Introduced Species, Impacts and Distribution of

Introduced species are numerous and have increased with globalization. All regions undergo invasions, but islands have suffered disproportionately. The greatest impact is habitat modification: vegetation grazed by introduced animals or overgrown by introduced plants, and changed fire, hydrological, and nutrient regimes. Invaders outcompete, eat, and infect natives, and hybridize with them. Invaders sometimes act indirectly, and they can exacerbate one another's impacts. Often impacts are delayed. Some delays end because of environmental changes. Introduced species evolve in their new environments, and this can exacerbate impacts. In some cases, newly introduced genotypes can cause a harmless species to become invasive.