Inter- and intraspecific effects of body size on habitat use among sexually-dimorphic macropodids



Body size affects key life-history parameters including dietary requirements and predation risk. We examined these effects on diel habitat use in a community of three sexually-dimorphic macropodid marsupial species: western grey kangaroo Macropus fuliginosus, red-necked wallaby M. rufogriseus and swamp wallaby Wallabia bicolor. In particular, our study seeks evidence of these effects operating concurrently at the intra- and interspecific levels. We used radio-tracking to quantify habitat use and characterised each used location by recording the cover of plant functional groups and the presence of plant species. During nocturnal foraging periods we predicted that smaller animals (between and within species) should use habitats with higher-quality forage, which is often less abundant, than larger animals, as metabolic demand scales with body size. During diurnal resting periods we predicted that smaller animals (between and within species), being more vulnerable to predation, should use greater concealment cover than larger animals. Western grey kangaroos and swamp wallabies behaved as predicted during foraging periods, but red-necked wallabies did not, using more open, poorer-quality habitats than expected. Only western grey kangaroos showed a within-species effect on habitat use: the relatively smaller females foraged in higher-quality patches. Habitats used by animals during the resting period generally offered greater concealment cover than those used during the foraging period, but there were no clear body size effects on the density of vegetation used. In our system, body size alone could not explain all of the observed patterns, suggesting that there may also be individual differences in habitat requirements influenced by factors such as reproductive costs, predation risk and social facilitation.