Research has demonstrated that differing levels of genetic diversity within a species can affect how populations respond to disturbance, interact with other species and expand into new ecological niches. The geographic variation in within-population genetic diversity is therefore an important factor in explaining species co-existence, speciation, extinction and ultimately, species responses to environmental change. Here we test 11 geographic, ecological and historical hypotheses that may explain the distribution of intraspecific genetic diversity using six tree species, and tested one of the 11 measures, latitude, with an expanded 129-species data set. When tested with six species, the hypotheses that correlate significantly with genetic diversity are ecological in nature: current ecological suitability calculated as probability of occurrence from the species distribution model, distance to the centre of the ecological niche, the distance to the edge of the ecological niche and the ratio of position in the ecological niche (distance to centre/distance to edge). When tested with 129 plant and animal species, latitude, a measure that confounds geography, ecology and history, also showed a significant correlation with genetic diversity. These results suggest that ecological niche position may be more important than geographic range position in determining spatial patterns in genetic diversity, but that further tests with larger datasets are needed for confirmation.
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