Effects of predaceous and nonpredaceous introduced fish on the survival, growth, and antipredation behaviours of long-toed salamanders

Abstract

Simultaneous introduction of complex suites of exotic organisms into indigenous populations have poorly known magnitudes and consequences. We compared the effects of introduced piscivorous rainbow trout ( Oncorhynchus mykiss (Walbaum, 1792)) and nonpiscivorous fathead minnows ( Pimephales promelas Rafinesque, 1820) on growth, survival, susceptibility to predation, and antipredator behaviours of naïve long-toed salamanders ( Ambystoma macrodactylum Baird, 1850). Trout reduced salamander hatchling and larvae survival to nearly zero in predation trials and caused a 39% reduction in salamander survival within outdoor mesocosms. Salamander larvae did not increase their refuge use or alter activity patterns in the presence of trout. These results imply that allotopic distributions of trout and salamanders observed in several field surveys likely result from the inability of larvae to recognize introduced predators as a threat. Minnows also caused significant reductions in salamander survival (41%) and growth (37%) in mesocosms, and exposure to minnow cues caused larvae to spend more time within a refuge. Reduced salamander survivorship and growth in the mesocosms was likely due to competition for limiting zooplankton and (or) cannibalism. These results indicate that introductions of small-bodied, nonpiscivorous fishes can reduce amphibian survival and growth to at least the same extent as introduced trout.