Energetic feasibility of an obligate marine scavenger

Abstract

Many predatory species also scavenge from the carcasses of dead animals. In terrestrial ecosystems, there are species (the vultures) that meet their energy needs almost entirely by scavenging. It has been claimed that equivalent obligate scavengers would be unfeasible in aquatic ecosystems, because such organisms could not find sufficient food to meet their energetic needs. Here we use an established model of the energetics of scavenging to probe this claim quantitatively. Although the model is conservative, in that its assumptions err on the side of making scavenging energetically expensive and/or unrewarding, we conclude that an obligate scavenging fish seems entirely energetically feasible. We also consider obligate scavenging among invertebrates to be feasible. Hence it may be that obligate marine scavengers exist but remain to be discovered, or that constraints other than energetics must be invoked to explain why this foraging niche has not been filled.