The effects of size-dependent predation risk on the interaction between behavioral and life history traits in a stream-dwelling isopod

In field surveys, laboratory observations and field-based assays of behavior, I examined the effects of size-dependent predation risk on the interaction between size at reproductive maturity and maternal care behavior in the stream-dwelling isopod, Lirceus fontinalis. L. fontinalis exhibit population-specific sizes at reproductive maturity which result in population differences in predation risk during the adult phase. Females from streams containing salamander larvae (that prefer small prey) mature at large sizes and then become relatively safe from predation. Females from streams containing fish (that consume all size classes of prey equally) mature at small sizes and remain at risk. I tested whether these differences in expected survival were reflected in the behavior of females during the maternal phase (i.e., the period during which females exhibit maternal care). Female L. fontinalis carry developing juveniles inside a brood pouch. I simulated predatory attacks on gravid female L. fontinalis from the different population types and found that female behavior correlated with population differences in risk. When “attacked”, females from streams with predatory fish (that experience high risk to adult females) released juveniles from the brood pouch, whereas females from populations with predatory salamander larvae (that pose relatively little risk to adult females) did not release juveniles. I discuss the results with reference to the joint evolution of behavioral and life history traits. Received: 6 March 1996 /Accepted after revision: 12 August 1996