Species → Brown-throated Sloth
Brown-throated Sloth
Bradypus variegatus
What if it disappeared?
Impact LowA landmark study documents a three-way "mutualism syndrome": the sloth descends to the ground roughly once a week to defecate, which gives the moths living in its fur a place to lay eggs; their droppings and decomposing bodies would then fertilize the algae growing on its coat, a lipid-rich algae the sloth would eat to supplement its low-energy diet.
DocumentedDetail
Pauli, J.N., Mendoza, J.E., Steffan, S.A., Carey, C.C., Weimer, P.J. & Peery, M.Z. (2014). A syndrome of mutualism reinforces the lifestyle of a sloth. Proceedings of the Royal Society B, 281(1778), 20133006.
The study establishes a statistical correlation between the number of moths present in the fur, nitrogen concentration, and algae quantity, in sloths captured and released in Central America. The risky ground-descent behavior, given predator exposure, is presented as the linchpin of the cycle.
The dependency also runs the other way: adult survival and reproductive success in the sloth are directly tied to the density of Cecropia trees, its main leaf source — a model shows that even a low Cecropia density (0.7 trees per hectare) is enough to sustain a growing sloth population.
DocumentedDetail
Garcés-Restrepo, M.F., Peery, M.Z. & Pauli, J.N. (2019). The demography of a resource specialist in the tropics: Cecropia trees and the fitness of three-toed sloths. Proceedings of the Royal Society B, 286(1894), 20182206.
Monitoring conducted in Costa Rica. The dataset combines demography, genetics, and space-use monitoring over several years. It flips the usual question asked in this reference's profiles: here, the availability of a plant resource shapes the sloth's trajectory, rather than the reverse — a reminder that not every animal in this reference is a cascade driver.
The 2014 scenario spread widely in popular science, but a critical re-evaluation raises inconvenient facts: the brown-throated sloth doesn't lick itself or other sloths, 83% of analyzed digesta samples contained no trace of algae at all, and ground predation risk turned out to be 5.5 times lower than the model predicted — the opposite of the assumed cost that justified the descent as a mutualistic sacrifice.
InsufficientDetail
Monge-Nájera, J. (2021). Why sloths defecate on the ground: rejection of the mutualistic model. Cuadernos de Investigación UNED, 13(1), e3438.
The author proposes a simpler alternative explanation: ground defecation would be an ancestral behavior retained across all sloth species, for lack of sufficient selection pressure to evolve canopy defecation — not evidence of a complex three-species mutualism.
Documentation
-
Pauli et al. (2014) — A syndrome of mutualism reinforces the lifestyle of a sloth, Proceedings of the Royal Society B
Accessed August 10, 2026
-
Garcés-Restrepo et al. (2019) — The demography of a resource specialist in the tropics: Cecropia trees and the fitness of three-toed sloths, Proceedings of the Royal Society B
Accessed August 10, 2026
-
Monge-Nájera (2021) — Why sloths defecate on the ground: rejection of the mutualistic model, Cuadernos de Investigación UNED
Accessed August 10, 2026
Last verified: August 10, 2026