PATTERNS OF RANGE CONTRACTIONS AND EXTINCTIONS IN THE NEW-ZEALAND HERPETOFAUNA FOLLOWING HUMAN COLONIZATION

Evidence from subfossils and from present distributions confirming range contractions and extinctions of New Zealand amphibians and reptiles is consistent with that from New Zealand landbirds, in which 40% of the fauna, including the largest species, has become extinct in the 1000 years since human arrival. The largest extant species of all higher taxa of herpetofauna-leiopelmatid frogs, tuatara, skinks, and geckos-are extinct on the mainland; 41% of the extant fauna (27 of 65 species) survive largely or entirely on rat-free offshore islands; and many species are now restricted to a few isolated locations, remnants of once wider distributions, a pattern called ''secondary endemism''. Habitat alterations and occasional human predation may have contributed to range contractions, but the primary factor in extinctions is almost certainly introduced mammals, especially rats. At least three lines of evidence support this view: (1) species diversities and population densities are both far higher on rat-free islands than on mainland sites and rat-inhabited islands; (2) nocturnal species have suffered far more than diurnal ones-all populations of tuatara, two of four* species of frogs, the largest Cyclodina skinks, and the largest species of Hoplodactylus geckos are now restricted to islands, most rat-free; (3) lizard populations on islands from which rats have been exterminated have shown rapid increases in range of habitats occupied, densities attained, and in reproductive success.