The delineation of natural areas in New Zealand: Natural areas in New Zealand—land snails

[First paragraph(s)...]
The species that can be present in an area are regulated by the interplay of the two factors of the geological history of the area and the power of dispersal of the animals concerned. Ecological processes in the area then determine which of these possible species will be present in the area. An attempt to delineate natural areas presupposes a belief that ecological processes will act on each member of a group of species in the same way and that the boundaries of each member of the group will be similar. If such were the case this symposium would be unnecessary because the boundaries would be self-evident.
It is the writer's belief that the distribution patterns of invertebrate animals owe more to the factors of geological history, powers of dispersal and the re-occurrence of certain quite limited ecological niches throughout New Zealand than they do to any broad ecological boundaries.