Will only the flexible survive?

Species adapt to long-term, predictable stressors through natural selection: They evolve. For example, desert bighorn sheep living in the Sonoran Desert have developed the ability to store water in their stomachs for several days between drinks. They can even skip drinking altogether for months during the winter, relying on the plants they eat for moisture.

But because of climate change, the stressors that wild animals face are becoming less predictable and more variable. Just in terms of weather, extreme events such as heat waves, droughts, and heavy downpours are increasing. It’s trickier for an animal evolve in response to such chaos. Now, one group of scientists is investigating a different route for species coping with a wildly fluctuating world: behavioral plasticity.

Behavioral plasticity is the ability of individuals to cope with new situations. Unlike evolution, which takes at least one generation, behavioral plasticity lets individual animals make a temporary change — a useful trait in an unpredictable world. “It’s a little bit of a hopeful, positive angle on how species are responding to contemporary climate change,” says Erik Beever, a U.S. Geological Survey research ecologist.

Beever and his colleagues are interested in understanding whether some species have the flexibility to effectively cope with climate change, and if so, what kinds of species. “Is it smaller bodied or larger bodied animals? Is it species that live longer or shorter?” Beever says. To begin answering such questions, the researchers reviewed published scientific studies of animal behavior that focused on responses to climate variability, coming up with 186 examples. In the American Southwest, on chilly mornings desert spiny lizards warm up by basking in the sun, for instance, while desert woodrats cool off by staying home on hot nights, coming out of their dens later than usual to forage.

One especially interesting example of behavioral plasticity came from pikas, mouse-sized rabbit relatives with rounded ears and loud squeaks, a species that Beever has researched extensively throughout the West. Many people never spy a pika, but, Beever says, “over ninety percent of the time, if you go where pikas live at the right time of the day and year, you will hear them.” Generally, pika habitat means ankle-twisting piles of rocky debris called talus slopes. Pikas inhabit mountains across the West, but because they are homebodies who don’t travel far, when local conditions get rough, pikas must adjust their behavior in order to survive. That makes pikas good subjects for studying behavioral plasticity.

Perhaps the cutest example of behavioral plasticity in pikas is the way that they regulate their body temperatures: when cold, they fluff up into bewhiskered fuzzballs; when warm, pikas stretch out to let off heat. Pikas have other behavioral flexibilities, too – although researchers thought that pikas stayed hydrated through their leafy green diet, they discovered recently that pikas will drink water if they get hot enough.

The ability to respond flexibly to their world may help some pika populations cope with climate change. However, different populations may cope with a changing world with varying degrees of success. Although pikas are vanishing from much of their historic range due to climate change, moving upslope over time, some pika populations are surviving. In the Columbia River Gorge and Grand Teton National Park, for example, the palm-sized puffballs are doing quite well, while Yellowstone National Park pikas are disappearing at lower elevations.

Columbia River Gorge pikas especially interest Beever because they behave very differently from their talus slope relatives. In summer, mountain pikas forage constantly in high-elevation alpine meadows to amass “haypiles” of wild plants for winter, but gorge animals live at just 70 feet above sea level. They forage in patches of rainforest, where they feast on wild plants and moss, an abundant year-round food source. Gorge pikas also keep active throughout the day in the shade, while higher-elevation pikas must hide out the sun-baking afternoons under rocks. Beever still has many unanswered questions about what’s driving the differences in behavior between the two. But that doesn’t change the fact that different populations of pikas can behave differently, if given different resources to work with.

There are limits to what animals can adjust to through behavioral plasticity, of course. If the talus slopes of the world got hot enough, even the most adaptable pikas living on them would cook. And behavioral plasticity has costs. A woodrat hunkering down in its den waiting for the evening to cool off has less time to get food, find water, or seek a mate, for example.

Ultimately, Beever hopes that his research will help wildlife managers determine how to help preserve species being affected by climate change, in ways that take advantage of animals’ behavioral plasticity. But, he says, this variability among different populations of the same species “raises the bar on what we need to understand. We want to go, ‘oh this (species) goes in the red light category, this one goes in the green light category, this one goes in the yellow light category.’ It requires a little more understanding than that.”

“There’s still so still so much to learn,” he adds, “so it’s kind of an exciting research frontier.”

 Maya L. Kapoor is an associate editor with High Country News.

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