Food Supplementation in a Tropical Mainland Anole, Norops Humilis: Demographic Effects

The concept of food limitation has played a key role in the theoretical framework of population and community ecology, especially for anoline lizards. A common hypothesis is that food is limited for island anoles but is relatively unlimited for mainland anoles. In this study I manipulated prey availability of investigate how food affects population parameters for Norops humilis at a site in the Atlantic lowland wet forest of Costa Rica. Mark—recapture data were collected on control and experimental plots over a 9—mo pretest and 7—mo test period during which 9910 observations were made on 1582 individuals. Manipulation (increase) of food resulted in an approximate doubling of population density. Significant increases in the numbers of hatchlings, immigrants, and survivors resulted in increased numbers of juveniles. However, I observed no increase in the numbers of juveniles recruited to adulthood. Instead, losses of juveniles due to death and emigration were significantly increased. The juveniles population represented a "doomed surplus" that had little direct effect on increasing the size of the reproductive population int he presence of extra food. The density of adult males and females increased survival and immigration. Population density increased proportionally more for adult females than for males and for juveniles than for adults. Increased female population density resulted in a significant increase in the number of eggs laid. Loss (mortality plus emigration) of adults was not affected by supplemental feeding. As the increased number of juveniles did not increase the number of adults recruited from these juveniles, must have increased in severity on experimental plots. These effects of food on N. humilis demography suggest a conceptual model for cycles of abundance of this species and other predators of arthropods within the leaf litter of primary wet forest. The cyclic increase in arthropod food resources later in the dry season appears to be triggered by leaf drop of forest trees, which in turn triggers demographic responses in predators of leaf—litter arthropods, such as N. humilis.