GRANIVORY AND MICROHABITAT USE IN AUSTRALIAN DESERT RODENTS - ARE SEEDS IMPORTANT

The diet and microhabitat use of two species of native Australian dese rt rodents, the spinifex hopping-mouse Notomys alexis and sandy inland mouse Pseudomys hermannsburgensis, were studied in the Simpson Desert , south-western Queensland. Contrary to expectation, both species were confirmed from analyses of their stomach contents to be omnivorous. T he diets of both species varied through time in a similar manner; seed s were important in summer and especially in winter, but in autumn inv ertebrates constituted nearly 50% and 60% of the diet of N. alexis and P. hermannsburgensis, respectively. Other plant material (root, leaf, floral part, stem) was found in appreciable amounts in the stomach co ntents of both species, and fungi were identified from a small number of individuals. Both species showed a high degree of overlap in the br oad types of food they ingested (seed, plant material, invertebrates); however, there was considerably less overlap in the species of seeds eaten. Analysis of microhabitat use suggested that this difference was due to differential foraging between the species; the larger, bipedal N. alexis forages in the open more than the smaller, quadrupedal P. h ermannsburgensis, which is found more commonly in or under hummocks of spinifex grass. Although our findings parallel patterns of morphologi cal specialisation and differential foraging on seeds that have been d escribed within communities of North American heteromyid rodents, we f ound little evidence that the foraging economics of N. alexis or P. he rmannsburgensis should depend solely or primarily on the distribution patterns of seeds. In the absence of dietary information, we suggest t hat ecological studies of desert rodents which focus solely on granivo ry, and neglect other important aspects of rodent foraging, can lead t o a misinterpretation of species coexistence and community structure.