SIZE-RELATED FUNCTIONAL AND ENERGETIC CONSTRAINTS IN THE FORAGING OF THE LIMPET PATELLA-VULGATA (MOLLUSCA, GASTROPODA)

1. The effect of size-related functional and energetic constraints (respiration, production of mucus, ingestion rate) on the foraging behaviour of a population of the limpet Patella vulgata L., inhabiting a sheltered shore at Menai Bridge (Anglesey, UK), was examined. 2. The minimum acceptable energy content per unit area (u(min)) that an algal pasture should have to be profitably exploited by a limpet of a given size was first determined. 3. Second each excursion was modelled as being made up by a linear sequence of discrete spatial locations, whose energy content per unit area (u(i)) linearly increased with the distance from the limpet's rest site. Each limpet was assumed to select suitable foraging sites by adopting a simple 'all-or-nothing' rule: to exploit completely a given location if ui greater than or equal to u(min), or, if u(i) < u(min), to skip to the next one. 4. The model foresees that specimens which select sites on this basis will have a greater net rate of energy intake than limpets exploiting all the locations. Moreover, among the selective limpets, larger specimens will have a lower net rate of energy intake over the whole excursion than smaller ones, if they cover the same number of locations. In addition, larger limpets should concentrate their foraging more around the point of maximum distance, than smaller ones. 5. Although including a minimum set of simple assumptions the model is able to reproduce the effects of size-related constraints on the behaviour of limpets in this population, In particular, the predicted difference in the spatial organization of foraging between different size classes agrees with the results of field observations.