PS 60-22
The role of forests on fish functional complementarity in western Amazonian streams
The functional structure of communities can be measured by the variability in functional traits, which can demonstrate complementarity or redundancy patterns, changeable along environmental gradients. Here, we tested the influence of environmental variables on the functional structure of fish assemblages in Amazonian streams along a deforestation gradient. We focused on the functional traits related to habitat use. We sampled 75 80-m stream reaches, measured one variable at a landscape scale and ten variables at a local scale. We took 13 morphological measurements from each fish species, which were used to calculate eight ecomorphological traits (related to water flow adaptations, swimming ability, and position in the water column) used to calculate the net relatedness index (NRI) and the nearest taxon index (NTI). Positive values of these indices indicate functional redundancy, and negative values indicate functional complementarity. We conducted a Redundancy Analysis to investigate the relationship between functional composition and environmental variables, a multiple linear regression to test the relationship between NRI and NTI and environmental variables, a QE-based index to describe the species as to its originality, and a hierarchical partitioning to identify the relative importance of each environmental variable in predicting the occurrence of each species.
Results/Conclusions
The first two axes of the RDA were significant (F = 2.6, P = 0.001) and explained 86.5% of the relationship between ecomorphological traits and environmental variables (proportions of forests, rocks, silt, gravel, attached vegetation, coarse litter, branches and trunks). Species with broad pectoral fins were associated with gravel, rocks, branches and trunks, which indicate hard-substrate dwelling habits; species with deep bodies, common in those that explore the water column, were associated the most to silted sites; small characins were associated to sites with great proportion of coarse litter, which was also associated with forests. Only the proportion of coarse litter and forests were related (negatively) to functional indexes. This result shows that the set of functionally distinct species (complementary assemblages) occurs in sites with greater proportion of coarse litter and forests. This is driven by the presence of original species, such as Carnegiella strigata and Gymnorhamphichthys petiti. Due to the dependence of fish communities on allochthonous matter from forests, the basin vegetation must be preserved to maintain the supply of coarse litter in Amazonian streams.