Spatial phylogenetics of butterflies in relation to environmental drivers and angiosperm diversity across North America

Broad-scale quantitative assessments of biodiversity and the factors
shaping it remain particularly poorly explored in insects. Here, we
undertook a spatial phylogenetic analysis of North American butterflies
via assembly of a time-calibrated phylogeny of the region coupled with a
unique, complete range assessment for ~75% of the known species. We
utilized a suite of phylodiversity metrics and associated environmental
data to test whether climate stability and temperature gradients have
shaped North American butterfly phylogenetic diversity and endemism. We
also undertook the first direct, quantitative comparisons of spatial
phylogenetic patterns between butterflies and flowering plants in North
America. We expected concordance between butterflies and angiosperms based
on both shared historical environmental drivers and presumed strong
butterfly-host plant specializations. We instead found that biodiversity
patterns in butterflies are strikingly different from flowering plants in
some regions of the continent. In particular, the warm desert regions of
the southwestern United States and Mexico showed surprisingly high
butterfly phylogenetic diversity and endemism, in contrast to much lower
values for angiosperms. Butterflies did not show patterns of phylogenetic
clustering as found in flowering plants, suggesting differences in habitat
conservation between the two groups. Finally, we found weak relationships
and spatially structured biases in relative branching timing between
angiosperms and butterflies. These results suggest that shared
biogeographic histories and trophic associations do not necessarily assure
similar diversity outcomes. The work has applied value in conservation
planning, documenting warm deserts as an important North American
butterfly biodiversity hotspot.