Population Experiments with the Anolis Lizards of St. Maarten and St. Eustatius

Abstract

During 1980 and 1981 population experiments were performed with two two—species guilds of Anolis lizards: A. gingivinus and A. wattsi pogus on the island of St. Maarten (Netherlands Antilles) and A. bimaculatus and A. wattsi schwartzi on the island of St. Eustatius (Netherlands Antilles). These experiments were designed to test the hypothesis that the strength of interspecific competition is inversely related to the degree of interspecific resource partitioning. The experimental design consisted of four field—enclosures (12 x 12 m) on St. Maarten and four on St. Eustatius. On each island two enclosures contained only the larger native species (A. gingivinus or A. bimaculatus), and two contained both native species. Resource partitioning was measured inside each of the two—species enclosures. There was more interspecific partitioning of space and prey (arthropods) on St. Eustatius than on St. Maarten. A comparison of the one— and two—species enclosures on St. Maarten revealed five competitive effects of A. wattsi pogus on A. gingivinus. In the presence of A. wattsi pogus, A. gingivinus individuals had lower growth rates and increased perch heights. Also, dissected A. gingivinus from the two—species enclosures contained smaller volumes of developing eggs per female, smaller volumes of insect prey per lizard, and smaller mean prey sizes than A. gingivinus from the single—species enclosures. In contrast, no consistent and significant competitive effects of A. wattsi schwartzi on A. bimaculatus were observed on St. Eustatius. These results support a central assumption of competition theory: the strength of interspecific competition increases as the amount of interspecific resource partitioning decreases.