Dietary constraints upon reproduction in an obligate pollen-and nectar-feeding marsupial, the honey possum (Tarsipes rostratus)

The tiny honey possum, Tarsipes rostratus, is the only marsupial that feeds solely upon nectar and pollen. Its daily energy expenditure is reduced by occasional short-term deep torpor but its overall nitrogen needs appear to be what would be predicted for its size (7-12 g). Tarsipes derives its nutr ients from digesting the contents of pollen grains. Simultaneously, it must eliminate the large volumes of water that accompany the energy-rich sugars in nectar. We suggest that these two time-consuming processes, together wi th the need to harvest small amounts of nectar and pollen from a large numb er of flowers, limit the rate at which Tarsipes can raise young. Tarsipes h as a small litter (2-4 young) compared with marsupials of similar size and its young grow only slowly, both traits that may stem from dietary constrai nts. However, it breeds first only 4 months after leaving the pouch and con tinuously thereafter, which may offset an annual adult mortality rate of 86 %. Unusually in a small marsupial, the young are carried in a pouch until a lmost weaned, rather than deposited in a nest. This too may be a correlate of the way it harvests nutritionally rewarding plant products. Nectar and p ollen are available all year from the flowers of a suite of banksias and dr yandras that are Tarsipes' favoured foodplants. Only the species-rich Medit erranean-climate heathlands of south-western Australia appear able to suppo rt a small marsupial with such extremely specialized dietary habits, whose life-history traits reflect the constraints of this unusual diet.