Mountains host a variety of unique ecosystems and an incredible number of species because of the temperature changes that come with changes in altitude. However, warming caused by climate change throws a wrench into this system, with tropical mountains being especially vulnerable. Tropical ectotherms (species that rely on behaviour instead of metabolism to maintain their body temperature) may be especially in jeopardy because many already live near the upper limits of the temperatures that they can endure. The limiting factors for species living on tropical mountains are the amount of time when it is warm enough for them to be active to find food, and whether or not they will experience temperatures that are too hot, causing heat stress. A group of researchers led by Martha Muñoz from Yale University, USA, and her colleagues from other US universities investigated how a warming climate will affect three species of mountain anoles on the Caribbean Island of Hispaniola.
Initially, the team focused on two high-altitude species, black-throated stout anole (Anolis armouri) and the Cordillera central stout anole (Anolis shrevei), both of which live on their own mountain ranges on the Caribbean Island of Hispaniola, and a third, widespread species, the large-headed anole (Anolis cybotes), which lives throughout the island, but on the edges of broadleaf forests at lower elevations. Having previously investigated the lizards’ basking behaviours, body temperatures and thermal preferences, the team used these observations to calculate how the lizards might behave at different environmental temperatures. They then built a detailed climate simulation to predict the temperatures that the lizards might experience when basking in the sun versus cooling off in the shade or when hiding while foraging. The team then linked the two models to predict how much time these Anolis species would be able to be active in different future climate predictions. Additionally, they looked at how close the predicted temperatures are to the upper and lower temperatures that these species can tolerate, as well as including predictions for how different types of forest will impact the conditions experienced by the reptiles living there.
Muñoz and her colleagues found that if climate change continues at its current pace, black-throated stout anoles and the Cordillera central stout anoles may be able to be active for an average of 441–472 h more per year than their current activity levels. This is because warmer environmental temperatures will reduce the number of cold mornings that the mountain lizards experience, which currently limits their activity in much the same way that you hesitate to jump out of bed if your room is freezing, but once the heating turns on, you're willing to move about. However, the increased temperatures experienced by the two mountain species won't be so extreme that the lizards are likely to overheat, simply because the slopes they live on are so cold. So, while this combination of predictions is great for the two species of high-altitude lizards, there may be some consequences in the form of the large-headed anole, which currently lives at lower altitudes. If the cloud forest that it inhabits moves up the slope as temperatures increase, this lower-altitude species may be able to invade the habitat of the higher-altitude lizards, directly competing with them for food and habitat.
Climate change is a double-edged sword; as some species enjoy the release from cold constraints, they may also be left simultaneously more vulnerable to invasions from species displaced by climate change. A species’ survival depends on a multitude of factors; studies investigating the effects of climate change must account for many moving parts. In this study, Muñoz and her team looked at broad issues ranging from heat stress to habitat availability, and suggest that future studies take a multi-dimensional approach when assessing species’ vulnerability to climate change to investigate the best potential avenues for conservation.