A state-dependent model of activity patterns in homing limpets: balancing energy returns and mortality risks under constraints on digestion.

1. Different species of limpets, and different populations of the same species, show an impressive variation in temporal organization of foraging activity. Field studies also reveal different patterns of activity among individuals of the same population. 2. Many hypotheses have been proposed to explain the observed behavioural patterns, in terms of effects of several biotic and abiotic factors acting in different tidal phases, yet without taking into account possible interactions among environmental and internal factors. Moreover, the importance of energy reserves and food processing has rarely been considered in this context. 3. The role of different environmental factors and functional traits in shaping the organization of foraging of limpets at different time scales was analysed by using a state-dependent optimal foraging model, based on stochastic dynamic programming. The model includes interaction among mortality risks and energy costs incurred during the different tidal phases, the effect of different levels of energy reserves, gut fullness and changing food availability. 4. The model is able to reproduce a variety of foraging patterns with reference to the tidal cycle when changing combinations of values assigned to the risk of mortality, energy costs and food availability. The model also shows that the level of energy reserves, gut volume and rate of food processing can be of major importance in determining the short-term organization of activity within each foraging phase.