—The diet of the brown bear ( Ursus arctos) is described for the territory of the southern taiga subzone illustrated by the example of the Central Forest Nature Reserve (West-European Russia)...

Biotic interactions are expected to influence species' responses to global changes, but they are rarely considered across broad spatial extents. Abiotic factors are thought to operate at larger spatial scales, while biotic factors, such as species interactions, are considered more important at local scales within communities, in part because of the knowledge gap on species interactions at large spatial scales (i.e., the Eltonian shortfall). We assessed, at a continental scale, (i) the importance of biotic interactions, through food webs, on species distributions, and (ii) how biotic interactions under scenarios of climate and land‐use change may affect the distribution of the brown bear (Ursus arctos). We built a highly detailed, spatially dynamic, and empirically sampled food web based on the energy contribution of 276 brown bear food species from different taxa (plants, vertebrates, and invertebrates) and their ensemble habitat models at high resolution across Europe. Then, combining energy contribution and predicted habitat of food species, we modelled energy contribution across space and included these layers within Bayesian‐based models of the brown bear distribution in Europe. The inclusion of biotic interactions considerably improved our understanding of brown bear distribution at large (continental) scales compared with Bayesian models including only abiotic factors (climate and land use). Predicted future range shifts, which included changes in the distribution of food species, varied greatly when considering various scenarios of change in biotic factors, providing a warning that future indirect climate and land‐use change are likely to have strong but highly uncertain impacts on species biogeography. Our study confirmed that advancing our understanding of ecological networks of species interactions will improve future projections of biodiversity change, especially for modelling species distributions and their functional role under climate and land‐use change scenarios, which is key for effective conservation of biodiversity and ecosystem services.

Brown bear (Ursus arctos) diet composition and seasonal food habits were examined in the Central Forest Nature Reserve (CFNR) in West-European Russia. This territory has 2 landscape types: (1) a mostly intact and strictly protected CFNR core area with southern taiga forests, and (2) a human-modified buffer zone around it. We collected 758 bear scats between March and November 2008–2021. Fleshy fruits were the most important food category in the bear diet and represented 30% of the annual estimated dietary energy content (EDEC). Among fruits, the most important food items were apples (Malus domestica; EDEC = 22%). Bears highly preferred bilberry (Vaccinium myrtillus) in the late summer and early fall seasons (EDEC = 9%). During the hyperphagia period, bears fed on apples, hazel nuts (Corylus avellana; EDEC = 17%), oat (Avena sativa; EDEC = 9%), rowan (Sorbus aucuparia; EDEC = 5%), and cranberry (V. microcarpum and V. oxycoccos; EDEC = 4%). Herbaceous plants were also important (EDEC = 6%) from late spring to early fall. Among insects, bears actively consumed ants (Formicidae; EDEC = 3%) and social wasps (Vespidae; EDEC = 3%). Ungulates, especially adult moose (Alces alces) and calves, comprised the most important food item for bears during spring, contributing 15% of the EDEC. The CFNR core area, which presents natural foods for bears, had a prevalence of bilberry in scat amount (Cliff's Delta = –0.20). The buffer zone had a prevalence of apples (Cliff's Delta = 0.19) and oat (Cliff's Delta = 0.14), whose distributions were associated with abandoned orchards and cultivated fields. Brown bear food habits in the CFNR are similar to those in southern and eastern Europe, with a great dietary contribution of plant materials (especially fleshy fruits and hard mast). However, at the same time, CFNR bears have a significant dietary impact associated with boreal ecosystems (high Vaccinium berry consumption and active moose hunting), which makes it similar to populations from northern Europe.

Most habitat suitability models and resource selection functions (RSFs) use indirect variables and habitat surrogates. However, it is known that in order to adequately reflect the habitat requirements of a species, it is necessary to use proximal resource variables. Direct predictors should be used to construct a real RSF that reflects the real influence of main resources on species habitat use. In this work, we model the spatial distribution of the main food resources of brown bear Ursus arctos L. within the natural and human-modified landscapes of the Central Forest State Nature Reserve (CFNR) for further RSF construction. Food-probability models were built for Apiaceae spp. (Angelica sylvestris L., Aegopodium podagraria L., Chaerophyllum aromaticum L.), Populus tremula L., Vaccinium myrtillus L., V. microcarpum (Turcz. ex Rupr.) Schmalh., V. oxycoccos L., Corylus avellana L., Sorbus aucuparia L., Malus domestica Borkh., anthills, xylobiont insects, social wasps and Alces alces L. using the MaxEnt algorithm. For model evaluation, we used spatial block cross-validation and held apart fully independent data. The true skill statistic (TSS) estimates ranged from 0.34 to 0.95. Distribution of Apiaceae forbs was associated with areas having rich phytomass and moist conditions on southeastern slopes. Populus tremula preferred areas with phytomass abundance on elevated sites. Vaccinium myrtillus was confined to wet boreal spruce forests. V. microcarpum and V. oxycoccos were associated with raised bogs in depressions of the terrain. Corylus avellana and Sorbus aucuparia preferred mixed forests on elevated sites. Distribution of Malus domestica was associated with meadows with dry soils in places of abandoned cultural landscapes. Anthills were common on the dry soils of meadows, and the periphery of forest areas with high illumination and low percent cover of tree canopy. Moose preferred riverine flood meadows rich in herbaceous vegetation and sparse mixed forests in spring and early summer. The territory of the human-modified CFNR buffer zone was shown to contain a higher variety of food resources than the strictly protected CFNR core area.