• stream;
  • reproduction;
  • behaviour;
  • fish;
  • sedimentation;
  • mutualism


  1. Although nest association among Nocomis chubs and other minnows (Cyprinidae) is common throughout North America, the overall outcome of this relationship and its mechanisms of costs and benefits remain unclear. Because imperilment of stream fishes is affected by reproductive traits, the implications of this widespread interaction must be understood.
  2. Nest association mechanisms were explored using a multiple working hypotheses framework on fish assemblage data from 25 reaches in three tributaries of the New River, Virginia, USA. Multiple linear regression models predicting reproductive success (age-0 abundance) of chubs and associates were compared based on model weights (wi) calculated from Akaike's Information Criterion, adjusted for small sample size (AICc), and relative change in AICc among models. For age-0 chubs, models represented hypotheses emphasizing the additive effects of adult abundance, nest abundance, and egg dilution by juvenile associates (causing decreased egg predation). For age-0 associates, models represented hypotheses emphasizing adult associate abundance, gravel substrate availability, nest abundance, parental care (as nest defence) from chubs, and egg dilution by chubs.
  3. Model evidence suggests that chubs can sustain themselves (w = 0.61), but their reproductive success is enhanced by a dilution effect from juvenile strong associates (w = 0.37). Strong associate reproductive success was best described by variables emphasizing nest association interactions (w = 0.46) and natural sources of habitat variability (w = 0.45), whereas that of weak associates was more closely related to availability of unmodified habitat (w = 0.50).
  4. Chubs and associates appear to receive a net benefit from the association, suggesting a mutualistic relationship. Community-wide conservation strategies may be useful for protecting symbiotic spawning fishes. In addition to competition and predation, conservation practitioners should consider positive interactions in conservation plans of imperiled mutualists.

Copyright © 2013 John Wiley & Sons, Ltd.