Physiological and morphological traits affect contemporary range expansion and implications for species distribution modeling in an amphibian species

Species range shifts due to climate alterations have been increasingly
well-documented. Although amphibians are one of the most sensitive groups
of animals to environmental perturbations due to climate change, almost no
studies have offered evidence of poleward distribution shifts in this
taxon in response to climate warming. Range shifts would be facilitated by
variation in traits associated with the ability of species to persist
and/or shift their range in the face of climate change, but the extent and
consequences of intraspecific variation in these traits is unclear. We
studied the role of intraspecific variation in the ongoing range shift of
green treefrogs (Hyla cinerea) in response to climate change. We explored
factors that are often associated with range shifts to test the hypothesis
that there are differences in these traits between recently range-expanded
and nearby historical populations. We then tested the consequences of
intraspecific variation for modeling climate-induced range shifts by
comparing species distribution models (SDM) that used as input either data
from the entire species range or separate inputs from ‘subpopulations’
corresponding to the historical range or the recently-expanded range. We
expected that building a separate SDM for each population would more
accurately characterize the species range if historical and expanded
populations differed in traits related to their response to climate.
 We found that critical thermal minimum decreased and thermal
breadth increased with latitude, but the effect of latitude was
significantly stronger for expanded populations compared to historical
populations. Additionally, we found that individuals from expanded
populations had longer leg lengths when compared to their historical
counterparts. Lastly, we found higher model accuracy for one of the
population-level SDMs than the species-level SDM. Our results suggest that
thermal tolerance and dispersal morphologies are associated with amphibian
distributional shifts as these characteristics appear to facilitate rapid
range expansion of a native anuran. Additionally, our modeling results
emphasize that SDM accuracy could be improved by dividing a species range
to consider potential differences in traits associated with climate
responses. Future research should identify the mechanisms underlying
intraspecific variation along climate gradients to continue improving SDM
prediction of range shifts under climate change.