Mara S. Zimmerman: Variation in brook stickleback (Culaea inconstans) size and shape associated with different predator communities

The present study explores the association of morphological traits of brook sticklebacks (Culaea inconstans) with two types of predator communities. Stickleback populations associated with these predator communities differ in the size at which they are vulnerable to predation. My comparison of brook stickleback morphology involves 25 populations in three adjacent river basins in Michigan’s upper peninsula. I hypothesize that morphological variation among brook stickleback populations can be explained, in part, by different predation pressures. To address my hypothesis, I compare age structure and two aspects of morphology, size and shape, among brook stickleback populations coexisting with each type of predator community. The results suggest that populations vulnerable to predation as adults have shorter-lived and smaller individuals than populations only vulnerable to predation as juveniles in which individuals live longer and attain a larger size. Both mean and age-specific body size differ among populations associated with the two types of predator communities suggesting that predators affect both growth rate and longevity of stickleback populations. In addition, populations that are vulnerable to adult predation have more fusiform individuals with more caudally placed fins than those vulnerable to juvenile predation only. The results support the idea that morphological variation among brook stickleback populations can be explained, in part, by predator-prey interactions within each community. Future work will investigate how ontogenetic investment in growth and shape differs among brook stickleback populations associated with different predator communities.