Dung beetles in the heart of Singapore: towards a comprehensive species checklist from the Central Catchment Nature Reserve

In 2022, the National Parks Board launched the comprehensive survey of the Central Catchment Nature Reserve (CCNR) for long-term forest monitoring, and the TEE lab joined as survey participants to checklist the dung beetle species found in the reserve.

Catharsius renaudpauliani, the largest extant dung beetle species in Singapore. Photographed in the CCNR

From January to March 2023, Xin Rui and Samuel surveyed dung beetles at 50 plots across the CCNR using baited pitfall traps at the ground level and suspended in the canopy. At that time, their efforts found 15 species, all of which were present at the ground level, but of which only 5 were present in the canopy. A summary of their results can be found here.

From Jul 2023 to Apr 2024, Sean returned to the 50 plots, this time to sample the dung beetles using ground-level flight intercept traps (FITs). Unlike the baited pitfalls, this trap type has no attractant, so while it only opportunistically captures whatever's flying by, the diversity of dung beetles are less likely to be biased by an attractant. This means that we were likely to survey a lower abundance, but higher diversity of dung beetles than a baited pitfall, as we could capture species that may not be attracted to the common bait.

Wan Lin and Shen with one of the FITs they helped to set up. Each of the 50 FITs were revisited every 48 hours for specimen collection and maintenance, till day 6 when they were removed. Sometimes, data and setups were lost when traps were destroyed either by storms or inquisitive monkeys.

We then plotted some of the data from earlier FIT sampling together with the data collected by Xin Rui and Samuel for the ground and canopy baited pitfalls to compare, and these were the initial results.

From the results, it appears that there was more overlap between communities sampled by ground pitfalls and ground level FITs, while the canopy pitfall community was more distinct. This is likely driven by canopy specialist species such as Onthophagus deliensis, which were found in large numbers in canopy traps but almost completely absent at the ground level. At the ground level, FITs and baited pitfalls also performed differently for the sampling of certain species. For example, species such as Onthophagus pedator and Onthophagus "hairy" were only collected from FITs, while Catharsius renaudpauliani and Onthophagus angustatus were collected in much higher abundances from baited pitfalls than FITs.

The CCNR surveys have yielded at least 19 species in total thus far, and the initial data corroborates Xin Rui's findings from Borneo that trap types do affect dung beetle species sampled, further illustrating the importance of using a variety of methods when comprehensively surveying dung beetles. Moving forward, Zann will be continuing to work on the remaining specimens to examine diversity using DNA barcoding and morpohological data to further identify and potentially describe new species from the survey. More to come!