THE ROLE OF LOCAL AND REGIONAL FACTORS IN THE FORAGING ECOLOGY OF BIRDS ASSOCIATED WITH POLYLEPIS WOODLANDS

Understanding the extent to which patterns of functional structure are repeated in space and the scale at which different factors (local and regional) operate to explain community patterns are of important in community ecology. I studied the extent of spatial variation in foraging ecology of birds in the Polylepis community, a vegetation system of the Andes, in regard to variation in local (vegetation structure, floristic composition, food resources) and regional factors (biogeography). Specifically, I studied foraging ecology of nine insectivorous bird species (and the assemblage they conform) across twelve disjunct woodlands embedded in three biogeographic regions of the Peruvian Andes. I examined spatial variation in foraging ecology at species level by assessing intraspecific variation in two foraging niche components: niche breadth, a relative measure of how specialist or generalist is a species relative to other species in the community; and niche plasticity, a measure of how restricted or plastic are intraspecific regularities in the niche. Results indicate that foraging strategies of birds varied from specialist-restricted to generalist-plastic. Moreover, foraging strategies seemed to be influenced mostly by fluctuations in local factors, in particular food resources. Lack of variation in foraging of the specialist-restricted species, despite fluctuations in local factors across Polylepis woodlands, may be a consequence of past events in the evolutionary history of the species that set a limit to the range of possible responses within a population, constraining the foraging niche. Lastly, I assessed the extent of spatial variation in the structure of avian assemblages using the guild approach, and focused on a) the relationship between food resource abundance and richness and abundance of birds within guilds; and b) the role of competition, using null models to determine if niche overlap in the assemblages were consistent with competition theory. Results revealed that guilds were largely consistent across woodlands but the number and identity of species associated with each guild was not so, which could be attributed to regional differences in species richness and intrapopulation variation in foraging ecology. Assemblage structure was not consistent with classic competition theory, but food resources were relatively more important in explaining patterns