Factors Influencing Biogeographic Patterns of Australasian Centropagid Copepods

Abstract

Bayly & Morton (Verh. Verein. Limnol. 20, 2537) suggested that the peculiar distribution of the centropagid copepod Boeckella triarticulata (Thompson), found in Australia, New Zealand, and Mongolia, may have been determined by continental drift. In this report, we examine the distribution patterns of over forty centropagid copepods found in Australia and New Zealand to consider the extent to which historical events, dispersal, and current ecological requirements affect distribution. The widely disjunct distributions of several of the species and the high degree of endemism in Western Australia species are consistent with the hypothesis that major events of speciation occurred at least 50 Ma BP and possibly much earlier, at a time when Australia and New Zealand were joined but eastern and western Australia were separated by an epicontinental sea. Furthermore, the morphology of these species has remained virtually unchanged since the Eocene or even earlier. Thus, the hypothesis put forth by Bayly & Morton is supported by additional facts. The present-day distribution of most of these species cannot be explained readily by more recent dispersal or by ecological requirements, although incidence in local areas is determined, in part, by these factors. However, dispersal may well have played a significant role in present-day similarities between the centropagid fauna of Australia and New Zealand.