16.13: With limited conservation resources, we must prioritize which species should be preserved.

Is it preferable to save one beautiful, well-studied bird species or 1,000 species of bacteria, none of which have even been described or named? And what about the 1,200 species of beetles in Panama that live in the evergreen tree Luehea seemannii, almost 200 of which live only in this one species of tree—how should we prioritize these species for conservation relative to, say, a single primate species? From locale to locale the particulars of these questions may change, but the underlying issue remains: in a world where species are being driven to extinction faster than we can save them, which should be singled out for preservation and which should we leave to almost certain extinction (FIGURE 16-33)? This is a question that biologists, policymakers, and, ultimately, citizens must address.

When setting conservation priorities, it is essential to articulate a goal. In an ideal world, the goal might be to protect “all biodiversity.” Barring that, options include protecting “most biodiversity”—that is, the most diverse subset of biodiversity (in terms of genes, species, and ecosystems)—or protecting the most valuable biodiversity. There are numerous arguments in favor of each goal, and each has significant flaws as well. Once a goal is decided on, a plan is needed that outlines priorities for achieving the goal. Frequently, such a plan involves an assessment of the degree to which various components of biodiversity are threatened. We can rank species, for example, as relatively intact, relatively stable, vulnerable, endangered, or critical. These rankings can then be used, in conjunction with measures of the biological value of the biodiversity to humans, in formulating a plan.

As we saw earlier in the chapter, biodiversity can be valued in many different ways, and its worth is not easily quantified or weighed. Sooner or later, many difficult and subjective decisions must be made in the goal-setting and prioritizing process. The undiscovered bacterial species may harbor the metabolic secrets to curing a devastating medical condition in humans, but the beautiful bird species may be much loved by bird-watchers or may serve as a powerful icon of strength or freedom, inspiring generations of people. The decisions are difficult, but not facing them is, in most cases, the same as making a decision.

In the United States, much conservation policy involves response to the Endangered Species Act (ESA), a law that defines endangered species as those in danger of extinction throughout all or a significant portion of their range. The law is designed to protect these species from extinction. As we noted earlier in the chapter, species that are dwindling are listed as endangered or threatened, according to an assessment of their risk of extinction. Once a species is listed, legal tools are available to help rebuild the population and protect the habitat critical to its survival.

Seemingly straightforward, the ESA has had the effect of focusing most conservation efforts on the preservation of individual species (and populations), sometimes at the expense of other elements of biodiversity and sometimes at the expense of efforts to reduce the loss of ecologically important habitats (FIGURE 16-34). Other difficulties are also associated with the ESA. Consider the task of determining the critical population size below which a population is endangered—is it 500 individuals or 5,000 or 50,000? With its emphasis on preservation of single species, the ESA does not effectively address ecosystem decline, which is an equally urgent and serious problem.

In spite of these difficulties, the species-focused approach to conservation has had some success in the United States. Since it became law in 1973, approximately 40 species that were listed as endangered—including the bald eagle, the peregrine falcon, the gray whale, and the grizzly bear—have been taken off the list as their numbers have recovered. In the final section, we examine other strategies that have been used in efforts to preserve biodiversity.