A Size-Based Approach to Examining Predator-Prey Relationships in Aquatic Predators

Aquatic populations are generally size-structured and length-based processes are rapidly becoming the basis of aquatic ecosystem level management. Predator-prey relationships are especially constrained by allometric patterns in morphology and behaviour of both predators and prey. We have used size-based approaches to understand general allometric patterns in predator-size prey-size relationships across piscivorous and teuthivorous species ranging in size from 20 cm to 2m.  Using this approach we have learned that predator-prey length scatters are generally wedge-shaped (minimum sizes independent of predator length and increasing mean sizes driven by the maximum), species-specific, and upper bounds often determined by mouth gape.  Trophic niche breadths (relative prey size as a function of predator size) are generally converging so that average trophic niche breadth declines as a function of predator body size.  We have also shown that cannibal gadid predator select larger prey than non-cannibal predators, and that predator species with wide distributions and site-specific diets  exhibit similar predator-size prey-size scatters suggesting that prey size is more constraining than prey type. The ecological generalities produced by this size-based approach provide a powerful method with which to produce predictions about ecosystem responses to exploitation and climate change.