Both rare and common species support ecosystem services in scavenger communities

Aim: Recent works on biodiversity–ecosystem functioning (BEF) relationships highlight abundance fluctuations of common species as more important for delivering ecosystem services than changes in species richness and composition in real-world ecosystems. However, evidence on BEF relationships in natural ecosystems is still limited, especially for large vertebrates. Here, we aimed to disentangle the relative roles of species richness, composition and abundance of vertebrate scavenger communities in the ecological process of carcass elimination, a pivotal ecosystem service, in natural ecosystems. We evaluated the variability in the scavenging function across ecosystems, and examined the factors explaining it. Location: Nine natural ecosystems, seven in Europe and two in Africa. Major taxa studied: Vertebrates. Time period: 2006–2013. Methods: We obtained BEF relationships from vertebrate scavengers consuming ungulate carcasses monitored through motion-triggered remote cameras. We used the Price equation to tease out the relative roles of species richness, composition and abundance in the scavenging efficiency of vertebrates. Results: We recorded 46 vertebrate scavenging species, 30 in Spain and 16 in South Africa. Two main patterns drove BEF relationships. Species richness and composition drove carcass consumption in ecosystems where functionally dominant scavengers were rare, whilst context dependent effects (including species abundance) did so where functionally dominant species were common. Contrastingly to previous studies, abundance fluctuations in vertebrate scavengers were not exclusively related to common species but to the specialization of obligate scavengers (i.e., Gyps vultures) to rapidly gather at carcasses and to the top-down control exerted by large predators. Main conclusions: Rare and threatened species such as vultures and top predators become functionally key species in scavenging processes, highlighting that the delivery of ecosystem services still stands as a general argument for biodiversity conservation in vertebrate communities. Human persecution of vultures and top predators worldwide is expected to alter ecosystem functioning and services such as nutrient recycling or disease control.