Meeting Abstract

P2.58  Saturday, Jan. 5  Despite resource partition, multiple predators reduce mortality risk for foundation species NELSON, H.R.*; GRIFFIN, J.N.; MCCOY, M.W.; NIFONG, J.C.; SILLIMAN, B.R.; Brown Univ.; Univ. of Florida; Univ. of Florida; Univ. of Florida; Univ. of Florida hannah_nelson@brown.edu

Multiple predators often interact in non-linear ways, which can enhance or reduce the risk for their shared prey. Many studies have investigated emergent multiple predator effects, but the role of prey size in shaping the interactions between predators has received little focus, even though prey-size preferences could strongly intensify or dampen the competition between predators. We studied the prey size preferences of two dominant predators common to Florida’s estuarine intertidal oyster reefs, the blue crab (Callinectes sapidus) and the crown conch (Melogena corona), and used the results to predict the type of impact multiple predators would have on oyster mortality. In our laboratory experiment, conchs showed a preference towards large oysters, while blue crabs preferred small oysters, suggesting that their combined effects on oyster mortality rates would be positively synergistic or additive. Results from our factorial mesocosm experiment, however, contrasted with these predictions by demonstrating that these two predators actually have antagonistic effects. Thus, despite evidence for a size-based resource partition, there was a significant risk-reduction in mortality with the combination of both predators, revealing the presence of an emergent multiple predator effect. While blue crabs did not kill conchs, their presence resulted in a non-significant trend in escape behaviors by conchs and reduced feeding, suggesting that the mechanisms underlying the negative multiple predator effect could be non-consumptive. This work cautions extrapolation of correlational data suggesting predator resource partitioning without experimental testing, and suggests that the impacts of recent increases in conch numbers on oysters can be diminished in areas where blue crabs are abundant.