Animals on the Move

Fuzzy, bright-eyed and no bigger than a baked potato, the American pika is the kind of critter you could imagine starring in a blockbuster animated movie for kids. With its high-pitched squeaks, its lightning quickness and its habit of racing around all summer to harvest and sun-dry “hay piles” of grasses and wildflowers for its winter meals, the tiny rabbit relative is one comical ball of fluff. But what’s happening to the pika is anything but amusing: Climate change has it in the hot seat.

Thick fur, heat-conserving roundish bodies and the use of snowpack as insulation help pikas survive in chilly alpine regions of the western United States and southwestern Canada. Their tolerance range is absurdly narrow, though. They can overheat to the point of death if exposed to too much summer heat. Extreme cold in the winter is just as deadly if they can’t take refuge under the snow.

As alpine temperatures warm and snowpacks shrink, pikas in some places have hightailed it upslope to find more tolerable conditions. But in the arid, mountainous region known as the Great Basin, pikas have disappeared altogether from 40 percent of the locales where they were found in the first half of the 20th century. Apparently already at the upper limits of their ranges, they’ve run out of places to run to.

The pika’s plight may be extreme, but the story line is not unusual. Worldwide — on land, in the sea and in rivers, streams and lakes — wildlife is responding to rising temperatures. The changes are sometimes to the animals’ benefit, sometimes to their peril, say scientists who have pored over reams of recent studies and data from centuries of naturalists’ observations.

Some animals are packing up and moving, generally heading toward the poles or up mountain slopes in search of more hospitable climes. Others are undergoing changes in physiology, behavior or body size — or they’re shifting the timing of seasonal events such as breeding, migration and emergence from hibernation to coincide with earlier springs and later autumns. Just last year, researchers reported seasonal shifts in animals ranging from snow geese in the Arctic to amphibians in a South Carolina wetland to penguins in Antarctica.

And though similar responses have been turning up in many sorts of animals, in many sorts of habitats, researchers are now finding that not all organisms are responding at the same rate or in the same direction. Long-standing associations between predators and prey, parasites and hosts, herbivores and food plants, flowers and pollinators are getting out of sync.

Communities are breaking up and reassembling with new mixtures of members, and it’s hard to predict the effects of such mash-ups, a team of environmental scientists concluded in a paper last year.

This shifting and reshuffling of the world’s wildlife presents conservation challenges, to which scientists are now turning their attention. What good are nature preserves if changing climate forces safeguarded species to flee into unprotected areas? Or if protected populations perish because, already at the very top of a mountain or at one or the other of Earth’s poles, they can go no farther? Or because, as one author wryly put it, “Los Angeles will be in the way” — meaning that suitable habitats into which animals might relocate have been turned into subdivisions and shopping malls, and escape routes to more distant habitat patches have been blocked.

Prospecting for patterns

Coming up with a cohesive picture of how biological systems are reacting to climate change is a tricky task. Two research groups took up the challenge about a decade ago and published their initial, landmark studies — both still widely cited — in 2003 in the same issue of Nature.

“At that time there wasn’t much out that was pulling things together at all,” recalls Stanford University biologist Terry Root, who headed one of those groups. “I had organized a workshop in 1995 for looking at impacts on species of climate change, and three talks in that workshop had the same plot — different continents and different species, but all showing that species were doing things earlier. I thought, we need to sit back and figure out if this is really going on worldwide.”

Root and coauthors synthesized information from 143 previously published studies and uncovered a consistent finger­print — a temperature-related shift in range, seasonal events, behavior or other traits — in species “from molluscs to mammals and from grasses to trees.” Of the species that showed changes, more than 80 percent were shifting in the directions you’d expect if the shifts were due to climate change.

In the other paper, biologist Camille Parmesan of the University of Texas at Austin and economist Gary Yohe of Wesleyan University in Middletown, Conn., performed various analyses on data from independent studies on more than 1,700 animal, plant and lichen species. Parmesan and Yohe also found biological trends that matched climate change predictions. Butterflies, birds and other organisms had shifted their ranges northward by an average of 6.1 kilometers per decade (or 6.1 meters per decade upward to higher altitudes). Amphibians and migratory birds, among others, were breeding earlier in the spring by an average of two days per decade (SN: 3/8/03, p. 152).

Since then, researchers around the world have been piling up more and more examples of particular animals or suites of species showing changes that fit the same patterns (as well as some that don’t). On the range-shifting side of the story, more than half of 305 common North American birds are wintering farther north than they did in 1966, a National Audubon Society analysis showed in 2009 (SN Online: 2/10/09). The shifts, which average 56 kilometers and are as great as nearly 700 kilometers for individual species, coincide with warmer winter temperatures over the same period.

In Michigan, opossums, white-footed mice and other mammals once confined to the southern part of the state have rapidly expanded northward, displacing some of their counterparts in the process. A 2009 paper ruled out forest regeneration and land-use changes as possible explanations for the expansion; the authors concluded that warming, documented in the area over the same period, was the probable cause. Meanwhile, chipmunks and other small mammals in California’s Yosemite National Park have moved to higher ground as temperatures in the park have increased in the last century, a 2008 study showed.

