Experimental Studies of Predator and Prey Interactions

The objectives of this cooperative effort of Florida International University, U.S. Geological Survey and the National Parks Service were to address questions about predator-prey, competitive and indirect interactions. The experimental mesocosm array was constructed in Everglades National Park. Two experiments that examined mosquitofish predation and competition with other cohabiting small fishes in the Everglades marshes have been completed.

Results showed that growth of juvenile mosquitofish could be limited by the presence of other juveniles at densities within the range found in the Everglades. This suggests that food limitation is a potential factor for juvenile fishes in Everglades marshes, as had been suggested by earlier field studies. The study of spotted sunfish nest predation by small fishes, especially mosquitofish, was completed and demonstrated a feedback loop in the Everglades food web. Mosquitofish prey upon eggs and larvae of spotted sunfish, which in turn eat mosquitofish as they grow. Water level was inversely related to the degree of nest predation and probably helps explain why sunfish populations grow during high water years. The mesocosm is now being used to address the role of nutrient inputs into the Everglades in causing shifts in marsh food webs.