Genetic and species-level biodiversity patterns are linked by demography and ecological opportunity

The processes that give rise to species richness gradients are not well
understood, but may be linked to resource-based limits on the number of
species a region can support. Ecological limits placed on regional species
richness should also affect population demography, suggesting that these
processes could also generate genetic diversity gradients. If true, we
might better understand how broad-scale biodiversity patterns are formed
by identifying the common causes of genetic diversity and species
richness. We develop a hypothetical framework based on the consequences of
regional variation in ecological limits set by resource availability and
heterogeneity to simultaneously explain spatial patterns of species
richness and neutral genetic diversity. Repurposing raw genotypic data
spanning 38 mammal species sampled across 801 sites in North America, we
show that estimates of genome-wide genetic diversity and species richness
share spatial structure. Notably, species richness hotspots tend to harbor
lower levels of within-species genetic variation. A structural equation
model encompassing eco-evolutionary processes related to resource
availability, habitat heterogeneity, and contemporary human disturbance
supports the spatial patterns we detect. These results suggest broad-scale
patterns of species richness and genetic diversity could both partly be
caused by intraspecific demographic and evolutionary processes acting
simultaneously across species.