Poças de rios intermitentes como modelos de metacomunidade: qual processo explica a organização desses sistemas?

Abstract

A metacommunity is a set of local communities linked by dispersal with possible interactions between them. In this context, the local and regional scales are addressed in the theory by the environmental and dispersal factors occurring in the communities. The dispersal will happen regionally, among the metacommunities patches (local communities), and the local process (the environmental factors and species interactions) will occur within each metacommunity patch. Currently, the metacommunities theory is based on four conceptual perspectives, neutral, patch dynamics, mass effects and species sorting, which guide the empirical studies. The main distinction among those perspectives is based on the habitat heterogeneity and dispersal capacity of the species. In the present study, we aimed to understand how fish metacommunities in intermittent rivers are structured through analyzes of species composition and abundance, environmental, biotic interaction (predation) and spatial data. We sampled the fish assemblages in pools of eight rivers sites located in three watersheds from semiarid region of Brazil. The number of seine haul were proportional to the size of each water pool and the environmental characterization was done by measuring variables that represented the micro and mesohabitat. The spatial variables were obtained through the geographic coordinates of each pool. Through analysis of variance partitioning (pRDA) and distance decay similarity relationship (DDR) we observed that spatial factors were the ones that most explained the variation in the fish community (patches). However, this result was observed only when analyzed on a large scale (all pools sampled). When analyzed at smaller scale (pools within rivers sites) the environmental factors were also determinant for structuring the fish communities. Predation also played a relevant role and when analyzed separately from environmental and spatial factors, it was the factor that most explained the variation of the fish communities. Our results highlight the importance of spatial processes through the limitation of dispersion, and scale used in structuring metacommunities, but also outlines how the spatial context of the intermittent river system can be determinant in structuring fish communities. Biological interactions, such predation, may also be relevant when taken into account. We also highlight how the use of two methods of analysis can bring complementary information to metacommunity studies. Finally, we could attest how fish metacommunities in intermittent rivers are structured mainly by the influence of spatial factors, with the dispersal mode of organisms and spatial context of the river system accentuating the dispersal limitation. In local scale, environmental factors also played a significant role in shaping the metacommunities through deterministic process such as predation and species sorting.