Such shifts can shake up communities, and the new assemblages that result may not get along as well as the old gang did. So concluded researchers who used climate and species-distribution models to project future bird communities in California. The upshot of their paper, published in 2009 in PLoS ONE: By 2070, more than half the state could be occupied by entirely new groupings of feathered fauna, with the potential for “dramatic community reshuffling and altered patterns of species interactions.”

Even when interacting species move together, they may not link up in the same way in the new location. When warming nudged Britain’s brown argus butterflies northward, their larvae were far less plagued by parasitoids in the new territory than they had been in the old home, researchers reported in Ecological Entomology in 2008. The parasitoids were in the new place, too, but apparently more interested in a different butterfly species.

As for changes in seasonal activity, frogs are calling, birds are nesting, salmon are migrating, walleye are spawning, loggerhead turtles are laying eggs and bees and butterflies are appearing earlier in the spring. Plants too are responding by leafing out and flowering earlier.

Underscoring the individual reports, a 2010 study found that seasonal events in the United Kingdom have advanced for most of the 726 terrestrial, freshwater and marine plants and animals examined and that the rate of change has sped up in recent decades. What’s more, change was speediest in organisms at the bottom of the food chain — plants and plant-eaters — and slower in predators, a situation that could result in empty bellies for the planet’s top diners.

Mismatches can happen, too, when interacting species respond to different cues — say, one to day length and the other to temperature. That’s what’s happening with caribou in West Greenland, which synchronize their seasonal migration to calving grounds with day length. The food plants on which they depend respond to temperature, however, and as spring temperatures in the area have risen by more than 4 degrees Celsius, plants have started growing earlier. Caribou are now arriving after peak foraging time, fewer calves are being born and more calves are dying, a 2008 study found.

How the shake-ups will all shake out is hard to tell, concluded authors of a review published last year in the International Journal of Biometeorology. In their roundup of climate-driven mismatches between interacting species, environmental scientist Alison Donnelly of Trinity College Dublin and colleagues found examples of both winners and losers, as well as some partnerships that stayed in sync and some previously mismatched pairs brought into synchrony by rising temperatures. It’s a complicated picture, and to get a handle on how individual species and whole ecosystems will respond to future climate change, scientists will need to delve deeply into relationships among species, the authors contend.

Root agrees: “What we need to be doing now is actually figuring out how the shifts are affecting biotic interactions so that we know what’s going to happen as far as extinctions go.”

Big picture projects

Teasing apart those interactions, while continuing to document overarching trends, will require heaps of data from long-term monitoring projects that span disciplines, environments, species and food chain levels, Donnelly and coauthors say. One such effort is the USA National Phenology Network. This consortium of researchers, citizen scientists and organizations collects and shares information on plant and animal phenology (the knowledge of when recurring life stages happen and how they relate to climate and change of season).

Changes in phenology are among the most sensitive indicators of global change and, fortuitously, some of the easiest to track. For centuries, people have been paying attention to the seasonal patterns of plants and animals, partly for enjoyment but also to know when to hunt and fish or be on the lookout for particular crop pests. Capitalizing on that interest, the Tucson-based network recruits volunteers to record phenological observations on 166 species of animals and 258 species of plants in an online Nature’s Notebook.

“The beauty is that we have scientists and citizen volunteers all using the same protocols to collect the information,” says Jake Weltzin, the network’s executive director. This process creates a seamless dataset on a wide variety of organisms across the nation that researchers, conservation groups and others can use to piece together the big picture.

In addition to monitoring what’s going on right now, the organization is tracking down and organizing records of what has happened in the past. “About 10 percent of the people in any audience I’m talking to have some kind of phenology records they’ve been keeping on anything from when maple syrup comes to when they applied insecticide on their grapes,” Weltzin says. “We want to create a clearinghouse for these kinds of historical datasets.”

Establishing cause

From the earliest studies through the current efforts, a major challenge has been verifying that observed changes in animal distribution, seasonal activities and so on are actually linked to climate change, and then disentangling the relative contributions of natural temperature fluctuations and human-caused temperature increases.

In their 2003 papers, both the Root group and Parmesan and Yohe relied on inference. The logic went like this: Their analyses revealed trends — across many species, ecosystems and geographic regions — that were in the direction you’d expect if climate change were driving the responses. Knowing that global warming had been clearly documented over the same period and that the Intergovernmental Panel on Climate Change had concluded that the warming was linked to the rise in greenhouse gases, the researchers felt justified in claiming that, as Parmesan later wrote in a review paper, “twentieth-century anthropogenic global warming has already affected Earth’s biota.”

Critics weren’t convinced. Some argued that data showing temperature increases were collected in hotter urban areas, not where the animals exhibiting trends actually lived.

