Elsevier

Biological Conservation

Volume 97, Issue 2, February 2001, Pages 229-237
Biological Conservation

Lizard species distributions and habitat occupation along an urban gradient in Tucson, Arizona, USA

https://doi.org/10.1016/S0006-3207(00)00115-4Get rights and content

Abstract

Despite expanding human populations in metropolitan areas world-wide, habitat relationships of lizards have seldom been examined along urban gradients. We tested three hypotheses addressing lizard species distributions, site occupation, and assemblage organization along the urban gradient in Tucson, Arizona, USA. One hundred twenty-nine random sampling plots were distributed from undisturbed-natural land beyond the boundary of development to highly developed land within the city. We recorded lizard species abundances and 19 variables describing habitat physiognomy, floristics, and spatial relationships of native remnant and developed land parcels in each plot. We ordinated lizard species and habitat data in a canonical correspondence analysis, and tested significance of relationships in a Monte Carlo randomization test. We then tested effects of individual habitat features on site occupation by lizards using a presence–absence transformation of lizard abundance data and multiple logistic regression. Both species distributions and site occupation were influenced by factors describing habitat physiognomy, floristics, and landscape spatial relationships. Finally, we examined total abundance, number of species, and evenness across five categories describing increasing residential density. All three measures of assemblage organization peaked at low–moderate levels of development, and declined markedly as residential density increased beyond moderate levels. Distinct attributes of urban development influence lizard species distributions, site occupation, and assemblage organization. Attention to these attributes will allow land developers to mitigate the effects of future urban development on lizard populations.

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.

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