A petition to resolve the Endangered Species Act taxonomy debate

Today, PLF and several allied organizations submitted a petition for rule-making to the federal agencies that administer the Endangered Species Act. The petition asks the agencies to define “species” and “subspecies,” terms which, although critical to the Act’s operation, are left undefined by statute and regulation. Not surprisingly, this lacuna has produced inconsistent and arbitrary decision-making (see, e.g., the litigious and ongoing debates over the coastal California gnatcatcher’s subspecies designation), with landowners typically shouldering the burden. The lack of guidance also has resulted, according to some critics, in the agencies’ playing of a “numbers game,” whereby a single species is split into multiple species or subspecies, and because each resulting taxonomic unit will have fewer numbers and smaller ranges, each will be at greater risk of extinction and therefore more likely to be listed.

Our petition seeks an end to the arbitrariness through the setting of clear, scientifically defensible and politically sensible definitions for the statutory terms “species” and “subspecies.” The petition recommends that, for the former, the longstanding and well-regarded biological species concept be adopted, according to which a species is delimited by reproductive isolation. For the latter, the petition asks for the adoption of a variant of the equally longstanding “75% rule,” pursuant to which individuals within a species must be diagnosed accurately at least 75% of the time as belonging to putative Subspecies A or B or C, etc., using genetic or other biologically significant characters.

Although not universally accepted in the scientific community, our proposed definitions are scientifically defensible. And in any event, no single definition of “species” or “subspecies” will receive unanimous support from the scientific community, in part because neither term is a pure function of science. Rather, both are terms of convenience, deriving their value from larger conservation policy. Informing that larger policy is the fact that the protection of all populations is economically and socially infeasible. Sound conservation demands prioritization. Many scientists believe that the priority of conservation should be the preservation of evolutionary potential—i.e., biodiversity. If that is correct, then being choosy about which populations can be eligible for protection makes sense as a matter of science.

But it also makes for good social policy. Moderating the Act’s economic impact through fewer listings—a likely consequence of adopting rigorous taxonomic standards that will eliminate outmoded classifications—lessens the chance of a public backlash that might undercut support for wildlife protection. Moreover, time and money that might have been spent on protecting insignificant populations instead can be directed toward those populations the preservation of which best serves biodiversity. We therefore hope that the agencies will respond promptly—and favorably—to our proposal.