Surveys of 196 lakes and ponds in Western Australia showed that most species of the centropagid copepods Boeckella , Calamoecia and Hemiboeckella have low incidence, although a few are common within restricted geographic areas. Records of co-occurrences indicate that many species have broadly overlapping ecological requirements, suggesting that dispersal or historical events are more important determinants of incidence and distribution than is colonization ability. However, some species prefer or are restricted to specialized environments. The roles of history, recent natural dispersal, and recent human-mediated dispersal in moulding present-day distributions are discussed. It is concluded that most species have low dispersal ability and that historical events have played a major role in determining present-day distribution patterns, although local dispersal and some human-mediated local and long-range dispersal have influenced incidence and distribution patterns.