Body size is known to play a crucial role in predator-prey interactions. For a given predator size, it has been suggested that prey mortality should be a dome-shaped function dependent on prey body size. In this study, we experimentally tested (i) the suggested mechanisms responsible for the dome-shaped prey vulnerability function and (ii) whether a prey refuge affected the form of this function. As prey, we used young-of-the-year Eurasian perch (Perca fluviatilis), and as predator, larger Eurasian perch. The prey mortality as a function of prey size was dome shaped for large and medium predators but decreased monotonically with prey size for small predators. Capture success of predators decreased monotonically with increasing prey size and was lower for small predators. in refuge trials, the mortality of prey declined monotonically with prey size for all predator sizes. Refuge use of prey increased with the sizes of both prey and predator. Our results suggest that the hypothesized dome-shaped relationship on prey vulnerability can be altered by the presence of an absolute prey refuge. Our results further suggest that the ability to perform more flexible foraging behaviors is of increasing importance when prey size increases.
