The influence of deforestation on taxonomic and functional diversity of fish communities in Neotropical lowland streams

Background/Question/Methods

Deforestation causes one of the most severe impacts to aquatic ecosystem, affecting biological communities in different ways. Changes in the taxonomic structure and composition of the aquatic communities are the most frequently reported effects related to deforestation in streams. However, other components of biological diversity are potentially affected by these alterations, such as functional diversity. In this study we investigated if deforestation induces changes in the taxonomic and functional diversity by evaluating patterns of fish communities in forested and deforested streams. Because deforested streams are simplified environments, constraining more specialized species occurrence while favoring most generalist species, we hypothesized that forested streams exhibit more diverse communities in both biological scales. Fish communities were sampled in 114 five meter long segments, representing the variability of mesohabitats, in six streams (three deforested and three forested) located in Southeastern Brazil. The taxonomic diversity was quantified using richness and evenness and functional diversity was quantified using independent components: richness, evenness, divergence, dispersion and richness of functional groups. Fish functions were evaluated through measurement of two traits, flow and depth preferences. Taxonomic and functional diversity indexes were compared between forested and deforested streams by using a Nested Anova, with mesohabitats as a random factor nested within presence/absence of forest factor.

Results/Conclusions

Deforested streams presented higher taxonomic richness than forested ones, mainly due to the increase of richness in the pools, but they exhibited similar evenness. The functional richness and functional divergence were similar between the groups of streams, but other aspects of the functional diversity were affected by deforestation. The functional evenness, dispersion and richness of functional groups were significantly higher in forested streams than in deforested ones. Our results indicate that, besides stream fish communities in deforested streams are more diversified taxonomically, they are more simplified functionally. Deforestation of streams riparian zones apparently triggers the decline of more specialized species (i.e. rheophilic ones), while favors the establishment of functionally redundant species. This result highlights the role of riparian forests in maintaining the functional diversity of Neotropical streams.