Quantifying resource partitioning in centrarchids with stable isotope analysis

Abstract

Stable isotope and gut content analyses were completed on multiple age classes of Detroit River rock bass (Ambloplites rupestris) and bluegill sunfish (Lepomis macrochirus) to determine the importance of resource partitioning in littoral centrarchids. d 15 N signatures ranged from 10.9‰ to 12.8‰ in young of the year (YOY) to 7-yrold rock bass and from 10.3‰ to 12.1‰ for YOY to 4-yr-old bluegills. YOY diets for both species had similar proportions of benthic and epiphytic prey, with YOY rock bass also having a planktonic dietary component. YOY rock bass consequently had a lighter d 13 C signature than similarly aged bluegills, suggesting that these individuals are able to exploit prey from more energetically efficient open water habitats. Rock bass became piscivorous during the first full year of growth, with concomitant depletion of the d 13 C signature with increasing age, typical of an isotopically depleted phytoplankton d 13 C signal. By 7 yr of age, rock bass diets were dominated by crayfish and cyprinids, with no further significant depletion of the d 13 C signature. For bluegills, diets were dominated by small benthic invertebrates, regardless of age. d 13 C signatures in YOY and 1-yr-old bluegills remained enriched relative to rock bass of the same age, suggesting that bluegill sunfish remain in nearshore shallower littoral habitats for a greater proportion of their life history because of increased predation pressure. This pairing of stable isotope and gut content analyses provides a quantitative resolution of foraging history and habitat selection of species coexisting in a littoral community.