The taxonomy, zoogeography and aspects of the ecology of the terrestrial amphipods (Amphipoda: Talitridae) of Tasmania

Amphipods of the family Talitridae form an important part of the cryptozoa of Tasmanian forests. This terrestrial amphipod fauna comprises fifteen species, and twelve of these are described as new. The currently widely-used grouping of land amphipods into the genera Orchestia and Talitrus is considered unsatisfactory and consequently new genera are proposed for the Tasmanian species. A key for the identification of these species is provided. The detailed distribution of each of these species is presented and discussed with respect to the environments present in Tasmania and their history. Four of the seven Tasmanian genera, but only one of the fifteen species, are found on the mainland of Australia. Examination of geological and paleoclimatic data leads to the suggestion that this situation is due to the particular conditions which prevailed on former land connections, during Tertiary and late Quaternary times. The world distribution of terrestrial amphipods is examined in the light of local knowledge. A Gondwanaland radiation of the Talitroidea is suggested, and the proposal that supralittoral talitrids were not present in the Laurasian continents until the late Tertiary is advanced. Ecological studies of land amphipods in Tasmania were focussed on the areas of niche partition and the dynamics of populations and their environment. All investigations were carried out at a site in wet sclerophyll forest in eastern Tasmania. Two species, sympatric at the study site, were found to display a number of ecological differences which may explain their coexistence. Keratroides vulgaris appears to be a litter-dwelling, actively-colonizing species, while K. angulosus possesses morphological and behavioural attributes which apparently fit it better for its demonstrated existence at a lower level in the litter/ soil profile. Litter fall and decomposition was studied at the study site over 18 months. Annual litter fall was 9390 kg/ha, which is high compared with results from studies in other Australian forests. While litter fell throughout the year, there was a distinct summer peak. Estimates of the rate of disappearance of litter indicated a low turnover time, approaching those found in forests in much warmer climates. The concentrations of several important nutrients in components of the newly-fallen litter and the forest floor at the study site were measured. Levels of most of these nutrients, especially phosphorus, proved higher than those found in other Australian forests. The numbers and structures of populations of K. vulgaris and K. angulosus were also monitored for 18 months. High densities of both species were maintained throughout this time, reaching maxima of 2431/m 2 and 6185/m2 respectively, in December 1977. Ovigerous females of both species were found almost exclusively between September and May, and photoperiod control of the winter resting stage is suggested. Both species displayed two-year life cycles and many individuals apparently bred during consecutive summers. Comparison of patterns of reproduction found in this and other populations of terrestrial talitrids reveals a wide diversity of strategies within this group.