Oecologia

, Volume 153, Issue 2, pp 461–470

Invading rainbow trout usurp a terrestrial prey subsidy from native charr and reduce their growth and abundance

  • Colden V. Baxter
  • Kurt D. Fausch
  • Masashi Murakami
  • Phillip L. Chapman
Community Ecology

DOI: 10.1007/s00442-007-0743-x

Cite this article as:
Baxter, C.V., Fausch, K.D., Murakami, M. et al. Oecologia (2007) 153: 461. doi:10.1007/s00442-007-0743-x

Abstract

Movements of prey organisms across ecosystem boundaries often subsidize consumer populations in adjacent habitats. Human disturbances such as habitat degradation or non-native species invasions may alter the characteristics or fate of these prey subsidies, but few studies have measured the direct effects of this disruption on the growth and local abundance of predators in recipient habitats. Here we present evidence, obtained from a combined experimental and comparative study in northern Japan, that an invading stream fish usurped the flux of allochthonous prey to a native fish, consequently altering the diet and reducing the growth and abundance of the native species. A large-scale field experiment showed that excluding terrestrial invertebrates that fell into the stream with a mesh greenhouse reduced terrestrial prey in diets of native Dolly Varden charr (Salvelinus malma) by 46–70%, and reduced their growth by 25% over six weeks. However, when nonnative rainbow trout (Oncorhynchus mykiss) were introduced, they monopolized these prey and caused an even greater reduction of terrestrial prey in charr diets of 82–93%, and reduced charr growth by 31% over the same period. Adding both greenhouse and rainbow trout treatments together produced similar results to adding either alone. Results from a comparative field study of six other stream sites in the region corroborated the experimental findings, showing that at invaded sites rainbow trout usurped the terrestrial prey subsidy, causing a more than 75% decrease in the biomass of terrestrial invertebrates in Dolly Varden diets and forcing them to shift their foraging to insects on the stream bottom. Moreover, at sites with even low densities of rainbow trout, biomass of Dolly Varden was more than 75% lower than at sites without rainbow trout. Disruption of resource fluxes between habitats may be a common, but unidentified, consequence of invasions, and an additional mechanism contributing to the loss of native species

Keywords

Hokkaido Japan Invasion ecology Oncorhynchus mykiss Resource subsidies Salvelinus malma 

Supplementary material

442_2007_743_MOESM1_ESM.doc (161 kb)
S1. Top Dolly Varden charr (Salvelinus malma), or oshorokoma, native to streams of Hokkaido, Japan, are threatened by the invasion of non-native rainbow trout. Bottom A spring stream in Hokkaido that has not been invaded by rainbow trout and which currently has high densities of native Dolly Varden. Photo credits: C.V. Baxter (top) and K.D. Fausch (bottom) (DOC 161 kb)
442_2007_743_MOESM2_ESM.doc (58 kb)
S2. Stream habitat and riparian vegetation characteristics at the six sites surveyed in the comparative study during summer 2003. Values are means + 1 SE, and sample sizes are in parentheses. Sites had either native Dolly Varden charr in allopatry (DV), Dolly Varden and low relative abundance of non-native rainbow trout (DV + low RBT), or Dolly Varden and rainbow trout in about equal relative abundance (DV = RBT) (DOC 59 kb)

Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Colden V. Baxter
    • 1
    • 4
  • Kurt D. Fausch
    • 1
  • Masashi Murakami
    • 2
  • Phillip L. Chapman
    • 3
  1. 1.Graduate Degree Program in Ecology, and Department of Fish, Wildlife, and Conservation BiologyColorado State UniversityFort CollinsUSA
  2. 2.Field Science Center for the Northern Biosphere, Tomakomai Research StationHokkaido UniversityTomakomaiJapan
  3. 3.Department of StatisticsColorado State UniversityFort CollinsUSA
  4. 4.Department of Biological SciencesIdaho State UniversityPocatelloUSA

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