Variation in growth and consumption among individuals and populations of dogwhelks, Nucella lapillus: a link between foraging behaviour and fitness

Body mass and consumption explained 15-24% of observed variance in production, defined as the combined energetic value of shell and body growth, among individual dogwhelks. In the laboratory, dogwhelks showed most shell growth on a diet of large barnacles Semibalanus balanoides, and highest rates of consumption on a diet of large mussels Mytilus edulis. Consumption and growth rates of naturally foraging dogwhelks were greater at an exposed, mussel-dominated site than at a sheltered, barnacle-dominated site. Sheltered-shore morphs grew faster than exposed shore morphs, both at their native, sheltered site and when transplanted to the exposed site. Shell growth was positively associated with shell mass in sub-adult dogwhelks with an actively growing shell lip, whereas body growth was negatively associated with body mass. Consumption was allometrically related to body mass. Statistical removal of these trends revealed no significant differences in size-specific shell growth between morphs, but there remained differences in shell growth between sites and in consumption and body growth between sites and morphs. If growth is an acceptable surrogate for fitness, those animals which maximize consumption also appear to maximize fitness. The energy maximization premise which underlies optimal foraging theory thus appears to apply in a complex natural situation. -from Authors