Missing, and Sorely Missed
We are enthralled by large predators, yet we have exterminated them throughout most of their historic ranges. We use them symbolically as mascots and they abound on crests, but for the most part we live apart from them: Few of us regularly cross paths with wolves or bears; any cougar attack is likely to make the national news.
In Where the Wild Things Were, science writer William Stolzenburg examines the dramatic role of large predators in maintaining biological diversity. The central idea of the book is that these animals produce a cascade of ecological effects, often by changing the behavior of their prey and of smaller predators. Thus ecosystems without predators may become profoundly impoverished. The book makes these points through a series of connected vignettes.
The action starts in 1963 with ecologist Robert T. Paine flinging ochre starfish (Pisaster ochraceous) off selected patches of rocky shore along the Olympic Peninsula. This experiment, still one of the most-cited studies in community ecology, showed that in the absence of the predatory starfish, space-hogging mussels took over what had been a diverse community.
Then the scene changes: It’s 1921 and we’re on Spitsbergen (an island in the Barents Sea about halfway between Norway and the North Pole), where Oxford naturalist Charles Sutherland Elton is conducting an ecological survey. After three summers in Spitsbergen, Elton would write Animal Ecology, a book that introduced what has become one of the most important concepts in the field of community ecology—food webs. Elton defined niche as an animal’s “relations to food and enemies.” Such insights were influential, but it took biologists some time to realize that ecosystems deprived of predators are decidedly abnormal.
Back to Paine: In the late 1960s, he and one of his students performed an experiment in which they removed sea urchins from tide pools and found that in their absence kelp quickly established itself. In 1971 Paine passed this information along to James A. Estes, a graduate student in zoology at the University of Arizona who was studying sea otters (which prey on sea urchins) on the Aleutian island of Amchitka. Estes had been watching the locally abundant otters
lying in the water, bellies to the sky, urchins between their paws, rolling them like little balls of dough to flatten the spines, and popping them down the hatch like popcorn, one after the other.
That this consumption might have far-reaching effects came as a revelation to Estes. When he looked at other islands where the sea otter population had been decimated by fur trading, he found that sea urchins were flourishing and that kelp and its many associates were largely absent.
Twenty years later, sea otter populations began to decline significantly, and Estes discovered that killer whales, who were running out of larger prey, were responsible for that and other declines, “rippling all the way to the base of the food web.” In a 2002 address Estes said,
Carnivorous animals are important. We have to stop thinking of them as passengers on this earth and start thinking of them as drivers.
Where the Wild Things Were describes predator research from all over the world; I’d like to mention a few studies dealing with problems in North America. In a chapter called “Bambi’s Revenge,” Stolzenburg notes that as wolf populations have declined and hunting restrictions have been imposed, deer—particularly white-tailed deer—are being found in unprecedented numbers in many areas. The abundance of deer threatens understory plants in forests. The population explosion among deer apparently triggered a huge increase in the tick population, with the result that Lyme disease became the fastest-growing infectious disease in the United States. (As adults, the ticks that carry the disease often live on deer, but it is when they are nymphs that they usually acquire the bacterium that causes it—most often from chipmunks and white-footed mice—and spread it to humans.) The problems of eastern forests now involve pests that were once “more commonly considered prey,” including chipmunks and Canada geese as well as deer. Because no place in the region has a full suite of predators, it is hard to document the effects of the missing predators. In essence, we have embarked on a vast ecological experiment with no control condition.
In some other places we can see the difference particular predators make by comparing areas with those predators to those without. In the mid-1980s, biologist Michael Soulé and his students examined chaparral fragments in the suburbs around San Diego and found an abundance of diverse native birds in the fragments that were inhabited by coyotes. The real threat to the birds had been smaller predators, particularly domestic cats, which were threatened by the coyotes. “Where the coyotes roamed,” says Stolzenburg, “the cats ran scared, and the chaparral birds sang.”
Another way to see the effects of predators is to track their return to an area. Coyotes have expanded their range, despite programs that kill some 70,000 of them per year (at taxpayer expense). The results suggest that we should welcome their presence. When coyotes come, birds often fare better, because egg predators such as foxes, raccoons and skunks live more circumscribed lives. The indirect effect of coyotes in protecting nests of quail and waterfowl more than makes up for their occasional predation of adults of those species; and by suppressing jackrabbits, coyotes may even improve range quality.
Sometimes predators are deliberately reintroduced to an area, as when wolves were returned to Yellowstone. Since their return, wolves have reduced elk numbers and have profoundly changed how elk live. By keeping elk from lingering near streams, wolves have promoted willow and cottonwood regeneration, increased songbird numbers, changed mineralization rates and allowed beavers to reestablish themselves. Hydrologist Robert Beschta says he would never have guessed “that wolves would control the character of rivers.” Yet the data are clear.
The book successfully documents that predators have important and often enriching effects on ecosystems. The science suggests that we cannot maintain large nature preserves without maintaining large predators. The going gets sticky when we move from wolves in Yellowstone to wolves at our door. When a group of scientists proposed rewilding North America to create some semblance of its Pleistocene diversity, reactions were widely and viscerally negative. Importing elephants to substitute for extinct mastodons went over comparatively well. But the suggestion that African lions be brought in to replace their bigger extinct American cousins was greeted like a proposal to institute child slavery. Preserving predators somewhere is generally popular. Restoring them everywhere is not thinkable at the present time. This book informs the ongoing public discussion both by summarizing the essential science and by warning us that deep prejudices about predators have the potential to trump the scientific evidence.
Stolzenburg achieves an impressive overview while following connections among the scientists who are the field’s insiders. Paine applies to go to graduate school in paleontology, but when he comes for an interview, the eminent zoologist Frederick E. Smith convinces him to become an ecologist instead. After establishing himself as an ecologist, Paine runs into Estes in a bar or at a movie (their recollections differ) and sparks him to consider the bigger picture for sea otters off Alaska. Stolzenburg shows that science is social and filled with large personalities. It is also a system for comparing ideas and evidence, carried out by social primates skilled in both competition and cooperation. Throughout the book, we see scientists probing, pondering and reexamining ideas they hold dear. Better ideas and new data do win out, although not always quickly or smoothly.
As a piece of science writing for a general audience, Where the Wild Things Were ranks with Jonathan Weiner’s The Beak of the Finch for its ability to convey the excitement of research while getting the details right. Stolzenburg knows when to let the scientists speak for themselves, and his own prose is striking. Here, for example, is his description of Wiwaxia, a Cambrian fossil:
A sluglike beast sheathed in a chain-mail suit of armor and—just to make sure—a minefield of dagger blades springing from its back: A headless armadillo crossed with a tailless porcupine.
Stolzenburg’s lively descriptions and penetrating insights make this book a delight. It led me to look at familiar things with fresh eyes. Where the Wild Things Were is a joy to read, and its subject is an important one; I recommend it to scientists and nature lovers of all types.
Peter A. Bednekoff is professor of biology at Eastern Michigan University. His research interests include the behavior of birds in the nonbreeding season and, more generally, how animals find food while avoiding predators.