A spatio‐temporal model for the invasion of the New Zealand archipelago by the Pacific ratRattus exulans

Abstract

New Zealand is at the southern limits of the human‐extended geographic range of the Pacific rat Rattus exulans On the two main islands, radiocarbon dates on rat bones from natural sites show that rat populations were established more than 1000 years before permanent human settlement, presumably during transient visits by Polynesian voyagers Both main islands were colonised after these first contacts, but offshore and outlying islands were not reached by rats until after Polynesian settlement about 700 years B P Chatham Island was not colonised by Pacific rats until about 650 years B P I present a model that relates the time of first appearance of rats in the fossil record and the exploitation of native fauna to the pattern of spread of the rat through the archipelago I hypothesise that the stepwise spread of the rat through the archipelago is mirrored by the pattern of reduction and extinction of indigenous fauna vulnerable to rat predation The 1000 year delay between the arrival of rats and permanent human settlement suggests that the New Zealand biota was already stressed by an introduced predator before humans added habitat destruction and over‐hunting