Bridging the divide between models of animal‐driven and microbial‐driven biogeochemical cycling: A zoogeochemistry‐informed framework

Most current terrestrial biogeochemical models formalize biogeochemical cycling as predominantly controlled by processes involving plants and soil microbes. However, growing evidence indicates that above‐ground animals could exert controlling feedback effects that alter soil microbial performance via trophic interactions on plants, release of chemicals in waste matter deposition, and biophysical impacts on soil properties. We present a conceptual and mathematical framework—a Coupled Aboveground‐Belowground Zoogeochemical (CAB–ZGC) cycling model—that explicitly links above‐ground animal direct and feedback effects in models of below‐ground processes. We then provide an empirical synthesis, informed by the conceptual framework, to quantify the potential direction and magnitude of vertebrate and invertebrate animal impacts on below‐ground microbial processes. The synthesis of 39 studies provides proof‐of‐concept showing that animal presence can alter key biogeochemical processes including soil nutrient availability for microbes, microbial and fungal activity, microbial litter processing, and carbon and nitrogen cycling by between 10% to 219% relative to their absence. Effects were enhancing in 65% of cases, and reducing in 35%, and invertebrate density was a strong predictor of the effect and magnitude for microbial activity and nitrogen cycling. These findings reveal the importance of considering animal effects in biogeochemical models to improve the accuracy of model predictions and empirical assessments of biogeochemical cycling in ecosystems. We conclude by highlighting two complementary research fronts to advance terrestrial biogeochemical models: (i) model development through case studies to build a more general CAB‐ZGS model and (ii) target empirical work to measure animal parameters including flux rates, forage intake, animal respiration and waste across a range of animal densities and contexts. Read the free Plain Language Summary for this article on the Journal blog.