia, porque são de onde eles extraem algumas das principais fontes de proteínas e renda, e, por isso, foram os dois tipos de áreas úmidas escolhidos para esse estudo. Entre as principais consequências das mudanças climáticas previstas para esses ambientes estão as alterações nos regimes hidrológicos, que podem causar grandes secas ou inundações. A possível redução das chuvas pode causar a diminuição das áreas de mangue e várzea, provocando um rápido declínio de suas espécies. Por outro lado, o aumento das chuvas teria como provável consequência a substituição de espécies de plantas, que não seriam capazes de sobreviver sob as novas condições por um longo período de tempo. As principais consequências do aumento da temperatura da água entre as áreas úmidas seria que nas várzeas este parâmetro aumentaria a frequência ou duração dos episódios hipóxicos e/ou anóxicos, podendo causar a redução da taxa de crescimento e prejudicando o sucesso reprodutivo de muitas espécies, enquanto nos manguezais esta mudança influenciaria no nível do mar, provocando a perda desses ambientes pelo processo de erosão costeira. Portanto, tais mudanças poderão levar à perda e/ou redução das áreas úmidas da Amazônia, refletindo na capacidade de adaptação, composição e distribuição de suas espécies, consequentemente afetando as populações humanas que deles dependem.(AU)

Possible impacts of climate change on wetlands and its biota in the Brazilian Amazon.

Wetlands cover approximately 6% of the Earth's surface. They are frequently found at the interface between terrestrial and aquatic ecosystems and are strongly dependent on the water cycle. For this reason, wetlands are extremely vulnerable to the effects of climate change. Mangroves and floodplain ecosystems are some of the most important environments for the Amazonian population, as a source of proteins and income, and are thus the types of wetlands chosen for this review. Some of the main consequences that can be predicted from climate change for wetlands are modifications in hydrological regimes, which can cause intense droughts or inundations. A possible reduction in rainfall can cause a decrease of the areas of mangroves and floodplains, with a consequent decline in their species numbers. Conversely, an increase in rainfall would probably cause the substitution of plant species, which would not be able to survive under new conditions for a long period. An elevation in water temperature on the floodplains would cause an increase in frequency and duration of hypoxic or anoxic episodes, which might further lead to a reduction in growth rates or the reproductive success of many species. In mangroves, an increase in water temperature would influence the sea level, causing losses of these environments through coastal erosion processes. Therefore, climate change will likely cause the loss of, or reduction in, Amazonian wetlands and will challenge the adaptability of species, composition and distribution, which will probably have consequences for the human population that depend on them.

Effects of isolation and environmental variables on fish community structure in the Brazilian Amazon Madeira-Purus interfluve.

Due to the existence of terrestrial barriers to freshwater fish dispersion, it is believed that its distribution is strongly associated with historical factors related to the formation of the habitats they occupy. By the other hand, some studies reveal the influence of abiotic conditions (such as size of water bodies, pH, conductivity) on the composition of fish fauna occurring in small streams. This study aimed to investigate whether drainage basins, because catchment boundaries are potential barriers to fish dispersion, or the physical structure and physico-chemical characteristics of water have a greater influence on fish community structure in small streams. We sampled 22 streams belonging to five drainage basins in the Madeira-Purus interfluve. Fish were caught with dip nets and a small trawl, and data were simultaneously obtained on structural characteristics of the streams and physico-chemical characteristics of the water. Community composition was analyzed using Non-Metric Multidimensional Scaling (NMDS), and variables related to structural and physico-chemical characteristics were summarized by Principal Component Analysis (PCA). Two explanatory models relating faunal composition to environmental factors were constructed: the first using only continuous variables and the second including the drainage basin as a categorical variable. The Akaike Information Criterion (AIC) and AIC weight were used to select the best model. Although structural and physico-chemical variables significantly contributed to explaining faunal composition, the model including the drainage basin was clearly the better of the two models (more than 90% support in the data). The importance of drainage basins in structuring fish communities in streams may have significant consequences for conservation planning in these environments.

Modelling the growth of tambaqui, Colossoma macropomum (Cuvier, 1816) in floodplain lakes: model selection and multimodel inference.

