The distribution of the fitness peaks may vary for different dimensions and fitness components under different conditions. Only a fraction of the fitness peaks are usually occupied by existing species at any one time. The long-term evolutionary trajectories of any given lineage are determined by the sequences of varying selection regimes that determine the transition probabilities for species to occupy other fitness peaks. The fitness functions depend in important ways on biotic interactions with the presence, absence, or densities of the interacting species, which may extend over extensive ecological and behavioural interacting networks. There is a limited number of potentially co-existing species under any particular ecological conditions, which are determined by interactions with resources, competitors, predators, and parasites.
New species can occur only within the available range of coexistence with the existing species.
New species modify the fitness function and the selection regime of interacting fitness peaks, and the coexistence function for both existing and potential species in the system. Existing species may be displaced genetically, and reduced or eliminated ecologically. New species may also generate new adaptive peaks. Newly derived species will coexist with existing parent species if the conditions for stable coexistence between the two species are satisfied. Both species will then evolve to the newly generated fitness peaks for both, possibly leading to resource partitioning and character displacement.