Any community of organisms which is made up of a population of different species there is opportunity for the organisms to interact with each other (Bianchi and Bianchi, 1995). If you consider two different populations living with each other, one of the interactions may occur (see opposite):

Which interaction occurs would depend on the nature of the resources (type and level of food and energy supply), the population density and diversity. For example commensalism favours communities with high diversity whereas neutralism is more likely in communities with a low number of individuals. Competition tends to reduce diversity where resources become limited.

The interactions which occur in soil can be complex due to soils’ spatial heterogeneity. For example, many species of protozoa prey upon bacteria. Physico-chemical factors (such as amount of water, pH, mineral surface chemistry – link to soil physical page) can affect the location, movement and binding of microorganisms to soil particles. This then affects how they are predated by predatory protozoa.

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