The prey is elusive. Always and everywhere. But here, on this day in May, in this meadow on Vancouver Island, it is especially so.
Derrick Parker, shown left, strides with a purposeful chuff-crunch, chuff-crunch, chuff-crunch through a field of knee-high grass that’s ringed with oak trees and speckled with purple and white wildflowers. He clutches a net in one hand, a clipboard in the other. With each step, his gaze sweeps slowly left, then right, like a department store security camera scanning for shoplifters.
He detects no quarry. There is no flittering, no flipping from flower to flower today. There are no skippers or swallowtails spastically swooping or stutter-stop soaring in this oak savannah in the shadow of Mount Tzouhalem. And that leaves Parker and his boss, Jessica Hellmann, totally bummed.
“These are the kinds of marginal days that drive us bonkers,” Hellmann sighs. The problem is the weather. If it’s too cold or too damp, the butterflies won’t come out to play. Today the thermometer must be a few ticks below “warm enough.” Where is global warming when you need it?
Weather is critical for butterflies. “If it’s too cold, you can’t fly. You can’t lay eggs. You can’t get nectar. You can’t find mates. Your life is worthless,” Hellmann observes. With a chill in the air, no butterflies flutter by today . . . or do they?
From out of the blue or, more accurately, out of the grass, a duskywing skipper abruptly takes flight, and tally ho! the chase is on. The little brown butterfly zigzags through the meadow, trailing a line of people swooping nets at empty air.
There are three skills essential to the art and science of butterfly capture, says Larry LaTarte, Hellmann’s husband and the Notre Dame assistant professor of biology’s self-proclaimed “best butterfly catcher.” First, the catcher must be totally committed to chasing the butterfly wherever it may lead—within reason. Some of Hellmann’s butterflies live on remote cliffs, so a certain amount of prudence is vital, cautions the attorney, who often helps his wife in the field. Second, the catcher must anticipate where the butterfly will move next because once you zig with your net, the butterfly has already zagged away from it.
Finally, the “swoop” must be very fast, “racquet-speed fast,” in LaTarte’s parlance. Related to that, he warns would-be butterfly hunters never to stalk in pairs. “Your net is at the end of a 4-foot pole,” he notes, “so if you hunt in twos, there’s a tremendous potential for clobbered heads.”
A really experienced catcher can actually tell a butterfly’s sex by how it flies, Hellmann says. Males have only one raison d’être: to find females. Consequently, their flight looks frantic and erratic. Females are heavier and therefore appear more purposeful and self-directed in the air. They feed more, always looking for that next sip of flower nectar, and so they land more. That makes them easier to catch. This one, in fact, settles right in front of Parker, and he pounces on the spot with his net.
A butterfly wing is composed of thousands of delicate, colored scales. Since these tiny mosaic tiles are easily wiped off with handling, Parker ever so gently plucks the insect from the mesh. To inflict the least damage, he holds its fragile wings immobile along the main vein running down the center of the wing and carefully places it in a clear, wide plastic tube open at both ends.
Parker inspects the butterfly intently. Female duskywings are a bit larger and a bit lighter brown than the males. The girls’ wings also have a bit more pattern, and their abdomens are exposed. This one, unfortunately, is too small, too dark, too patterned and its abdomen is covered: A male. With a gentle nudge, he pushes the butterfly out the tube and watches it flutter off. Males, unfortunately, won’t do. Parker, one of Hellman’s grad students, needs mated females for his research project.
Hellmann’s lab is trying to understand how species cope with climate change. The conservation biologist and her colleagues want to know what will happen to the wild things in the years ahead as Earth’s blanket of greenhouse gases continues to thicken and warm the planet.
Depending on which climate model you consult, Earth is facing anywhere from a 2- to-6-degree Celsius increase in overall temperature this century. That is a change equal to the climate shift when the Earth came out of the last ice age, 10,000 years ago. While there are uncertainties in the predictions, which disagree on specifics, they all agree the mercury is rising.
