Is this stool taken? – On dung beetle-megafauna trophic networks

by and | Sep 2, 2020 | Asian School of the Environment, Earth & Environment, Ecology, PhD, Research, Women in Science

Ong Xin Rui has just started her PhD on dung beetles and their feeding networks working in the Tropical Ecology & Entomology Lab at ASE with Assistant Professor Eleanor Slade. In the last month, she has been awarded the Nanyang President’s Graduate Scholarship, and kicked off her PhD with a publication. Congratulations!

Some of the beetle specimens in the Tropical Ecology & Entomology lab.

When you think of a dung beetle, you might picture a beetle rolling a ball of fecal matter. Found everywhere except in Antarctica, these insects not only consume the excrement of other animals, but also use dung for nesting. As with many other insects, dung beetles have some specialised abilities. Take for instance, their sense of direction – while most dung beetles navigate using the sun and wind, Scarabaeus satyrus orients themselves by the stars of the Milky Way.

All of this, of course, helps the dung beetles consume, move and manipulate dung. As “essential workers” of a tropical rainforest, dung beetles play key roles in secondary seed dispersal and the nutrient cycling. So, while they may be small, dung beetles are actually hugely important to tropical forests and the continued functioning of a healthy ecosystem.

Xin Rui examining a beetle under a microscope.

Unfortunately, large-scale deforestation has resulted in the fragmentation of Southeast Asian forests, leading to major habitat loss. The subsequent reduction of many populations of large animals (megafauna), resulting in the extinction of many species, has made dung beetles more vulnerable to ecological cascades than ever before. As the populations of a key mammal species decline, a chain reaction is set off through the network – causing significant degradation to both the functioning and stability of the ecosystem.

There is still much we do not know about dung beetle populations, especially in Southeast Asian forests, where logging and forest clearance have led to huge losses in biodiversity. To address this knowledge gap, Xin Rui’s recent paper, titled Dung beetle-megafauna trophic networks in Singapore’s fragmented forests, was published in Biotropica, and is the first of its kind that delves into dung beetle networks in Southeast Asia.

Dung samples from six megafauna species (obtained from Wildlife Reserves Singapore) were used as bait. The animals included both the locally extinct species tapir, tiger and sun bear, and sambar deer, reticulated python, and common palm civet, which are currently present in Singapore’s forests. The experiment was conducted at five sites across Bukit Batok, Central Catchment Nature Reserve, and Bukit Timah Nature Reserve.

Site locations in the five nature reserves. Top inset: Map of Singapore (by Teo Siyang). Bottom inset: Diagram showing hexagonal grid arrangement of pitfall traps.

After collecting 561 dung beetles from across 12 species, the results align with the results of studies in temperate regions and South America – dung beetles, being attracted to both extinct and extant dung types, were mostly generalists. However, the study showed that Singapore’s dung beetle-megafauna networks were quite resilient, suggesting that the beetles can switch to another dung type when other dung resources become less available. The sole exception was Bukit Batok, the most isolated site, which had a highly reduced network structure.

Xin Rui working in the lab.

The study also demonstrated an example of the resourcefulness of dung beetles, and presented a first recorded instance of the use of reticulated python dung in Southeast Asia by the dung beetle species Onthophagus semifex.

So what comes next? The dataset from this study is likely to serve as a foundation for future research on dung beetle demographics in Southeast Asia. Xin Rui has also declared her continued interest in investigating Southeast Asian dung beetles, and is looking towards conducting a more rigorous studies focusing both on the forests of Southeast Asia and on Singapore. She will be using the research technique DNA metabarcoding to extract DNA from the gut content of dung beetles and match it to the DNA of larger animals in the forest to determine exactly what megafauna that the dung beetles feed on.

 

References

Xin Rui Ong, Eleanor M. Slade, Matthew L. M. Lim. 2020. Dung beetle-megafauna trophic networks in Singapore’s fragmented forests. Biotropica; 00:1-7.

Dacke, M., Baird, E., Byrne, M., Scholtz, C. H., & Warrant, E. J. (2013). Dung beetles use the Milky Way for orientation. Current Biology, 23(4), 298-300.

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