3 years ago

A response-surface examination of competition and facilitation between native and invasive juvenile fishes

A response-surface examination of competition and facilitation between native and invasive juvenile fishes
Greg G. Sass, Kirsten A. Nelson, David H. Wahl, Scott F. Collins
Ecological theory has long recognised the importance of positive and negative species interactions as drivers of food web structure, yet many studies have only focused on competition. Because competitive and facilitative mechanisms operate simultaneously, but through different food web pathways, the balance of their combined effects can produce complex and variable responses. We used a response-surface experimental design to assess the roles of negative (e.g. intra-, interspecific competition) and positive (e.g. facilitation) interactions between native and invasive juvenile fishes. We tested whether these interactions alter the densities of planktonic and benthic invertebrates to evaluate the magnitude and mechanism(s) influencing the acceptance or resistance of biological invaders. Interactions between bighead carp (Hypophthalmichthys nobilis) and bluegill (Lepomis macrochirus) or common carp (Cyprinus carpio) were evaluated in mesocosms. Intraspecific interactions were 1.5–2.4 times stronger than interspecific interactions between carp species. The only instance of interspecific competition resulted in bighead carp reducing the daily growth of bluegill, whereas the reciprocal interaction resulted in facilitation. Facilitation occurred when bluegill increased the daily growth of low density bighead carp treatments, despite increased numbers of fishes. Bighead carp also increased densities of benthic Chironomidae larvae, which were subsequently consumed by bluegill, but did not result in enhanced bluegill growth. These suites of interactions were not observed between common and bighead carp. Our response-surface design proved useful for comparing the relative magnitude of intra- vs. interspecific competition, identifying facilitation among species, and tracing attendant effects on invertebrate communities. By accounting for the directionality of interactions within our experimental framework and tracking responses of prey at lower trophic levels, we provide a clearer understanding of how competitive effects and stressed consumers alter prey communities and influence facilitation. plain language summary is available for this article. Plain Language Summary

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/1365-2435.12922

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