Global change is restructuring biotic communities, altering species interactions, and eroding ecosystem services. The foraging composition of animal communities may inform predictions of species interactions and ecosystem service provisioning. Savannas are experiencing widespread shrub encroachment and land-use intensification that endangers biodiversity and threatens human livelihoods. Birds are an ideal model for describing associations among community compositional change, shrub encroachment, and land-use intensification in savannas because birds make important contributions to ecosystem services and their diets have been described. We quantified associations among bird foraging group composition, shrub encroachment, and land-use intensification by sampling bird abundance from December 2014-March 2015 at 371 sites on 4 occasions across gradients of shrub-encroachment and land-use intensity in the Lowveld of Swaziland. The land-use intensity gradient included, from lowest to highest intensity: protected areas; community pastures; subsistence agriculture; and sugar cane plantation. We related foraging group composition to land-use intensity and shrub encroachment using a hierarchical abundance model that accounted for imperfect detection.
Results/Conclusions
The foraging group composition of savanna bird communities shifted away from granivory in open savanna toward frugivory and nectarivory in shrub-encroached savanna. The relative abundance of predatory birds also increased with shrub encroachment and this change was strongly moderated by land-use intensity. Shrub encroachment frequently interacted with land-use intensity in predicting foraging group composition, creating divergent implications for ecosystem service provisioning among land-use types. This creates challenges for managing bird diversity and associated human benefits in the face of continued land-use intensification and shrub encroachment. Further, predatory bird relative abundance was strongly associated with interactions among land-use and land-cover gradients, suggesting that species interactions may be an important driver of bird community assembly in the world’s rapidly-changing savannas.