The detail in the examples covered in this chapter is necessary because interactions mostly tend to be portrayed in terms of their population consequences (rather than their function) and in this respect they are seen simply as positive, negative or neutral. Such an approach to ecological generality even excludes those interactions that involve aspects of the
environment itself, like temperature, despite such variables being critical to the survival of all organisms. Interactions also tend to be oversimplified by the common two-way division of the environment into an abiotic component, which is mainly physico-chemical, and a biotic component that is interpreted primarily in relation to the density of the organisms concerned. The mathematical formalization of interactions in relation to the environment deals particularly starkly with interactions. Of all possible interactions in ecological systems, only predation and competition seem to have been modeled generally in this way, mainly through the extension of the logistic equation, and with the primary emphasis on density relationships to represent the biotic component. The term “biotic” is thus used in a far more restrictive sense in demographic ecology than is usual elsewhere (see Glossary).