PARENT SESSION
Oral Session # 10: Predator-Prey Ecology I: Terrestrial I: Theory and Cues.
Presiding: A Liebold
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 202.

Nonadditive effects of multiple predators on treefrog tadpoles.

Gunzburger, Margaret¹, ¹ Florida State University, Tallahassee, FL

ABSTRACT- Many studies demonstrate the importance of a single predator on a prey species, but most prey are subject to predation by more than one predator species in nature. Experiments evaluating the effects of multiple predators on prey typically confound predator density with predator identity, thus prohibiting an assessment of the additivity of predator species. The objective of this research was to implement an experimental design that controls for total predation rate across treatments to determine the additivity of three predator types (bass fish, aeshnid and libellulid odonate naiads) on green treefrog tadpoles (Hyla cinerea). The predation rate of each predator species on the prey in isolation was measured. I then determined the density of predators necessary in each treatment (all possible combination of the three predator species) that would produce the same total predation rate if all predator effects were additive. Each predator contributed equally to the total predation rate in treatments with combined predators. I performed this experiment in large mesocosms with a depth gradient and measured survival and habitat use of the tadpoles in response to the 8 different predator treatments. Survival of tadpoles differed across treatments, indicating that there are nonadditive effects of predators in this system. Tadpole survival was highest in the control (no predator), aeshnid and libellulid combination, and libellulid treatments. Comparison of observed survival of tadpoles to that expected if all effects were additive indicated that tadpoles had higher than expected survival in the aeshnid and libellulid combination treatment and lower than expected survival in the libellulid and bass combination treatment. Tadpoles did not alter their use of shallow or deep areas of the mesocosm directionally in response to predator treatment. Predators interacted directly and indirectly to result in the nonadditive effects on tadpole survival.

Key words: facilitation, predation, Hyla cinerea, inhibition