Scavenging is a common feeding behavior by many species that plays an important role in ecosystem stability and function while also providing ecosystem services. Despite its importance, facultative scavenging on large animal carcasses has generally been overlooked in Asian temperate forest ecosystems. The aim of this study was to determine the composition and feeding behavior of the facultative scavenger guild as it relates to sika deer (Cervus nippon) carcasses in Japanese forests. There are no obligate scavengers or large predators that kill adult ungulates, but humans fill the role of large predators by culling deer for population management. We documented nine vertebrate species scavenging on deer carcasses and found that mammals were more frequent scavengers than birds and also fed for longer durations. This result suggests that there is a facultative scavenger guild composed mainly of mammals in our forest ecosystem and that carcass utilization by birds was restricted to only forest species. Raccoon dogs (Nyctereutes procyonoides) and Asian black bears (Ursus thibetanus) were the most frequent scavenger species and also fed for longer durations than other scavengers. There were significant seasonal differences in scavenging by Asian black bear, Japanese marten (Martes melampus), and mountain hawk‐eagle (Nisaetus nipalensis), suggesting the availability of other food resources may alter facultative scavenging by each species. Our results support that scavenging is widespread in this system and likely has important functions including building links in the food web.

The organization of ecological assemblages has important implications for ecosystem functioning, but little is known about how scavenger communities organize at the global scale. Here, we test four hypotheses on the factors affecting the network structure of terrestrial vertebrate scavenger assemblages and its implications on ecosystem functioning. We expect scavenger assemblages to be more nested (i.e. structured): 1) in species‐rich and productive regions, as nestedness has been linked to high competition for carrion resources, and 2) regions with low human impact, because the most efficient carrion consumers that promote nestedness are large vertebrate scavengers, which are especially sensitive to human persecution. 3) We also expect climatic conditions to affect assemblage structure, because some scavenger assemblages have been shown to be more nested in colder months. Finally, 4) we expect more organized assemblages to be more efficient in the consumption of the resource. We first analyzed the relationship between the nestedness of the scavenger assemblages and climatic variables (i.e. temperature, precipitation, temperature variability and precipitation variability), ecosystem productivity and biomass (i.e. NDVI) and degree of human impact (i.e. human footprint) using 53 study sites in 22 countries across five continents. Then, we related structure (i.e. nestedness) with its function (i.e. carrion consumption rate). We found a more nested structure for scavenger assemblages in regions with higher NDVI values and lower human footprint. Moreover, more organized assemblages were more efficient in the consumption of carrion. However, our results did not support the prediction that the structure of the scavenger assemblages is directly related to climate. Our findings suggest that the nested structure of vertebrate scavenger assemblages affects its functionality and is driven by anthropogenic disturbance and ecosystem productivity worldwide. Disarray of scavenger assemblage structure by anthropogenic disturbance may lead to decreases in functionality of the terrestrial ecosystems via loss of key species and trophic facilitation processes.

Species assemblages often have a non-random nested organization, which in vertebrate scavenger (carrion-consuming) assemblages is thought to be driven by facilitation in competitive environments. However, not all scavenger species play the same role in maintaining assemblage structure, as some species are obligate scavengers (i.e., vultures) and others are facultative, scavenging opportunistically. We used a database with 177 vertebrate scavenger species from 53 assemblages in 22 countries across five continents to identify which functional traits of scavenger species are key to maintaining the scavenging network structure. We used network analyses to relate ten traits hypothesized to affect assemblage structure with the "role" of each species in the scavenging assemblage in which it appeared. We characterized the role of a species in terms of both the proportion of monitored carcasses on which that species scavenged, or scavenging breadth (i.e., the species "normalized degree"), and the role of that species in the nested structure of the assemblage (i.e., the species "paired nested degree"), therefore identifying possible facilitative interactions among species. We found that species with high olfactory acuity, social foragers, and obligate scavengers had the widest scavenging breadth. We also found that social foragers had a large paired nested degree in scavenger assemblages, probably because their presence is easier to detect by other species to signal carcass occurrence. Our study highlights differences in the functional roles of scavenger species and can be used to identify key species for targeted conservation to maintain the ecological function of scavenger assemblages.

The mating system of an animal population or species refers to the general behavioral strategies that are used by males and females to obtain mates, and include mate acquisition and the number of mates obtained by an individual (Emlen & Oring, 1977). Mating systems and strategies across animals are driven by parental care, social and ecological environment, and the strength of sexual selection, which is determined by male-male competition for females and female mate choice (Shuster, 2009;Shuster & Wade, 2003).

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