In many arid ecosystems, mammals are considered the dominant seed predators. However, in Australia, ants are described as the dominant seed predators and mammals as insignificant consumers. Since European settlement, many native Australian mammal species have become rare or extinct, their declines have preceded any understanding of their role in vegetation dynamics. In arid areas, native mammal decline has coincided with vegetation change.
Our research explores granivory by Australia’s declining mammal species and the loss of mammals as drivers of vegetation change. To assess the potential of rare native mammals as seed predators, we conducted foraging tray experiments (seed cafes) using shrub seeds in areas with and without native mammals. To determine the influence of rare native mammals on the soil seedbank and above-ground vegetation composition, we established factorial exclosure experiments in areas where native mammals have been reintroduced. Using these experiments, we tested several hypotheses: 1) that mammals are underestimated as seed predators in arid Australia, 2) that native mammals change the composition of the soil seedbank and 3) that the loss of mammals from arid Australia may have been a significant driver of vegetation change.
Results/Conclusions
In our foraging tray experiments we found that native mammals such as hopping mice (Notomys spp.) and bettongs (Bettongia spp.) were more important seed predators than ants, with mammals taking up to three times as many shrub seeds as ants from foraging trays. We found that there were differences in the soil seedbank inside and outside our exclusion fences, with more exotic species present and fewer seeds from nitrogen-fixing species in areas accessed by mammals. We found corresponding differences in vegetation composition, with fewer nitrogen-fixing species and fewer shrubs in areas where native mammals were abundant.
Overall our data suggest that the loss of mammals and granivory from the Australian arid zone has facilitated vegetation change. Reintroducing these mammals will likely restore lost ecological functions such as seed predation to arid Australia.