A TEST OF THE HIERARCHICAL MODEL OF HABITAT SELECTION USING EASTERN MASSASAUGA RATTLESNAKES (Sitrurus catatenatus)

Harvey, D.S. and Weatherhead, P.J.
Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, Champaign, IL 61820

Understanding how animals select habitat, rather than just documenting the habitat they use, should improve the ability to predict how the animals use habitat in other locations, or how they will respond to changes in habitat. It is often assumed that habitats are selected hierarchically, where animals preferentially use specific macrohabitats at a landscape scale, and specific microhabitats within the preferred macrohabitats. We used four years of telemetry data from 34 individuals to test this hierarchical model of habitat selection with eastern massasauga rattlesnakes (Sistrurus c. catenatus) in Ontario. Contrary to predictions of the model, massasauga rattlesnakes used habitats in similar proportion to their availability at a landscape scale. Snakes were selective at the microhabitat scale, however, preferentially using locations with closer retreat sites, more ground structure, and less canopy cover than random. Habitat use varied by reproductive condition, month, and study site. Gravid females were most selective, using sites that were rockier and with less canopy cover than sites used by males and non-gravid females. In contrast to foraging and gestation sites, hibernation sites were almost always in forested areas, presumably reflecting subterranean features available in forests. The failure of the hierarchical model of habitat selection appears to be a consequence of fine-grained differences between habitats at a landscape scale that allow massasauga rattlesnakes to find suitable microhabitats in all available macrohabitats. In terms of conservation, landscape-scale modeling will be ineffective at identifying rattlesnake habitat at our study site, although the generality of this problem remains to be determined.

Keywords: eastern massasauga, rattlesnake, Bruce Peninsula Ontario, hierarchical habitat selection

MICROHABITAT USE IN Anolis LIZARDS:
THE IMPORTANCE OF PERCH CHOICE

Johnson, M.A., R. Kirby, and S. Wang
Department of Biology, Washington University, St. Louis, Missouri 63130

Habitat use is a function of two components: 1) the microhabitats available within the habitat, and 2) the preference of an organism for particular microhabitats. If an organism has no preference for particular microhabitat characteristics, its use of that microhabitat should reflect the extent to which it is randomly available within its range. In contrast, if an organism prefers certain microhabitats, it should occur in a non-random subset of the available habitat. To examine the influence of microhabitat preference in two species of Anolis lizards (A. gundlachi and A. krugi), we measured both microhabitat use and availability in five different forest types in Puerto Rico. To determine if lizards of these species consistently occur in certain microhabitats, we measured the height, diameter, angle of inclination, and visibility of male lizard perches in each of the forest types. To determine if available perches in the five forest types differ in the above characteristics, we measured potential lizard perches along a 30-50m transect in each forest type. Using multivariate analyses of variance (MANOVA), we found that although the five forest types differ in available perch characteristics, both species of lizards perch in a similar microhabitat regardless of forest type. These results indicate that A. gundlachi and A. krugi use a non-random subset of available microhabitats and suggest that perch choice is an important component of habitat use in Anolis lizards.

Keywords: Anolis lizards, microhabitat, perch choice, availability

INFLUENCE OF MICROHABITAT ON TERRITORIAL BEHAVIOR
IN THREE PUERTO RICAN LIZARDS

Kirby, R., Johnson, M.A., Wang, S.
Department of Biology, Washington University, St. Louis MO 63130

Variations in microhabitat have been shown to affect territoriality in some animal species. In this study, we examined the relationship between microhabitat characteristics and territorial behaviors using three Puerto Rican Anolis lizards (i.e., anoles): Anolis gundlachi, A. cristatellus, and A. krugi. Anolis gundlachi and A. cristatellus are trunk-ground habitat specialists that typically perch on the trunks of trees a few meters from the ground, while A. krugi is a grass-bush specialist. These Anolis species are known to defend territories using visual displays: dewlap extensions, pushups, head bobs, and tail movements. We predicted that the territorial behaviors of the trunk-ground species would be more similar to each other than to those of the grass-bush species. We established a study plot for each species and individually marked all adults in the plot. We determined individuals’ microhabitat characteristics (perch heights and perch diameters) and performed 20 minute focal observations, timing total displays and counting all territorial behaviors. The microhabitat data indicated that the two trunk-ground species perched on significantly higher and broader perches than the grass-bush species. Behavioral data also indicated that male A. gundlachi and A. cristatellus perform significantly more displays than A. krugi, particularly dewlap and pushup displays. Additionally, although females across all species perform fewer displays than males, female A. gundlachi and A. cristatellus display more frequently than A. krugi. Our analyses lend support to the hypothesis that the trunk-ground species (A. gundlachi and A. cristatellus) have territorial behaviors more similar to each other than to the grass-bush species (A. krugi).

Keywords: Anolis lizards, territoriality, microhabitat, display behavior