Fish can affect amphibian larvae directly through consumption or indirectly by eliciting antipredator behaviours that incur fitness costs. Because of predation, long-toed salamanders (Ambystoma macrodactylum) typically show an allotopic distribution with fish. Linnet Lake (Waterton Lakes National Park, Alberta, Canada) represents the unusual situation in which salamanders coexist with a small-bodied cyprinid, lake chub (Couesius plumbeus). However, the salamander population resident to Linnet Lake has declined in recent years. Our objective was to assess the role of lake chub in the decline of this salamander population by combining field observations and laboratory experiments. We used mark-recapture techniques to estimate the size of the 2 populations. We found little evidence of successful salamander reproduction, and the adult population had decreased by 60% in 14 y. In contrast, a large population of lake chub was present. Experiments showed that lake chub between 70 and 100 mm could consume salamander larvae < 40 mm in length. Larvae responded to the presence of lake chub by reducing activity and increasing refuge use, especially during the day. Our study is one of few to document the ability of a native small-bodied fish to consume amphibian larvae. The coexistence of fish and salamanders may result from a dynamic interplay between periodic extirpation of fish by winter hypoxia and of salamanders by predation, punctuated by episodes of re-colonization or strong recruitment.
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Vol. 18 • No. 1