COSTS AND BENEFITS OF GROUP LIVING IN A RECENTLY SOCIAL UNGULATE - THE ALASKAN MOOSE

Risk of predation is considered a major influence on foraging behavior and the evolution of social groups. We measured foraging efficiency (percentage of active time spent foraging) for Alaskan moose (Alces alces gigas) in various categories of predation risk in Denali National Park, Alaska, in 1991. For a particular group size, foraging efficiency declined significantly with distance from cover. Foraging selectivity by moose for diamondleaf willow (Salix planifolia pulchra) also decreased as distance from cover increased. Adult females accompanied by young foraged less efficiently than either females without young or adult males. Group size was positively correlated with distance from cover, which suggests that social grouping in moose is an adaptation to increased predation risk. Surprisingly, group size was inversely related to foraging efficiency because of the overriding negative effects of aggressive behavior. This finding contrasts with behavioral trends in more social ungulates, which display increased foraging efficiency with increasing group size. We suggest that the lowered foraging efficiency in Alaskan moose is a result of the recent evolution of gregarious behavior in this subspecies and that increased foraging efficiency within groups of social ungulates may be a subsequent adaptation rather than an a priori selective advantage that led to the evolution of social behavior.