Seasonal Niche Relationships of Rain Forest Anoles

Abstract

In this paper, seasonal changes in resource partitioning among Anolis lizards in the Luquillo rain forest in eastern Puerto Rico were investigated with the aim of understanding how climatic variation, competition and resource availability interact to affect niche relationships and community structure. Arthropod densities within the Luquillo forest were found to remain stable between the summer (July 1976) and winter (January 1977) seasons at lower levels of the forest but to decrease during the winter season at higher levels. Seasonal changes in the niche relationships of Anolis gundlachi, A. evermanni and A. stratulus included: (1) a winter season decrease in spatial overlap and spatial niche widths, (2) an expansion of the prey size and prey taxa components of the food niche during the winter. However, compared to anoles in more seasonal environments at Maricao and Guanica in southwestern Puerto Rico, anoles in the relatively aseasonal Luquillo forest exhibited greater niche stability between seasons and greater niche overlap during both seasons. At Maricao and Guanica, spatial niche widths and spatial overlap also decreased during the winter dry season but to a much greater extent than at Luquillo. Data on seasonal changes in food abundance, food consumption, and reproductive condition suggest that food competition is more intense during the prolonged dry seasons at Maricao and Guanica. Thus within Anolis communities, spatial overlap and spatial niche widths may be an inverse function of food competition and the degree of seasonal change in niche relationships may be directly correlated with the magnitude of seasonal fluctuations in food supply. Finally, loss rates of anoles from census areas at Luquillo were analyzed and suggested high rates of predation. The hypothesis was advanced that greater predation pressure may explain the generally higher levels of niche overlap among anoles in stable environments compared to more variable environments.