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.

Multi-predator effects across life-history stages: Non-additivity of egg- and larval-stage predation in an African treefrog.

Vonesh, James^*,1, Osenberg, Craig¹, Bolker, Benjamin¹, ¹ Department of Zoology, University of Florida, Gainesville, Florida

ABSTRACT- Recent studies of multiple predator effects on shared prey indicate that aggregate predator effects on prey are frequently less than expected from their independent effects–a result referred to as risk reduction. However, studies to date have focused on interactions of predators of a single life-stage, where risk reduction results from interactions among predators such as intraguild predation. For prey that undergo ontogenetic habitat shifts, multiple predators may feed on different life stages that occupy different habitats and may not interact directly. Thus, the primary mechanism that gives rise to risk reduction in previous studies is absent. However, predator effects across stages, habitats, or sizes may still be non-additive due to indirect effects mediated through prey traits (e.g., size, morphology, behavior) and density. We examined the effects of sequential stage-specific predators of the arboreal eggs and aquatic larvae of the African reed frog, Hyperolius spinigularis. To quantify the overall effect of egg and larval predators and isolate the mechanisms leading to emergent effects, we conducted an experiment in which we mimicked the effects of the egg predator on initial tadpole density and initial larval size/age in the presence and absence of aquatic larval predators. Egg and larval predator effects were non-additive: more Hyperolius survived than predicted from their independent effects. Egg-stage predator effects on both larval density and size/age contributed similarly to reduce the effectiveness of larval-stage predators to a level indistinguishable from background mortality. Because many animals from diverse taxa exhibit complex life histories, non-additive multi-predator effects across stages and habitats are likely common in nature. In addition, it appears that risk reduction may arise through a variety of mechanisms and thus may be a common feature of many within- and across-stage multi-predator systems.

Key words: predator-induced hatching, multiple predators, indirect effects, complex life history