Ecological Correlates of the Variable Mating System of an Iguanid Lizard

Abstract

We studied the mating system of an insectivorous iguanid lizard (Urosaurus ornatus), from 1983 to 1987, in desert habitat of southeastern Arizona. We determined that polygyny was habitat dependent. We also examined three features of lizard body size: sexual dimorphism, size differences between monogamous and polygynous males, and size differences between lizards establishing home ranges (females) or territories (males) and those not establishing residence. Data were collected during summer months in two habitats (dry wash and flatland desert scrub). The mating system is highly variable (0 to 67% males polygynous), depending on habitat, year, and season. Polygyny is very common in the dense mesquite woodland of dry washes and is less frequent in flatland desert. Female spacing plays an important proximate role in the pattern of polygyny. Tree lizards are sexually dimorphic, and polygynous males are significantly larger than monogamous males. Consistent with a hypothesis of competitive mate searching, we also discovered a significant size advantage in male tree lizards establishing territories compared to males that did not establish residence. No such difference was observed between females surviving to establish residence and females that disappeared.