Determinants of spread in an urban landscape by an introduced lizard

Context

Urban landscapes are a mixture of built structures, human-altered vegetation, and remnant semi-natural areas. The spatial arrangement of abiotic and biotic conditions resulting from urbanization doubtless influences the establishment and spread of non-native species in a city.

Objectives

We investigated the effects of habitat structure, thermal microclimates, and species coexistence on the spread of a non-native lizard (Anolis cristatellus) in the Miami metropolitan area of South Florida (USA).

Methods

We used transect surveys to estimate lizard occurrence and abundance on trees and to measure vegetation characteristics, and we assessed forest cover and impervious surface using GIS. We sampled lizard body temperatures, habitat use, and relative abundance at multiple sites.

Results

At least one of five Anolis species occupied 79 % of the 1035 trees surveyed in primarily residential areas, and non-native A. cristatellus occupied 25 % of trees. Presence and abundance of A. cristatellus were strongly associated with forest patches, dense vegetation, and high canopy cover, which produced cooler microclimates suitable for this species. Presence of A. cristatellus was negatively associated with the ecologically similar non-native A. sagrei, resulting in reduced abundance and a shift in perch use of A. cristatellus.

Conclusions

The limited spread of A. cristatellus in Miami over 35 years is due to the patchy, low-density distribution of wooded habitat, which limits dispersal by diffusion. The presence of congeners may also limit spread. Open habitats—some parks, yards and roadsides—contain few if any A. cristatellus, and colonization of isolated forest habitat appears to depend on human-mediated dispersal.