Wildlife and Anthropogenic Changes in the Arid Southwest - Design with the Desert: Conservation and Sustainable Development - page 179

species on native species and lead to decreases in lower trophic level food production
(e.g., algal and invertebrate food bases). In Arizona, this pattern of habitat alteration along
the many tributaries of the Colorado River has apparently allowed for the expansion of
Woodhouse's toad, a species that thrives in many disturbed habitats, relative to the native
stream-dwelling Arizona toad that has declined. 81

9.4.3 Habitat Fragmentation and Alteration in Urbanized Sonoran Desert

Anthropogenic effects in urbanized landscapes are receiving greater attention: recent stud-
ies of reptiles indicate that many forms have been affected by habitat loss and alteration,
leading to local extirpation of many taxa. 82 Reptiles respond individualistically to remain-
ing fragments of desert habitat associated with preserves, and both the size of the preserve
as well as floristic and geological structure can be important to viability of populations. 82
Relatively large lizards and snakes appear especially vulnerable to effects of urbaniza-
tion in the Sonoran Desert, especially in the Phoenix metropolitan area. 83 The common
chuckwalla is a large, herbivorous lizard inhabiting the Mohave and Sonoran deserts,
and though an extreme habitat specialist restricted to rocky microhabitats, it continues to
inhabit the Phoenix Mountain Preserve system. It may be that the more restricted micro-
habitat preferences of common chuckwallas allow them to persist while other large lizards
of the Sonoran Desert preferring open areas (e.g., desert iguanas, long-nosed leopard liz-
ards, regal horned lizards) have declined in these same preserves. This may be a common
occurrence for rock dwelling lizards: in many metropolitan regions, rocky slopes may be
the least likely area of a preserve to be affected by human activity (Figure 9.12), although
off-trail activities (rock-climbing) and collection of common chuckwallas for the pet-trade
may contribute to degradation of crevices. 84 In contrast to the habitat specialist common
chuckwallas, birds persisting in urban areas generally had broader environmental toler-
ance than rural congeners. 85
Other studies suggest that squamate reptiles can be negatively affected by habitat altera-
tion, even when preserves of natural habitat are set aside. Some lizards are more attuned to
variation in habitat quality (thermoregulation sites, percentage of ground cover) than pre-
serve size per se. 82 Habitat diversity within preserves is associated with lizard diversity;
presumably, increased habitat variation allows for a larger number of specialized forms to

(a) (b)

FIGURE 9.12
Chuckwallas (a) still occur in the Phoenix Mountain Preserves though they are surrounded by a sea of urban-
ization. Unfortunately, rocks can be permanently damaged by collectors and other off-trail activities leading to
the loss of vital crevice refuges (note exposure of underlying light colored rock in (b) center).