Tropical ectotherms such as anoles are considered to be especially vulnerable to climate change. Given that tropical lizards already function near their upper tolerances, even a modest increase in ambient temperature can have disproportionately large negative fitness consequences. Most models that predict how climate warming will impact tropical ectotherms rely on ambient temperature. Michael Logan, a graduate student at Dartmouth College, presented a study suggesting that temperature alone is insufficient to predict the impacts of environmental warming on organismal fitness. He points out that other abiotic factors, such as humidity and wind speed, may be equally important in determining whether and how organisms will be impacted by climate warming.
For this study, Michael explored how daily variation in temperature, humidity, and wind speed interact to determine the abundance of two species of anole, Anolis allisoni and A. lemurinus, from the Bay Islands of Honduras (see map above). He deployed sensors that recorded temperature, humidity, and wind speed in a forest site, where A. lemurinus is found, and an open-habitat site, where A. allisoni is found.
Contrary to expectations, he found that environmental temperature alone is a poor predictor of lizard abundance in the open habitat. Rather, wind speed constrained lizard activity in the open habitat more than any other environmental factor. Further, environmental temperature predicted lizard abundance only when wind speed was low. Michael posits that there might be a trade-off between thermoregulation and evaporative water loss on windy days, such that the ability to achieve high body temperatures through basking may be counterbalanced by the ability to maintain water balance. Michael found that in the closed forest habitat, the variance in environmental temperature and the degree to which the temperature varied from the lizard’s optimal range were important predictors of A. lemurinus abundance. These results suggest that this species might thermoregulate more than was previously thought, as forest anoles are generally considered to be thermoconformers.
Together, Michael’s results suggest that factors besides temperature are important determinants of lizard abundance, and that they should be more explicitly considered in predictive models for the biological impacts of climate warming.