Importância de processos históricos e ecológicos para estruturação funcional de comunidades de peixes de riachos neotropicais

Abstract

Evolutionary and biogeographic history play an important role in shaping patterns of regional diversity of species (i.e., species pool) within and between biogeographic regions. Recent syntheses suggest that these events act from three fundamental processes: speciation, extinction, and dispersal. On the other hand, local ecological processes (i.e., habitat filtering) are recognized to explain the patterns of structure of local communities (e.g., species composition and abundance). This idea has been confronted by large-scale empirical studies, even those that address functional diversity, a facet of biodiversity recognized to be strongly related with ecological processes. Possibly, at large spatial scales, historical and ecological processes act together to explain local patterns of biological diversity. To test this hypothesis, we used a fish database from streams with refined information on environmental conditions, species composition and abundance, as well as information on ecomorphological, trophic and behavioral attributes of two Brazilian biomes: Amazon and Caatinga. Our main aim were: 1) to estimate the importance of phylogenetic history, spatial and environmental factors in explaining the dynamics of fish metacommunities from Caatinga streams; 2) investigate the mechanisms by which Amazonian stream fish assemblages are organized (habitat filtering and limiting similarity) and how they are influenced by historical and ecological drivers; and 3) to determine whether differences in the functional structure of the species pool between Amazon and Caatinga can modulate the importance of stream environmental conditions in predicting the local functional structure of stream fish. For the first objective, we used 27 headwater streams of the Caatinga distributed in three different “brejos de altitude” and evaluated the relative importance of phylogenetic history, spatial and environmental factors in explaining the taxonomic and functional structures of the assemblages. We observed that phylogenetic history explains much of the taxonomic and functional variation of stream fish metacommunities. This result is already expected for the taxonomic approach but represents an important finding for the functional approach. Thus, in small headwater streams of the Caatinga, phylogenetic history appears as an important driver of the functional patterns that would presumably be explained by environmental factors. For the second objective, we used 307 streams distributed in 21 sub-basins of 11 hydrographic basins in the Brazilian Amazon with different evolutionary histories. For example, Western sub-basins show relative historical stability, while Eastern sub-basins have submerged by seawater ~5 Mya ago, which possibly eliminated all freshwater fauna. We built specific null models to investigate how fish assemblages are organized from the global pool of species (375 species) to local assemblages, assuming a dispersion limitation algorithm and that the importance of the environmental filtering and the limiting similarity act at different scales. We found that fish assemblages from Amazon streams are predominantly governed by limiting similarity. In addition, we found that past marine incursion events together with stream environmental conditions and water type modulate the environmental filtering signal and limiting similarity across 21 sub-basins. Thus, we conclude that the consequences of historical events are currently observed in the assembly patterns of assemblages in fish from Amazon streams. Finally, we investigated whether local environmental conditions (e.g., water velocity) yield similar functional structure between 53 streams in the Amazon and 54 in the Caatinga. We found that the functional structure of the species pool differs significantly between biomes and that local conditions do not explain the differences in functional structure between biomes. This result was better understood after performing a balanced parametric resampling technique that samples 10 streams from each biome, in which we found that the greater the difference in the functional structure of the species pool, the lower the capacity of environmental conditions to explain the structure. function of fish assemblages between Amazon and Caatinga. We believe that these results together provide important advances in functional ecology over large spatial scales, particularly for tropical stream fish ecosystems.