Abstract: Habitat loss is the main cause of biodiversity loss, but the effects of the ensuing fragmentation are contentious. Some question if habitat fragmentation is bad for biodiversity or has any effect at all. Generally, the studies that find no harm of habitat fragmentation invariably assume that it is distinct from loss. However, dissociating habitat loss from fragmentation is questionable because the two are inevitably linked, and it can be insightful to test for their joint effects. Accordingly, we used structural equation modelling to analyze the joint effects of forest area, mammal abundance and fragmentation on dung beetle abundance and diversity.
We sampled 87 species among 113,959 dung beetles from 288 plots located in 12 forest fragments in Tana River Kenya. Majority of the species were small (92%) sized tunnellers (78%), but in terms of numbers tunnellers were as many as the rollers were.
Our optimal model explained a significant 26% of the beetle abundance and 89% of the diversity. The abundance was driven by positive direct influences of fragment area and mammal abundance and by negative edge effects. The diversity was primarily driven by the direct effects of the abundance, but also by indirect effects of (1) positive associations with forest area and abundance of mammals, and (2) the negative influence of edge effects. Thus, the amounts of habitat and its fragmented state jointly influenced the abundance and diversity of the beetles in direct and indirect ways.
