Effect of fragmentation on the Costa Rican dry forest avifauna
Deforestation and land use change have reduced the tropical dry forest in the northwestern region of Costa Rica into isolated fragments. We examined the effect of fragment area and length of the dry season (seasonality) on nestedness for the community (entire species matrix), assemblages (forest fragments), and species occupancy across fragments for the native avifauna, and for a subset of forest dependent species. Area or distance between fragments did not correlate with species richness across fragments. Similarity in bird community composition between fragments was related with habitat structure; fragments with similar forest structure have higher similarity in their avifaunas. Fragment area determined the pattern of nestedness of the bird community and species occupancy, but not the nestedness of assemblages across fragments in northwestern Costa Rican avifauna. Forest dependent species (species that require large tracts of mature forest) and assemblages of these species were nested along forest fragments ranked by seasonality gradient, but only occupancy of species nested by fragment area.