Dung Beetles as Hydrological Engineers

Figure 1. An example of a microcosm experiment conducted in this study

New paper by TEE Lab associated PhD student Nadine Keller! Dung beetles are important nutrient recyclers in both tropical and temperate ecosystems. Most dung beetles in the tropics bury their dung balls in tunnels under the ground, creating a mass of tunnels of different sizes and depths underneath dung deposits. This bioturbation of the soil is thought to improve the infiltration rates of water into the soil, yet there are hardly any studies that have investigated this important role of dung beetles.

Figure 2. Example of the steps for processing photographs of the blue dye experiments. (a) and (d) the original photos with marked corners and tape measure. (b) and (e) the original photographs cropped to the corners of the rectangle and georectified based on location of the markers. (c) and (f) the colour-coded cropped and georectified pictures: black pixels where blue dye is present and white pixels where no dye is present.

Combining hydrological and ecological techniques, Nadine Keller and colleagues designed a neat mesocosm experiment to test if the tunnelling action of dung beetles helped increase water flow through tropical forest soils in Sabah, Malaysian Borneo. A mesocosm experiment is a manipulated field experiment, in which enclosures with and without dung beetles were constructed, and then the water infiltration rates measured in each set of mesocosms (Figure 1). This study utilised the hydrological method – blue dye tracer – in a novel way, allowing the water flowing through the tunnels of the dung beetles to be identified and traced through the soils (Figure 2).

Figure 3. The average steady-state infiltration rates (Ksat) for the different treatments (soil-only, dung-only, and dung beetles) and time periods (day 1, day 5 and day 10; points). Figure 4. Percentage of blue dye-stained pixels (%) as a function of depth below the soil surface (mm; averaged per 10 mm depth) for the soil-only (left column) and dung beetle (right column) treatments on day 1 (top) and day 5 (bottom).

The study found that dung beetles increased both the infiltration of water through the soils, and the depth that it reached (Figure 3 and 4). This activity could therefore be especially important in disturbed and compacted soils and has the potential to affect other ecosystem processes such as nutrient cycling and plant productivity.

Read more about the experiment and the exciting results here: https://doi.org/10.1111/een.13094