Relative influence of local and landscape factors on bird communities vary by species and functional group

Abstract

Introduction

Both fine scale patterns of vegetation and coarser scale landscape patterns affect bird community composition, but the relative importance of these two sets of patterns tends to be context dependent, varying by location and taxonomic group. Here, we explore the relative roles of landscape pattern and stand structure and composition in defining bird communities in 44 remnant oak stands in the Willamette Valley, Oregon. We focused on: (1) whether bird communities are influenced more by landscape (matrix and patch) patterns or stand composition and structure, and (2) in what contexts each of these spatial scales are more important. Specifically, we focused on how different groups of bird species (functional groups, synanthropic and non-synanthropic species, and individual species) were differentially influenced by landscape and more local patterns.

Methods

We conducted point counts to determine avian abundance, richness and evenness and categorized birds into functional groups based on diet and foraging tactics. We then used canonical correspondence analysis and generalized linear models to analyze overall community patterns, functional group diversity, synanthropic and non synanthropic species diversity and individual species’ abundances.

Results

Both local and landscape factors significantly influenced each group of avian species for every measure of diversity we tested, but their relative importance varied markedly. Local factors explained four times more variance than landscape factors for overall species diversity, whereas for functional groups, landscape factors explained one quarter to ten times the variance of local factors, depending on the group. For example, landscape factors were five times more important for the corvidae omnivores and ten times more important for the flycatchers than were local factors. By contrast, local factors were twice as important for seed eaters, frugivores and ground foragers, and bark foragers than were landscape patterns. We found the same high variability for individual species.

Conclusion

We conclude that the relative contribution of factors at different scales to the structuring of bird communities (as with the effects of so many other ecological processes and patterns) strongly depends on context—in this case, the specific group of species being considered.