The spatial distribution of threatened species: macro-scales and New World birds

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Abstract
Despite the urgent need to understand how threatened species are distributed across the globe, empirical analyses of geographical patterns of threat at large scales across physically, rather than politically, defined areas are scarce. Here, we examine the geographical distribution of threatened species in the avifauna of the New World, across an area spanning the tropics and two temperate regions. Both the absolute number and the proportion of threatened species in an area are highest in the tropics; the latter is especially high in the Caribbean and Brazilian coastal forest areas. Areas in the southern hemisphere, areas with high levels of endemism, and areas rich in species and higher taxa have high numbers of threatened species. Tropical areas may contain more threatened bird species either because these areas suffer higher levels of threatening processes, or because they are inhabited by species which, on average, are more vulnerable to given levels of threatening processes. We present evidence that both of these mechanisms may cause the patterns of threat observed in this avifauna. Whereas the general coincidence between areas rich in species, higher taxa and threatened species could give cause for optimism that strategies aimed at protecting one aspect of biodiversity might also protect others, we put forward reasons why such optimism may be premature, and urge caution when interpreting the consequences of these patterns for conservation.