Using energetics and diet to predict the movements of northern flying squirrels (Glaucomys sabrinus) in the managed forests of southeast Alaska.

摘要

In 1997, the Tongass Land Management Plan identified the endemic northern flying squirrel (Glaucomys sabrinus griseifrons) as a design species for small old-growth reserves on Prince of Wales Island. The reserve program and harvest plan assumed that flying squirrel populations on the island will exist as a metapopulation in the fragmented landscape. Two life history characteristics, gliding and diet, appear to be closely linked to old-growth habitats. Because timber harvest results in loss of gliding structure and hypogeous fungi, flying squirrels likely will not exist as a functioning metapopulation because of limited dispersal. To assess effects of fragmentation on flying squirrel dispersal, I measured direct costs of transport of quadrupedal locomotion using flow-through respirometry and captive northern flying squirrels. I estimated diet of wild flying squirrels using stable isotope and fecal analyses. Because of potential misinterpretation of linear mixing model results in stable isotope analyses to estimate diet in a fragmented habitat, I modeled habitat effects on resource use and niche. Finally, I measured fine-scale movements of flying squirrels in all three habitat types and estimated perceptual range in the managed stands. I found that cost of quadrupedal locomotion was higher than expected for northern flying squirrels and they may realize over 64% energy savings through gliding. Lichen, conifer seeds, and fungi were main dietary items consumed and assimilated by the wild flying squirrels and old-growth had significantly higher food availability than second-growth stands and clearcuts. Modeling indicated that habitat use could affect isotopic patterns of consumers suggesting that knowledge of habitat use and individual foraging behavior are critical for correct quantification of the ecological niche of flying squirrels and other animals. Perceptual range of flying squirrels was greater in clearcuts than second-growth stands but was significantly shorter than predicted for both habitats. Furthermore, flying squirrels pause more often in clearcuts, leading to higher energetic costs of dispersing through this habitat. Thus, habitat fragmentation through logging may have created barriers to dispersal among forest patches possibly leading to isolation and eventually, localized extinction. With limited dispersal, flying squirrels on Prince of Wales Island will not function as viable metapopulations.