Within-group variation in the willingness to risk exposure to a predator: the influence of species and size

The costs and benefits associated with feeding in the vicinity of a predator should vary within and among species, depending on an individual's vulnerability to a predator. in this paper, we investigate how willingness to risk exposure to a predator in order to gain access to food is expressed within groups of fish. We provided groups of six individually marked brook sticklebacks (Culea inconstans) and fathead minnows (Pimephales promelas) with the opportunity to feed in safety, or in the presence of a single predator (walleye, Stizostedion vitreum). Sticklebacks and fathead minnows are commonly found in the same locations at the same time. but sticklebacks also possess armour and spines that provide defence against some predators. Despite this morphological variation, patterns of individual behaviour were consistent between species. While feeding close to the predator, there was a positive relation between the size of the individual and the proportion or food consumed. No relation existed on the side farthest from the predator. These data suggest that fish may risk exposure to predators to exploit size-related differences in vulnerability to gain a competitive advantage for access to food.