“I was getting fed up with the naysayers,” Root says, “so in 2005 I looked at species change in relation to actual temperatures recorded at the particular study sites.” The study that she and her coauthors published that year in the Proceedings of the National Academy of Sciences showed a strong link between local temperatures and the timing of biological events. The researchers then looked to see how the observed biological changes fit various climate scenarios generated from three different versions of global climate models: one based only on natural climate variability, one based only on human-caused climate change and one that factored in both natural and human-caused changes. The best fit was with the combined model; the worst was with natural climate variation alone.

“That was just a way of showing that yes, indeed, humans are a part of this,” says Root, who endorses efforts to further clarify the relative contributions of natural and anthropogenic climate change, while conceding that it makes no difference to plants and animals what’s causing the warming. “From a species perspective, it does not matter why the climate is changing, just that it is. From a human perspective, it does matter a lot, because knowing the reason can help us to stop our behavior that is driving the rapid changes.”

Parmesan, however, thinks the pursuit amounts to unproductive hair-splitting. In a commentary published last year in Nature Climate Change, she and coauthors argued that the whole picture is too complex to ever say with certainty that a particular response in a given animal species is due to human-induced climate change. For one thing, animals respond to local climate, but human-caused climate change can be detected only on a larger spatial scale. What’s more, other factors can interact with climate change, enhancing or masking its effects.

“Changes at the local level are going to be a complete mix of interactions among regional climate, habitat loss and local pollution sources,” Parmesan says. Assessing and seeking to understand these interactions is a better use of time and resources than figuring out the specific role of greenhouse gases in driving biological change. Other researchers in the field also are calling for an integrated approach to future research that takes into account interacting environmental pressures, interconnected species and the varied sensitivities of different species to changing conditions. And because temperature isn’t the only driver — some animals are showing behavioral and physiological changes in response to changing carbon dioxide levels or altered precipitation patterns — there are plenty more interactions to factor in.

Another factor to consider is how quickly climate change is moving across the land, says Scott Loarie, a postdoctoral researcher who works with global ecologist Chris Field at Stanford. In 2009, Loarie, Field and colleagues found that, overall, species will need to move about two-fifths a kilometer per year to keep up with changing conditions, 10 to 100 times faster than they’ve ever had to move before to cope with changing climates. Mountain dwellers won’t have to move as far as critters in flatter landscapes to find a new home — just 10 or so kilometers over the next century, compared with more than a hundred.

One recent study suggests ocean-dwelling animals may need to move as fast or faster than land species — and to advance the timing of breeding, spawning, migration and other seasonal life events even more. The work, from the marine biological impacts working group at the National Center for Ecological Analysis and Synthesis at the University of California, Santa Barbara, was published last year in Science.

The conclusions of Loarie and coauthors echo the 2003 findings of Parmesan and Yohe. But instead of documenting changes that have already occurred, Loarie’s group developed an index that can be used to predict future range shifts. Applying their predictions to nature preserves worldwide, the researchers arrived at the dire conclusion that traveling temperatures will force wildlife out of all but 8 percent of those reserves within a century.

Looking at the problem from a slightly different angle — how far animals actually are able to travel to establish new homes and how inclined they are to do so — researchers at the University of Washington in Seattle also came up with grim figures. This year in the Proceedings of the National Academy of Sciences (SN Online: 5/14/12), Carrie Schloss and colleagues found that about 9 percent of mammal species in the Western Hemisphere won’t be able to move fast enough to keep pace with climate change. In some areas, more than half the mammal species will be unable to keep up.

The Loarie and Schloss studies don’t just spin out gloomy scenarios, though. They also point to conservation strategies, such as designing reserves that include a range of landscapes — and associated climate regimes — and creating linked networks of protected areas.

Given the complex, interconnected pressures on animals these days, the varied ways species are responding and the projections that temperature may rise another 1.8 to 4 degrees by the end of the 21st century, it’s time to completely rethink conservation aims and approaches, says paleoecologist Anthony Barnosky. People have been accustomed to setting aside reserves and expecting them to simultaneously protect the natural landscape, the species that live there and the associated “ecosystem services” — ecological interactions that provide humans with food, clean water, recreational opportunities and the like. But now, with plants and animals moving around, old associations breaking up and new ones forming, it may no longer be possible to protect all three facets of nature at once.

“You have to decide, am I interested in a species? Am I interested in a landscape? Or am I interested in a feeling of wilderness?” says Barnosky, of the University of California, Berkeley. Saving species may mean actively intervening and helping animals move to areas they can’t reach on their own. Protecting ecosystem services may — or may not — depend on keeping specific groups of species together. That’s still an open question. And preserving wilderness, nature free from human meddling, will require “realizing that the species that live there today are probably going to be very different from the species that live there tomorrow.”

Nancy Ross-Flanigan is a freelance writer based in Newaygo, Mich.

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Climate responders
Over the last dozen years or so, scientists have linked a plethora of changes in the animal community to a warming climate.

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