The effects of introduced fish on the long-toed salamander (Ambystoma macrodactylum) in southwestern Alberta, Canada

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Species that are introduced outside of their native ranges are an important threat to biodiversity. In southwestern Alberta, Canada, sport and bait fish have been introduced into most water bodies. The author examined the effects of introduced trout and minnows on the distribution, demography, and behavior of larval long-toed salamanders through a combination of field surveys, laboratory experiments, and an outdoor mesocosm experiment. Results from field surveys at 30 high-elevation (>1500 m) lakes confirmed previous studies showing an allopatric distribution of trout and long-toed salamanders. The same pattern was also documented at 27 low-elevation (< 1500 m) ponds. In a mesocosm experiment, salamander survival was significantly reduced in ponds containing trout or minnows. Surprisingly, larvae exposed to minnows were 28–65% smaller than larvae in control ponds, suggesting strong interspecific competition for zooplankton prey. In a series of laboratory studies, trout preyed directly on salamander hatchlings and larvae, whereas minnows injured hatchlings but did not consume them. In laboratory aquaria, salamander larvae spent significantly more time within a refuge when exposed to minnow cues, but showed no behavioral response to trout. This confirmed my expectation that long-toed salamanders lack specific behavioral responses to trout, but respond generally to disturbances within the water column. Thus, direct predation and a lack of specific antipredator behavior are among the likely mechanisms responsible for the observed allopatric distribution of trout and long-toed salamanders. My data also show that gape-limited fish reduce growth and survival of salamanders, perhaps more so than trout, through mechanisms such as competition and behavioral alteration.

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ELECTRONIC FILE - Zoology