VARIATION IN FORAGING BEHAVIOR AMONG INDIVIDUALS AND POPULATIONS OF DOGWHELKS, NUCELLA-LAPILLUS - NATURAL CONSTRAINTS ON ENERGY-INTAKE
Authors: Burrows, MT., Hughes RN.,
Year of publication:1991
Journal: Journal of Animal Ecology, , Volume: 60(2), Pages: 497-514.
Publisher: Blackwell Science Ltd
(1) The behaviour of dogwhelks, Nucella lapillus (L.), predatory gastropods of rocky shores, was quantified by tracking populations of tagged individuals at two sites over three periods of 4-6 weeks. The dogwhelks fed upon mussels, Mytilus edulis L., or barnacles, Semibalanus balanoides (L.). Prey consumption and use of refuges by individuals were recorded on each daytime low tide. Variation among diets thus characterized was analysed to determine the effects on foraging behaviour of locality and previous experience of prey, and to compare observed behaviour with predictions of Optimal Foraging Theory. (2) Path analysis allowed the largest source of variation among individuals to be traced to the predominant species of prey in the diet, largely reflecting availability at specific sites. Dogwhelks transplanted between sites retained a slight preference for their original prey type. (3) Diets comprised largely of mussels included fewer, larger prey and provided a greater energy intake than diets comprised largely of barnacles. Dogwhelks feeding on barnacles spent a greater proportion of time foraging and were more likely to engage in extended bouts of sequential attacks. (4) Larger dogwhelks tended to include a greater proportion of mussels in their diet and to take more, larger prey of either type, resulting in greater energy intake. Larger dogwhelks were also more likely to engage in longer foraging bouts. (5) Differences in time- budgets between individuals taking smaller, less profitable prey and those taking larger, more profitable prey are consistent with the idea of a digestion-rate constraint or the miximization of absorption rate, given an optimal rate of gut processing. Further reduction in the time spent foraging is due to sheltering in refuges during harsh conditions. Dogwhelks thus appear to be able to integrate characteristics of their internal state with those of the environment (prey availability and mortality risk) when making foraging decisions.