An example food web including green and brown food chains.
Nutrients flow between animals, organisms, and the non-living parts of ecosystems. These pieces exist in green (plant-based) and brown (detritus-based) food webs in almost all ecosystems. Predicting the joint impact of changes in each of these food webs is quite complex because there are so many interacting species and processes. Consequently, Shawn Leroux, Os Schmitz, and I have been developing models to track how changes in green and brown food chains feedback onto each other. Our focus has been on the cycling of nutrients as one important way these food webs interact.
Nutrient limitation (stoichiometry) is important in coupled systems
Our recent work has shown that the limitation status of microbes and animals may be critical to predicting how these two food webs interact. We've shown using a model of an entire ecosystem that including the microbial and animal limitation for carbon or nitrogen changes how that ecosystem behaves. Microbial limitation partitions carbon and nitrogen between green and brown food chains, while animal limitation changes how these food chains process nutrients and how they respond to changes in the relative availability of nutrients.
We've also shown how different assumptions about how animals and microbes eat (functional responses) can change whether nutrient limitation propegates from one food web to the other. If feeding rate is strongly determined by the prey and predators than it is more likely that changes in each food web will feedback on the other.