INTRAGENERIC PREDATION BY FIDDLER CRABS IN SOUTH CAROLINA

Abstract

In South Carolina, two species of fiddler crab, Uca pugilator and U. pugnax, often feed in droves on the sand flats of smooth cordgrass salt marshes. Another fiddler crab, U. minax, does not drove, but large males of this species occasionally move onto sand flats and prey on members of the other smaller species. Successful predatory attacks entail a pounce, entrapment of prey in ambulatory appendages, reorientation of the predator to the supine position, maneuvering of the prey between the dactyl and propodus of the major cheliped, killing the prey by piercing or crushing its carapace with the major cheliped, and consumption. Females are successfully attacked with higher frequency than males. The frequency of predatory attacks declines exponentially as the composition of droves becomes biased towards larger males. This may indicate that predators face injury when attacking large males because only males possess potentially defensive claws and claw length increases with the square of body width. Uca pugilator individuals form pods in response to the approach of a predator. Pods are tight clumps of fleeing individuals that may function as mini-selfish herds. Pod composition is biased towards individuals most susceptible to U. minax predation, females and males of small body size, suggesting that pod formation is a selectively advantageous behavior.