The tambaqui, Colossoma macropomum, is one of the most commercially valuable Amazonian fish species, and in the floodplains of the region, they are caught in both rivers and lakes. Most growth studies on this species to date have adjusted only one growth model, the von Bertalanffy, without considering its possible uncertainties. In this study, four different models (von Bertalanffy, Logistic, Gompertz and the general model of Schnüte-Richards) were adjusted to a data set of fish caught within lakes from the middle Solimões River. These models were adjusted by non-linear equations, using the sample size of each age class as its weight. The adjustment evaluation of each model was based on the Akaike Information Criterion (AIC), the variation of AIC between the models (Δi) and the evidence weights (wi). Both the Logistic (Δi = 0.0) and Gompertz (Δi = 1.12) models were supported by the data, but neither of them was clearly superior (wi, respectively 52.44 and 29.95%). Thus, we propose the use of an averaged-model to estimate the asymptotic length (L∞). The averaged-model, based on Logistic and Gompertz models, resulted in an estimate of L∞=90.36, indicating that the tambaqui would take approximately 25 years to reach average size.

Effects of isolation and environmental variables on fish community structure in the Brazilian Amazon Madeira-Purus interfluve / Efeito do isolamento e das variáveis ambientais na estrutura de comunidades de peixes do interflúvio Madeira-Purus na Amazônia brasileira

Due to the existence of terrestrial barriers to freshwater fish dispersion, it is believed that its distribution is strongly associated with historical factors related to the formation of the habitats they occupy. By the other hand, some studies reveal the influence of abiotic conditions (such as size of water bodies, pH, conductivity) on the composition of fish fauna occurring in small streams. This study aimed to investigate whether drainage basins, because catchment boundaries are potential barriers to fish dispersion, or the physical structure and physico-chemical characteristics of water have a greater influence on fish community structure in small streams. We sampled 22 streams belonging to five drainage basins in the Madeira-Purus interfluve. Fish were caught with dip nets and a small trawl, and data were simultaneously obtained on structural characteristics of the streams and physico-chemical characteristics of the water. Community composition was analyzed using Non-Metric Multidimensional Scaling (NMDS), and variables related to structural and physico-chemical characteristics were summarized by Principal Component Analysis (PCA). Two explanatory models relating faunal composition to environmental factors were constructed: the first using only continuous variables and the second including the drainage basin as a categorical variable. The Akaike Information Criterion (AIC) and AIC weight were used to select the best model. Although structural and physico-chemical variables significantly contributed to explaining faunal composition, the model including the drainage basin was clearly the better of the two models (more than 90% support in the data). The importance of drainage basins in structuring fish communities in streams may have significant consequences for conservation planning in these environments.(AU)

Devido à existência de barreiras terrestres à dispersão de peixes de água doce, acredita-se que sua distribuição é fortemente associada a fatores históricos relacionados à formação dos habitats que ocupam. Por outro lado, alguns estudos revelam a influência de condições abióticas (tais como o tamanho do corpo d'água, pH, condutividade) na composição da fauna ictiíca de rios de pequena ordem. Este trabalho teve como objetivo investigar se bacias hidrográficas, cujo divisor de águas representa uma potencial barreira para a dispersão dos peixes, ou a estrutura física e características físico-químicas da água têm maior efeito sobre a estrutura de comunidades de peixes de riachos de pequena ordem. Foram amostrados 22 riachos, pertencentes a cinco bacias hidrográficas no interflúvio Madeira-Purus. Os peixes foram capturados com puçás e uma pequena rede de arrasto, e simultaneamente foram obtidos dados sobre as características estruturais dos riachos e físico-químicas da água. A composição das comunidades foi analisada por meio de um Escalonamento Multidimensional Não-Métrico (NMDS) e as variáveis relacionadas às características estruturais e físico-químicas foram sintetizadas por meio de uma Análise de Componentes Principais (PCA). Dois modelos explicativos relacionando a composição da fauna aos fatores ambientais foram construídos: o primeiro utilizando apenas variáveis contínuas, e o segundo incluindo as bacias hidrográficas como variável categórica. O Critério de Informação de Akaike (AIC) e o peso do AIC foram utilizados para a seleção do melhor modelo. Apesar de variáveis físicas e físico-químicas terem contribuído significativamente para explicar a composição faunística, o modelo incluindo bacias hidrográficas foi claramente superior (mais de 90% de suporte nos dados). A importância de bacias de drenagem para a estruturação da comunidade de peixes de riachos pode ter consequências relevantes para o planejamento para a conservação desses ambientes.(AU)

Modelling the growth of tambaqui, Colossoma macropomum (Cuvier, 1816) in floodplain lakes: model selection and multimodel inference / Modelagem do crescimento do tambaqui (Colossoma macropomum Cuvier, 1816): seleção de modelos e inferência multimodelos

