The Role Of Food In Regulating Population Density In A Tropical Mainland Anole, Norops Humilis (demography, Food Limitation, Costa Rica)

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Degree Name

Doctor of Philosophy (Ph.D.)




The concept of food limitation has played a key role in the theoretical framework of anole population and community ecology. It has been hypothesized that food is limited for island anoles but is relatively unlimited for mainland species. In this study I manipulated food levels to investigate how the availability of food affects Norops humilis in the Atlantic lowland wet-forest of Costa Rica. Changes at the level of the population and individual were monitored on supplementally fed vs. control plots.Manipulation of food resulted in a doubling of population density. Increased numbers of juveniles resulted from significantly increased recruitment, immigration, and survivorship. However, no increase in recruitment of juveniles to adulthood was observed. Instead, juveniles were lost as a result of significantly increased death and emigration. The density of adult males and females increased as a result of increased immigration and survival, respectively. The increased number of females resulted in significantly increased numbers of eggs on plots with supplemental food. The number of adults lost from mortality and emigration was not affected by experimental treatment.The immediate effect of supplemental feeding was one of individual lizards allocating extra food energy to various functions. Home range size was not affected by food supplementation, but, home range overlap was increased for all groups except females relative to other females and juveniles relative to females. The shape of the growth curve for adult females was not altered. However, there was a significant increase in the asymptotic largest size of males. No change in body mass relative to length was observed for either sex. Eggs were produced significantly more rapidly by females on plots with supplemental food.I discuss these results relative to how alteration of demography results in limitation of the reproductive population and how selective pressure increases on sites with supplemental food. I also propose how these results relate to natural cycles of abundance for predators upon leaf-litter arthropods. I then discuss the spatial adjustments made by lizards, how males and females compare and differ, and how island and mainland anoles compare and differ in response to food supplementation.


Biology, Ecology

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