In Australia, soil-foraging marsupials are known as ‘ecosystem engineers’ because they turn over the soil and create ideal sites for seed germination. The recent extinction of some these species is believed to have contributed to the decline of Australian ecosystems, and their reintroduction is seen as a possible tool for restoration. In 2012, eastern bettongs (Bettongia gaimardi) were successfully reintroduced to Mulligans Flat Nature Reserve – a predator-proof sanctuary on the outskirts of Canberra in south-eastern Australia. However, it remains unknown if bettongs will have a positive effect on plants and soils, or if they may in fact contribute to degradation by facilitating weed invasion. Understanding these complex ecological relationships will have implications for management of bettongs within the reserve, as well as future reintroductions.
I conducted a series of experiments to examine the impacts of bettongs on the soils and vegetation in the reserve. In this presentation, I will focus on the results of a germination experiment. We surveyed seedlings growing in bettong diggings to determine whether seedlings germinated in higher numbers in diggings, and which plant species were most successful.
Since the reintroduction of eastern bettongs, their digging behavior has had a marked effect on ecosystem processes in the reserve. The bettongs have been estimated to dig around 200 pits per individual per night, adding up to 3 tons of soil turnover each year. The digs influence soil nutrients, moisture and temperature.
I found that bettong digs had significantly higher abundance and species richness of seedlings compared to 'non-dig' control areas, suggesting that digs provide a favorable niche for seed germination. This effect was particularly strong in denser grasslands, where diggings create gaps that provide opportunity for new plant establishment. Surprisingly, native species benefitted more from the presence of diggings than exotic species. This was contrary to our expectation that exotic species would be more likely to take advantage of the disturbance created by bettong diggings.
My results indicate that bettongs play an important role as ecosystem engineers in grassy woodlands by creating new opportunities for seedling germination, and their diggings are likely to have a positive effect on grassland diversity.