Body Size in Freshwater Crayfish: An Intercontinental Comparison

Body sizes (overall length) of 125 Australian and 230 North American freshwater crayfish were extracted from the literature in order to compare the two major radiations of freshwater crayfish. The size distribution of Australian species is strongly skewed to the right and contains at least 13 species that exceed the maximum size of North American crayfish, however the median size class (74 mm) is the same for both faunas. When the burrowing habits of each species are overlain on the distribution, the Australian fauna is shown to have a higher proportion of primary burrowers, and these are significantly smaller than North American primary burrowers. These differences are discussed in terms of the perceived absence of large predators in Australia, and the long term drying and unpredictability of the Australian climate, but no firm causes can be deduced.