The study of interacting populations of different species. The term comes from biology and was originally used in investigations of the
dynamic effects of food chains and cycles (of species feeding on each other or using common resources and thereby mutually determine their relative size). The inclusion of human beings and the generalization of the notion of species to include species of man-made objects has made ecology the study of complex interactions in the terrestrial environment of man (
see ecosphere, eco system ). Typical forms of interactions among species are cooperation, parasitism, predation, competition,
dominance, independence , succession. An important task of ecology is to investigate the conditions under which population sizes are in
equilibrium. With the inclusion of human
technology into ecological equations, an important problem of ecology is to predict environmental changes and to evaluate the effects different corrective measures may have on short range and long range ecological balances (
see externalities ). (
Krippendorff )
The proportion of benefits to costs, the relationship between a level of performance and the resources expended to achieve this level. (
Krippendorff )
