Foraging Behavior of Anolis stratulus in a Puerto Rican Rain Forest

Abstract

The foraging behavior of Anolis stratulus was studied in tabonuco rain forest near El Verde in the Luquillo Mountains of Puerto Rico. Daily foraging rates were calculated at 20.5 prey items/lizard during wet season and 18.0 prey items/lizard during the dry season. An average consumption rate of 3.4 x 105 prey/ha each day was calculated which demonstrates the importance of this species in the rain forest food web. Time of day and seasonal differences in foraging activity indicate that these factors are important even in the relatively constant tropical rain forest environment. RAND (1964) DESCRIBED THE ECOLOGICAL DISTRIBUTION of anoline lizards (Anolis spp.) in Puerto Rico and explained species differences based on variations in structural habitat (perch height and perch diameter) and climatic habitat (shade conditions). Subsequent studies have produced additional information on the lizard community in Puerto Rican rain forests (Turner & Gist 1970, Schoener & Schoener 1971, Moll 1978, Lister 1981). All of these studies incorporated the same sampling constraint (observations were made from ground level), and none addressed seasonal differences in the activity or distribution of anoles within a forest habitat. From February 1980 through September 1983 I investigated anoline lizards in tabonuco rain forest near El Verde, Puerto Rico. Field observations were made from ground level and from various levels on a 20 m high tower within the forest. My initial research on the three common species determined that the two most conspicuous species (Anolis gundlachi and A. evermanni) were abundant only in the lower few meters of the forest; that A. stratulus, formerly considered uncommon in the forest (Turner & Gist 1970, Schoener and Schoener 1971, Moll 1978, Lister 1981), inhabited the canopy at extremely high population densities 10 to 22 m above ground level (Reagan et al. 1982); and that A. stratulus shifted its vertical activity to lower forest strata during the dry season and during midday. Stomach content analyses revealed that many A. stratulus collected during the dry season had empty or nearly empty stomachs while the stomachs of the other common anoles A. gundlachi and A. evermanni showed no seasonal change. These data support the hypothesis that at least some insular anole species are food limited (Licht 1974, Andrews 1976). The new findings on the abundance, vertical distriReceived 27 March 1984, revision accepted 10 April 1985. 2Present address: 131 Hillside Drive, Castle Rock, Colorado 80104, U.S.A. bution, and seasonal movements of A. stratulus prompted additional research on its foraging behavior. Therefore, the present study was conducted to determine the feeding rate of Anolis stratulus during the wet and dry seasons, and to test the hypotheses of seasonal, sexual, and timeof-day differences in foraging activity for this species.