arid parts of the ranges. Two or three years of unsuccess-
ful reproduction on a level with what has been observed
in single years (Van Horne et al. 1997) would be devastat-
ing. Because of their dependence on existing burrow sys-
tems, range expansion following localized extinction can be
slow and is sensitive to physiographic barriers. Although
conservation concern is reduced for species found across
a broad area, range extent is no assurance of population
persistence.
Several ground squirrels are subject to some of the same
threats to habitat as have been experienced by the more im-
periled species. For instance, Piute ground squirrels have
been reduced by invasion of exotic annuals (Van Horne et
al. 1997). Species and subspecies with very small ranges are
also threatened by broadscale climate and habitat change.
Like the Utah prairie dog, the Mexican prairie dog is found
in habitats potentially affected by climate change, and has
a limited range amid the dry and hot southern limits of prai-
rie dog extent.
Understanding and predicting these threats is essential
to the long-term persistence of these species. Recording
general habitat associations provides insufficient data to
predict population behavior. It is essential, for both com-
mon and rare taxa, to understand the processes that affect
the populations, particularly food availability. Once under-
stood, these linkages must be placed in the context of past
and predicted climatic trends and fluctuations, current and
expected habitat changes caused by invasive species and
land use changes, and current and expected disease epide-
miology. Successful conservation of populations requires
scientists and managers to identify the important regulating
processes and predict how they will change. The effects
of these changes on population persistence will need to
be further deduced. It is important to concentrate on the
bottom-up understanding of food habits and factors influ-
encing energy and nutrient flow through the primary pro-
ducers to ground squirrels.
Habitat fragmentation can be viewed as a secondary
phenomenon that interacts with habitat change to produce
both genetic and population effects. Fragmentation of hab-
itat reduces interconnectedness of populations. Such frag-
mentation can interact with disease, such as plague, by
reducing the likelihood of recolonization following local-
ized extinction. Understanding and predicting the effects
of habitat fragmentation requires an understanding of pop-
ulation dynamics across a broad scale. For socially struc-
tured species, such as prairie dogs, metapopulation struc-
ture may be pronounced. In such a situation, synchronous
change in populations (such as produced by climate) can
have a much greater effect on extinction than asynchronous
change (as might be produced by episodic plague; see den
Boer 1979). The degree of population interconnectedness
can be ascertained through genetic studies. Effects of ge-
netic discontinuities in space on the evolution of adapta-
tions, such as plague resistance, should not be discounted.
For this reason, the transport of animals for recolonization
should be considered only as a last resort for preventing ex-
tinction of the larger population or metapopulation.
The bottom line is that maintaining these species re-
quires that we first understand broadscale habitat change,
as from invasives or climate change, and the interaction of
habitat change with food habits of target species (Sherman
and Runge 2002). Second, we need to understand the ge-
netic structuring and dynamics of populations across the
landscape and the role of dispersal in influencing genetic
change and recolonization. This is particularly important
for the more highly social species that exhibit a metapopu-
lation structure. Low mobility of those species that are tied
to burrow systems and terrestrial navigation means that re-
colonization and range expansion is slow and difficult, as
in Idaho ground squirrels (Gavin et al. 1999; Sherman and
Runge 2002). Hence, for both habitat change and frag-
mentation considerations conservation efforts must focus
on long-term climate and population change, not just the
short-term fixes to population density.
Conserving ground squirrels will require some change
in human perception and values. The historic classification
of these species as varmints seems to imply an ability of the
populations to rebound and recolonize, if not overrun, ar-
eas of occupancy. Yet ground squirrels are far less mobile
than avian species, large-bodied mammals, or most small
rodents because of their dependence on burrow systems.
Populations are easily diminished by disease or lack of food.
Hence, as a group, they are exceptionally sensitive to habi-
tat change associated with factors such as climate change,
invasives, fragmentation, and land-use changes. Avian spe-
cies receive far more attention relative to such threats;
indeed, much of the ground squirrel research has been stim-
ulated by the role of these species as avian prey. A compre-
hensive, multinational evaluation of ground squirrel habi-
tat, and current and projected threats to that habitat, could
provide the foundation for educational and political changes
that would help preserve not only these species but also the
ecosystems on which they depend. This would be an impor-
tant first step in avoiding multiple near-term extinctions.Conservation of Ground Squirrels 471