Diet of four rock-dwelling macropods in the Australian monsoon tropics

An unusually high diversity of macropods inhabit the rocky areas in the monsoon tropics of the Northern Territory, Australia, yet the mechanisms that allow their niche separation are not clear. Previous studies suggest that the nabarlek, Petrogale concinna, may have a more grazing diet than the short-eared rock-wallaby, Petrogale brachyotis, with whom it coexists. Thus, diet may be an important mechanism of niche separation between these species. We examined the diet of the four sympatric species (the black wallaroo Macropus bernardus, common wallaroo Macropus robustus, P. brachyotis and P. concinna) to determine whether there are differences in the dominant plant groups eaten by the species across the landscape and with season. Diets were determined with a macroscopic analysis of the seed and fruit content of scats and an analysis of the 12C to 13C isotope ratios of scats using mass spectrometry. In the dry season the rock-wallaby species predominantly consumed browse and/or forbs, and the larger wallaroos predominantly consumed grass. However, there was large variation across the landscape in the dry season diets of P. brachyotis, M. bernardus and M. robustus; including high proportions of grass eaten at some sites and high proportions of browse at other sites. In the wet season, greater proportions of grass were eaten by P. brachyotis and M. bernardus than in the dry season. Generally, there was little evidence to support the previous suggestion that P. concinna is more of a grazer than P. brachyotis, but there was some evidence than M. bernardus consumes greater amounts of browse and/or forbs than M. robustus. © 2006 Ecological Society of Australia.