Sexual Differences in Foraging Behavior of an Anoline Lizard, Norops humilis

Abstract

The amount of time male anoles (Squamata: Polychrotidae) spend interacting with other anoles can be quite high, and is usually much greater than that of females (Andrews, 1971; Fleming and Hooker, 1975; Talbot, 1979; Lister and Aguayo, 1992). For example, Rand (1967) watched one male Norops (Anolis) lineatopis for 11 hr that performed 181 displays (averaging about one every 3.5 min). The reproductive success of male anoles is related to opportunities for mating; therefore, males should maximize time spent displaying and defending territories. In contrast, the reproductive success of females is constrained by the amount of energy procured for the development of eggs. Female anoles can produce an egg as rapidly as every eight days, and apparently oviposit throughout the year in tropical regions (Fitch, 1970; Andrews, 1979; Guyer 1986, 1988). This energetically costly activity can be quantified by examining differences between sexes in energy intake. Estimates of food intake from scat output for Norops limifrons in the field were 63, 124, and 90 cal/g/day for adult males, females, and immatures respectively (Andrews and Asato, 1977). While males expend energy in social interactions and need food for maintenance purposes, females need additional energy for egg production, and juveniles for growth. Optimal foraging theory predicts that some individuals (time minimizers) should spend as little time feeding as possible to maximize the amount of time available for other activities, whereas others (energy maximizers) should maximize the amount of time spent foraging (Schoener, 1971). Theoretical (Kiester and Slatkin, 1974) and numerous empirical studies (e.g., Andrews, 1971) lead to the prediction that adult female anoles are energy maximizers but adult males are time minimizers. If these predictions are true, male anoles should spend less time foraging and be less likely to pursue a prey item than females. A prediction for juveniles is more difficult because high predation pressure on relatively small lizards may cause them to be energy maximizers to allow for the most rapid possible growth, or they may be time minimizers to minimize exposure to predation. Norops humilis, the most common leaf-litter lizard at La Selva, Costa Rica (Lieberman, 1986), was used to investigate these predictions. Prey items were offered to freeranging males, females, and juveniles, and the time required to orient toward and attempt to consume the prey was recorded. The Arboretum at the La Selva Biological Reserve in northeastern Costa Rica was searched for Norops humilis on 3-6 March and 11-14 March 1992 (during the dry season). An assortment of small (< 8 mm) orthopterans and spiders was placed in clear glass vials, and the contents changed every 30 min to maintain prey activity. These organisms are known prey of N. humilis (Lieberman, 1986). When an individual lizard was found, the prey vial was carefully placed on the ground within its sight at one of two distance categories, either near (ca. 10 cm) or far (ca. 25 cm) from the Norops according to a predetermined random order. It would be difficult to extend the distance