Range shifts are a common predicted response to climate warming for many species. However, predictions of how species will move often ignore the variation that can occur both between populations of a species and between individuals within populations. Individuals can vary in their thermal phenotypes, with some naturally preferring cooler temperatures and some naturally preferring warming ones. How will this intraspecific variation, which can sometimes be as strong as interspecific variation, affect individual dispersal as a mechanism for species range shift in a changing climate?
In their new paper in Ecology Letters, Bestion et al. look at dispersal under different climatic conditions for common lizards (Zootoca vivipara), who show a greater range of thermal preference within populations than between populations. They first measured preferred temperature (as a proxy for thermal optimum) of neonatal lizards, then released them along with adults in the Metatron, a semi-natural experimental corridor system. Enclosures within the Metatron were kept at either “present climate” or at “warm climate” (~2-3 degrees warmer). They then looked at the probability of an individual dispersing and how dispersal decisions translated into survival probability.
They found that individuals who preferred warmer temperatures were more likely to disperse when placed in “present climate” conditions and less likely to disperse when place in “warm climate” conditions. Individuals who remained as residents in either climatic conditions had preferred temperatures that fell in the middle of the temperature range, whereas individuals who dispersed were more likely to prefer extreme temperatures. Dispersers from “warm climates” survived better when released into “present climate” enclosures than when released into “warm climate” enclosures, suggesting adaptive dispersal decisions. Overall, there was no global change in dispersal propensity in warmer climates, although climatic conditions did change individual dispersal propensity based on natal preferred temperature.
Their results argue for the importance of considering intraspecific variation on thermal preferences and how it may affect dispersal in a warming climate. Differences in dispersal probability could result in the spatial segregation of thermal phenotypes across a gradient that could facilitate local adaptation. By assuming that all individuals of a species will disperse in the same manner in response to temperature changes, range shift models may miss the true population response.