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

Abstract

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.

Body Size as a Driver of Scavenging in Theropod Dinosaurs

“…Our extant model was successful in predicting the necessity of soaring flight as a requirement in obligate scavenging in birds (Ruxton and Houston 2004) and in predicting the higher scavenging efficiencies in species with high levels of observed scavenging, such as hyenas and marabou storks, in comparison to species with lower levels of scavenging, such as bateleurs and jackals. Scavenging is becoming more recognized as a vital component of ecosystem structure and functioning (DeVault et al 2003), with facultative scavengers often taking the role of the main consumers (Moleón et al 2015). Despite this, scavenging is often omitted from ecological models, and instead all carnivory is considered to be the result of predation (Wilson and Wolkovich 2011).…”

Potential threat to Eurasian griffon vultures in Spain from veterinary use of the drug diclofenac

“…In South Africa, the proportion consumed ranges from 90·6% for medium‐sized ungulates to 79·1% for large ungulates and megaherbivores (Moleón et al . ). We assumed that these relatively constant proportions (around 80%) can also be applied to domesticated ungulates fed upon by vultures, and therefore take the proportion of the weight of carcasses of domesticated cattle, pigs and horses Equus caballus available to vultures.…”

Scavenging in the Anthropocene: Human impact drives vertebrate scavenger species richness at a global scale

“…This was calculated by identifying the highest number of individuals of a scavenger species simultaneously observed or appearing in a picture (e.g., Mateo-Tomás et al, 2017;Moleón, Sánchez-Zapata, Sebastián-González, & Owen-Smith, 2015). Carcass size ranged from rodents (e.g., 20 g, mice) to large ungulates (e.g., 900 kg, bison).…”