Divergent habitat use of two urban lizard species

Abstract

Faunal responses to anthropogenic habitat modification represent an important aspect of global change. In Puerto Rico, two species of arboreal lizard, Anolis cristatellus and A. stratulus, are commonly encountered in urban areas, yet seem to use the urban habitat in different ways. In this study, we quantified differences in habitat use between these two species in an urban setting. For each species, we measured habitat use and preference, and the niche space of each taxon, with respect to manmade features of the urban environment. To measure niche space of these species in an urban environment, we collected data from a total of six urban sites across four different municipalities on the island of Puerto Rico. We quantified relative abundance of both species, their habitat use, and the available habitat in the environment to measure both microhabitat preference in an urban setting, as well as niche partitioning between the two different lizards. Overall, we found that the two species utilize different portions of the urban habitat. Anolis stratulus tends to use more "natural" portions of the urban environment (i.e., trees and other cultivated vegetation), whereas A. cristatellus more frequently uses anthropogenic structures. We also found that aspects of habitat discrimination in urban areas mirror a pattern measured in prior studies for forested sites in which A. stratulus was found to perch higher than A. cristatellus and preferred lower temperatures and greater canopy cover. In our study, we found that the multivariate niche space occupied by A. stratulus did not differ from the available niche space in natural portions of the urban environment and in turn represented a subset of the niche space occupied by A. cristatellus. The unique niche space occupied by A. cristatellus corresponds to manmade aspects of the urban environment generally not utilized by A. stratulus. Our results demonstrate that some species are merely tolerant of urbanization while others utilize urban habitats in novel ways. This finding has implications for long-term persistence in urban habitats and suggests that loss of natural habitat elements may lead to nonrandom species extirpations as urbanization intensifies.

Keywords: Anolis cristatellus; Anolis stratulus; Puerto Rico; anole; niche partitioning; urbanization.

Figure 1

Anolis cristatellus (top; photo EJC) and Anolis stratulus (bottom; photo KMW) occupy different portions of the urban habitat

Figure 2

(a) Locations of sites sampled. Inset: in Arecibo, three locations were surveyed (indicated by stars): (1) University Ineteramericana Arecibo, (2) a residential neighborhood, and (3) University of Puerto Rico Arecibo. Dashed lines indicate major highways (thick dash) and major surface roads (small dash). (b) Distribution of hours sampled across all sites

Figure 3

(a) Relative abundances differed dramatically: we encountered many more A. cristatellus across all sites. (b) Anolis cristatellus used artificial perches at a higher frequency than natural perches and at a similar rate to what was available. Anolis stratulus used natural perches almost exclusively (Fisher's Exact test, p < .001)

Figure 4

Mean and SE for habitat variables sampled for habitat availability (“A”), and each species use (“C”—A. cristatellus, “S”—A. stratulus). Differences between utilized and available habitat (summarized in Table 2) represented by gray lines and significance level: ***p < .001, **p < .01, *p < .05

Figure 5

Classification tree for habitat use differences in A. cristatellus and A. stratulus. Species percentages indicate the percentage of all sampled individuals of each species in each group (high canopy cover, low canopy cover and high temperature, low canopy cover and low temperature)

Figure 6

Principal components 1, 2, and 3 plotted with 95% confidence interval ellipses for utilized habitat by each species. PC1 and PC2 differed between species at significance levels p < .001 (***) and p < .01 (**), respectively

Figure 7

Principal components 1 and 2 plotted with 95% confidence interval ellipses grouped by perch type for available habitat (left) and utilized habitat (right)