Bioturbation

By: Georgia Randall, Grasslands Program Ecologist and PhD candidate, Odonata

The act of bioturbation, which includes digging, foraging, burrowing, denning, and ground nesting, is carried out by a range of species across many taxa, including marine species. Each style of soil manipulation comes with varying impacts on the landscape around it, both positive and negative. The abundance and intensity of these ecosystem engineers, and the biotic (vegetation, bugs, competition) and abiotic (rainfall, temperature, soil type) conditions surrounding them have the potential to influence decomposition rates, nutrient levels, soil compaction, water infiltration, fungal and bacterial activity and abundance.

The direct impacts of diggers on these soil functions are known to have further indirect and cascading effects on vegetation establishment and complexity, habitat heterogeneity (diversity), invertebrate health and root growth. For example, the digging of Mole species has been associated with decreased soil bulk density (less compacted soil) and therefore also linked to increased amount and depth of water filtration. While a myriad of positive impacts have been recorded, there is also a significant negative trend associated with increased disturbance. For example, the burrowing activities of Pocket Gophers can result in reduced soil carbon levels and plant establishment. However, even these processes provide other beneficial ecosystem services, such as providing sheltered habitat for invertebrates or fostering a unique population of soil microbes, thereby encouraging diversity in the landscape. Unfortunately, this may not always be the case, especially when discussing introduced species.

After the significant loss of digging mammals across Australian ecosystems, James et al. (2011) suggested that the European rabbit, as a fellow bioturbator, could potentially replace the important functional role of the native diggers.

However, multiple studies have now shown that the impact of rabbit burrowing has negative implications for soil processes and ecosystem health, alongside significant vegetation decline. Therefore, attention has shifted toward identifying the impacts of native diggers to replicate their critical soil functions or to strengthen arguments for population recovery and reintroduction programs. However, this approach faces significant challenges.

Climate, soil conditions, and faunal communities have changed dramatically since digging mammals disappeared from much of their range and will continue shifting in unpredictable ways.