Sympatric species diversity of new zealand land snails

Abstract

Surveys for land snails of several bush patches on or near the Manukau Peninsula, southwest of Auckland, resulted in finding up to 60 species (only 3 introduced) in a single 4 ha patch of bush. Analysis of records from all bush patches suggests that an essentiallysympatric community of about 72 native species is a probable reality, whereas in most areasof the world the sympatric existence of more than 15 land snail species is highly unusual. Afirst attempt at indicating the moisture, space, and foraging preferences of the 89 land snailspecies recorded from the Manukau Peninsula is presented, and an attempt is made toindicate broad categories of species association or habitat preference within this area. Manyspecies occur throughout litter types (40-7591 of all species in one bush patch would be ina 20 x 30 cm bag of litter from one spot), and it is hypothesised that the qualities ofmoisture retention and air space are more significant to the snails than the species of plantthat provided the litter. This sympatric land snail diversity is normal from the centralNorth Island up into Northland, but diversity levels drop sharply in the far north andsouthward from Mt Egmont/East Cape. Most of the South Island has 15-20 sympatric landsnail species, with even greater reduction on Stewart Island and the subantarctic islands.It is hypothesised that the high sympatric diversity level reached in the Manukau arearesults from equability of the moisture regime. This diversity is based in accumulation ofphyletically unrelated taxa, not localised speciation. The land snail population here has theaspect of a mature community. Even few-hectare patches of bush can hold near maximumland snail communities, if they are protected against burning, clearing, and trampling ofthe litter by stock. The preservation of such patches is urged, for the conservation not onlyof the land snails but of the other soil micro-organisms that coexist. © 1981 Taylor & Francis Group, LLC.