Recent research suggests that anthropogenic impacts on ecosystems act selectively against animals in higher trophic levels. However, there have been few empirical analyses of the influence of broad-scale landscape alteration on the functional composition of ecological communities. We examined the taxonomic and functional composition of the South African avifauna inside and outside protected areas, pairing equivalent and well-sampled cells at a quarter-degree resolution using the South African bird atlas, the South African National Land Cover data set, and ancillary environmental data. The control data consisted of cells in protected areas; the treatment consisted of paired cells in landscapes used primarily for row crops. 

Results/Conclusions

Our functional classification placed 826 species of bird into 9 different functional groups. The results showed that while protected areas contain more species in total than areas under agriculture, this trend is not uniform across functional groups. Numbers of scavenger and raptor species were higher in protected areas, supporting the hypothesis that trophic collapse occurs top-down. Numbers of nutrient disperser and grazer species were higher in agricultural areas. In general, studies of broad-scale biodiversity change (such as the Millennium Ecosystem Assesment scenarios) that have assumed a high degree of species loss in agricultural areas may be painting a darker picture than the data suggest. Since anthropogenic impacts operate selectively on particular functional groups, efforts to conserve avian biodiversity outside protected areas may be best focused on understanding and reversing the decline of groups (such as scavengers) that appear to be at particular risk in agricultural landscapes. Our analysis also shows unambiguously that protected areas in South Africa are serving a useful role as islands of habitat for a set of functionally important species that might otherwise be lost from the system.