Thus there appears to be significant competition between bacterial-feeding predators for the bacterial prey. Whether this is indicative of the type of bacteria present in the soil, and whether this has any relationship to productivity in agricultural situations is not known. Testate amoebae are only found in significant and constant numbers in forest soils, and are never found in temperate agricultural soils. Why this is the case is not known, but continues to be observed. While most of Cairns work has been performed in aquatic systems, the same concepts have been suggested for soil.
All nematodes are predators, and thus reflect to some extent the availability of their prey groups.
However, other organisms prey upon these nematodes as well, and thus nematode numbers can also reflect the balance between the availability of nematode prey, as well as feeding by nematode predators. Bongers, in the Netherlands, has suggested the use of a Maturity Index for nematodes in soil. Certain species of nematodes are more commonly found following disturbance, while other species are more typical inhabitants of less-disturbed soils. A number of researchers have shown that the lack of VAM inoculum, or the lack of the appropriate inoculum can result in poor plant growth, in poor competition with other plants or inability to reproduce or survive under certain extreme conditions. However, most crop fields have adequate VAM spores present, especially if crop residue is turned back into the field.