Abstract. How dispersal, environmental filters, and local extinctions affect species diversity depends on the species requirements for habitat, dispersal limitations, and abundance. Few studies have been able to properly separate these processes and to show how they affect the beta diversity patterns for multiple organisms. We investigated how the composition of birds and mammals changed along geographical and environmental gradients in an environmentally complex South American region. Using mantel tests and a null model approach we disentangled the effects of dispersal, environment, and stochastic processes in the species beta diversities. The similarity on species composition was negatively associated with the geographical distance separating areas for both groups. The changes in bird species composition likely resulted from their dispersal limitation over large geographical regions. In contrast, the composition of mammals in a given area was a partially random subset of the regional species pool, to some extent, filtered by the vegetation. Small communities tended to have more variable species composition, whereas dispersal limited birds showed a stronger distance-decay pattern. Neither local randomness nor dispersal limitation prevented species from being filtered by the environment. Other groups are likely to show similar patterns depending on their dispersal abilities, environmental requirements and community size.

Many animal species participate in interspecific groups which can provide benefits such as better detection of predator presence, but may also lead to costs such as interspecific competition. In interspecific groups, species with particular functional traits should be aggregated in a way that maximizes the benefits and minimizes the costs of these interactions. Further, the balance between costs and benefits depends on the resource availability and the spatial scale in which species interact. We aim to determine how species traits are distributed within and among interspecific groups and how intrinsic (group size) and extrinsic (environmental conditions) factors relate to aggregation patterns. We surveyed 192 bird species distributed in 355 mixed-species bird flocks along an environmental gradient in southwest Brazil and analyzed data at both scales of individual flocks (n = 355) and sites (n = 29). We used mixed-effect and multiple regression models to test if the functional richness of coexisting species changes with increasing group size and in response to environmental covariates that may influence the selection of specific traits. Using a null model approach, we inferred the differences between observed and simulated associations (random expectations). We found that groups with more than 20 species have greater diet variation (i.e. more omnivores) and are more similar in body mass than expected randomly. Indeed, larger groups consume more resources, increasing competitive dynamics and decreasing facilitation among species. Thus such groups should take advantage of a more profitable trait variation among co-occurring species. Our results suggest that the distribution of species in close associations is determined mostly by ecological processes occurring at local scales (i.e. not dependent on regional spatial context). Additionally, larger groups maximize foraging trait variation (diet diversity) and minimize predator scape variation (similar body mass) potentially increasing the benefits of the aggregation.

This study presents data on behavioural acts performed by the Common Moorhen Gallinula chloropus in southern Brazil, and compares these with the behaviours previously reported for other populations. Focal observations of individuals were conducted in the municipality of Santa Maria, in the central region of the state of Rio Grande do Sul, Brazil. The sampling was done in 2-hour sessions, between January and March of 2007. A total of 20 behavioural acts, grouped in seven categories, were identified and described: locomotion (N=5 acts), grooming (N=4), intra-specific behaviour (N=2), inter-specific behaviour (N= 3), foraging (N=2), reproduction (N=2) and rest (N=2). Among the observed behaviours were acts that are not described in the literature such as greeting of offspring and some feeding acts. Regarding the use of habitat, we observed that this species has a preference for water or aquatic macrophytes, which is contrary to other reports. In the analysis of behavioural daily variation, overall behavioural categories did not vary significantly throughout the day,

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