“We tend to think of climate and climate change as monolithic, as if you have one climate and then wham! you have a new climate,” says Hellmann. “But it doesn’t work that way.” Our overall trend may be up, but there can be a great deal of variation over the years. “That’s why some people have difficulty grasping the reality of climate change,” she says. “After a cold spring, they’ll say, ‘See, there’s no climate change.’ It’s hard to think about variance and the mean at the same time.”
Butterflies are excellent tools to study all this, the ND ecologist says. They are the canaries in the coal mine, highly sensitive living meters responding to changing weather conditions. The larvae, in particular, are vulnerable to climate variation. All of which explains Parker’s fixation on capturing lady butterflies. No females = no eggs = no larvae = no study = no Ph.D. for him.
A migration
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For some time now, a subtle, secret migration has been going on behind our backs. While people have been debating the reality of climate change, many species from plants to insects have been quietly voting with their feet or whatever form of locomotion they have, slowly making their way to higher altitudes and latitudes in response to the warmth they feel. As climate changes even more in the years ahead, even more creatures great and small are likely to leave their increasingly sultry old neighborhoods in search of cooler climes.
All this poses some interesting research questions for conservation biologists like Hellmann. Ecologists want to know which organisms will engage in this push to Earth’s poles. How will they do it? What forces constrain them? And, perhaps most worrisome, what happens to the ones who can’t move? Will Earth lose much of its biodiversity in the process? Can we avoid that cataclysm?
The response to climate change is anything but simple. There is no one-size-fits-all reaction among species. “Everybody doesn’t just pick up and leave,” Hellmann notes. “For a whole host of reasons there are as many not moving as moving.”
In some cases, certain plants or sedentary insects might not be able to move themselves. In other cases, a natural barrier such as a mountain range or large body of water might prevent migration. “It could also be that some organisms don’t ‘want’ to move,” the ND ecologist observes. Within a species, subpopulations can evolve differently, she points out, and sometimes those genetic differences are tailored so narrowly to the place they live that they may not have the right genes for the new, warmer conditions.
In addition to her fieldwork, Hellmann, with Notre Dame mathematician Mark Albers, has been developing a computer model that predicts how many heat-tolerant individuals a population would need to survive in various scenarios. Unfortunately, it doesn’t look good for those who don’t move. “Most of the populations in our model go extinct,” she says. “If you change climate as much as they’re predicting, the heat-tolerance genes are not enough to save a population.”
To explore the vagaries of climate change in real life, Hellmann has been studying an odd couple of the butterfly world: the duskywing skipper and anise swallowtail. Except for sharing roughly the same range extending from Mexico to British Columbia, the two species have little in common. They are as different as can be, a lepidopteran Mutt and Jeff.
The duskywing is a little, fat-bodied, drab brown butterfly that looks more like a moth; the swallowtail is a large, elegant, colorful butterfly. The duskywing flies like a rock with wings, darting from place to place. The swallowtail is, by butterfly standards, a strong, graceful aerialist. Duskywing caterpillars are picky eaters, munching exclusively on oak leaves. Swallowtail caterpillars chow down on a wide variety of plants in the parsley family.
Duskywings tend to stay put because they are so dependent on oak trees. Since they live in isolated pockets, they’re more likely than the wide-ranging swallowtail to evolve genetically distinct subpopulations adapted to local conditions. That could mean they would have difficulty migrating north, Hellmann says. At least that’s the theory.
When it comes to climate change, the edge of the range is where the action is. If there is to be a push to the pole, it’s the edge folks who will make that push. However, Hellmann warns that if these butterflies prefer their current edge-of-the-range conditions over those at the center, as the duskywing presumably does, they might not move north if and when the edge climate becomes like the center. Since Vancouver Island is the edge boundary for both the duskywings and swallowtails, Hellmann has been comparing them with their southern, range-center cousins in Oregon to see how this bears out.
