In contrast, researchers who work with fauna believe that comminution is a central part of decomposition. On the otherhand, delta C13 has been used to infer what an organism eats. These direct trophic effects can lead to indirect effects. These effects can be small or large. Thus earthworms, in contrast to bacteria and fungi, make little direct contribution to decomposition, because most ingested C is egested and very little is mineralized.
Direct contributions are metabolic.
Indirect contributions are sometimes referred to a modulating effects. Soil fauna usually have small metabolic effects but can have large modulating effects. Soil microorganisms have large metabolic effects. For example, leaves falling into a stream greatly affect stream organisms, but stream organisms do not affect the rate of leaf fall into the stream. Donor control differs from reciprocal control , in which the consumer affects input into the resource pool and the resource affects input into the consumer pool.