Functional traits driving species role in the structure of terrestrial vertebrate scavenger networks

Abstract

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.

Functional differences in scavenger communities and the speed of carcass decomposition

“…Although such obligate scavengers were absent from our study system, we found wild boar to be the dominant scavenger, with its presence enhancing the carcass decomposition speed (Figure 4a). Wild boar belonged to the species with the highest intraspecific interaction behavior (Table 2), indicating their social nature (e.g., Dardaillon, 1988; Maselli et al, 2014; Sebastián‐González et al, 2021). These results do not suggest that interspecific interactions between wild boar and other species did not occur, but is presumably a limitation of the annotation protocol that we used since we only annotated the longest and second‐longest shown behavioral type.…”

“…Different scavenger species may fulfill different functional roles in the carcass decomposition process (Sebastián‐González et al, 2020, 2021), which would be reflected in differences in behavior and preferences for tissues types. For example, Young et al (2014) observed that common buzzards ( Buteo buteo ) fed primarily on soft tissues in the early stages of decomposition, while carrion crows ( Corvus corone ) increased their feeding as carcasses went into later stages of decomposition and exploited more different body parts.…”

Landscapes shaped from the top down: predicting cascading predator effects on spatial biogeochemistry

“…However, there are key differences that may drive divergent predator-prey dynamics and zoogeochemical effects in aquatic versus terrestrial environments (Strong 1992); for example, wet environments can promote bone decomposition (Subalusky et al 2017) whereas nutrients may remain locked in bones for longer periods in dry terrestrial ecosystems, and nutrients deposited into flowing water may be transported over much greater distances than terrestrial inputs. We see research that focuses on functional traits of animals (sensu Schmitz and Leroux 2020, McCary and Schmitz 2021, Sebastián-González et al 2021, Suraci et al 2021 combined with an understanding of key ecosystem characteristics as the way forward for disentangling these context dependencies to yield broader insights. As an example, identifying which predator-prey interactions are most likely to yield strong spatial responses in food webs with multiple predators and prey (Palmer and Packer 2021), how individual prey species responses to predators aggregate to determine net prey community effects on biogeochemistry (le Roux et al 2018(le Roux et al , 2020 and understanding underlying patterns of nutrient colimitation (Kaspari and Powers 2016), will allow for a stronger mechanistic understanding of the role animals play in spatial ecosystem configuration.…”

Carcass detection and consumption by facultative scavengers in forest ecosystem highlights the value of their ecosystem services

“…Obligate scavengers are excellent at detecting carrion, as a result, lead to carcasses being consumed faster 8 , 9 . Specifically, while obligate scavengers are highly efficient at consuming carrion, they also promote the interspecific interactions with other scavengers by signaling carcass locations while also opening large carcasses and allowing other scavengers access, thereby enhancing the carcass consumption rate 6 , 10 , 11 . But scavenging by facultative scavengers (species that opportunistically feed on carrion such as carnivora and raptors 12 ) is also widespread, even in the absence of vultures (e.g., Refs.…”

“… 13 , 14 ). Facultative scavengers also include some key species, with high olfactory acuity and social foragers, playing an important ecological role in the facilitation of carrion consumption in a scavenger community 11 . Thus, it is important to understand ecosystem function (i.e., carrion consumption) by the facultative scavenger community in a system where obligate scavengers are absent.…”