Lizard species distributions and habitat occupation along an urban gradient in Tucson, Arizona, USA
Introduction
Expanding human populations are altering natural environments world-wide at an accelerating rate (Wilson, 1986). Anthropogenic disturbances often result in habitat fragmentation, degradation, and loss, and these phenomena threaten biological diversity (Primack, 1993). Nowhere are anthropogenic effects on environments more apparent than in urban areas.
As urbanization intensifies locally, the physical structure and species composition of native habitat becomes increasingly altered from a natural state (Whitney and Adams, 1980, Theobald et al., 1997). As development progresses, native vegetation is replaced by man-made features, building density increases, soils become compacted, and micro-climates becomes less stable (Bradley, 1995). Non-native vegetation increasingly replaces native plants in developed areas, and undeveloped native habitat remnants become increasingly insularized (Soulé et al., 1988, Germaine, 1995). Land within the matrix surrounding native remnants may become increasingly impenetrable as developmental alterations continue (Goszczynski, 1979). Isolated native habitat remnants support fewer species than similar-sized plots located in undeveloped areas (Bolger et al., 1997a). Consequently, developed areas become increasingly less able to support populations of many native wildlife species (Gavareski, 1976, Dickman and Doncaster, 1987, Sears and Anderson, 1991).
Reptile population responses to urban development are perhaps the least understood of all classes of vertebrates in urban environments. Although losses of lizards from urban areas have been documented in recent literature, cause is seldom determined, and in some cases reports of losses are purely retrospective and anecdotal (e.g. McCoid et al., 1994, Walker et al., 1996). Herpetofauna populations in urban areas have been impacted by destruction of protective ground cover (Minton, 1968, Orser and Shure, 1972), entrapment in window wells (Heck, 1971), increased predation (Schaaf and Garton, 1970), collecting (Beebe, 1973), and pollution and pesticides (Anderson, 1965, Scott, 1973). Roads act as barriers to dispersal and increase mortality for both herpetofauna and small mammals (Gibbs et al., 1971, Mader, 1984, Fahrig et al., 1994). In addition, human disturbance to critical habitat components can result in the loss of microhabitats needed for predator avoidance and reproductive activities (Hecnar and M'Closkey, 1998). Finally, the cumulative effects of urban development of landscapes over time and space may constitute a major impact on wildlife in affected areas (Theobald et al., 1997).
Using multivariate analyses, we examined habitat relationships of lizards along the rural–urban gradient in Tucson, Arizona. Germaine et al. (1998) documented three patterns of habitat disturbance (changes in habitat physiognomy, floristics, and spatial relationships of habitat patches) associated with urban development that affected avian communities. We hypothesized that these patterns of habitat disturbance resulting from urban residential development also affect lizard communities. Specifically, we tested the following hypotheses concerning lizard–habitat relationships along the urbanization gradient: (1) lizard species distributions (abundance) are not related to habitat features describing the urbanized gradient; (2) habitat composition does not affect site occupation (presence) by lizards; and (3) habitat changes along the urban gradient do not affect total abundance, species richness, or evenness of the lizard assemblage.
Section snippets
Study area
We conducted this study in the greater Tucson metropolitan area, in southeastern Arizona. The study area included land within 19.2 km of the center of Tucson (a point mid-way between the geographic and population centers), and comprised 1158 km2, most of the Tucson Basin. Tucson contains Lower and Upland Sonoran vegetative types, as well as riparian and xeroriparian vegetation (mixed riparian desert scrub series; Brown, 1994). While relicts of these cover types are found within the urbanized
Lizard assemblage
We encountered nine species of lizards during the surveys. Whiptail lizards were the most abundant, totaling 192 individuals, in part because members of this genus were not identified to species. Within the Cnemidophorus, western whiptail lizards (C. tigris) were most abundant, while Sonoran spotted whiptail lizards (C. sonorae) were the only other species identified. However, Gila spotted (C. flagellicaudus) and giant spotted (C. burti stictogrammus) whiptail lizards also occur in the Tucson
Lizard species distributions
Lizard species distributions among sites were related to habitat features describing the urban gradient in Tucson (Ho: 1). Additionally, the CCA generated axes that distinctly described the urbanized gradient, floristic and structural complexity of plots, and the presence of intact riparian vegetation. Areas of natural, undisturbed vegetation became increasingly diminished and fragmented as housing density and amount of paved area increased. This was demonstrated by the positive relationship
Acknowledgments
Funding for this study was provided by a grant from the Arizona Game and Fish Department Heritage Fund. Jen Wennerlund performed the random point selection in Arc/Info, and Kirby Bristow assisted with plot location on the ground. John Koloszar measured vegetative cover in plots from aerial photographs. We thank R. Gerald Wright, Mark Andersen, and an anonymous reviewer for offering suggestions which improved an earlier draft of this paper.
References (45)
- et al.
Effects of human disturbance on five-lined skink, Eumeces fasciatus, abundance and distribution
Biological Conservation
(1998) Animal habitat isolation by roads and agricultural fields
Biological Conservation
(1984)- et al.
Estimating the cumulative effects of development on wildlife habitat
Landscape and Urban Planning
(1997) Problems in the measurement of evenness in ecology
Oikos
(1981)The Reptiles of Missouri
(1965)Arizona County Population Projections
(1996)Observations concerning the decline of British amphibia
Biological Conservation
(1973)- et al.
Effects of urbanization on avian community organization
Condor
(1982) Land use and avian species diversity along an urban gradient
Ecological Applications
(1996)- et al.
Response of rodents to habitat fragmentation in coastal southern California
Ecological Applications
(1997)
Breeding bird abundance in an urbanizing landscape in coastal southern California
Conservation Biology
Urban forest landscapes: integrating multidisciplinary perspectives
Biotic Communities: Southwestern United States and Northwestern Mexico
Diversity in tropical rain forests and coral reefs
Science
The ecology of small mammals in urban habitats. I. Populations in a patchy environment
Journal of Animal Ecology
An experimental study of interspecific competition between the iguanid lizards Sceloporus merriami and Urosaurus ornatus
Ecological Monographs
Effect of road traffic on amphibian density
Biological Conservation
Relation of park size and vegetation to urban bird populations in Seattle, Washington
Condor
Relationships among breeding birds, habitat, and residential development in greater Tucson, Arizona
Ecological Applications
The live frog is almost dead
Bioscience
Penetration of mammals over urban greenspaces in Warsaw
Fragmentia Theriologica
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