Determinants of genetic diversity and species richness of North American amphibians

Aim: Ecological limits on population sizes and the number of species a
region can sustain are thought to simultaneously produce spatial patterns
in population genetic diversity and species richness due to the effects of
random drift operating in parallel across population and community levels.
Here, we test the extent to which resource-based environmental limits
jointly determine these patterns of biodiversity in amphibians. Location:
North America. Taxon: Amphibians. Methods: We repurposed open, raw
microsatellite data from 19 species sampled at 554 sites in North America
and mapped nuclear genetic diversity at the continental scale. We then
tested whether ecological limits defined by resource availability and
environmental heterogeneity could simultaneously shape biogeographic
patterns in genetic diversity and species richness with structural
equation modeling. Results: Spatial patterns of population genetic
diversity run opposite patterns of species richness and genetic
differentiation. However, while measures of resource availability and
niche heterogeneity predict 89% of the variation in species richness,
these landscape metrics were poor predictors of genetic diversity. Main
conclusions: Although heterogeneity appears to be an important driver of
genetic and species biodiversity patterns in amphibians, variation in
genetic diversity both within and across species makes it difficult to
infer general processes producing spatial patterns of amphibian genetic
diversity. This result differs from those found in endotherms and may be
due to the considerable life history variation found across amphibians.