Why Top Carnivores are Essential to a Healthy Planet

Caroline Fraser’s book Rewilding the World is a call to retrofit more than a century of nature conservation in the United States and around the world. Why, at this late date, is it so important that we redesign the global conservation system? Conservationists are rightly proud of their collective accomplishment in bringing some 12 percent of the earth’s land under protection so that future generations may know and enjoy nature.

Why should this success now be in question?

The answer lies in the fact that our zeal for conserving nature far outran the science of how to do it. The modern conservation movement dates to the founding of the World Wildlife Fund in Europe and the Nature Conservancy in the United States after World War II.

Both organizations hired scientists to advise them, but the scientists found themselves having to invent programs and priorities out of thin air. Conservation did not have a solid scientific basis until a conference in San Diego in September 1977. Before that, scattered articles presented results of studies that could, by inference or extension, suggest conservation strategies, but as often happens in science, controversy erupted over the interpretation of the results, and when scientists disagree among themselves, everyone else stops listening. The San Diego conference was brilliantly conceived to bring the scientific community together in a consensus that would move the field forward.

Conservation biology had failed to develop earlier because it confronted a methodological impasse: the difficulty of studying the process of extinction of species. Indeed, one definition of conservation biology is that it is the science of why extinctions occur and how to prevent them.
Until the 1970s, nearly all scientists who studied extinction were paleontologists who studied fossils. Extinctions are abundantly registered in the fossil record, but the great majority of ancient organisms appeared and disappeared without apparent cause. Exceptions occurred in
rare global mass extinctions, of which there have been only five since the origin of multicellular life, one of which was the meteorite impact that ended the age of dinosaurs.

Between mass extinctions, which have occurred at intervals of roughly 100 million years, there were countless extinctions of individual species taking place in the “background.” But the rate was so slow, approximately one in a million species per year, that it didn’t appear relevant to a
world in which native habitats were disappearing at an alarming rate and countless animals and plants were being exploited for commercial purposes. If humans were going to “manage” nature so as to prevent extinctions, an entirely new branch of science was needed to address the

The need to retrofit the current conservation system arises out of science that developed during the latter half of the twentieth century. Fraser provides an introduction to this science as the rationale behind her call for “rewilding the world.” What, exactly, she means by “rewilding”
will emerge from the following condensed account of the relevant science.

ven today, when extinctions are occurring with unprecedented frequency, they are extremely difficult to verify. The ivory-billed woodpecker is a prime example. The last substantiated photographs and sound recordings were made in the late 1940s, yet rumors about the bird’s existence and fervent claims of sightings continue to emerge from the Southeast. Is the ivorybilled woodpecker extinct? No one can say. Hence the extraordinary difficulty of studying extinction as a process.

As often happens in science, a solution to this impasse came from unexpected quarters. Two brilliant young biologists, Robert MacArthur, then of the University of Pennsylvania, and Edward O. Wilson of Harvard, published The Theory of Island Biogeography in 1967. The theory is based on a relatively simple finding: the number of species of birds, lizards, or other animals that occupy an island can be quite accurately predicted if one knows nothing more about the island than its area and its distance from a source of colonizing species. Nearby islands are more frequently colonized by new species than distant islands, and large islands support more species, on average, than smaller islands.

MacArthur and Wilson proposed that the number of species of a given type (birds, lizards, etc.) that occupies an island is maintained by a dynamic equilibrium between colonization of the island by new species and extinction of those already present. Colonization and extinction are thus represented as normal, ongoing processes that interact to regulate the number of species present at any time. Over long periods (decades, centuries, or millennia, depending on the size of the island), an island’s complement of species was posited to change while the total number
of species remained more or less constant.

Soon after publication of this theory, biologists began to realize that it could be applied to conservation if one assumed that shrinking remnants of natural habitat, or parks surrounded by agricultural lands, were analogous to islands. There followed a rush to search for historical records listing which species had been found on a given island or in a particular suburban park decades or even a century earlier. Such efforts quickly yielded support for the theory by showing that, indeed, the species complements of some small islands and habitat fragments had changed over the time elapsed between surveys, whereas the faunas of large islands and habitat fragments appeared to remain constant.

