Biology and Impacts of Pacific Island Invasive Species. 20. Rattus exulans, the Polynesian Rat (Rodentia: Muridae)

Polynesian rats (Rattus exulans) are perhaps the fourth most widespread detrimental species of invasive commensal rodent on the planet. Here, we review their biology, impacts, and management in Pacific Islands. Their temperate to tropical distribution resulted from accompanying ancestral Polynesian settlers during their migration 700–4,000 yr ago. This invasive species is unique for several reasons: (a) R. exulans do not hybridize with any other species; consequently; (b) they have been used as a proxy to test hypotheses about the prehistoric movement and colonization of people throughout the Pacific islands; and (c) they have recognized value among some Pacific Island peoples. Nonetheless, introductions of R. exulans are associated with extinctions of some plants and animals prehistorically, and still have detrimental effects on native species, agriculture, human health, and infrastructure. There is great interest in reducing R. exulans populations and eradicating them from many islands to recover native and endemic plants and animals and to reduce harmful effects to humans. However, the behavior and ecology of this species present some challenges for managers in that they are considered more difficult to eradicate than more widespread invasive rat species.