Consideration of extinction risks for salmonids
Under the National Forest Management Act of 1979, the USDA Forest Service is charged with maintaining viable populations of all existing native vertebrate species on lands they administer. Accomplishment of this responsibility requires complete assessment of all federally authorized, funded, or implemented projects that may jeopardize the continued existence of a species. An understanding of the processes of extinction and the characteristics of populations that make them more or less likely to persist is fundamental to such assessments. We review processes contributing to extinction and characterize them as deterministic, stochastic, and genetic. Factors that strongly influence risks of local and regional extinction include replication, dispersal and connection among populations representing a regional metapopulation. Project planning and assessments must address habitat disruption and population responses at both the local and regional scale. Maintaining strong populations in the best possible habitats throughout the landscape and preserving the ecological processes characteris tic of metapopulations are the best hedges against extinction.