The Role of Stochastic and Deterministic Processes in Structuring Neotropical Bat Communities

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Abstract
The extent to which deterministic or stochastic processes affect the composition and morphological structure of communities is an intense debate in evolutionary ecology. For many years, competition was considered to be the dominant deterministic factor that affected structure of animal communities. More specifically, interspecific competition can affect morphological patterns within communities by either size assortment or size adjustment. We investigated the extent to which size assortment could have structured bat assemblages from two well-defined bat communities from northeast Brazil by comparing real ecomorphological characteristics (mean and variance of segment lengths of minimum-spanning trees from principal component scores) to the distribution of like statistics obtained from simulations derived from nested-species pools. Regardless of species pool, the ecomorphological patterns of bat assemblages were no more structured than expected by random selection of taxa from the available species pool. This was true for frugivorous, nectarivorous, and foliage-gleaning insectivorous guilds, and for the phyllostomid community in general, from both Caatinga and edaphic Cerrado biomes. The alternative hypothesis, that coevolutionary processes determine ecomorphological patterns in these neotropical communities, similarly is not supported by our results. The characteristic spatial and temporal heterogeneity of northeast Brazil, combined with the mobile nature of bats, could decrease the intensity, pervasiveness, or predominance of deterministic interactions, thereby leading to an ecomorphological structure indistinguishable from that produced by stochastic processes.