PERES-NETO, Pedro R.; University of Quebec at Trois-Rivieres: Patterns in the co-occurrence of fish species in streams: the role of site suitability, morphology and phylogeny versus species interactions

A number of studies at large scales have pointed out that abiotic factors and recolonization dynamics appear to be more important in structuring stream-fish assemblages than biotic interactions. In contrast, experimental and field studies at small scales show the importance of competition among stream fishes. However, given the highly variable nature of stream systems over time, competition may not be intense enough to generate complementary distributions via competitive exclusion at larger scales. Complementary distribution is a recurrent pattern observed in fish communities across stream gradients, though it is not clear the instances whether this pattern may be due to competitive interactions or to individual species requirements. In this study, I introduce a series of null models developed to provide a more robust evaluation of species associations by facilitating the distinction between different processes that may shape species distributions and community assembly. These null models were applied to test whether conspicuous patterns in species co-occurrences are more consistent with their differences in habitat use, morphological features and/or phylogenetic constraints, or with species interactions in fish communities in streams of an eastern Brazil watershed. I conclude that patterns in species co-occurrences within the studied system are driven by common species-habitat relationships and species interactions may not play a significant role in structuring these communities. I suggest that large-scale studies, where adequate designs and robust analytical tools are applied, can contribute substantially in understanding the importance of different types of processes in structuring stream-fish communities.