Foraging behaviour in fishes: perspectives on variance

Synopsis The positive relationship between size of prey and frequency of ingestion by predators has been a focal point of investigations in foraging ecology. Field studies compare the frequency distribution of prey sizes in the predator's gut with that in the environment. Laboratory and field (enclosure) studies are based upon comparison of the frequency distributions of prey sizes in controlled environments, before and after the introduction of a predator. Optimal caloric return for foraging effort (i.e. the theory of optimal foraging) has been widely used as a guiding principle in attempts to explain what a fish consumes. There is a body of information, however, which seems to indicate that the perceptual potentialities and cognitive abilities of a predator can account for both the direction of the prey size versus ingestion frequency relationship and the variance surrounding it. Part of this variance may be evidence of systematic ambiguity, a property of cognitive skills causing predators to respond to the same stimulus in different ways and to different stimuli in the same way. More extensive examination of cognitive skills (minimally defined as learning, remembering and forgetting) in fish may permit causal interpretations (immediate and ultimate) of variance in predatory skills. In such a paradigm of foraging behaviour, environmental stimulus is not taken as the predator's object of response (percept); a cognitive representation connects mind to stimulus and this is the criterion for the act of perception. Cognition, here considered as a formal system which acts upon representations, connects mind to response and thus to adaptation. Studies of the relationships among rates of learning, long and short-term memory, rates of forgetting, prey behavior, size and population turnover rates, lateralization of brain functions, diel fluctuations in predator activity levels and sleep, experience, and critical periods in the development of the predator's nervous system should be examined in relation to foraging behaviour.