It makes sense to commence a discussion of conservation biology with a concise definition of the discipline. There are, however, a variety of definitions for this emerging field, ranging from those that focus on the biological elements of biodiversity to those that emphasize integration of the biological and social sciences. Proponents of the former believe that the field should focus mainly on developing biological principles for conservation, often on the assumption that training someone in all the relevant fields will result in practitioners who know a little about many things but do not have the depth of knowledge in biology needed to make effective decisions. Others believe that the social sciences are equally important elements, as it is clear that knowledge of biological principles alone is insufficient for successful management of biodiversity. Political, cultural, and economic factors heavily influence the success of any particular conservation strategy. A number of excellent undergraduate texts on Conservation Biology are currently in use (for example, Hunter, 2001; Meffe and Carrol, 1997; Pri-mack, 1995, 1998; see also http://conbio.net).
For the purposes of this essay, we will define conservation biology as an applied discipline that integrates the natural and social sciences for the purpose of maintaining the earth's biological diversity.
Setting boundaries for the field of conservation biology has been and continues to be a major undertaking. In principle, conservation biology emerges as a distinct field in at least three major ways (Meffe and Carroll, 1997a). First, it is an interdisciplinary field, embracing input from both the social and biological sciences. Biological information is most effective when placed into a political, economic, or social context. Therefore social sciences—philosophy, economics, political science, urban planning, anthropology, and so forth—are often critical to successful conservation measures.
Second, previous conservation efforts were overwhelmingly undertaken at the species level and focused on utilitarian objectives (for instance, high yield of game species). Conservation biology, on the other hand, encompasses all levels of biodiversity (from genes through populations, species, communities, and ecosystems to landscapes), and emphasizes the importance of diverse and functioning ecosystems as well as so-called noncharismatic organisms, such as invertebrates, fungi, and bacteria. Knowledge of the patterns of biodiversity distribution and the processes of evolutionary change are critical to effective management of resources.
Third, as originally conceived, conservation biology is designed to meld theoretical and applied approaches, and though the feasibility of this is still in question, conservation biologists still aspire to this fusion.
Several other general principles underlie (and further complicate) conservation biology. The natural world is dynamic—maintenance of ecological structure and function often depends upon natural disturbances such as fire, flooding, drought, hurricanes, and storms. Conservation biologists try to consider these
(often decade-scale) disturbances when making decisions. Lack of data on these issues often compels them to turn to modeling and a focus on large-scale patterns. Conservation biologists use similar approaches as they seek to sustain the evolutionary processes that lead to the generation and maintenance of biodiversity. The unpredictability of the natural world forces them to incorporate uncertainty into their models and decisions. Another important element of the field is that humans must be included in every aspect of conservation planning.
The field of conservation biology is a relatively young one. Impetus for its development arose from heightened awareness of the impact of human actions on the natural world. Conservation biology arguably emerged as a full-scale discipline in the late 1970s, with the First International Conference on Conservation Biology held in San Diego, California, in 1978, and the resulting book, Conservation Biology (Soule and Wilcox, 1980). The attending scientists highlighted the sense of urgency in responding to the increasing scale and scope of species and habitat loss, calling conservation biology a "crisis discipline." They advocated looking at biodiversity broadly, emphasizing diverse and functioning ecosystems in place of a focus on economically valuable or threatened species. Early efforts that set the stage for this movement by fusing evolutionary ecology with resource conservation include Dasmann's Environmental Conservation (1959) and Ehren-feld's Biological Conservation (1970).
Scientists from a medley of disciplines (including wildlife ecology, natural resource management, agronomy, forestry, fisheries biology, and basic biological sciences such as ecology, genetics, zoology, and botany) who were writing and researching in the decades preceding the 1980s contributed to the genesis of the field. For instance, the first issue of the Jour nal of Wildlife Management (1937) is replete with references to the "new and growing field of conservation biology" (Errington and Hamerstrom, 1937) and called for study and conservation more than just economically important species (Bennitt et al., 1937). Yet in subsequent years, the focus of wildlife management was predominately on managing game species (mammals, birds, and fish) for sport. Conservation biology arose because none of these individual disciplines was broad enough to address the complex issue of biodiversity conservation.
Studies at the genetic level have been prominent since the emergence of the discipline, because of the fear that increasing fragmentation and decreasing population size would lead to a loss of genetic variation and the concomitant decrease in fitness of wild populations. Conservation biologists use both theoretical and empirical methods to assess the impacts of fragmentation on wild populations. These studies have allowed decision-makers, scientists, and managers to estimate the viability of populations and to guide protected area design. Employing paradigms from evolutionary biology and systematics, conservation biologists have worked to better identify natural units—definitions critical for managing translocation and reintroduction efforts, prioritizing taxa for conservation, tracking trade in endangered species, and designing captive breeding programs for targeted species.
Early species-level conservation efforts in conservation biology concentrated on rarity and loss, exploring how to maintain genetic diversity in small populations. In the mid-1990s, Caughley (1994) suggested that intervening when a population is already in crisis might not be the most effective strategy, and instead recommended that efforts be made to identify and mitigate the factors that lead to declining populations. Both of these perspec tives are important for effective management in the field, but individual practitioners may have more use for one or the other, depending upon the problem they are trying to solve. Increasingly, conservation biologists are focusing on monitoring and management of populations.
