Consumption of fungal sporocarps by Yellowstone grizzly bears

Sign of grizzly bears (Ursus arctos horribilis) consuming fungal sporocarps (mushrooms and truffles) was observed on 68 occasions during a study of radiomarked bears in the Yellowstone region, 1977–96. Sporocarps also were detected in 96 grizzly bear feces. Most fungi consumedby Yellowstone's grizzlybearsweremembersofthe Boletaceae(Suillus spp.), Russulaceae (Russula spp. and Lactarius sp.), Morchellaceae (Morchella elata), and Rhizopogonaceae. Consumption of false truffles (Rhizopogon spp.) was indicated by excavations that were deeper, on average (1.1 dm), than excavations for mushrooms (0.6 dm). Consumption of sporocarps was most frequent during September (7% of all activity), although median numbers of sporocarps excavated at feeding sites peaked during both August and September (22–23 excavations/site). Almost all consumption (75%) occurred on edaphically harsh sites typically dominated by lodgepole pine (Pinus contorta). At broad scales, consumption of sporocarps was most likely where these types of lodgepole pine-dominated sites were extensive or where high-elevation sites supporting mature whitebarkpine (P albicaulis) were rare. The number of sporocarps excavated atafeeding site was greatest when conecrops of whitebarkpine were smallandinstands with abundantlodgepolepine. At finescales, consumption of fungi was positively associated with lodgepolepine basalarea and negatively associated with total ground vegetation cover. Because of the strong association of sporocarp consumption with lodgepole pine and its disassociation at broad scales with availability of whitebark pineseeds, consumption of mushrooms and truffles by grizzly bears will likely increase in the Yellowstone ecosystem with global warming. Lodgepole pine is predicted to increase and whitebark pine to decline with global warming.