More than just meat: Carcass decomposition shapes trophic identities in a terrestrial vertebrate

Authors: BARCELO, GONZALO - University Of Wisconsin; PERRIG, PAULA - University Of Wisconsin; DHARAMPAL, PRARTHANA - University Of Wisconsin; DONADIO, EMILIANO - University Of Wisconsin; Steffan, Shawn; PAULI, JONATHAN - University Of Wisconsin

Submitted to: Proceedings of the Royal Society. B. Biological Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2022
Publication Date: 3/21/2022
Citation: Barcelo, G., Perrig, P., Dharampal, P., Donadio, E., Steffan, S.A., Pauli, J. 2022. More than just meat: Carcass decomposition shapes trophic identities in a terrestrial vertebrate. Proceedings of the Royal Society B. 36:1473–1482. https://doi.org/10.1111/1365-2435.14041.
DOI: https://doi.org/10.1111/1365-2435.14041

Interpretive Summary: Andean condors are an endangered species and exist almost exclusively in the high Andean plains of South America. Despite much global attention, the trophic tendencies and niche dimensions of condors are not well known. Understanding these fundamental aspects of condor biology and ecology will aid in the conservation of this species. This paper examines the importance of microbes in condor nutrition, specifically the gut microbes within the carcasses of Andean herbivores. The study reports how condors rely primarily on puma-killed vicunas, and reveals that female condors consume significant amounts of plant matter (gut digesta) within the stomachs of vicuna carcasses. Conversely, male condors focus on the microbe-rich musculature and organ tissues. Such sex-based partitioning of a carcass is noteworthy because it re-frames scavengers as potentially fickle consumers, as opposed to indiscriminate consumers of carrion. These findings have relevance to the populations of detritivores in any food web, including agroecosystems.

Technical Abstract: Carcasses are microbe-rich resources in a community and may represent a common nexus for the macro- and microbiome, uniting autotrophs, consumers, predators, and microbiota. Obligate scavengers, then, can feed from multiple trophic groups. To evaluate the foraging of an obligate scavenger across trophic positions, we studied a simple community of camelids (Vicugna vicugna and Lama guanicoe) pumas (Puma concolor) and condors (Vultur gryphus) in the High Andes. Our analysis of condor pellets and bulk isotopes revealed non-trivial plant consumption, close to 10% of condor diet. Isotope analysis of amino-acids revealed that condors had highly variable trophic positions (TP=2.9±0.3) compared to pumas (3.0±0.0) and camelids (2.0±0.1) likely representing “trophic omnivory,” wherein the condors consume plants (TP=1.0±0.1) and microbe-colonized carrion (TP=2.3±0.1). Female condors exhibited a lower TP (2.8±0.2) relative to strict carnivory than males (3.1±0.3). Females may be consuming more plant biomass in a carcass, while males are likely consuming more microbe-rich animal tissue. Our study highlights that carcasses represent a trophically heterogeneous resource, and that obligate scavengers can feed preferentially on certain trophic groups from the macro- and microbiome.