Granivory and microhabitat use in Australian desert rodents: are seeds important?

The diet and microhabitat use of two species of native Australian desert rodents, the spinifex hoppingmouseNotomys alexis and sandy inland mousePseudomys 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. The diets of both species varied through time in a similar manner; seeds were important in summer and especially in winter, but in autumn invertebrates constituted nearly 50% and 60% of the diet ofN. alexis andP. hermannsburgensis, respectively. Other plant material (root, leaf, floral part, stem) was found in appreciable amounts in the stomach contents of both species, and fungi were identified from a small number of individuals. Both species showed a high degree of overlap in the broad 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, bipedalN. alexis forages in the open more than the smaller, quadrupedalP. hermannsburgensis, which is found more commonly in or under hummocks of spinifex grass. Although our findings parallel patterns of morphological specialisation and differential foraging on seeds that have been described within communities of North American heteromyid rodents, we found little evidence that the foraging economics ofN. alexis orP. hermannsburgensis should depend solely or primarily on the distribution patterns of seeds. In the absence of dietary information, we suggest that ecological studies of desert rodents which focus solely on granivory, and neglect other important aspects of rodent foraging, can lead to a misinterpretation of species coexistence and community structure.