A few surprises
Each of Hellmann’s doctoral students has a slice of the lab’s action. Like most research projects, there have been surprises and mixed results. For the past few years Shannon Pelini has been essentially swapping butterflies from different parts of their habitat to see if they “like it better” where their cousins live. To track their home preference, she studies the butterflies in the field and in growth chambers back at Notre Dame that mimic conditions in Vancouver and Oregon.
The grad student has had some unexpected findings. Contrary to predictions that Vancouver duskywings should like their edge-of-range home best because of their genetic isolation, they did well in Oregon. “That was a surprise and suggests the duskywings may be able to expand their range if and when the center climate moves north,” Hellmann says.
However, it would be a complicated dance. Before the pudgy brown butterfly makes its move, oak trees would have to move first since they are the duskywing caterpillars’ sole food source. That could be a problem since it’s not easy for an oak forest to move quickly on its own.
The Vancouver swallowtails, meanwhile, didn’t fare as well. A heat wave in Oregon last summer decimated the transplanted butterflies. “We had some serious mortality from the high temperatures, and that doesn’t bode well for their survival during climate change,” Hellmann says.
One of the most critical pieces of the butterfly climate change study is Parker’s project. In a nutshell, the first-year Ph.D. student is trying to learn what limits duskywings and swallowtails from expanding their range northward. It’s a two-fold question: Why are they not now moving? And could they? “It may be that the butterflies like it here, but they could stand it even colder and for some unknown reason haven’t moved further north,” Hellmann suggests.
To answer those questions, Parker collects females and brings them back to greenhouses at the lab’s base camp, a rented ranch house in the resort town of Parksville. There, using a regimen of heat and light, he coaxes the females to lay their eggs. The eggs are placed in mesh cages and transported to places beyond the current habitat, where they are left to develop from caterpillar to mature butterfly.
Preliminary results show the survival rates of the two species as nearly identical—and neither is doing very well. This year Parker found the butterflies were slower to develop and smaller in size. That isn’t a good sign for their ability to move farther north, he says.
“We think that out beyond the range edge there may be a little too many marginal days. It’s just a little bit too cold to develop quick enough, and so fewer survive,” Hellmann adds. “It’s slightly too frosty in winter. When you add up all these things, the population can’t make a go of it up there.”
Graduate student Travis Marsico, meanwhile, is studying the plant piece of the climate change puzzle. Marsico is investigating three species of parsley-related plants that swallowtail caterpillars consume. His work is similar to Parker’s, only with plants, examining how well they fare beyond their historical range. Marsico’s research results so far have been good news for the plants as well as the swallowtails that feed on them. He has found that the transplanted vegetation does just fine beyond its historical habitat.
“That suggests if the climate changes and they have trouble surviving in the southern part of their range, they could live up north. The problem, however, as with the oak trees and the duskywings, is getting there. While the swallowtails may be able to make the move on their own, the plants, absent the advantage of wings, are not likely to make the same jump without a little help from a friend.”
Kirsten Prior’s project, studying the gall wasp invasion of Vancouver Island, is tangential to the main butterfly study but has a bearing on it. Beginning in the 1980s Vancouver Island was invaded by gall wasps, insects so tiny—about the size of a seed—that Prior has counted as many as 500 on a single oak leaf.
The problem for duskywing butterflies is that the wasps lay their eggs on oak leaves. The tree, in turn, responds by cutting nutrients to the wasp larvae, forming a puffy layer, or gall, around it. If enough galls form on a leaf, it turns brown and dies. This leaves the duskywing caterpillar with less nutritious food or no food at all. Not surprisingly, Prior has found the duskywing population declining in areas infected with gall wasps.
“The leaves have lower nutritional value and that results in smaller caterpillars, and the resulting smaller pupa are more likely to die over the winter,” she says.
Back to the past
Across the country and across time, one of Hellmann’s Notre Dame colleagues, Jason McLachlan, is using ancient plants to investigate essentially the same set of problems that she is. McLachlan has an informed perspective on climate change. He’s seen it all before. The assistant professor of biology is a paleoecologist who studies changes in the environment that occurred after the last ice age, 10,000 years ago. He uses fossilized pollen found in buried lake sediments to chart changes in tree distribution, how tree populations moved when climate changed and how interactions with species affected them.
