A length-based approach to predator–prey relationships in marine predators

Abstract

Body size is a critical feature of the ecology of most organisms and has been used to describe and understand predator–prey interactions in both terrestrial and aquatic environments. Most previous studies have used prey mass to examine the relationships between predator size and prey size; however, using prey lengths may provide a different perspective, particularly for gape-limited fishes. Using a large database of predator and prey lengths for marine aquatic predators, I found the expected positive wedge-shaped relationship between predator length and prey length and a negative converging relationship between relative prey length (prey–predator length ratio = a measure of trophic niche breadth) and predator length. Distinct patterns in the size scaling of this measure of trophic niche breadth were identified using quantile regression: converging relationships were common among adults but absent among larvae. This difference suggests contrasting ontogenetic foraging opportunities between adults and larvae: a lack of large relative prey sizes for the largest adult predators, and a greater ability of larvae to include larger prey items in their diet as they grow.