become invasive through their ability to tap resources unused or underused by native species.

  • 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.

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