Response of avian diversity to habitat modification can be predicted from life-history traits and ecological attributes

Habitat conversion for agriculture is a major driver of global biodiversity loss, partly because of homogeneity within agri-ecosystems. Anthropogenic landscapes can also increase habitat heterogeneity and primary productivity, however, augmenting regional biodiversity, as species that exploit resources associated with human activities expand their ranges into novel ecological regions. We used birds as a model in the Kruger to Canyons Biosphere, South Africa, to ask whether agriculture can add habitat components and bird species complementary to those already present, and whether habitat variables and bird functional traits can be used to identify bird species most likely to respond to such habitat changes. We surveyed birds and measured habitat structure in 150 fixed-radius point counts each in natural habitat and mango orchards, and assessed relationships between habitat variables and bird functional traits. Despite mango orchards having greater vertical height structure because of tall (average 20 m) Casuarina windbreaks, they were missing the low-scrub (1-2 m woody cover) component of natural vegetation. We found that species whose life-history traits and ecological attributes were associated with structures missing from mango orchards were correspondingly absent from the orchards, which translated into the exclusion of 35 % of the bird species; bird assemblages within mango orchards were only a subset of those found in natural habitat. These findings suggest that knowledge of habitat structure, along with species' functional traits can provide a predictive framework for effects that anthropogenic habitats may have on regional biodiversity, and allow management to reduce negative effects.