Research Communications

Vanishing Act 

Biologist Don Miles searches for the lizards-declining on a hotter planet-that hold clues to wildlife diversity, behavior, and ecology

June 3, 2011

The lizards were missing.

From the bogs of Buzy, France, to the deserts outside Mexico City, a group of biologists searched for the lizards theyíd seen a few years before. Though it should have taken 5 to 10 minutes to spot a native spiny lizard or common lizard, they spent fruitless hours peering at cacti or clumps of heather.

"Everything looks like it should support a lizard population, and yet theyíre not there," says Ohio University biologist Don Miles.

Miles and an international team of colleagues suspected that climate change was to blame. They already had begun monitoring lizard populations around the world to determine the consequences of climate warming, from shifts in breeding behavior to changes in the patterns of light-absorbing melanin that decorate many lizards' backs.

Don Miles
Don Miles. Photo credit: Kevin Riddell

"We thought there would be adaptation," Miles says. Instead, they were looking at extinctions. When the data rolled in from Australia to California to Madagascar, as many as 21 percent of local lizard populations had disappeared. A computer model they built predicted that 20 percent of all lizard species will be gone by 2080.

The team's combination of field research and a survey of global data online showed definitively that climate change was the culprit. They made sure to "quadruple" their lizard search efforts at each site to avoid recording false extinctions, Miles says, and avoided sites where the habitats themselves had been disrupted by human activity, in order to exclude factors other than a warming environment.

"What is alarming to us is the speed with which we're seeing populations vanish," he says. "To witness the decline and extirpation of populations in a few years is frightening and depressing."

The team reported its results in the journal Science in May 2010. Previous work had shown that amphibians are going extinct globally, but this was the first study to show a similar decline in lizards-and tie it directly to climate change.

"A lot of us had been thinking about what the impacts of climate warming would be on lizards in the future," says Raymond Huey, a professor and chair of biology at the University of Washington who wrote a review of the Science paper. "But I think none of us was expecting that itís already had major impacts."

More than lizards are at risk, too. "Entire ecosystems are collapsing," says University of California, Santa Cruz ecologist and evolutionary biologist Barry Sinervo, a longtime collaborator of Miles' and lead author on the Science study. "The lizards are just a harbinger of things to come."

Many herpetologists had thought that lizards could take the heat. However, as Miles discovered, they're "being hammered by rising temperatures," which limits their ability to hunt and impacts their reproductive success.

In Mexico, Miles observed that temperatures climbed most significantly from January to April, when female viviparous lizards carry their developing young in utero. The females' body temperatures rise, in turn, damaging the unborn lizards. Meanwhile, in Europe-which suffers not only from hotter temperatures, but longer and more frequent warm spells-the nests of the genus Lacerta heat up and can kill the embryos inside.

Madagascar, where 21 percent of local lizard populations have disappeared, is an extinction hotspot. Species in five lizard families, including chameleons and gekkos, have been impacted. (Photos courtesy of Ignacio de la Riva.)

Miles and colleagues already are documenting additional climate-driven changes in lizard populations on five continents. He received a grant from the National Science Foundation to determine whether climate change is affecting when lizards lay their eggs and how well their hatchlings survive. He's trying to find out what happens if lizards donít hibernate during higher winter temperatures. Miles continues to revisit sites across the southwestern United States and Mexico to check if lizards are still there, and is building a database with information about each location. In addition, he's measuring and comparing temperatures at sites where lizards have and haven't gone extinct.

Ultimately, Miles says, "We're hoping to achieve a model to explain the risk of extinction of a population as a consequence of rising temperatures, and to find the critical stage of a life cycle that allows a species to persist or not." Because lizards have an important role in the many ecosystems in which they occur, their absence could reverberate up and down the food chain-from the insects they eat to the birds, snakes, and mammals that eat lizards.

Scientists also might lose key information on species diversification. Studying the "remarkable diversity of shapes and colors" that allow lizards to exploit their specific habitats can teach us about the behavior and ecology of other species- including our own, Miles says. In addition, understanding how different lizard lineages have diversified will allow biologists to look for patterns across many kinds of animals and explain why there are so many species on the planet.

"We can learn a lot about how the world is structured by looking at lizards," he notes.

Miles, who has studied lizards since he was a boy, is especially fascinated with how lizards, birds, and other animals adapt to their environments, and how various processesósuch as time, natural selection, reproductive isolation, and invasions of new species-affect their diversity. He specializes in studying how lizards' forms, or morphologies, determine their function, such as head shape (which impacts bite force) and limb shape (which affects how lizards move).

He has spent countless hours observing in the field, from the birthplace of evolutionary theory-the Galapagos Islands-to Namibia, the Amazon, and the Sonoran desert. And he has taken thousands of lizards back to the lab to run them on miniature treadmills and racetracks to measure their speed and endurance.

He has also worked with Sinervo to characterize "rock-paper-scissors" dynamics in certain lizard communities, in which three belly or throat colors correspond to three types of male reproductive behavior.

One current project investigates why different families of iguana have different numbers of species. Miles wants to know if the key to adapting to a variety of ecological niches is having a variety of morphologies.

Back home, Miles loves teaching his students about how "wicked awesome" lizards are and gives public lectures about climate change. He's hired students as field assistants for his lizard research, and also has been taking students on ornithology field trips to locations such as South Carolina since the late 1980s. The excursions highlight endangered species and field exercises that can prepare students for jobs as wildlife biologists or graduate school, he says.

From field work to education, he "brings not only his natural history and ecological skills, but just a love of doing biology that's infectious," Huey says. "He's an all-around biologist. He's good in the field, he knows how to design an experiment that is relevant to the animals he's studying, he has good analytical skills, and he understands conceptually what's important."

Although Miles may be thinking big, he always comes back to the basics. For him, the best part of the job is "learning about the wonder of life. It's amazing to learn the intimate details of species. There's always a sense of awe for me."

By Stephanie Dutchen

This article appears in the Spring/Summer 2011 issue of Perspectives magazine.