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 spec ies, show an impressive variation in temporal organization of foraging acti vity. Field studies also reveal different patterns of activity among indivi duals of the same population. 2. Many hypotheses have been proposed to explain the observed behavioural p atterns, in terms of effects of several biotic and abiotic factors acting i n different tidal phases, yet without taking into account possible interact ions among environmental and internal factors. Moreover, the importance of energy reserves and food processing has rarely been considered in this cont ext. 3. The role of different environmental factors and functional traits in sha ping the organization of foraging of limpets at different time scales was a nalysed by using a state-dependent optimal foraging model, based on stochas tic dynamic programming. The model includes interaction among mortality ris ks and energy costs incurred during the different tidal phases, the effect of different levels of energy reserves, gut fullness and changing food avai lability. 4. The model is able to reproduce a variety of foraging patterns with refer ence to the tidal cycle when changing combinations of values assigned to th e risk of mortality, energy costs and food availability. The model also sho ws that the level of energy reserves, gut volume and rate of food processin g can be of major importance in determining the short-term organization of activity within each foraging phase.