EFFECTS OF COVER AND PREDATOR SIZE ON SURVIVAL AND DEVELOPMENT OF RANA-UTRICULARIA TADPOLES

Size-limited predation is an important process during the development of many aquatic species, and mortality rates of early larval stages an d small individuals can be particularly high. Structurally complex hab itats can mediate predator-prey interactions and provide a potentially important mechanism for decreasing predation pressure on larvae, To d etermine whether structurally complex habitats mediate predation on ta dpoles of the southern leopard frog (Rana utricularia), we designed a factorial experiment, crossing two levels of cover with three predator treatments (none, small: or large Tramea carolina naiads). Predator s ize had a larger effect on tadpole performance (survival, mass and age at metamorphosis) than did cover level, largely because small predato rs were ineffective. Within the large-predator treatment, however, tad pole survival was higher (78%) under high than under low cover (46%), suggesting that increased cover decreased predator foraging efficiency allowing more larvae to reach a size refuge. This study demonstrates that habitat structural complexity can play an important role in media ting predator-prey interactions, even when tadpoles start out at a siz e disadvantage relative to predators. Consideration of habitat structu ral complexity in future research should provide a more complete under standing of the role of size relationships in predator-prey systems.