Still, there were skeptics who maintained that appearances and disappearances of species from tiny islands and habitat patches were trivial because of the small numbers of individuals involved, and who asserted that there was no evidence that species went extinct in insular areas
large enough to be of relevance for conservation. So long as these dissenting voices were contesting the validity of the MacArthur- Wilson theory, conservation planners and managers remained gun-shy and conservation practice continued as the opportunistic process it had always been.

ny lingering doubts about whether island biogeography theory was relevant to conservation were dispelled in 1987 by a paper published in the prestigious British journal Nature, a study that Fraser calls “a bombshell, the kind of logical observation that seems obvious only in
retrospect.” Written by William Newmark while he was a graduate student at the University of Michigan, it presented startling evidence that numerous mammal species had disappeared from national parks in the western US and Canada. Newmark benefited from research conducted
decades earlier by the US Biological Survey, a precursor of today’s Fish and Wildlife Service.

The survey had systematically documented the mammal species present in each national park at the time it was established. Most of the parks Newmark studied dated to the early decades of the twentieth century and were between sixty and ninety-five years old at the time of his
research. Using a variety of approaches, Newmark compiled contemporary data on the mammals occupying each park and compared the lists to those assembled earlier by the Biological Survey.

The contrasts between the two sets of lists stunned the entire conservation world. Bryce Canyon, Lassen Volcanic, and Zion, the three smallest parks, had each lost more than a third of the mammals larger than rats and chipmunks known to be present at the parks’ establishment.
As expected from island biogeography theory, small parks had lost many species whereas large parks had lost few. The only parks in the study that retained all their species were Banff, Jasper, Yoho, and Kootenay, a back-to-back cluster of parks in the Canadian Rockies comprising an
area roughly the size of Massachusetts. All US parks in the study lost species although the largest, Yellowstone, lost only one, the gray wolf, and that was owing to a campaign of extermination initiated by the US government. Still, populations of all the species Newmark documented as disappearing from US parks survive today in other locations.

Mount Rainier, Rocky Mountain, Yosemite, Grand Canyon—these are among the crown jewels of conservation in the United States and they were demonstrably failing to retain their biodiversity. Only a few years later, Newmark and another American biologist, Justin Brashares, produced similarly disturbing data for national parks in East and West Africa, respectively. It seemed as if parks could not save biodiversity, and ideological opponents of parks seized upon the results to make the claim that parks didn’t work, so why have them? The conclusion was a simplistic overreaction by people who did not comprehend the underlying science. Island biogeography predicted that a contraction in area, such as that experienced by a park after its surroundings have been converted to human uses, would lead to local extinctions, but it could not predict which species would disappear or why. Again, conservation science desperately needed a new theory, and fortunately, intimations of one soon appeared in the form of an ecological phenomenon known as “mesopredator release.”

As Fraser notes, the landmark paper that established mesopredator release as a driver of local extinctions was written by Michael Soulé, a professor at the University of California–Santa Cruz, and his graduate student Kevin Crooks. The two of them studied bird communities in
twenty-eight canyons in San Diego County and found that some of the canyons resounded with the songs of a full complement of native birds, whereas others supported barely more than house sparrows, starlings, and park pigeons. The important difference between the two sets of
canyons turned out to be the existence of habitat corridors that allowed coyotes to enter the canyons that supported vibrant native bird communities. In contrast, the ornithologically dead canyons were embedded in an urban/suburban landscape that offered no access to coyotes
living outside the city.

Coyotes and birds? What was the connection? Coyotes don’t eat songbirds; they have nothing directly to do with them. The connection was cats, both domestic and feral. Coyotes can and do eat cats, and where coyotes are present, they impose a reign of terror on neighborhood cats,
deterring them from entering canyons and hunting birds. So, indirectly, coyotes are good for birds. Where there are no coyotes, cats have nothing to fear and dedicate themselves to hunting, with strongly negative consequences for the bird community.

