Patterns of Dung beetle diversity in a biodiversity hotspot in eastern Kenya
Authors:Amanda Edwards, David N. M. Mbora
Mentor:David N. M. Mbora, Professor of Biology, Whittier College
Dung beetles (Coleoptera: Scarabaeinae) provide important ecosystem services such as decomposition and nutrient cycling, supporting the rivet hypothesis (Speight, Hunter, & Watt 2008). Species richness in the Tana River landscape has been proven to correlate with the main environmental gradient of the system, increased depth of the water table with increased distance from the river (Edwards et. al. 2010). Our current study explored the patterns of diversity at the landscape, forest, and sampling point level. One question we have is; 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. Sampling was done in twelve forests over four sampling periods, during wet and dry seasons.
One hundred eighteen beetle species were identified. Six hundred and seventeen individuals were found in July 2009, 52,700 in November 2009, 11,876 in 2010, and 49,263 in 2011. Rank abundance curves for sampling points, transects, forests and for the landscape yielded four species which were consistently abundant; Onthophagus variegatus, O. simplex, Sisyphus seminulum, and Anachalcos convexus. S. seminulum and A. convexus were also small compared to the average for their tribes, 7.0-10.0 mm for Sisyphus and 14.5 – 38.0 mm (Davis, 2005).
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). The data we collected, including bi-catch, will continue to yield important entomological and ecological findings.