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The relationship between the production of hypogeous sporocarps and the denisity and diet of northern flying squirrels in western hemlock forests of coastal British columbia Anderson, Janice

Abstract

The northern flying squirrel, Glaucomys sabrinus (Shaw), is an arboreal sciurid inhabiting forested habitats across North America. Hypogeous fruit bodies of mycorrhizal fungi (truffles) are a predominant food eaten by northern flying squirrels. Previous studies have suggested that the abundance of truffles in a stand may be an important factor associated with the density of northern flying squirrels. Over a twoyear period, five second-growth western hemlock (Tsuga heterophylla (Raf). Sarg.) forests in coastal British Columbia were used year-round to sample truffles and to live trap northern flying squirrels, in order to: (1) describe the occurrence and production of truffles; (2) determine the importance of truffles in the seasonal diet of squirrels; (3) identify which truffle taxa were selectively consumed by this species; and 4) evaluate associations between the density of northern flying squirrels and the production of truffles. Truffle production from each site was determined using results from the primary collection period, which included four samples at 10-week intervals from April 1998 to December 1998. Eleven species representing six genera of truffles were collected, with Elaphomyces making up over 9 3% of the total number and 99% of the total biomass. Truffle production at each site during the primary collection period ranged from 1.68 kg ha⁻¹ year⁻¹ to 15.72 kg ha⁻¹ year⁻¹. Plant material was a major year-round component of the diet of northern flying squirrels, suggesting a more generalist feeding strategy than reported elsewhere. Truffle spores were most frequent in the summer and fall diets. Nine additional truffle taxa were present in squirrel diets than were collected in the field. Northern flying squirrels consumed on average 1.9 times more truffle taxa than were found during concurrent fungal surveys. The fungi genera Elaphomyces and Hydnotrya were under-represented and several taxa were over-represented in squirrel feces relative to their abundance at the site. Densities of flying squirrels could not be explained by truffle production alone at the five sites. Efforts to enhance populations of northern flying squirrels to improve foraging habitat for the endangered northern spotted owl (Strix occidentalis caurina Merriam) should consider measures that affect a broad array of food items and that enhance diversity as well as abundance of food supply.

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