Zoogeography of Triturus vulgaris (L.) and T. cristatus (Laurenti) (Amphibia) in Norway, with notes on their vulnerability

Abstract

The distribution of Triturus vulgaris (L.) in Norway is separated into a southeastern distribution area, extending westwards along the coast, and a central Norwegian area in the Trøndelag region. T. cristatus (Laurenti) has three separate distribution areas: a southeastern, a southwestern, and a central Norwegian area. It is thought that T. cristatus reached southwestern Norway through mountain passes from southeastern Norway. Possibly T. vulgaris also reached this region, but it did not tolerate the change to a colder and more humid, atlantic climate. The many fjords and the high mountains in southwestern Norway may today be an important dispersal barrier for the species. Hydrochore dispersal by rafts seems to be fairly common. Both newts reached central Norway from Jämtland, Sweden, probably also from southeastern Norway. The later climate deteriorations have reduced the maximum distribution area of the species, as has also human activity. Summer, and possibly also winter temperature, precipitation, length of activity season, day length and the amount of direct sun radiation all cooperate in the limitation of the newts' distribution and abundance. With respect to growth in the larvae, long day conditions in central Norway are thought to compensate for the higher average temperatures further south.

In Norway the newts may disperse locally, but T. cristatus is threatened, and locally even in danger of extinction, especially in central and southwestern Norway, by forestry practices and introduction of fish to newt localities. The better dispersal abilities of T. vulgaris vs. T. cristatus can be explained by the wider ecological amplitude, less nocturnal habits and more terrestrial way of life of T. vulgaris.