Wildlife and Anthropogenic Changes in the Arid Southwest - Design with the Desert: Conservation and Sustainable Development - page 168

9.2 Anthropogenic Change
The arid Southwest has been profoundly affected by anthropogenic activities. Efforts
to secure adequate water, followed by conversion of land to agricultural use, and more
recently, urbanization, have greatly altered much of the region. Human population
growth, given the attraction of the “Sunbelt,” has been especially dramatic in the four
deserts of the Southwest: the Mojave Desert of southeastern California, the Great Basin
Desert of Nevada and adjacent states, the Sonoran Desert of Arizona and extreme northern
Mexico, and the Chihuahuan Desert of north central Mexico, western Texas, and southern
New Mexico (see Chapters 1 and 26). The unique Sonoran Desert has been fragmented
because of widespread development, 4,5 especially given rapid growth in the Phoenix and
Tucson areas (Figure 9.1). Riparian corridors, vital to so many wildlife species, were often
the primary targets of anthropogenic change, given the importance of water to permanent
human population centers. Alteration of water sources, including impoundment construc-
tion, lowered water tables, and draining of springs, was intimately associated with the
expansion of human populations in the Southwest. Introduction of non-native species,
especially large grazing mammals, including cattle, horses, and burros, also changed
existing habitats and thereby took a toll on native fauna. 6,7 Although direct loss of habitat
due to conversion of landscapes to urban and agricultural areas has been a highly visible
anthropogenic effect on desert wildlife, 8,9 other activities such as logging, fire suppression,
and livestock ranching profoundly altered biotic communities while superficially main-
taining natural habitats.
Over the past decade, studies have documented a variety of responses of vertebrates to
anthropogenic activities, but some generalities have emerged. Here, we examine anthro-
pogenic effects on wildlife in the arid Southwest with a focus on the two major rivers of
the region, the Colorado and Rio Grande, and on the organisms of the Sonoran Desert.
These examples highlight the nature of human-related effects on wildlife populations and
also indicate the successes and failures of conservation policy. For convenience, we group
anthropogenic effects on the fauna of the North American deserts into three basic sources:
direct habitat loss, habitat fragmentation, and habitat alteration. We examine each of these
in turn while addressing individual examples drawn primarily from the Sonoran Desert
before considering the two major watersheds and more detailed examples associated with
urbanization.
9.3 Habitat Loss
Development, leading to conversion of habitat to urban, rural, and agricultural areas, has
occurred throughout the Southwest over the past century. The past few decades have
witnessed the expansion of human populations onto landscapes initially converted to
agriculture in the early twentieth century. Metropolitan centers in the Southwest typically
exhibit extensive sprawl in which outlying areas are developed with little focus on
building “up” rather than “out” (Figure 9.2). The widely accepted notion that deserts are
largely lifeless wastelands with little if any inherent value no doubt contributed to the
lack of concern regarding the loss of these surprisingly diverse landscapes. Habitat loss is
the most obvious aspect of anthropogenic effects on wildlife, and in the Southwest, it has