Species assembly patterns and protected area effectiveness in times of change: a focus on African avifauna
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The challenge of conserving biodiversity is daunting. Despite some local conservation gains, most indicators of the condition of global biodiversity show declines since the 1970’s, while indicators of the threats to biodiversity all show increases. Humanity has in part responded to the global biodiversity extinction crisis by establishing protected areas (PA) and they are widely considered cornerstones of conservation. However, their efficacy in maintaining biodiversity is much debated. Previous studies have been unable to provide a general answer because of their typically restricted geographic and/or taxonomic focus, or qualitative approach. Using a global meta-analysis with 861 pairwise comparisons inside and outside PAs from 86 studies across five major taxon groups, I tested the hypothesis that PAs achieve significant conservation outcomes measured as higher biodiversity values compared with alternative land covers. I found that globally, PAs typically contain higher abundances of individual species, higher assemblage abundances and higher species richness. Variation in effect sizes among taxa nonetheless underscores that PA efficacy can be context specific. To examine factors driving the context specific nature of PA efficacy, an exact distance, timed point count methodology was used to assess PAs ecological effectiveness in terms of bird assemblages of the Kruger National Park (KNP), South Africa, in the Phalaborwa section. Bird assemblages inside the KNP were compared to matched sites in rural and urban land cover, as well as the connecting habitat matrix outside the KNP. Species richness and abundance were significantly lower inside the KNP compared to other land covers. However, the species assemblages are markedly different. The artificial addition of resources in an otherwise resources poor area, mainly in terms of gardening, provide suitable habitat for a range of species, consistent with the more individuals hypothesis. Large-bodied and ground nesting species are virtually absent outside the KNP. Thus species richness and abundance differences between land cover regions mask insidious changes in species traits. Nonetheless, not formally protected land can contribute positively to the regional biodiversity portfolio. Since an understanding of the mechanisms that structure species assemblages can aid in the consequences of anthropogenic drivers disentangling them, I describe and analyse the body size frequency distributions (BSFDs) of avian assemblages at several spatial scales in the Afrotropical biogeographic realm. I found that the African avifaunal continental BSFD is unimodal and right-skewed. African avifaunal BSFDs are quantitatively dissimilar to the African mammal BSFDs, which are bimodal at all spatial scales. Much of the change in median body size with spatial scale can be captured by a range-weighted null model, suggesting that differential turnover between smaller- and larger-bodied species might explain the shift in the central tendency of the BSFD. My results for the first time quantitatively demonstrate that PAs are a vital component of a global biodiversity conservation strategy. However, I also show that PA ecological effectiveness can be context specific, and understanding which species traits are at risk outside of PAs is critical to predicting their efficacy.