Dry Season Habitat Use by Lizards in a Tropical Deciduous Forest of Western Mexico

Abstract

Tropical deciduous or dry forests are characterized by strong seasonality in precipitation, typically having a prolonged dry season lasting at least four months (Bullock, 1986; Murphy and Lugo, 1986). As the dry season progresses, the forest canopy changes from a relatively homogeneous dense cover of the wet season to a more variable and open canopy (Lott et al., 1987; Bullock and Solis-Magallanes, 1990). As deciduous trees lose their leaves, more sunlight penetrates the canopy and creates a variety of forest gaps and thermal microenvironments on or near the ground. In contrast, forest habitat near seasonally dry watercourses (arroyos), remains green throughout the dry season, providing shaded habitats with dense canopy cover (Lott et al., 1987; Bullock and Solis-Magallanes, 1990). The dry season in a tropical deciduous forest represents a challenging time of year for most ground dwelling vertebrates. Water and energy resources are at the yearly low (Janzen and Schoener, 1968; Lister and Garcia, 1992), and thermal options may also be reduced, especially in the more shaded habitats of arroyos. Many vertebrates show reduced activity or seasonal changes in habitat use during the dry season (Beck and Lowe, 1991; Ceballos, 1995). Other species may move away from upland habitats and into arroyos or watercourses, which are used as dry season refuges (Ceballos, 1990). Those that remain active tend to be juveniles or adults of smaller species (Fleming and Hooker, 1975; Lister and Garcia, 1992; Casas-Andreu and Gurrola-Hidalgo, 1993; Fitzgerald et al., 1999). We know little about how dry forest lizards respond to seasonal changes in habitat structure or of the patterns of activity exhibited by lizards that remain active during the dry season. Our study examines how lizard habitat use and activity (i.e., species found to be active, timing, and amount of activity) are influenced by the variability in forest structure during the dry season in a tropical deciduous forest in southwest Mexico. We address the following questions: (1) During the dry season, does lizard activity differ between arroyo and upland habitats? (2) Is lizard activity related to forest canopy cover during the dry season?