Patterns of dung beetle diversity in a biodiversity hotspot in eastern Kenya

Background/Question/Methods

Dung beetle (Coleoptera: Scarabaeinae) species richness provides important ecosystem services of decomposition and nutrient cycling, supporting the rivet hypothesis(Speight, Hunter, & Watt 2008). Functional diversity, the variation in which dung is utilized, proves the importance of each individual species (McGavin, 2001). Dung beetle species richness in the Tana River landscape correlates with the main environmental gradient of the system, increase in depth of the water table with increased distance from the river (Edwards et. al. 2010). The current study explored the patterns of diversity at three scales; the landscape, between forests, and within forests. What are the ecological correlates of the species showing the highest abundance within the landscape, between forests and within forests? We used standardized, baited pitfall traps to sample dung beetles in 24 hour cycles at 50 meter intervals on transects laid perpendicular to the river channel. Traps were filled with a solution of detergent and ethanol to break surface tension and to preserve specimens. Beetles were identified and counted in the field then preserved and stored at the National Museums of Kenya. Sampling was done in twelve forests over four sampling periods, during wet and dry seasons.

Results/Conclusions

We constructed rank abundance curves for sampling points along transects, for each forest and at the landscape level. Four species were consistently abundant across all forests through the four sampling periods; Onthophagus variegates, O. simplex, Sisyphus seminulum, and Anachalcos convexus. The two former demonstrate tunneling behavior, whereas the two latter demonstrate ball rolling behavior. By processing the dung in different ways, they have reduced competition between one another and therefore have higher fecundity rates. S. seminulum and A. convexus were small compared to the average for their tribes, 7.0-10.0 mm for Sisyphusand 14.5 – 38.0 mm (Davis, 2005).

One hundred eighteen dung beetle species were identified. The number of different species within the forests fell within a range of 11 and 47 with an average of ≈ 29.3 species. Six hundred and seventeen individuals were found in July 2009, 52,700 in November 2009, 11,876 in 2010, and 49,263 in 2011.

We found high evenness in the dung beetle diversity species within and among Tana River forests landscapes. We calculated an overall Shannon-Weiner diversity index of 2.66 for the landscape; a level of diversity which is comparable to West African tropical forests (range 0.91-2.34; Davis & Phillips, 2005) and Amazonian forests of northern Brazil (range 0.91-2.63; Klein, 1989).