An international team of biologists has found an alarming pattern of population extinctions attributable to rising temperatures. If current trends continue, up to 20 percent of all lizard species are predicted to go extinct by 2080. The study was published in the May 14th issue of Science.
The researchers, led by Barry Sinervo, professor of ecology and evolutionary biology at the University of California, Santa Cruz, conducted a major survey of lizard populations worldwide, studied the effects of rising temperatures on lizards, and used their findings to develop a predictive model of extinction risk. Their model accurately predicted specific locations on five continents (North and South America, Europe, Africa, and Australia) where previously studied lizard populations have already gone locally extinct. Based on the predicted probabilities of local extinction, the probability of species extinction was estimated to be 6 percent by 2050 and 20 percent by 2080. As the ongoing extinction of populations is directly related to climate change, limiting the carbon dioxide production that is driving global warming is crucial for avoiding the wave of lizard extinction in future.
"We did a lot of work on the ground to validate the model and show that the extinctions are the result of climate change," Sinervo said. "None of these are due to habitat loss. These sites are not disturbed in any way, and most of them are in national parks or other protected areas." While recent global extinctions of amphibians are not directly related to climate change, but largely due to the spread of disease, the ongoing extinctions of lizards are due to climate warming from 1975 to the present.
The disappearance of lizard populations was first recognized in France and then in Mexico, where 12 percent of the local populations had gone extinct since the lizards had previously been studied. Although the lizards normally bask in the sun to warm up, higher temperatures exceeding their physiological limits keep them in the shade, restricting their activity and preventing them from foraging for food. The researchers used these findings to develop a model of extinction risk based on maximum air temperatures, the physiologically active body temperature of each species, and the hours in which its activity would be restricted by temperature. The model accurately predicted the disappearance of Mexican lizards and was then extended globally to lizards in 34 different families on five continents and validated by comparing the predicted results with actual local extinctions.
Data for African lizards was provided by Villanova University professor Aaron Bauer, whose research focuses on the evolution of geckos and other reptiles in the Southern Hemisphere. Bauer, who is the Gerald M. Lemole M.D. Endowed Chair of Integrative Biology, has worked in southern Africa for more than 20 years and has described more than 100 new species of lizards from around the world. Although the predicted extinction risk for the African lizards studied was low, neighboring Madagascar can expect to lose many species and extensive local extinctions have already been documented. "In many parts of the world, lizards are almost certainly going extinct due to climate change before their very existence is known to biologists" said Bauer, whose research is funded by the National Science Foundation.
Bauer believes that most Americans, particularly those in the northeast, where there are few – often inconspicuous – lizard species, are unaware of their ecological importance. However, the disappearance of lizard populations is likely to have repercussions up and down the food chain. Lizards are important prey for many birds, snakes, and other animals, and they are important predators of insects.
The climate projections used to model extinction risks assume a continuation of current trends in carbon dioxide emissions from human activities. Many of the extinctions projected for 2080 could be avoided if global efforts to reduce emissions are successful, but it may be too late to avoid the losses predicted for 2050.
Funding for this study came from grants from the National Geographic Society, National Science Foundation, and a diversity of international funding bodies.
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Research Team: Barry Sinervo, Fausto Mendez-De la Cruz, Donald B. Miles, Benoit Heulin, Elizabeth Bastiaans, Maricela Villagran-Santa Cruz, Rafael Lara-Resendiz, Norberto Martínez-Méndez, Martha Lucía Calderon-Espinosa, Rubi Nelsi Mesa-Lázaro, Héctor Gadsden, Luciano Javier Avila, Mariana Morando, Ignacio J. De la Riva, Pedro Victoriano Sepulveda, Carlos Frederico Duarte Rocha, Nora Ibargüengoytía, César Aguilar Puntriano, Manuel Massot, Virginie Lepetz, Tuula A. Oksanen, David Chapple, Aaron Bauer, William Branch, Jean Clobert, Jack W. Sites, Jr. Erosion of lizard diversity by climate change and altered thermal niches. Science 328, 5980 (2010).