Putting the heat on lizards: Cimate, physiology and climate impacts across latitude

Background/Question/Methods: Biological impacts of climate warming are predicted to increase with latitude, paralleling increases in warming. However, the magnitude of impacts depends not only on the degree of warming but also on the number of species at risk, their sensitivity to warming and their options for compensation.  Lizards are useful for evaluating risks of warming because their thermal biology is well studied. We conducted macrophysiological analyses of 70 diurnal lizard species from diverse latitudes to assess their physiological and behavioral sensitivity to changing temperatures, and coupled this with a focal species analysis of Puerto Rican Anolis lizards, for which we have extensive data. In our macrophysiological analysis, we examine the influence of latitude, habitat use, basking behavior and phylogeny on critical thermal temperatures (CTmin, CTmax), optimal performance temperatures (To), and body temperatures (Tb).  Our field sites on Puerto Rico have already warmed by 2.1 degrees in the past 35 years.  In our focal species analysis, we use data for several Puerto Rican lizards on thermal preference (Tp), as well as  Tb, To, CTmin and CTmax, all collected 25-35 years ago, to describe the thermal biology of these lizards and predict how warming is affecting their interactions and performance.

Results/Conclusions: Although tropical lowland lizards live in environments that are warm all year, macrophysiological analyses indicate that many tropical lineages are active at low body temperatures and are intolerant of warm temperatures.  These species are abundant in tropical forests, and appear most at risk from warming, as current temperatures are approaching, and in some cases exceeding optimal temperatures during the warmest three months of the year.  Any further increase in temperature should reduce performance and force lizards to retreat to the coolest microclimates, limiting foraging options.  In contrast, most temperate lizards should not suffer reduced performance with warming, even though predicted increases in temperature are greater than in the tropics.  In fact, many species should benefit from higher temperatures. Our focal species analyses show that some tropical forest lizards were already experiencing stressful body temperatures in summer when studied several decades ago. Simulations suggest that warming will not only further depress their physiological performance in summer, but will also enable warm-adapted, open habitat competitors and predators to invade forests. Forest lizards are key components of tropical ecosystems, but appear vulnerable to the cascading physiological and ecological effects of climate warming, even though rates of tropical warming may be relatively low.