Cats are considered a “mesopredator,” one of a group of medium-sized predators that are normally held to low abundance by top predators, in this case coyotes. Other mesopredators are raccoons, foxes, and opossums. Where top predators like wolves, coyotes, and mountain lions
are persecuted, their prey tend to increase, and can become up to ten times more abundant than where the top predators are present. Fox, feral cat, and raccoon populations have exploded all over the United States following eradication of top predators in the nineteenth (in the East) or
early twentieth century (in the West) and, as Fraser aptly puts it, “ran wild in an orgy of predation.” Another consequence of predator elimination is “herbivore release,” familiar to many dwellers of suburbia as an overabundance of deer, beavers, and woodchucks.

Population explosions of mesopred- ators and herbivores have dire consequences for biodiversity. Mesopredators not only prey upon songbirds, but seek myriad other small prey as well, including frogs, lizards, snakes, salamanders, and small mammals. Many once-common species, Fraser observes, are now scarce or locally absent as a consequence. Overabundant herbivores have equally dire effects on vegetation, completely suppressing forest regeneration in the worst cases and eliminating many wildflowers.

These chain reactions, called a “trophic cascade,” can have major economic implications beyond loss of biodiversity. Oak forests, once dominant throughout most of the eastern United States, are gradually being replaced by red maple, tulip poplar, and other low-value species through a
combination of two factors: the suppression of fires, which oaks survive more easily than other species, and deer browsing on acorns and oak seedlings. As these degenerative processes run their course, the landscape and its biotic communities are being transformed into what
ecologists term an “alternative state,” a topsy-turvy ecosystem in which formerly abundant species (oaks) become rare and formerly uncommon species (maples) abound. The diversity of such an alternative ecosystem is likely to be far less than that of the original.

Wholesale transformation of familiar ecosystems into alternative states is an unsettling prospect.  The good news is that conservation science can prescribe a remedy, even if it is one some will deplore. The remedy is to restore the function of predators to natural communities by
reintroducing them. Interior Secretary Bruce Babbitt knew this when he released wolves into Yellowstone National Park in 1995 after they had been absent for seventy-five years. In the subsequent fifteen years, wolves have transformed the Yellowstone ecosystem. Thickets along
rivers and lakes that had been browsed out of existence by elk and moose have recovered dramatically, providing habitat for beavers. Beavers have obligingly recolonized after a long absence. By building dams, beavers create wetlands that provide habitat for fish, frogs, and
nesting waterfowl. Revegetated stream banks reduce erosion and lower water temperature, favoring trout over less desired species, and invite the return of formerly common birds. The Yellowstone ecosystem is on the way to recovery. This is what Caroline Fraser means by
“rewilding”—the restoration of natural function to ecosystems, thereby stabilizing their biodiversity.

Rewilding is the current conservation fad, but is it the real thing? So many conservation fads have come and gone in the past; why isn’t rewilding just another? My own assessment is that this time, the situation is different. Rewilding didn’t just emerge as a fund-raising gimmick; it is
the application of a now mature science of conservation biology, theoretically grounded in the concepts of island biogeography, trophic cascades, and alternative states.

Rewilding seeks to stabilize native ecological communities by encouraging and restoring the processes that, in unperturbed nature, prevent mesopredator release, herbivore (deer) overabundance, and transitions to alternative states. Foremost among these natural processes is
predation, a biological process, but physical processes such as fire and flooding are also important. For more than a century our government has aggressively implemented predator control programs over much of the West to favor livestock growers and, to support other constituencies, has systematically suppressed wildfires and dammed rivers. Mesopredator release, deer overabundance, dangerous accumulations of fuel for fires in western forests, and blocked migrations of salmon, sturgeon, and other fish are the direct consequences of these policies. In other words, we have deliberately, if unwittingly, created the problems; rewilding is a prescription for fixing them.

The emotive ring of the word “rewilding” conceals the fact that it is much more than simply a hazy ideal; lying behind it are the proudest achievements of conservation science. Rewilding is shorthand for the three C’s: carnivores, cores, and connectivity, practical applications that
follow directly from established theory. Island biogeography showed that species disappear from small preserves, affirming the need for large, strictly protected core areas, such as national parks. But island biogeography offers no hint about why species disappear so quickly from
small areas.

