Land cover change homogenizes functional and phylogenetic diversity within and among African savanna bird assemblages

Abstract

Conversion of natural ecosystems into anthropogenic landscapes can result in biotic homogenization, whereby differences in species composition among sites are diminished through colonization or local extinction. This may reduce the resilience of assemblages to further perturbation and the range or quality of ecosystem services they offer. We investigate how land cover change has altered patterns of compositional, functional and phylogenetic diversity of avian communities in a typical African savanna. We investigate if there has been selection for closely-related or functionally similar species with increasing land use intensity and how this has affected alpha and beta components of diversity. We conducted point counts over 2 years in four distinct land cover types (urban, rural, protected and a transitional matrix), representing a gradient of land cover change. We compared alpha and beta phylogenetic, compositional and functional diversity between sites to assess whether land cover change has homogenized avian communities. While alpha diversity tended to be higher in transformed land cover types (urban, rural and matrix), measures of beta diversity among sites within these types were significantly lower than beta diversity within the protected area. Furthermore, assemblages in transformed areas were functionally and phylogenetically more similar than expectation based on a null model, particularly in the urban area. While transformed areas may support higher diversity than natural habitats inside the protected area, human impacts are filtering for species with specific traits and thus homogenizing functional and phylogenetic diversity within and between sites in our study system.