Nutritional value of hypogeous fungus for a forest-dwelling ground squirrel

Abstract

Investigated the nutritional quality of sporocarps (fruiting bodies) of the hypogeous fungus Elaphomyces granulatus in the diet of golden-mantled ground squirrel Spermophilus saturatus, which is highly mycophagous throughout its season of activity in the Cascade Mountains, Washington. The sporocarps had a high N concentration, but 80% of this was in the totally indigestible spores and the relatively indigestible cell walls of the peridium, and only half of the remaining 20% was protein N. The digestible energy content of the fungus was low compared with that of conifer seeds and similar to that of grasses and legumes that are naturally eaten by the ground squirrels in small amounts. The overall (dry-matter) digestibility of E. granulatus sporocarps (60%) appears to be near the minimum digestibility on which the squirrels are able to maintain themselves. Therefore, sporocarps of E. granulatus cannot be regarded as a high-quality dietary item in terms of the availability of nutrients. This is probably true for hypogeous fungi in general and their value as a food resource derives mainly from their great abundance during the active season of small mammals such as ground squirrels and from thei remission of strong odors, which makes mature sporocarps highly detectable. These features should maximize the yield of energy and nutrients to small mammalian mycophagists in relation to foraging effort. -from Authors Show more