Forest fragmentation is likely to make it difficult for juvenile amphibians to move to new habitats, according to a new study reported by Betsie Rothermel and Raymond Semlitsch of the University of Missouri–Columbia. Because such movement is crucial to maintaining gene flow and survivability of declining populations, the findings suggest that amphibian populations will continue to decline as more trees are cut and land use intensifies.

To determine whether amphibians initially move in the direction of a particular habitat when they leave a breeding pond, the researchers added larvae of three amphibian species—spotted salamanders, small-mouthed salamanders, and American toads—to experimental pools situated on the edge between a forest and an open field. The experiments were performed in the midwestern United States, where much of the land around amphibian breeding sites is agricultural cropland or pasture.

A circular drift fence surrounded the experimental pools, with pitfall traps and two enclosures that extended into forest and old-field habitats. Each morning the researchers collected the amphibians in the traps and documented whether they were found headed toward the forest or the field, and how far they had traveled.

The spotted salamander and American toad juveniles significantly avoided the open field habitats when leaving the pools, but the findings for the small-mouthed salamander were inconclusive. In addition, salamanders trapped in open fields showed signs of greater dehydration, suggesting that mortality is higher in fields than in forests. On the basis of these results, the researchers conclude that habitat fragmentation is likely to reduce the dispersal rates between populations of the three amphibian species and contribute to their decline. (Conserv. Biol. 2002, 16, 1324–1332)