The tambaqui, Colossoma macropomum, is one of the most commercially valuable Amazonian fish species, and in the floodplains of the region, they are caught in both rivers and lakes. Most growth studies on this species to date have adjusted only one growth model, the von Bertalanffy, without considering its possible uncertainties. In this study, four different models (von Bertalanffy, Logistic, Gompertz and the general model of Schnüte-Richards) were adjusted to a data set of fish caught within lakes from the middle Solimões River. These models were adjusted by non-linear equations, using the sample size of each age class as its weight. The adjustment evaluation of each model was based on the Akaike Information Criterion (AIC), the variation of AIC between the models (i) and the evidence weights (wi). Both the Logistic (i = 0.0) and Gompertz (i = 1.12) models were supported by the data, but neither of them was clearly superior (wi, respectively 52.44 and 29.95%). Thus, we propose the use of an averaged-model to estimate the asymptotic length (L). The averaged-model, based on Logistic and Gompertz models, resulted in an estimate of L=90.36, indicating that the tambaqui would take approximately 25 years to reach average size.(AU)

O tambaqui, Colossoma macropomum, é uma das espécies de peixes amazônicos de maior valor comercial, sendo capturado em rios e lagos da planície alagável da região. Até o presente, a maioria dos estudos sobre essa espécie tem ajustado um único modelo de crescimento, o de von Bertalanffy, sem considerer as possíveis incertezas associadas ao uso do modelo. Neste estudo, quatro modelos diferentes (von Bertalanffy, Logístico, Gompertz e o modelo geral de Schnüte-Richards) foram ajustados a um conjunto de dados de peixes capturados no interior de lagos situados no médio Solimões. Esses modelos foram ajustados por equações não lineares e o número de tambaquis em cada classe de tamanho foi usado como peso no ajuste. A avaliação do ajuste de cada modelo foi baseada no Critério de Informação de Akaike (AIC), na diferença do AIC entre os modelos (i) e nos pesos de evidência (wi). Tanto o modelo Logístico (i = 0,0) como o de Gompertz (i = 1,12) foram suportados pelos dados, mas nenhum deles foi claramente superior (wi, respectivamente, de 52,44 e 29,95%). Assim, é proposto o uso de um modelo médio para estimar o comprimento assintótico (L). O modelo médio, baseado nos modelos Logístico e de Gompertz, resultou em uma estimativa de L = 90,36 e indicou que o tambaqui levaria aproximadamente 25 anos para atingir esse tamanho.(AU)

Effects of fragmentation on Thamnophilus stictocephalus (Aves, Thamnophilidae) in semideciduous forest of Alter-do-Chão, Pará.

Effects of fragmentation on biodiversity have received much attention in recent decades, as fragmentation can greatly reduce viable areas for living organisms. We studied its effect on Thamnophilus stictocephalus (Thamnophilidae), an understory bird, in semideciduous forest fragments in Alter-do-Chão, Santarém, Pará. We tested whether the density of Thamnophilus stictocephalus was a function of fragment size and shape, density of vegetation, or arthropod biomass. Density of Thamnophilus was positively related to fragment size, but not to the other factors analyzed. Arthropod biomass was positively related to fragment size. The density of T. stictocephalus in fragments was significantly higher than it was in continuous forest. Fragmentation processes had a pronounced effect on the relative density of T. stictocephalus.

Effects of fragmentation on Thamnophilus stictocephalus (aves, Thamnophilidae) in semideciduous forest of Alter-do-Chão, Pará

Os efeitos da fragmentação sobre a biodiversidade têm recebido muita atenção nas últimas décadas, pelo fato de reduzirem, drasticamente, áreas viáveis para organismos vivos. Estudou-se o efeito da fragmentação de habitat sobre Thamnophilus stictocephalus (Thamnophilidae), uma ave de sub-bosque, em fragmentos de floresta semidecídua em Alter-do-Chão, Santarém, Pará. Testou-se a densidade de Thamnophilus stictocephalus como função de tamanho e forma de fragmentos, da densidade da vegetação de sub-bosque e da biomassa de artrópodes. A densidade de Thamnophilus foi positivamente relacionada ao tamanho de fragmentos e não foi relacionada significativamente aos outros fatores analisados. A biomassa de artrópodes foi positivamente relacionada ao tamanho de fragmentos. A densidade de Thamnophilus stictocephalus foi significativamente maior em fragmentos do que em floresta contínua. A fragmentação teve um efeito pronunciado na densidade relativa de T. stictocephalus.