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Zachary K. Lange, Brooke L. Bodensteiner, Daniel J. Nicholson, Gavia Lertzman-Lepofsky, Alexander H. Murray, Edita Folfas, Saúl F. Domínguez-Guerrero, D. Luke Mahler, Martha M. Muñoz, and Luke O. Frishkoff: Read the article
W hat determines the distribution of species? This is a longstanding question in biology, but it is becoming increasingly relevant as climate change and other human-driven factors change environments worldwide. For example, global warming is associated with changes in species’ distributions and survival. This suggests to scientists that temperature may be one of the essential drivers of species’ distributions.
In this study, researchers sought to understand whether the temperature extremes that 21 species of anoles can tolerate, as well as their temperature preferences, are associated with their distribution across Puerto Rico and Hispaniola. To measure the hottest and coldest temperatures the lizards could stand, they gradually increased or decreased the anoles’ body temperatures in the lab until the lizards were no longer able to stand back up after being placed on their backs. The inability of the animal to right itself when placed on its back indicates that they would not be aware enough to escape from harmful situations. So, for example, if a lizard in the experiment could not stand back up at 35 °C, then we would expect this lizard to be unable to escape hot temperatures or hide from predators (likely leading to death for that lizard). Anole temperature preferences were also measured by placing them in an enclosed arena with a gradient of temperatures for them to choose from over three hours.
These values were then compared to the range of temperatures that populations of the corresponding species of anole experience in their natural habitat. This was done to see if the hottest and coldest temperatures the lizards experience in their natural environment could be predicted by the hottest and coldest temperatures the lizards were able to handle in the experiments. The researchers determined these species' distribution limits by visiting various sites across both islands, representing the full range of climates where anoles occur, and searching for anoles in standardized forest plots. Lizards were captured and marked with non-toxic paint before being released. This mark-resight methodology ultimately allowed the researchers to estimate how many individuals of each species were present in each location and, therefore, in each climate. They found that limits measured in the lab and environmental extremes were generally correlated, suggesting that temperature is likely an important factor in determining where species occur. This suggests that as the climate continues to change, we may expect some changes in species distributions.
However, the researchers also found that a species' ability to tolerate a wide range of temperatures in the experiment was not always associated with the species occurring in a wide range of climate conditions. This, along with a relatively large degree of error in the overall model, suggests that other factors, such as competition, predation, and other non-temperature habitat characteristics are partly responsible for setting species’ distributions. The researchers also determined that the conditions where species were most abundant were not best predicted by the temperatures that lizards preferred from lab experiments, demonstrating that the best conditions for population growth may differ from the conditions that individual lizards enjoy the most. While we still don’t know everything that leads to a species’ specific range, this study grants a great deal of insight into the role that temperature may play and the possible limitations of considering just one factor in explaining species’ distributions.
Jamie Cochran is a postdoctoral scholar in Dr. Andrea Durant’s lab at the University of Washington. Jamie’s work lies at the intersection of aquatic entomology, ecotoxicology and organismal physiology and largely looks to understand the interactive effects of stressors on aquatic macroinvertebrate physiology and performance. In her free time, she enjoys traveling, hiking, crocheting, and reading.
