Optimal Foraging? Patch Use by Horned Lizards (Iguanidae: Phrynosoma)

Abstract

The theoretical works of Charnov (1976) and McNair (1982) provide predictions concerning the optimal timing of departure from resource patches. (1) Foragers should depart when their rate of harvesting in that patch has fallen to the average rate of harvesting for the habitat as a whole; (2) foragers should stay longer and stay to harvest more food items in the better of two patches. I tested these predictions in the field by observing horned lizards foraging for ants in patches at or near ant colony entrances. I conclude that (1) the behavior of horned lizards is generally consistent with the first prediction; and (2) the second prediction is not met if foraging bouts are compared over their full duration, but is met if the test criteria are relaxed (an optimal solution is no longer guaranteed) so that colonies are only compared at a threshold, the lower of the residence times or the lower of the total yields, and if I disregarded foraging bouts that were apparently terminated for reasons unre...