Carcass size shapes the structure and functioning of an African scavenging assemblage

The particle size of the food resource strongly determines the structure and dynamics of food webs. However, the ecological implications of carcass size variation for scavenging networks structure and functioning have been largely overlooked. Here we investigate differences in scavenging patterns due to carcass size in a complex vertebrate scavenger community, Hluhluwe-iMfolozi Park, South Africa, while taking into account seasonality. We monitored the consumption of three types of experimental carcasses: 'small' (< 10 kg), 'medium' (10-100 kg) and 'large' (> 100 kg). We employed general lineal models to explore the influence of carcass size on 1) scavenging network structure (scavenger species richness per carcass) and 2) functioning (carcass detection time, consumption time, consumption rate and percentage of carrion consumed). We also tested whether the structure of the scavenging network of each carcass size was nested, i.e. whether the scavenging assemblage in species-poor carcasses was a subset of the assemblage consuming species-rich carcasses. We found strong evidence indicating that carcass size is a major factor governing the associated scavenger assemblage. Scavenger species richness per carcass and carcass consumption time and rate increased with carcass size, while carcass detection time and percentage of carrion biomass consumed were negatively related to carcass size. Strikingly, most of the carrion biomass was consumed by facultative scavengers, represented by large mammalian carnivores, rather than by obligate scavengers (i.e. vultures). Scavenging network nestedness tended to be higher at larger carcasses, and nestedness was sensitive to the removal of the most connected species in the network (spotted hyena) rather than vultures. When comparing scavenging and predation assemblages, crucial size-dependent differences emerge. Also, we identified a traditionally ignored mechanism by which hunting large prey could be relatively less profitable for predators, namely the costs associated with competition from scavengers and decomposers.