Quantifying resource partitioning in centrarchids with stable isotope analysis

نویسندگان

  • Gordon Paterson
  • Kenneth G. Drouillard
  • Douglas Haffner
چکیده

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. d15N 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 d13C 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 d13C signature with increasing age, typical of an isotopically depleted phytoplankton d13C signal. By 7 yr of age, rock bass diets were dominated by crayfish and cyprinids, with no further significant depletion of the d13C signature. For bluegills, diets were dominated by small benthic invertebrates, regardless of age. d13C 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. Understanding habitat selection and use in fish species is a timeand resource-intensive venture, often requiring the collection of high numbers of individuals and various collection methods to distinguish interspecific habitat preferences (Weaver et al. 1993). For littoral centrarchids such as sunfish (Lepomis sp.), crappie (Pomoxis sp.), rock bass (Ambloplites rupestris), and largeand smallmouth bass (Micropterus sp.), spawning periods often overlap (Scott and Crossman 1973), and the resulting young of the year (YOY) populations are likely to seek refuge under macrophyte cover (Werner et al. 1977; Weaver et al. 1997) with predator avoidance reinforcing such selection (Mittelbach 1981; Weaver et al. 1997). Additionally, prey selection, especially in small, gape-limited individuals, is restricted to small invertebrates, and prey selection can overlap among YOY of such species (Mittelbach and Persson 1998). With growth in size, these individuals pass through a series of ontogenetic niches (Werner and Gilliam 1984) whereby successively larger prey become potential forage, and habitat selection can change to reflect such preferences (Weaver et al. 1997). Yearling and older rock bass and smallmouth bass are observed to typically select the habitat complexity provided by structures 1 Corresponding author ([email protected]).

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تاریخ انتشار 2006