Biotic agents, including competitors and mutualists, play a role in the transition of an established species to a proliferating and spreading species. However, there appear to be no consistent relationships across groups (plants, arthropods, and plant pathogens).

The roles of biodiversity and habitat disturbances in influencing species invasions are hotly contested. At best, conclusions depend on the invasive group.

The genetic consequences of invasions vary widely among taxonomic groups. High genetic diversity of an established species is not a requirement for its transition to an invader. However, multiple introductions of a species into a new range often facilitate the emergence of new genotypes, some of which will have higher fitness than their parents. The result is an increased probability of yielding an invading population.

Agricultural practices associated with a crop tend to provide intense and highly directional selection of invasive species which results in locally adapted races limited only by the area of the crop.