Intraguild predation and cannibalism in a size-structured community of marine amphipods

Body size differences can impact the strength and type of interaction among and within species. This study examines the effect of body size differences on intraguild predation (IGP) and cannibalism in regulating the relative abundance of two species of temperate marine amphipods throughout a season. Intraguild predation was asymmetrical, with primarily Jassa marmorata preying on Apocorophium acutum (with little predation by A. acutum on J. marmorata). Intraguild predation increased significantly as body size difference increased. Cannibalism in J. marmorata was only significant among individuals of different body sizes. Tube building by A. acutum was also found to be effective in protecting against IGP, especially in the presence of large J. marmorata. Experimental results suggest an ontogenetic niche shift occurs in J. marmorata, which may provide a potential explanation for observed patterns of abundance in a natural population.