One of McLachlan’s research projects is especially germane to the current looming climate difficulties. He and his graduate student, Greg Snowden, have been experimenting with bulrush seeds that have been buried for more than 100 years in East Coast salt marsh sediments. One of the open questions regarding climate change is whether species can adapt quickly enough to changing conditions, allowing them to stay put rather than chase their old climate when it moves. Since these old seeds are still viable Snowden and McLachlan can compare their performance with today’s plants.
“When these seeds were born, the carbon dioxide level in the Earth’s atmosphere was near pre-industrial levels, around 280 parts per million,” McLachlan says. "The level has increased now to 370 millions parts per million, and it’s still rising. So we want to see whether these plants have evolved to accommodate the higher levels of CO2 they now live in, whether they perform better in this environment than their ancestors.
“We’d really like to know how much evolutionary change can take place in 100 years. How far can a species spread? The more we know about the biology of these processes, the better we can respond to the challenge we face.”
Since every species living today already has successfully survived a climate change of equal magnitude 10,000 years ago, McLachlan says it can be argued that current species should meet the climate-change challenge. On the other hand, he says a case also can be made that existing species are in for a rough ride because they have never faced this particular condition before—going from “warm” to “warmer.” The last climate change moved from a glacial period to the current interglacial period. “Back then there was a mile-high hunk of ice resting on top of South Bend,” McLachlan notes.
There is support for both views, the paleoecologist says. He points out that all species have the ability to disperse, so enough may move to avoid extinction. Or this climate change may be categorically different with dire implications for biodiversity.
During other episodes of climate change, McLachlan explains, populations would move north as the ice retreated, in the process becoming less diverse genetically. As another ice age would advance these populations might die out, but a reservoir of genetic diversity always remained intact in the southern populations during these pulses of northerly migration and recession. The uncertain and worrisome wild card today, however, is that these core genetic populations of diversity might go extinct this time around as a result of the warmer conditions.
“If that happens, then you’ve lost the genetic engine that has enabled species to accommodate climate shifts in the past,” McLachlan warns. In effect there won’t be enough diversity for natural selection to select out the individuals that can adapt.
For that reason, biodiversity may be more threatened this time. This next climate shift could be categorically different with profound implications for the future. That has a lot of people worried and wondering what to do about it.
Assisted migration
A paper by Hellmann, McLachlan and Mark Schwartz of the University of California, Davis, published in April 2007 in the journal Conservation Biology, confronted the “what to do about it” question head-on. The stir it caused in ecology circles is still swirling today. “This was something that was being talked about in the hallways at professional meetings,” Hellman says. “We brought it out into the open.”
The “this” she refers to is “assisted migration,” or AM, the deliberate moving of a species to a new habitat to save it from extinction. Their paper, “A Framework for Debate of Assisted Migration in an Era of Climate Change,” has launched a sometimes heated discussion within the conservation community about the advisability of AM.
In fact, Hellmann and McLachlan find themselves on opposing sides, with Hellmann being more open to the idea. “I used to be very reserved about things like this,” she says. “Scientists are always supposed to say, ‘Oh, well, we need more research. The science isn’t in.’ And that’s certainly true. But modern climate change is different. The stakes are too high, and there just isn’t time enough for the slow pontificating that academics like to engage in. So I’m willing to say that assisted migration might be a viable option, something we should consider.”
For his part, McLachlan says he has serious reservations about AM for two main reasons. First of all, and least important, he admits, he objects to it on aesthetic grounds. “I’m an old school wilderness-liking kind of guy, and since assisted migration means artificially creating new communities, that’s not ‘nature’ to my way of thinking. Second, and more importantly, there are serious scientific questions about the associated risks versus the perceived benefits,” he says. “I’m a pessimist about our track record in making a big decision like this, but I hope I’m wrong.”
