Predicting Ontogenetic Niche Shifts in the Field: What can be Gained by Foraging Theory?

Abstract

Foraging theory has been developed greatly since the pioneer papers on this topic (MacArthur and Pianka 1966; Emlen 1966). Even though one of the original aims was to advance an economic theory of diet and habitat choice of animals in the field (MacArthur 1972), surprisingly few field studies have included quantitative predictions of diet choice in the field. For example of the 35 field studies testing the classical diet model listed by Stephens and Krebs (1986), only 9 included quantitative predictions. Considering only experimental studies reduces this figure to 3. One reason for this scarcity of field tests of optimal foraging theory is that foraging studies during the last decade have focused more on the purely behavioural aspects of animal foraging than community organization. For this purpose, laboratory experiments have been regarded as more powerful and appropriate than field studies (Stephens and Krebs 1986, but see Schoener 1987 for artificial laboratory experiments). This behavioural research has led to the questioning on experimental and theoretical grounds of the many assumptions in the classical diet and patch models, such as sequential encounter, complete information and constancy of encounter rate and handling time. Recent foraging theory has also to some extent rejected static optimization in favour of dynamic optimization (Gilliam 1982; Houston and McNamara 1986; Mangel and Clark 1986). However, from the population ecologist’s point of view it can be argued that simplifications have to be made, and that the incorporation of even the classical foraging models into population models may involve a significant advancement compared to previous population models (see Comins and Hassell 1979 for the patch model; Gleeson and Wilson 1986 for the diet model).