Assembly patterns of mixed-species avian flocks in the Andes

The relative contribution of deterministic and stochastic processes in the assembly of biotic communities is a central issue of controversy in community ecology. However, several studies have shown patterns of species segregation that are consistent with the hypothesis that deterministic factors such as competition and niche-partitioning structure species assemblages in animal communities. Community assembly provides a theoretical framework for understanding these processes, but it has been seldom applied to social aggregations within communities. In this research we assessed patterns of non-randomness in Andean mixed-species flocks using three assembly models: (a) co-occurrence patterns (b) guild proportionality; and (c) constant body-size ratios using data from 221 species of resident and Neotropical migrant birds participating in 311 mixed-species flocks at 13 regions distributed in Venezuela, Colombia, Ecuador, and Peru. Significant assembly patterns for mixed-species flocks based o...