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 are likely to fare in the face of various natural and human-caused impacts. PVA featured prominently in the rancorous debate over the conservation of old-growth forests and northern spotted owls in the late 1980s. It has subsequently become an integral tool in conservation planning for endangered species around the world.
Given our improved knowledge of the factors influencing the persistence of populations, how do we design effective reserves for species in trouble? In chapter V.3, Haddad reviews the growing literature on reserve design. He summarizes the numerous theoretical, empirical, and experimental studies that bear on this issue, with special emphasis on habitat area, connectivity (achieved via habitat corridors and stepping-stones), and edge effects. As Haddad notes, the objective behind much of this work is to maximize the effective area of reserves—in other words, to protect blocks of habitat of the right size, shape, and distribution to preserve their target species for as long as possible. Thus, there is a clear linkage between the PVAs discussed by Doak et al. and the reserve design issues discussed by Haddad.
Although conservation biologists and practitioners continue to devote time and attention to the protection of individual species, the sheer scope of the contemporary biodiversity crisis requires them to think in terms of networks of reserves that protect multiple species. In chapter V.4, Turner and Pressey review the new and rapidly growing field of systematic conservation planning. They highlight the development of increasingly sophisticated algorithms designed to help planners deal with the painful realities of contemporary conservation: inadequate funding, incomplete data, ongoing losses of wild lands, unpredictable opportunities to acquire key parcels of land, and the differing area requirements of species. The goal of these algorithms is to identify systems or networks of conservation areas that meet explicit, quantifiable biodiversity targets with maximum efficiency and effectiveness. It is probably fair to say that, at the present time, the sophistication of these algorithms exceeds the abilities of many organizations to use them. Nonetheless, as more institutions become familiar with these tools, and as the tools themselves become more user friendly, they will surely be used far more frequently.
The final three chapters focus on topics that were, to varying degrees and for different reasons, neglected in the early years of contemporary conservation but that are now at the forefront of the field.
In chapter V.5, Jackson documents the frightening degree to which humans have degraded marine ecosystems. In particular, he highlights the pervasive impacts of overfishing and pollution, which he identifies as the main drivers of change in the world’s oceans. The problem of overfishing, Jackson notes, is so vast that, across the globe, most populations of whales, sea turtles, and large predatory fish have been hunted to the point of ecological extinction; their current densities are so low that these species play no significant ecological role in the ecosystems where they persist. Readers familiar with the history of wildlife in North America may be reminded of the late nineteenth century, when a seemingly insatiable demand for pelts, flesh, and feathers, coupled with a hatred of large predators, led to the elimination or endangerment of bison, wolves, bears, mountain lions, wading birds, shorebirds, and other species across much of the continent. Conservation of the seas appears to be a century or more behind conservation of terrestrial ecosystems, a lapse made all the more dangerous by the fact that our destructive powers at the start of the twenty-first century vastly exceed those at the start of the twentieth.
A century ago, the notion that people could alter the earth’s ecosystems by inadvertently altering its climate would have seemed ridiculous to most scientists. Needless to say, that is no longer the case. In chapter V.6, Debinski and Cross tackle the challenges that climate change poses for conservation. They argue that the abiotic changes stemming from climate change—for example, rising sea levels, altered precipitation patterns, and disruptions of natural disturbance regimes—will affect the distribution and abundance of species. As individual species fade in or out, other species (e.g., predators, competitors, mutualist partners) will be affected too, leading to cascading effects. Incorporating the effects of climate change into PVAs (chapter V.2) and reserve design algorithms (chapter V.4) remains a major challenge in conservation biology. The oceans, too, are hardly immune to global climate change. One such threat, highlighted by Jackson in chapter V.5, is increasing acidification of the seas; the possible consequences are almost too frightening to imagine.
Given the gaps in our network of protected areas, habitat destruction, climate change, and continuing losses of ecosystem services essential to human welfare, the ability to repair damaged ecosystems is surely one of the most important weapons in our conservation arsenal. In chapter V.7, Hobbs discusses the underappreciated but rapidly growing field of restoration ecology. Defined as the science underlying the practice of repairing damaged ecosystems, restoration ecology draws heavily from ecology and environmental engineering. Hobbs is careful to point out that ecological restoration is not simply an exercise in time travel, an attempt to restore an ecosystem to what it was like at some arbitrary point in the past. After all, many ecosystems are inherently dynamic; their composition and structure change naturally over time. Moreover, it may not be possible to restore all of the species that once occupied the ecosystem, regardless of how important they may have been. No restoration plan for the hardwood forests of eastern North America includes the passenger pigeon, and very few include the gray wolf or mountain lion. Thus, as Hobbs notes, practitioners of ecosystem restoration are increasingly of the opinion that there can be a range of outcomes for any given place. The challenge then becomes one of developing a “transparent and defensible method of setting restoration goals that clarify the desired characteristics for the system in the future, rather than in relation to what these were in the past” (chapter V.7).
The chapters presented in this section are, at best, a limited subset of the range of topics that fall under the umbrella of conservation biology. Some of the chapters in other sections (e.g., invasive species) could easily have been placed here. Conversely, many of the chapters in this section would fit equally well in other sections of the volume. This healthy ambiguity is a reflection of the fact that conservation biology has successfully borrowed from and contributed to a wide range of subjects in ecology.
Groom, M. J., G. K. Meffe, and C. R. Carroll. 2006. Principles of Conservation Biology, 3rd ed. Sunderland, MA: Sinauer Associates.
Koford, C. B. 1953. The California Condor. National Audubon Society Research Report No. 4. New York: National Audubon Society.
Shelford, V. E. 1926. Naturalist’s Guide to the Americas. Baltimore: Williams & Wilkins.
Tanner, J. 1942. The Ivory-billed Woodpecker. National Audubon Society Research Report No. 1. New York: National Audubon Society.