Endemism, species selection and the origin and distribution of the vascular plant flora of New Zealand

Aim To evaluate competing views on the origin and distribution of the New Z ealand flora by testing the hypothesis that the geographical distribution o f species is unrelated to ecological traits such as habitat requirements an d dispersal capabilities. Location The New Zealand archipelago. Methods An analysis of the factors correlated with distribution and endemis m for alpine plants within New Zealand, and for the New Zealand biota as a whole. Results Woody plants are highly endemic; nonendemic plants tend to be herba ceous and are concentrated among the highly dispersible ferns and fern alli es, orchids and wetland plants. These groups make up 32% of the total flora but contribute 78% of nonendemics. Alpine plants with wide spatial distrib ution tend to have greater altitudinal ranges, a broader habitat preference and better dispersal ability. Main conclusions Most vascular plants reached New Zealand by long-distance transoceanic dispersal, probably during the Late Miocene to early Pleistoce ne period. During the Miocene and Pliocene, similar climates and landscapes to those of Australia and northern island groups, and highly invasible ter rain, permitted dispersal of woody plants. Cooling climates and formation o f a more mountainous, more compact landscape after that time reduced disper sal of woody plants and favoured herbaceous, wetland and highly dispersible plant groups. The prominence of dispersal has led to intense selective imm igration, and is responsible for many characteristic features of the flora. Species selection by glacial-interglacial cycles has restricted acquisitio n or retention of cool or arid climate adaptations, particularly in the low land flora. Endemic and range disjunction patterns in the New Zealand mainl and are not, in general, directly caused by Pliocene inundations or the fau lting and associated horizontal displacement of terrain that has continued since the Miocene. They have arisen mainly through Pleistocene extinctions, speciation and dispersal, and some patterns are strongly linked to repeate d glaciation. Endemic centres are associated with differentiated terrain an d climates providing isolation, distinctive environments, and habitat conti nuity conducive to speciation.