A satiation model for the temporal organisation of grazing in limpets.

1. A compartmental model of the limpet alimentary system was designed to simulate the effects of functional constraints and substrate characteristics on the temporal patterning of grazing in these gastropods. Limitations are imposed by gut capacity and processing time. A maximum operating frequency is set for the radula activity, and a negative feedback on the grazing frequency is related to gut replenishment. 2. When holding constant the 'morphofunctional' parameters of the model, variations in the 'richness' of the substrate (i.e. in the amount of matter extracted per single rasp) generated different patterns of grazing activity, from constant grazing at different frequencies, to the appearance of distinct grazing-non-grazing subphases with a periodicity corresponding to the processing time. Moreover, when varying the digestibility of the matter (i.e. its processing time), temporary saturations were produced. 3. Automatic recording of radula activity in specimens of Patella caerulea L. collected from a Mediterranean boulder beach and transferred to tidal tanks showed that each activity phase (performed during the high-tide period) may be differently structured: from almost continuous grazing, with more or less pronounced and sometimes periodic oscillations, to alternation of grazing and non-grazing subphases. Continuous and non-continuous grazing patterns are shown also by the same specimen during subsequent activity phases. 4. The results of the model are consistent with empirical observations and suggest that satiation events related to the characteristics of the substrate encountered by the limpets when foraging, can produce highly variable grazing patterns with implications for the energetics of foraging in this group of grazers.