Effects of Temporal Variability in Resources on Foraging Behaviour

Trait plasticity in physiology, behaviour, morphology and life history enables organisms to survive and populations to persist despite temporal variability in environmental conditions and resource availability. Through non-linear responses, the effect of adverse periods outweighs that of benign conditions, following Jensen's inequality. This chapter considers how large mammalian herbivores adjust broader aspects of their foraging behaviour to cope with variability over different temporal frames: within a day, day versus night, between days, over seasonal cycles and between years. It outlines the conceptual foundation for ‘adaptive resource ecology’, covering changes in diet composition, daily time allocation, foraging movements, metabolic rate, digestive capacity and fat stores. The functional response relating food intake rate to food availability changes its form depending on the temporal scale. To link resource variability in time and space to population dynamics, the intake response needs to be transformed into a biomass or energy gain response over a seasonal time frame. Foraging models based on rate averaging can be misleading, while challenges in applying dynamic optimisation models need to be surmounted. Models assuming equilibrium relationships between resource supplies and population growth are inappropriate for coupling resource gains to population dynamics.