Atlantic Forest birds are more functionally and taxonomically diverse in valley bottoms relative to uplands

Abstract

The theory behind metacommunity was recently reframed to incorporate the concepts of community ecology. Here we investigate how slight topographic variations might locally create habitat heterogeneity and a system of interchanging bird species (i.e., a metacommunity) in a continuous tropical forest. We studied the distribution of birds in a large and protected Neotropical Forest in southwestern Brazil to understand the influence of valley bottom sites on the taxonomic and functional diversity of the bird communities. As previous studies have shown that specialist species have spatially regular distribution when compared to generalists, in the present study we investigate if topography could influence those local patterns of distribution. We expected (1) to find higher taxonomic and functional diversity in communities of valley bottom areas and (2) lower beta taxonomic and functional diversity of the generalists at the valley bottom, but not of specialists, that should exhibit a somewhat consistent distribution. We gathered information on the composition of local bird communities by deploying eight automatic recording units, four in the valley bottoms and four in the uplands, along 4.3 km trail in the forest interior. Our data showed that bird diversity at the valley bottoms tended to be higher than that at the uplands. Specialist passerine assemblages presented high spatial stability and were regularly distributed throughout the forest. In contrast, generalist passerines have limited trait distribution due to valley bottoms. Because bird communities were distinct from each other, deforestation should have stronger impact in the system if only upland areas are left in the landscape. In this case, species dispersal and coexistence as well as complementary traits have predicted implications for the remaining forest fragments, and management actions should prioritize the conservation of forest fragments that include both bottom valleys and uplands areas.