This increasing emphasis on understanding the causes underlying the declines of species or communities led conservation biologists to consider even larger, ecosystem-level approaches to managing processes that influence many species' status. To develop principles for the design of protected areas, early conservation turned to ecological and bio-geographical theories such as MacArthur and Wilson's 1967 theory of island biogeography and the species-area relationship, which describes the interplay between island size, isolation, immigration, extinction, and the number of species that can ultimately inhabit a given island. This concept was adapted for use in fragmented terrestrial landscapes, where reserves become "islands" of natural areas in a "sea" of human-dominated landscapes. Using this paradigm, Jared Diamond (1975) and others developed a set of recommendations for spatial location and shape of terrestrial protected areas.
Although conservation biologists aspire to take an ecosystem approach to studying, managing, and conserving biodiversity, logistics and resources often limit the feasibility of its implementation. One avenue they have taken for large-scale conservation is to design effective systems of protected areas given the distribution of available wildlands and the ranges of species of concern. Rarely do biologists or decision-makers start from scratch in designing systems of reserves, so the first step in a regional system of reserves is to determine what is already protected. A "gap analysis" is often used to compare what is currently pro tected with what "should" be protected (essentially looking for "gaps" in the protected-area system). This analysis uses satellite remote sensing, geographic information systems, and other techniques to help assess the current status and distribution of biodiversity, to locate areas managed primarily for biodiversity, to identify biodiversity that is not present or is underrepresented in managed areas, and to set priorities for conservation action.
Conservation biologists have recently embraced broader scales (including landscapelevel conservation efforts that promote conservation on private lands), as well as newer tools such as adaptive management—essen-tially learning by doing—developed to help deal with uncertainty at all levels of biodiversity. Each management decision becomes an experiment, testing outcomes against proposed goals. If the goals are not met, an alternative management strategy is proposed, forming another experiment, and so on.
As the field of conservation has evolved, several challenges have emerged. First, there is an inherent tension in the field between academics struggling to capture the complexity and unpredictability of natural systems in bodies of theory and practitioners who need to make finite decisions quickly, often based on little available empirical data. Important basic research on community dynamics, population and community modeling, and levels of genetic diversity contributes to effective management of populations and communities. Baseline data on distribution of species across space are critical to setting priorities effectively and to monitoring populations over time to assess conservation strategies.
However, academics generally do not get credit within their institutions for undertaking applied conservation, and they are often actively discouraged from participating in practical conservation work. Conversely, prac titioners ordinarily do not have the time to read the kinds of papers and books for which academics do get credit. The fact is that both perspectives are important to managing biodiversity. As the field continues to develop, this gap clearly needs mending.
A second tension lies with the question of advocacy. Conservation biologists are by definition interested in the preservation of biodiversity. Some fear that using their data to argue for one conclusion or another in the political arena taints their objectivity as a scientist. Others feel that conservation biologists are best placed to offer opinions that influence policy, as they are most familiar with the indications of problems such as population decline.
The complexity of biodiversity, spanning levels from genes to landscapes, and encompassing interactions and processes between and among the levels, sets a cumbersome task for conservation biologists. We know effectively little about how natural systems work and much less about how they respond to perturbations, both large and small. We are just beginning to think about how altered systems can be restored to a "natural state." As humans transform both terrestrial and aquatic environments—for instance, by appropriating extraordinary amounts of primary productivity, by moving species from one ecosystem to another (willfully or no), and by releasing beings created in the laboratory into the environment—the term natural takes on new meaning. These are some of the challenges that confront future conservation biologists concerned with maintaining the earth's biodiversity in an increasingly human-dominated world.
See also: Conservation, Definition and History; Ethics of Conservation; Organizations in Biodiversity, The Role of; Stemming the Tide of the Sixth Global Extinction Event: What We Can Do; What Is Biodiversity?
Bennitt, R., et al. 1937. "Statement of Policy." Journal of Wildlife Management 1: 1-2; Caughley, Graeme. 1994. "Directions in Conservation Biology." Journal of Animal Ecology 63, no. 2: 215-244; Dasmann, R. F. 1959. Environmental Conservation. New York: John Wiley and Sons; Diamond, Jared. 1975. "The Island Dilemma: Lessons of Modern Biogeographic Studies for the Design of Natural Reserves." Biological Conservation 7: 129-146; Ehrenfeld, David W. 1970. Biological Conservation. New York: Holt, Rinehart and Winston; Errington, P. L., and F. N. Hamerstrom, Jr. 1937. "The Evaluation of Nesting Losses and Juvenile Mortality of the Ring-neck Pheasant." Journal of Wildlife Management 1: 3-20; Hunter, Malcolm L. 2001. Fundamentals of Conservation Biology, 2d ed. Cambridge: Blackwell Science; MacArthur, R. H., and Edward O. Wilson. 1967. The Theory of Island Bio-geography. Princeton: Princeton University Press; Meffe, G. K., and R. Carroll. 1997. Principles of Conservation Biology, 2d ed., Sunderland, MA: Sinauer; Meffe, G. K., and R. Carroll. 1997a. "What Is Conservation Biology?" In Principles of Conservation Biology, 2d ed., edited by Meffe and Carroll, pp. 3-27. Sunderland, MA: Sinauer; Primack, R. B. 1995. A Primer of Conservation Biology. Sunderland, MA: Sin-auer; Primack, R. B. 1998. Essentials of Conservation Biology, 2d ed. Sunderland, MA: Sinauer; Soule, Michael E., and Bruce A. Wilcox. 1980. Conservation Biology: An Evolutionary-Ecological Perspective. Sun-derland, MA: Sinauer.
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