Brown bear (Ursus arctos)
Brown bears consume the soft mast of at least 101 plant species spanning 24 families and 42 genera (García-Rodríguez et al. 2021). A single fecal deposit from a brown bear can contain thousands of seeds (Willson 1993), creating a massive seed dispersal event. While brown bears do not form cooperative packs, social dominance and subordination within populations has predictable effects on individual resource access and space use. In salmon-supported populations, dominant individuals (typically large males) displace subordinate individuals (particularly females with cubs) at salmon streams (Ben-David et al. 2004; Gende & Quinn 2004). Since time spent at a salmon stream is positively correlated with salmon assimilation in brown bear diets and negatively correlated with plant matter assimilation (Deacy et al. 2018), it is likely that the monopolization of salmon streams by dominant individuals leads to consistently greater quantities of seed-dispersal services by subordinate individuals. Moreover, since the vast majority of long-distance movement by bears is done by dispersing subadults (Bartoń et al. 2019), these subordinate individuals are most likely to disperse plant species beyond current range boundaries (Fig. 3A). Lamb and colleagues (2020) also show that urban habitats serve as demographic sinks for brown bear populations, and urban populations are supported by immigration by dispersing subadults. These subordinate, subadult bears may therefore contribute substantially to the dispersal and persistence of some plant populations in urban areas (Fig. 3B). Since hunters typically target resident male bears (Gosselin et al. 2017; Leclerc et al. 2019), this form of selective harvest disrupts brown bear social structure, leading to increased infanticide when immigrant males disperse into newly opened territories (Gosselinet al. 2017). Whether or not the persistent disruption of brown bear social structure by selective harvesting generates cascading effects on seed dispersal remains an open question. Moreover, it is widely appreciated that brown bears use corridors to access otherwise isolated habitat patches, and corridors are particularly important for the dispersal of subadults into urban habitats (Clevenger & Waltho 2005; Ford et al. 2017; Lamb et al. 2020). Corridors designed to facilitate brown bear movement through fragmented landscapes may therefore have unappreciated benefits for the dispersal of many bear-dispersed plant species.