Functional redundancy in carrion decomposition by temperate forest ant communities

Abstract

Scavenging of small avian corpses may provide ants with a valuable source of nutrients, a possibility poorly studied. Here, we assessed whether ants are efficient carrion-decomposers of avian corpses in Mediterranean dehesas through an exclusion experiment comparing decomposition rates among three treatments: vertebrate exclusion, vertebrate + invertebrate exclusion and control. Treatments were applied in a paired design in bird cavities and on the ground in two zones to assess functional redundancy. Ant community was characterized by pitfall traps, and key functional traits influencing ants' presence on carrion were identified by using phylogenetic comparative methods. Carrion decomposition was influenced by the exclusion treatment, being significantly faster when ants and other invertebrates were not excluded, but not by location (cavity/ground). Vertebrates were less likely to detect baits in cavities and removed more bait mass in the most transformed zone. Twelve of 25 ant species in the community were found foraging on baits. Ant communities differed between carrion location and localities. Phylogenetic analyses revealed that the proneness of ant species to forage on carrion was unrelated to morphological or social traits, but behavioural, being higher among species foraging collectively. Our results show that ants play a functionally unique role in the decomposition of small corpses in dehesas, and particularly so in trees and less transformed pastureland. Decomposition involves different species in different microhabitats, suggesting high functional redundancy across ants. Our findings provide new insights into the role of ants as scavengers and expand our understanding of the functioning of Mediterranean communities.