Key Ecological Function Peaks at the Land–Ocean Transition Zone When Vertebrate Scavengers Concentrate on Ocean Beaches

Abstract

Ecotones can form hot spots of biodiversity by containing species from multiple ecosystems. Because biodiversity is often linked to ecological function, we posit that rates of key ecological functions are highest at ecotones and decline away from them. Here we test this hypothesis by measuring spatial decays in the function of carrion scavenging on a gradient ranging from ocean beaches upland into abutting coastal dunes. A large field experiment in Eastern Australia, at the ecotone formed by ocean beaches, employed multiple carrion placements and motion-triggered cameras to identify the animals consuming carcasses and the removal rates of necromass. Significantly more carrion was consumed by vertebrate scavengers at the beach interface (50–80% of total necromass removed) and declined significantly with distance (max. 350 m) into the abutting coastal dunes (20–25%). This marked cline was due to the consumption of carrion by both dune-dwelling and beach-dwelling animals at the beach–dune interface and a decline in scavenging activity by both groups farther upland. These spatial effects were consistent between sites, but the lower carrion removal away from the beach became less pronounced as the carcasses putrefied, suggesting that microbial actions can modify carrion suitability for vertebrate scavengers and hence change spatial patterns in ecological function. Our findings provide quantitative support for the widespread notion that ecological transition zones are hot spots of ecological functions and highlight the importance of managing functionally important species at ecotones.