By processing quantities of dung to eat, dung beetles provide important services in forest ecosystems. But, forest destruction and associated loss of mammals put these beetles at risk. Accordingly, we evaluated the combined effects of forest area, edge effects and the abundance of mammals, on the abundance and diversity of dung beetles in forest fragments using Structural Equation Modelling. We aimed to contribute to the understanding of how changes in forest habitats influence these insects and to the bigger concern about insects declines worldwide. Our study was located in forest fragments in Tana River Kenya, where two endemic monkeys were the main source of dung.
Our optimal model explained a statistically significant 26% of the variance in the abundance of the beetles, and 89% of the variance in their diversity. Forest area and abundance of mammals influenced beetle abundance positively, but edge effects had a negative influence on the abundance. In turn, beetle abundance influenced diversity directly and positively. Further, forest area and abundance of mammals influenced beetle diversity positively, but these effects were indirect. Similarly, edge effects influenced the diversity indirectly, but the effects were negative.
These findings imply that primates are crucial to maintaining the dung beetles in forest fragments and the forests themselves because of the essential services beetles provide there. We recommend that future studies investigate the factors, other than forest area, edge effects and the abundance of mammals, which drive the abundance of the beetles.