By dispersion we mean that a species can be analyzed in terms of its traits, but that individuals from that species are not identical in each of the traits, but that there is variation for the traits. It is as if the values of each of the parameters characterizing the trait are randomly distributed about a mean, where the mean represents the species but individuals within the species can have any of the values within that distribution.
By selection we mean that individuals within the species may have differential reproduction rates and survival probabilities depending on where they fall within the dispersion of the trait.
By secondary processes we mean processes such as adaptation, learning, and mimicry where the underlying mechanisms are the primary processes of evolution.