Patterns of range contractions and extinctions in the New Zealand herpetofauna following human colonisation

Abstract

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.

A sphenodontine (Rhynchocephalia) from the Miocene of New Zealand and palaeobiogeography of the tuatara ( Sphenodon )

“…In marked contrast to its Early Mesozoic relatives, Sphenodon is restricted to approximately 35 islands off the coast of New Zealand (MacAvoy et al 2007), mainland populations having become extinct with the arrival of humans (and associated animals, such as rats) ca 750 years ago ( Towns & Daugherty 1994, Higham et al 1999. Sphenodon bones are known from several Holocene localities (e.g.…”

Predicting the fate of a living fossil: how will global warming affect sex determination and hatching phenology in tuatara?

“…The introduction of mammals by human colonizers drove tuatara to extinction on the mainland islands ( Towns & Daugherty 1994), but two species, Sphenodon punctatus and Sphenodon guntheri, survived on offshore islands and are now protected. The largest population (estimated at 30 000 individuals) occurs on Stephens Island in Cook Strait, but most of the remaining 34 populations consist of 10-300 individuals on islands less than 5 ha in size (Gaze 2001) and have low levels of genetic variation (Hay et al 2003;MacAvoy et al 2007).…”

Discovery and spatial assessment of a Hochstetter's frog(Leiopelma hochstetteri)population found in Maungatautari Scenic Reserve, New Zealand

“…Rats (Rattus spp.) are considered a primary factor contributing to the extinction of New Zealand's herpetofauna (Worthy 1987;Bell 1994;Thurley & Bell 1994;Towns & Daugherty 1994). At present, only ship rats (Rattus rattus) are abundant on Maungatautari, replacing the kiore (R. exulans) and the Norway rats (R. norvegicus) that attained great numbers in the past.…”

“…Pigs are known to feed on lizards and tuatara (Towns & Daugherty 1994) and are also likely to opportunistically kill Hochstetter's frogs. Pig disturbance was considered high in more than a third of streams surveyed; only one of 20 frogs was found proximal to areas disturbed by pigs.…”

“…Feral pigs can destroy frog habitat by trampling and foraging on the edge of streams (Towns & Daugherty 1994;Mussett 2005). Pigs are known to feed on lizards and tuatara (Towns & Daugherty 1994) and are also likely to opportunistically kill Hochstetter's frogs.…”