Abstract
The functional structure of communities is commonly measured by the variability in functional traits, which may demonstrate complementarity or redundancy patterns. In this study, we tested the influence of environmental variables on the functional structure of fish assemblages in Amazonian streams within a deforestation gradient. We calculated six ecomorphological traits related to habitat use from each fish species, and used them to calculate the net relatedness index (NRI) and the nearest taxon index (NTI). The set of species that used the habitat differently (complementary or overdispersed assemblages) occurred in sites with a greater proportion of forests. The set of species that used the habitat in a similar way (redundant or clustered assemblages) occurred in sites with a greater proportion of grasses in the stream banks. Therefore, the deforestation of entire watersheds, which has occurred in many Amazonian regions, may be a central factor for the functional homogenization of fish fauna.
Highlights
The functional diversity of a community can be greatly influenced by the loss or addition of species with different traits from most species (Cianciaruso et al, 2013)
The partial regression with the net relatedness index (NRI) and nearest taxon index (NTI) showed that explanatory variables only explained the NTI
The variables that significantly explained the NTI were the percentage of forest cover in the watershed, the percentage of grasses in the stream banks, and depth (Table 3), indicating that most of variation in functional diversity can be explained by the combined effects of landscape and local environmental predictors
Summary
The functional diversity of a community can be greatly influenced by the loss or addition of species with different traits from most species (i.e., functionally unique) (Cianciaruso et al, 2013) These changes may occur due to different processes, and deforestation has been associated with decreases in functional diversity in different communities (Tilman et al, 1997; Dolédec et al, 2006; Flynn et al, 2009; Barragán et al, 2011). Considering that the influence of these variables on species occurrence depends on their functional traits (Goldstein & Meador, 2005; Teresa & Casatti, 2012), it is presumable that the effects of deforestation on the functional structure of communities are mediated by changes at finer spatial scales
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