Research on mesopredator release and herbivore overabundance has revealed that powerful drivers of extinction are unleashed by the elimination of top predators. Thus the way to restore full ecological function is by establishing core protected areas that can sustain breeding
populations of top carnivores like wolves and mountain lions and then connecting them via  habitat corridors that permit movements of individuals between cores. Connectivity across the landscape is crucial because small populations of wolves, bears, or other species trapped in
isolated core areas are vulnerable to inbreeding and accidental extinction, as Newmark so powerfully demonstrated. Maintaining connections between protected areas, in other words, expands effective population size and allows the interconnected whole to resist forces of extinction.

At the end of the first decade of the twenty-first century we find ourselves with an (albeit magnificent) set of national parks established long before anyone ever imagined such a thing as conservation science. Consequently, in light of what we now understand about conserving nature, our parks are too few, too small, and not in the best places; hence the need for retrofitting. Such a belated realization was succinctly articulated by Álvaro Ugalde, former director of national parks of Costa Rica:

Out of ignorance, we created a park that is too small. At the time, we thought it was gigantic. What the years have proven, though, is that Corcovado [a Costa Rican national park] is very small,…especially when we talk about critical species such as the jaguar, peccary, and harpy

This sums up the global picture.

aroline Fraser, a host of scientists, and a swelling throng of conservationists in all corners of the globe are calling for rewilding as the best hope for restoring something resembling primordial nature on this overstressed planet. The science they rely on is sound and now thoroughly
vetted, though not yet entirely free of controversy, for old ideas always die hard. Some conservation organizations and government planning agencies have already accepted the idea of rewilding and are running with it. Rarely has new science found such quick and enthusiastic

Fraser dedicates much of her book to telling the varied stories of how the three C’s are being applied around the world, in the Americas, Europe, Africa, Asia, and Australia. Each story explores a different setting, distinct in its economic, cultural, and biological features. The goals
range from modest (making a greenbelt out of the former death zone that marked the iron curtain) to grandiose (a four-nation transboundary megareserve in southern Africa), but the purpose is always the same, that of restoring connectivity to a fractured landscape.

The movement to rewild the earth benefits from the virtue of common sense—we should restore the processes that sustained nature before humans disrupted them. It is big-picture conservation. It offers a vision of a more nature-friendly world, with something for everyone, a
clean and spacious environment available for hunters, fishers, campers, hikers, and adventurers, encompassing private lands and managed commercial activity in addition to strictly protected core areas. But how do we achieve it? This is the big question that has yet to be resolved, and it is the question that Fraser addresses in nearly every chapter.

Science can prescribe the three C’s, but science can’t save nature; only people can save nature. People represent both the hope and the challenge, for the goal of rewilding does not sit well with everyone. The first attempt at reintroducing the Mexican wolf to the Southwest is a case in
point. Following the success of gray wolf reintroduction into Yellowstone, in 1998 Secretary Babbitt opened gates that released eleven Mexican wolves into Catron County, New Mexico.

Shortly afterward, Fraser writes, the alpha female was shot “along with her mate and several pups”; rumors swirled that local ranchers were offering a bounty of $10,000 for a dead wolf. Within months the program had failed; all the wolves had been killed or removed by federal authorities.

In contrast, in my state, North Carolina, red wolves were reintroduced in 1987 with little incident and have thrived, spreading from the release site into several nearby counties. Local communities now proudly advertise the animal’s presence with road signs cautioning “red wolf
crossing.” The difference between the two situations is that North Carolina suffers from an overabundance of deer and lacks an outdoor livestock industry in the part of the state where red wolves now roam.

Of the three C’s, carnivores top the list, for without them all else will fail. And as the example of Catron County, New Mexico, demonstrates, carnivore reintroduction is fraught with challenges. Wolf reintroduction is hotly opposed in the West, in part because wolves have been absent for a
hundred years and ranchers have not had to accommodate to them. Wolves are much less controversial in Canada, where they were never systematically eliminated. Tolerance is the key to successful carnivore reestablishment, but tolerance of big, dangerous animals is in short
supply in the US. Contrast, for example, our attitudes with those prevalent in India, where tigers kill many citizens every year yet benefit from widespread public support.

