Human infrastructure, surface water and tree cover are important drivers of bird diversity across a savanna protected area-mosaic landscape

Abstract

Context: Protected areas are important in mitigating threats to biodiversity, including land conversion. Some of the largest protected areas are located in biodiverse savanna systems where a mosaic of land-uses exist beyond their borders. The protected areas located in such systems are often host to threatened species and diverse animal communities. In spite of the ecosystem services birds provide, we do not know how functionally and evolutionary diverse the community is in north-eastern South Africa, or what the drivers of such diversity are inside and outside one of the world’s largest savanna protected areas: Kruger National Park (KNP). Objectives: Firstly, we aimed to investigate how bird species richness, functional richness, phylogenetic and beta diversity (including its components), and rarity differed across the KNP protected area and its adjacent mosaic. Secondly, we aimed to investigate the habitats and proximity to the KNP boundary that drove patterns across three biodiversity metrics. We also investigated whether differences in sample sizes of the citizen science data we employed, impacted results in a significant manner. Methods: To investigate our aims, we used bird species records from the Southern African Bird Atlas Project 2 (a citizen science project that collects data at a 5 min latitude by 5 min longitude resolution), and for elucidating drivers of community composition, we used a finer scale remotely sensed product. Results: Human infrastructure, water sources and tree cover were overall the most significant and strongest drivers of bird diversity in the region; however, the patterns were complex. Specifically, we found that species richness was strongly and positively influenced by seasonal water and infrastructure mostly inside the protected area (KNP). Most significantly and somewhat concerning, though, were the strong negative effects that infrastructure had on bird functional and phylogenetic diversity inside KNP and, to a lesser extent, inside the mosaic. Seasonal water had a similarly strong but positive effect on species richness in the protected area, a random sub-sample of the former and the mosaic. Tree cover also had a negative and significant effect across the region on phylogenetic diversity and was the strongest driver of this diversity metric. Conclusions: Our results displayed the significant but negative influence that relatively little infrastructure had on bird functional- and phylogenetic diversity inside the KNP protected area despite its positive effect on species richness. Water sources across the protected area-mosaic landscapes also significantly affected regional savanna bird community richness. An increase in tree cover negatively affected phylogenetic diversity inside and outside the protected area as well as the mosaic: a similar finding to other studies in South African savanna systems. We showed the importance of habitat heterogeneity, specifically its components such as infrastructure, freshwater systems and tree cover, and how these impact independently and differently on bird communities across a large biogeographical savanna region.