Carcass type not patterns of patch connectivity affect scavenging of medium-sized carcasses

Background/Question/Methods

The death of an animal leads to intense competition between microbes, invertebrates, and vertebrates for the resources sequestered in its body. In these competitions most carcasses are scavenged at least in part by vertebrates. The competitions arise because the energy cycled through an animal carcass is not trivial. In fact, nutrient flux from large carcasses can be detected in soil and vegetation for years, creating hotspots of biodiversity and promoting landscape heterogeneity. Previous work has shown that the process of carcass removal is mediated not only by temperature, but also by the composition of local scavenger guilds. In this study we investigate how carcass type and landscape-level patterns of patch connectivity affect carcass removal as an ecosystem service.

We conducted twelve, 1-month trials in which 5 raccoon (Procyon lotor), Virginia opossum (Didelphis virginiana), and domestic rabbit (Oryctolagus sp.) carcasses were monitored using remote cameras in separate forest patches in north-central Indiana. The 3 carcass types were deployed among forest patches in a Latin square design blocked by 4 seasons and 3 patch-connectivity classes (connected, intermediate, and isolated forest patches). Experimental blocks (season x patch-connectivity class) were assigned 5 replicates of each carcass type for 60 carcasses of each type monitored. 

Results/Conclusions

Contrary to our expectations, carcass type and not patch-connectivity affected the diversity of local scavenger guilds and the profile of scavenging activity at carcasses. The differences were driven by a more diverse scavenging guild at raccoon carcasses, and more intense scavenging by opossums on raccoon carcasses than on opossum or rabbit carcasses. Expected seasonal changes in the diversity of local scavenger guilds were driven by the winter absence of the obligate scavenging and migratory turkey vulture (Cathartes aura). The effect of these patterns on the process of carcass removal as an ecosystem service was complicated. Neither carcass type nor patch-connectivity affected the mean time elapsed to the arrival of the first scavenger, or the mean time elapsed until the carcass was opened by scavengers. Elapsed time to carcass depletion was greater in intermediate-connectivity patches and for raccoon carcasses, but the proportion of carcasses that remained un-scavenged was <5% overall and these carcasses were evenly distributed among connectivity classes and carcass types.  Taken together, these results suggest that substantial functional redundancy among scavengers making up local scavenging guilds maintains the provisioning of carcass removal across the landscape.