Letter to the Editor
Endangered Species and Peripheral Populations: Cause for Conservation
Jennifer L. Nielsen
U.S. Geological Survey, Biological Resources Division, Alaska Biological Science Center, Anchorage, Alaska 99503;
J. Michael Scott
U.S. Geological Survey, Idaho Cooperative Fish and Wildlife Research Unit, College of Natural Resources,
P.O. Box 44-1141, Moscow, Idaho 83844-1141; mscott@uidaho.edu
Jocelyn L. Aycrigg
P.O. Box 441136, Department of Fish and Wildlife Resources, University of Idaho, Moscow, Idaho 83844-1136;

Peterson (2001) suggests that conservation efforts aimed at peripheral populations of species dilute the effectiveness

of the Endangered Species Act (ESA). Furthermore, he states that specific peripheral populations are often not viable,

could be considered sink populations, or are often species of little conservation concern. He goes on to say that the

biology of the species should be considered when deciding which species to put on the endangered species list.

We strongly agree with the assertion that the biology of the species should be fully considered when assessing

the conservation status of a species. Lack of such information is one of the biggest hurdles to a species' recovery

(Schemske et al. 1994; Tear et al. 1995). However, we differ from Peterson (2001) in the conservation value of

peripheral populations. In contrast to Peterson's (2001) statement that peripheral populations have always been marginal,

it is well documented that species' ranges change dramatically with global shifts in climate. Global warming could affect

species that reach northern extremes along the U.S. southern border by shifting their ranges further north

(Abbitt et al. 2000). Peripheral populations may survive in isolated refugia that later, with different environmental

conditions, serve as a source population for an expanded range and subsequent adaptive radiation (Flannery 2001). What

constitutes a peripheral population today could be the center of a species' range in the future. For example, the present

California condor (Gymnogyps californianus) population is peripheral to its historical distribution, which ranged from

California to New York (Snyder and Snyder 2000). We are unable to anticipate the future geographical distribution

of species. We ignore the dynamic nature of the natural world if we assume that common species in one location

(e.g., the gray wolf, Canis lupus, in Alaska) do not need protection elsewhere in their range where they may be rare

(e.g., gray wolf in Idaho) (Botkin 1990). Even abundant and widespread species have gone extinct (e.g., the passenger

pigeon, Ectopistes migratorius). Moreover, peripheral populations survive more frequently than do core populations

when species undergo dramatic reductions in their range (>75%; Channell and Lomolino 2000). Thus, we believe

peripheral populations are vitally important to a species' past, present, and future existence. The ESA, by allowing

for the listing of subspecies and distinct population segments, explicitly identifies the evolutionary potential of

each species as our conservation goal in law. We contend that ultimately the management unit of interest for a

species is its full range of variation, for only then can a species' evolutionary trajectory be possible.