Although some ecological effects of top predators are well established, we know less about how carnivores affect communities through scavenging, which can include facilitative or competitive relationships. Some obligate scavengers, too, have declined severely, such as the staggering decline of vultures ( Gyps spp.) across much of Africa and Asia. These cascades can affect herbivores and vegetation and can trigger mesopredator release, sometimes resulting in the extinction of smaller prey species. Top-carnivore populations have suffered widespread global declines, often causing cascading effects throughout food webs. Almost all carnivores are facultative scavengers, although obligate scavengers such as vultures are few, and vertebrates consume the majority of carrion globally. Because of its high nutritional quality, there is intense competition for carrion among microbial decomposers, and invertebrate and vertebrate scavengers. Carrion is abundant and ubiquitous, and in some ecosystems, most large animals die from causes other than predation. Scavenging is an important ecological function that stabilizes trophic dynamics in complex communities, affecting species assemblages and ecosystem function. This case study provides a little-studied potential mechanism for mesopredator release, with broad relevance to the vast areas of the world that have suffered carnivore declines. Population trends of ravens increased 2.2-fold from 1998 to 2017, the period of devil decline, but this increase occurred Tasmania-wide, making the cause unclear. The major beneficiary of increased carrion availability was the forest raven ( Corvus tasmanicus).
Nonetheless, carcasses persisted approximately 2.6-fold longer where devils have declined, highlighting their importance for rapid carrion removal. Reduced discovery of carcasses by devils was balanced by the increased discovery by mesopredators. Carcass consumption by the two native mesopredators was best predicted by competition for carrion, whereas consumption by the invasive mesopredator, the feral cat ( Felis catus), was better predicted by the landscape-level abundance of devils, suggesting a relaxed landscape of fear where devils are suppressed. Using remote cameras and experimentally placed carcasses, we show that mesopredators consume more carrion in areas where devils have declined. Tasmania's top carnivore, the Tasmanian devil (Sarcophilus harrisii), has suffered severe disease-induced population declines, providing a natural experiment on the role of scavenging in structuring communities. We know less about how carnivores affect ecosystems through scavenging. Top carnivores have suffered widespread global declines, with well-documented effects on mesopredators and herbivores.