19 - Source–sinks, metapopulations, and forest reserves: conserving northern flying squirrels in the temperate rainforests of Southeast Alaska  pp. 399-422

Source–sinks, metapopulations, and forest reserves: conserving northern flying squirrels in the temperate rainforests of Southeast Alaska

By Winston P. Smith, David K. Person and Sanjay Pyare

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Reserves are a common strategy used to ensure the viability of wildlife populations, but their effectiveness is rarely empirically evaluated. The Tongass National Forest implemented a conservation plan (TLMP) in 1997 to maintain biological diversity across Southeast Alaska, the cornerstone of which was an integrated system of large, medium, and small old-growth reserves (OGRs). Small OGRs were intended to facilitate functional connectivity between larger reserves and ensure well-distributed populations of forest-dependent wildlife. The northern flying squirrel (Glaucomys sabrinus) was selected as an indicator of wildlife communities that operate at small spatial scales because its abundance has been correlated with old-growth forest structure and processes and because of specific habitat requirements for efficient locomotion. Previous research predicted that small OGRs were unlikely to support flying squirrels over a 100-year time horizon. Consequently, the presence and persistence of flying squirrels in small OGRs depended on dispersal from larger reserves. Using data from telemetry experiments, we determined effective distances immigrants could move through landscapes composed of old-growth and managed forests. Effective distance accounted for the resistance of habitats such as clearcuts that are difficult for flying squirrels to traverse. We used findings of previous studies to parameterize a logistic population growth model incorporating dispersal to determine the number of dispersers necessary to enable a flying squirrel population in a small OGR to persist for 25 and 100 years. We combined that information with a function relating the probability of successful dispersal with effective distance to estimate the maximum effective distances between OGRs that would ensure flying squirrels colonize and persist in small OGRs for 25 and 100 years. Our findings underscore the essential role of immigration in sustaining sinks and facilitating metapopulation viability among unsustainable fragmented populations (i.e., sinks). They also demonstrate the extent to which permeability of landscape elements can influence the probability of dispersal and functional connectivity of subpopulations in a managed matrix.

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