Facultative predation and scavenging by mammalian carnivores: seasonal, regional and intra-guild comparisons

The extent to which vertebrate carnivores shift facultatively between predation and scavenging has recently been emphasized. Potentially, all carnivores have to do is wait until animals succumb to the debilitating effects of advancing age. However, this may be insufficient because of intense competition among other scavengers and decomposers for food. Moreover, the availability of carcasses of animals dying from causes other than predation varies seasonally, so carnivores must be adapted to exploit various sources of food through the seasonal cycle. We explore how mammalian carnivores cope with seasonality in carrion supply and in prey vulnerability to predation. We focus mainly on large carnivores and ungulates, and compare especially ecological communities in northern temperate and African savanna ecosystems. When carrion is scarce, carnivores can (i) take advantage of temporarily vulnerable segments of prey populations, such as newborn young, heavily pregnant females and males distracted or debilitated by reproduction, (ii) switch to carcass remains left by or stolen from other carnivores, or (iii) exploit small animals and non-animal food sources. Relationships between carnivores tending towards predation or scavenging can be both competitive and facilitative. Top carnivores may provide a supply of carcasses throughout the year, which subsidizes scavengers when carrion availability from other sources is low. Alterations of seasonal patterns due to anthropogenic environmental change may enhance the role of top carnivores as buffers of anthropogenic perturbations of natural processes. Megaherbivores, which are not normally regarded as prey but can provide huge carrion subsidies, may strongly influence interspecific interactions between carnivores and the proportion of food flowing towards scavenging relative to predation. Relationships among carnivores based on hunting vs. scavenging strategies are flexible and subject to changes in response to circumstances. Their functional complexity is relevant for assessing the effects of global change on ecosystem function.