Let me be clear about one point. No one, not even the most ardent proponent of rewilding, is proposing to restore wolves and grizzly bears to suburban backyards. In part, it is the very impossibility of doing this that creates the need for rewilding. Rewilding is necessary to save
nature in all its beauty and diversity, but where wild nature includes animals like elephants, lions, tigers, or grizzly bears, conflicts between them and local populations are almost inevitable. Where big, dangerous animals are involved, rewilding can best be accomplished in expansive landscapes supporting low human densities. The romantic notion that people and nature can coexist in harmony is fanciful and came out of Europe after large, threatening animals had long been eliminated. The reality is that most people simply do not tolerate large carnivores in the vicinity of children or domestic animals. Segregation via remoteness or elephant-proof fences, as in South Africa, offer the best practical solutions.

Fraser is keenly aware of this and plows straight furrows through the ideological minefields of conservation politics, applying a clear-eyed empiricism to allaying the fears of ranchers and tempering the idealism of politically correct big-city conservationists. She keeps her eye on the
larger goal while dispassionately analyzing the human dimension of each situation. The basic goals of rewilding are universal—the construction of ecological corridors and the piecing together of megareserves linking cores, corridors, and buffer zones. How to achieve these goals in an overcrowded, resource- hungry world is the central question of the book.

“We are realizing,” Fraser writes, “that conservation is not about managing wildlife as much as it is about managing ourselves—our appetites, expectations, fears, our fundamental avariciousness. If we do not succeed at that, other forces assuredly will.”

Conservation is indeed not so much the management of nature, but the management of people.

And wherever one goes, people have distinct traditions, outlooks, and economies. Every project requires deep insights into the psychology, aspirations, and circumstances of the local residents.

Huge amounts of money—billions—have been wasted because international donors did not take such nuances into account—just as our military made serious miscalculations in Vietnam, Iraq, and Afghanistan by failing to comprehend the historical and cultural setting of its engagements.

Fraser examines the tensions between conservation and development, between people and wildlife, and between top-down and bottom-up approaches to conservation. She describes a bottom-up (or “grassroots”) process that is working well in southwestern Australia because
farmers, ranchers, and aboriginals, even when tensions exist among them, all see positive benefits in rewilding. Aboriginals have seen the native vegetation and the game it supports disappear, whereas farmers and ranchers, through clearing the bush on huge scales, have created a dust bowl that threatens their livelihoods. Unfortunately, such happy convergences of interests are more often the exception than the rule.

A top-down, government-mandated approach can work in wilderness zones where there are no people to be affected by imposed land-use restrictions—indeed, there can be no other approach. But promoting conservation in regions that already support a human population requires close attention to the needs and aspirations of the people. In many parts of the world, but especially in Africa and India, wild animals are viewed as competitors of livestock and threats to agriculture and human safety. People do not want to share their habitat with wildlife unless
there are ways of mitigating the effects of doing so. How to provide mitigations in a way that promotes both conservation and economic progress is a theme that Fraser pursues with sensitivity and realism.

Obviously, top-down and bottom-up approaches are not alternatives; they are complements. The forging of national or international commitments necessarily involves top-down processes, whereas land tenure issues, usufruct rights, and tourism development must be addressed at the
local level. Neither approach, in itself, is likely to be sufficient. An appropriate balance between the two is optimal, but achieving such a balance requires a sophisticated knowledge of the politics at both levels, something that is rarely achieved in short-term projects financed by

To many the notion of rewilding will be dismissed as romantic fantasizing, and indeed it may so prove. But before dismissing the idea, one should consider the alternative—an entirely utilitarian world, scientifically managed perhaps, but lacking in the aesthetic rewards nature provides. The beauty and splendid solitude of wild nature will become memories recalled in schoolbooks, no more relevant to the here and now than stories of dinosaurs and wooly mammoths. If this is the world you want to pass on to your offspring, then go ahead and ignore Caroline Fraser’s book. But how could a world without nature, however many its material comforts, be a better world for anyone? Rewilding offers a more balanced vision of the future world, and what could be a more powerful inspiration than that?

Why We Must Bring Back the Wolf
by John Terborgh
The New York Review of Books JULY 15, 2010

Rewilding the World: Dispatches from the Conservation Revolution
by Caroline Fraser
Metropolitan, 400 pp., $28.50


For the cats,

Carole Baskin, CEO of Big Cat Rescue
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