Hellmann and McLachlan agree that placing species together that haven’t lived together before can be a calamity in the making. The case of the cane toad in Australia is a classic example. The amphibian had been successfully used in the Caribbean and Hawaii as a biocontrol agent to combat a pest there. However, when it was imported to Australia in 1935 for the same purpose, not only did the toad ignore the pest, but, with no predators, it bred like bunnies hopped up on Viagra and quickly overran large areas of the continent, wreaking havoc on the indigenous wildlife.
Assisted migration has already begun, however. A homely, little conifer known formally as Torreya taxifolia, or less formally as T. tax by those who love it and “stinking cedar” by those less enamored, has become the poster child for the movement. The tree lives and, unfortunately, with increasingly regularity, has been dying in its tiny, natural habitat along the Apalachicola River in Florida’s panhandle. In an effort to avert extinction, an ad hoc activist conservation group known as the Torreya Guardians has decided to save the tree. Fewer than 1,000 trees, none reproducing, remain in its native range.
Since 2006, the group has been planting T. tax in North Carolina and Tennessee and other northern areas in an effort to save the species. Their effort appears successful. The transplanted trees are doing well without any reported adverse effects to indigenous species.
Hellmann believes AM will be a strategy sparingly employed, used only for a few species of significant interest or value. Timber companies, for instance, already have expressed interest in planting different varieties of trees in their forests if they believe the future climate will favor a different species. With no commercial value and little interest beyond a few scientists, she doubts duskywings are likely to make the cut.
As climate change accelerates and more organisms are threatened, informal efforts such as the Torreya Guardians or perhaps government-sponsored programs are likely to be launched. With the melting of the North Pole ice cap this summer, in fact, the idea was floated out that perhaps some polar bears should be moved to Antarctica, where there still is plenty of year-round ice. It was quickly noted, however, that the idea might not be so good after all, since the polar bears likely would wipe out the indigenous penguin population. This emphasized the fact that the risks and benefits of any assisted migration effort must be weighed carefully.
However, since AM is already happening to a limited degree now and is likely to increase officially or unofficially, McLachlan and Hellmann both argue that it needs to be seriously examined and assessed by the scientific community so a reasoned policy to serve the common good can be adopted.
To that end, last summer they established an Assisted Migration Working Group, composed of biologists and including some National Academy of Sciences members, law professors, climatologists, economists and ethicists to chart out recommendations for policy makers. The task force, partially funded by a National Science Foundation grant, had its first meeting this past August in Milwaukee and will meet two more times, in Santa Barbara, California, in January and at Notre Dame next summer.
McLachlan expects the group to come up with a list of recommendations, decisions that need to be made now, others that can be deferred until more information is in, and possibly some scenarios in which assisted migration might be implemented.
Notre Dame political scientist Debra Javeline is devising a survey for the group to poll leading ecologists and representatives from federal and state agencies as well as environmental and conservation groups. “We want to know what they know about climate change and species response, what they wish they knew, how much certainty they have, and what risks and benefits they see with assisted migration,” McLachlan says.
Alejandro Camacho, a Notre Dame associate professor of law who is an authority on the Endangered Species Act and a member of the AM group, is exploring legal strategies and frameworks that might allow regulation of assisted migration, while allowing for new scientific information to change and adapt that regulatory framework. “This is contrary to the way the law generally works,” Camacho says. “The law usually wants firm definitions, but in this case with the science in flux it might not be possible.” Regulating assisted migration represents a challenge for the rule of law as well as the environment, he notes.
“It’s a race,” McLachlan says. "Even as we work on policy mechanisms such as assisted migration or biological mechanisms such as dispersal or adaptation, we’re trying to figure out ways of accommodating the coming changes. Things are indeed changing, so we had better get ready.
“The more we put things off, the fewer choices we’ll have.”
John Monczunski is an associate editor of this magazine.
Photo of Derrick Parker and photo of duskywing butterfly by Jason Dzurisin.