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Vance T. Vredenburg, Ph.D. Background: Many amphibian species are experiencing population declines and extinctions world-wide. Environmental contamination as well as the introduction and spread of nonnative predators are proposed causes of these declines. Studies have shown a negative relationship between introduced fishes and declining amphibian populations, but little direct experimental evidence is available. This study manipulated the presence and absence of rainbow and brook trout to test the hypothesis than their introduction had contributed to the decline of the mountain yellow-legged frog. Advance: From 1996-2003, introduced trout were removed from 5 lakes in a remote and protected area of the Sierra Nevada mountain range. Sixteen nearby lakes were used as controls; 8 with introduced trout and 8 without. Rainbow trout were placed in cages in three lakes containing the frogs to determine the vulnerable life stage of the frogs. Implication: Removal of the introduced trout resulted in a rapid recovery of the mountain frog population. In the caging experiments, trout were observed to strike at and eat hatching tadpoles, but did not consume egg masses. Together these experiments indicate that introduced trout species can have dramatic effects on populations of amphibians. Other amphibian declines in other parts of the world may have be the result of more complicated interactions of weather patterns or environmental contaminants. Trout are effective predators on mountain frog tadpoles and suggest that the introduction of trout is the most likely mechanism for decline of the mountain frog. The study also shows that this decline can be rapidly reversed with the removal of the trout. Citation: Vredenburg VT. Reversing introduced species effects: Experimental removal of introduced fish leads to rapid recovery of a declining frog. Proc Natl Acad Sci U S A. 2004 May 18;101(20):7646-50. Epub 2004 May 10. |
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