Bryophyte Island Biogeography: A Study in Lake Manapouri, New Zealand

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Abstract
Seventeen islands in Lake Manapouri, New Zealand, were sampled for species richness of bryophytes in beech (Nothofagus solandri) forest. Up to four quadrats were examined per island. There was little evidence for an isolation effect on species richness; a significant relation was found only with overall (i.e. all macroenvironments), total (i.e. all microenvironments) bryophyte richness when in a multiple regression with area, and with only one of the two measures of isolation used. However, area (log transformed) was strongly related to bryophyte richness, explaining up to 83% of the variation in it. In the case of the total bryophyte flora, the relation was significantly curved, with little effect of island area among small islands. The combination of a strong area effect and an isolation effect is compatible with the equilibrium hypothesis; however, the weakness of the isolation effect, and the curvilinear relation with area, raise doubts. The results are also compatible with the small island habitat hypothesis - that habitats on small islands are not comparable with any on large islands, even on the edge of the latter, perhaps because of differences in exposure.