of an environment that already contains organisms and in which those organism are displaced by the colonizer.
In secondary succession inferior are displaced by superior competitor species, at least under the conditions in which the displacement occurs. Typically this takes place because the original colonizer has modified its environment in such a way that it has paved the way for colonization by the superior competitor.
This process can take place with animals or even microorganisms. It is best appreciated, however, in terms of plants, with replaced by newer species and ultimately with climax species.
Contrast with primary succession. See also simply ecological succession.