Microhabitat Use and Activity Patterns of Holbrookia maculata and Sceloporus undulatus at White Sands National Monument, New Mexico

Abstract

White Sands National Monument (WSNM), New Mexico, was established as a National Park to preserve the biotic and abiotic features of the gypsum dunes environment. The lizards of WSNM are characterized as having special adaptive qualities that enable them to survive in gypsum sand. The lesser earless lizard (Holbrookia maculata) and the eastern fence lizard (Sceloporus undulatus) are white forms of their respective species that reside at the Monument (Ruthven, 1907; Smith, 1943; Lowe and Norris, 1956). At WSNM, Holbrookia maculata is short, stout, and dorsally pallid with fairly well-defined ventro-lateral blotches, and Sceloporus undulatus is medium-sized with a dorsal coloration of pale gray to nearly white with faint black shoulder patches (Smith, 1943). Dixon and Medica (1966) reported food of these lizards, and Dixon (1967) studied their activity and reproduction. MacFarland (1969) found that H. maculata and S. undulatus overlap greatly in daily activity, behavior, and food but differ in substrate preferences in seminatural enclosures at WSNM. Holbrookia maculata at WSNM had lower body temperatures and thermoregulated differently than a population of H. mniaculata from outside the dunes proper (Hager, 2000). Human-induced landscape alterations and increased land management practices threaten taxa adapted to aeolian habitats. Preservation of these organisms requires basic knowledge of their biology. Consequently, my goal was to understand more about the activity patterns and habitat use of H. maculata and S. undulatus in the gypsum dune field at WSNM. To my knowledge, this is the first systematic field study of these two lizards in their natural habitat across an entire activity season. For each species, I evaluated daily and seasonal surface activity and how this activity relates to the lizard's structural environment, use of microhabitats, proximity to vegetation, and population density. These data will allow monument personnel to make more informed management decisions on behalf of these lizards and the biotic resources, in general, and will ultimately contribute toward the preservation of the biodiversity of the gypsum environment. In broad terms, this information sheds more light on community structure in sand dune habitats. White Sands National Monument, New Mexico, (32?45'N; 106?15'W) encompasses approximately 450 km2 of active, moving dunes. Its edges house various