Bioeconomics of foraging route selection in limpets.

Homing limpets are central place foragers whose activity is constrained to restricted diel and tidal phases. The limpets' slow motion and high energy requirements render the problem of early choice of suitable foraging sites a critical issue. Mucous trails could be used, however, to relocate previously visited foraging areas. In this paper we describe a simulation model comparing 3 possible patch-choice tactics. These are random choice (RC) and 2 strategies (MVK and MVU) based on a marginal-value rule. The MVK strategy assumes that the forager is able to perceive and keep track of changes in energy return from successive visits to the same patch, while the MVU does not. The average long-term energy gain provided by the 3 strategies was calculated under a set of external factors: variability in the distance of patches from the central place, average value and variability in standing crop and predictability of rewards from the same foraging site when visited over successive times (auto correlation). In the absence of variability in food sources, the different tactics yielded comparable energy returns, irrespective of average standing crop level, distance from home and auto-correlation in rewards. As variability in food sources increased, the final energy gain provided by MVK and MVU strategies changed according to the degree of autocorrelation. The MVK strategy performed increasingly better than RC for increasing autocorrelation values. The MVU strategy performed better than RC when energy returns from successive visits were positively correlated. On the contrary, in the case of a negative correlation the RC strategy was better than the MVU one.