David S. Wilcove
Given the rate at which humans are changing the biosphere—altering land cover and nutrient cycles, extirpating some species while spreading others around the globe, even changing the very climate of the planet—it is easy to understand why so many ecologists choose to focus their research on questions relevant to conservation. Indeed, a seemingly new discipline, conservation biology, replete with its own society and journal, arose in the late 1980s to capture the growing enthusiasm for research directed toward maintaining the earth’s biodiversity. But, as many authors have noted, the roots of conservation biology go back decades, even centuries. In 1917, for example, the Ecological Society of America created a committee “charged with the listing of all preserved and preservable areas in North America in which natural conditions persist.” The committee’s report, published in 1926 as Naturalist’s Guide to the Americas (Shelford, 1926) represented an early, crude “gap analysis” of protected ecosystems in southern Canada and the United States. Starting in the late 1930s, the National Audubon Society hired young biologists to study North America’s rarest birds, including the ivory-billed woodpecker, California condor, and whooping crane, in an effort to prevent those species from disappearing (e.g., Koford, 1953; Tanner, 1966).
In some respects, these early assessments of declining ecosystems and imperiled species presage much of the contemporary literature in conservation ecology. The question naturally arises, what is new about conservation biology? Much of the novelty of conservation biology lies in its synthesis of many other disciplines, including evolutionary biology, ecology, economics, and sociology, for the purposes of understanding and ultimately addressing problems related to the loss of biodiversity (Groom et al., 2006). Moreover, contemporary conservation biology draws heavily from ecological and evolutionary theory with the goal of developing principles and insights that transcend particular species or ecosystems.
The chapters in this section cover some (but by no means all) of the “hot topics” in conservation biology, and they somewhat crudely trace the growth of the discipline itself. The section begins with a focus on species. Species extinction is, after all, one of the most visible and irreversible manifestations of biodiversity loss, and it remains the subject of much current research. Sodhi, Brook, and Bradshaw (chapter V.1) provide an overview of our current knowledge of human-caused extinctions. They compare the current rate of species loss (driven almost entirely by human activities) with the five great extinction events recorded in the geological record and find the destructive power of humans to be comparable to that of asteroid strikes and other abiotic events that have eliminated vast numbers of species in the past. Sodhi et al. also review the myriad ways in which human activities endanger biodiversity as well as the life-history traits that make certain species more vulnerable than others. They conclude with an alarming summary of the ways in which the loss of particular species, such as large predators and small pollinators, can trigger the extinction of many other plants and animals.
In reading the accounts of the biologists who studied ivorybills and condors more than a half-century ago, one cannot help but be impressed by their superb natural-history skills and their willingness to endure great discomfort and danger in pursuit of research. Yet the resulting work lacks predictive power. These scientists knew these animals were teetering on the brink of extinction, and in most cases they understood the reasons why. But they could not say how many individuals and populations needed to be saved in order to prevent extinction or what arrangement of habitat reserves would suffice to protect these birds for another century or two. The field of population viability analysis (PVA), discussed by Doak, Finkelstein, and Bakker in chapter V.2, strives to answer those types of questions. It entails the use of quantitative models to predict how populations of different sizes and configurations