Human-habitat associations in the native distributions of alien bird species.
The role of human tolerance is increasingly being proposed as a key driver of invasion success by alien species. Human-habitat associations may facilitate both transport - making a species more available for introduction - and establishment - by creating environmental matching between human-altered habitats at the sites of origin and introduction. Nevertheless, the assumption that alien species exhibit associations with human habitats in their native ranges has been largely overlooked. We conduct the first global assessment of the relative importance of human-habitat associations in shaping the native distributions of species introduced world-wide, in relation to other key important drivers, that is climate and land-use. For this, we applied deviance partitioning analysis and species distribution models (SDM) to 776 introduced alien bird species from five continents. While an independent effect of climate, and a joint effect of climate and non-urban land uses, appear as major factors governing alien species distribution in their native ranges, significant independent contributions of anthropogenic variables were found for most species. The effect of anthropogenic variables was mostly positive, or concave with highest responses at intermediate values. Notably, human-habitat associations in the native distributions of alien birds were significantly higher than expected, relative to a pool of available species from the same bird families (N = 3,565). Thus, introduced alien birds are a non-random sample with respect to their association with human-altered habitats. However, an increase in introduction rates of species showing no response, or a negative response, to human influence has occurred over recent decades. Synthesis and applications: To prevent invasions, understanding which species are most likely to become successful aliens outside their native range is essential. Our results support the hypothesis that association with humans may be an important driver of alien bird species distribution in their native ranges, and thus increase the likelihood that these species will end up being introduced and established elsewhere. To provide policymakers with robust predictions of invasion risk, we recommend including human-habitat associations in invasion risk assessments, and accounting for them in species distribution models.