Letter to the Editor
Endangered Species and Peripheral Populations:
Cause for Conservation
Introduction
Jennifer L. Nielsen
U.S. Geological Survey, Biological Resources Division, Alaska Biological Science
Center, Anchorage, Alaska 99503;
jennifer_nielsen@usgs.gov
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;
aycr8488@uidaho.edu
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.