Wildlife and Anthropogenic Changes in the Arid Southwest - Design with the Desert: Conservation and Sustainable Development - page 183

argue that the “new ranch” breaks with historical practices and adopts ecologically
sound principles in which cattle are mere tools to achieve conservation goals such as
bio d ive r s it y. 94 Nathan Sayre's recent critique of abstractions such as “natural” (used herein
to denote “historical”) notwithstanding, conservation goals must be implemented relative
to some baseline, and for the arid Southwest, the recent evolutionary past is defensible.
In the absence of agreement on this issue, one could defend the maintenance of highly
artificial reservoirs in Arizona because they achieve the conservation goal of increasing
biodiversity. These highly altered habitats support many more species of fish (dozens)
today relative to historic aquatic habitats (e.g., Aravaipa Creek, with seven native forms
historically), but at the expense of the native forms. 66 Characterization of ranchers as
champions of nonequilibrium community ecology in which livestock grazing is recast as
a form of disturbance contrasts with efforts of the livestock industry to establish that cattle
have simply “replaced” extirpated wildlife. 103 Nonetheless, shifts in perception of aridland
grazing in the Southwest cannot obscure the fact that ranching entails enormous effort to
transform local biotic communities to a highly altered state with empirically documented
negative consequences for arid adapted wildlife. 32
The aquatic examples outlined earlier portend adverse effects for endangered south-
western fish given the extreme decline documented for so many populations of many
species. Predictions of extinction rates have been based largely on the demonstrated rela-
tionship between number of species in a given group and habitat area. 104 Principles of
metapopulation theory predict that the amount of extinction caused by habitat destruction
is an accelerating curve; thus, if a high proportion of habitat is already destroyed, even
a very small increase in habitat destruction will dramatically increase extinction risk. 105
Furthermore, there is a limit, termed the extinction threshold, which is the percentage of
habitat destruction beyond which a species will ultimately head for extinction. 106,107 In one
model, effects of habitat destruction became important with only 28% habitat loss, when
some patches became isolated; extinction thresholds occurred at 66% habitat destruction
or less. 108 Given sufficient habitat destruction, the equilibrium can be extinction; many rare
and endangered species may already be committed to extinction, unless the loss and frag-
mentation of their habitat are reversed. Global climate change will undoubtedly exacerbate
these issues for fish of the arid Southwest as human population growth results in ever
increasing demands for water. 109
Maintenance and restoration of historic aquatic ecosystems (i.e., flow rates, flood regimes,
temperature profiles) are perhaps the single most difficult challenge facing conservation
biologists and concerned citizens today. Thus far, the section of the Little Colorado River
inhabited by humpback chub essentially functions as a free flowing river, characterized by
an annual spring runoff, periodic episodes of highly turbid water, and by seasonally warm
water temperatures. However, depletion of the aquifer(s) that feed the lower 13 miles of the
Little Colorado River and maintain a year-round flow in this stretch of river would seriously
threaten this self-sustaining population of endangered fish. For razorback sucker, if large
self-sustaining mainstem populations cannot be established, off-channel populations in
predator-free habitat are likely the remaining option. 110 For many species of native fishes
in the southwest, the construction of physical barriers in small order streams, followed by
the removal of non-native fish and the reintroduction of the native fish fauna appears a
viable option.
Our review highlights three primary issues with respect to conservation of wildlife
of the Southwest. First and foremost, preservation of intact habitat is vital. In situations
where habitat alteration and fragmentation have occurred or are inevitable, low density
housing with patches of intact habitat may allow for at least some wildlife species to