In a mixed forest-savanna landscape of tropical Guyana researchers found that mammal diversity is positively related to carbon concentration in the soil. The authors explain that this is due to increased feeding interaction associated with greater mammal diversity, and specify that animal abundance per se did not increase carbon content in the soil. “The lack of effect of both tree biomass and animal abundance on the response variables highlights the relevance of species richness” [Sobral 2017: 2].
“…mammal and tree richness increase the number of feeding interactions observed. The amount of organic remains (fruit and seed parts, non-fruit plant parts, faeces and animal parts) on the ground is predicted by the number of feeding interactions, and is positively related to carbon concentration in the soil. The organic remains that most affect soil carbon concentration were animal and fruit remains, which were themselves driven by carnivory and frugivory interactions suggesting that both processing of fruits and direct biomass contributions by vertebrates and plants affect soil carbon concentration” [Sobral 2017: 3]
Sobral, Mar, et al, 2017, Mammal diversity influences the carbon cycle through trophic interactions in the Amazon, Nature Ecology and Evolution, https://www.nature.com/articles/s41559-017-0334-0.
 “Frugivory” is consumption of fruits.