Comments on “Mechanisms Determining Large-Herbivore Distribution”

How many prey to take of a certain type or how long to stay in a patch are key questions of a foraging animal according to the optimal foraging theory (OFT) (Krebs and Davis 1986). Within the OFT, the goal for herbivores generally is some form of energy maximisation within the limits of certain constraints. Although the application of energy as single currency has had some success, it is widely recognised that focusing on energy alone is not sufficient to explain the foraging behaviour of herbivores. Especially the complex, and ever changing, nature of their diet, together with the many constraints to be taken into account, poses problems (Krebs and Davies 1986; Simpson et al. 2004; Illius et al. 2002; Bailey and Provenza, Chapter 2). Essential here is that herbivores tend not to stay in a patch as long as predicted, and/or do not select a diet which provides maximal energy gain (Van Wieren 1996; Bailey and Provenza, Chapter 2). Because of this, alternative models have been developed, among them the sufficing principle (defined by Ward (1992) as choosing between different options when information-processing limits the ability of an animal to make optimal decisions), and the satiety hypothesis. The question here is if and/or how the satiety hypothesis fits into the OFT.