Disentangling the effects of dung pat shape and mass on greenhouse gas emissions in the presence of dung beetles.

Dung beetles (Coleoptera: Scarabaeoidea) can influence greenhouse gas emissions (GHG) from pasture systems by altering dung decomposition processes. However, the magnitude and direction of the effect of dung beetle presence on dung GHG emissions are not consistent across studies, potentially due to variations in experimental practices. To better understand dung beetles' emission mitigation potential, this study seeks to evaluate how the interactions between dung shape, mass, and dung beetle presence affect dung GHG emissions. A laboratory experiment was conducted to assess the effects of Onthophagus nuchicornis presence, dung shape, and dung mass on dairy cattle dung GHG emissions over a 21-day period. Results revealed that dung mass can significantly impact the effect of dung beetle presence on dung CO2 emissions. The presence of dung beetles in mesocosms containing 100 g dung pats increased CO2 emissions by 29%, while their presence in mesocosms containing the 400 g dung pats increased emissions by 64%. Additionally, the interaction between dung shape and mass, as well as dung shape and beetle presence significantly impacted CH4 emissions. Flattening 100 g dung pats resulted in a 44% reduction in CH4 emissions, while flattening 400 g dung pats reduced CH4 emissions by 13%. Beetle presence in flattened dung pats resulted in a 72% reduction in CH4 emissions, whereas their presence in non-flattened dung pats only resulted in an 8% reduction in CH4 emissions. These findings reveal the importance of methodological decisions when studying the relationship between dung beetle activity and GHG emissions from dung pats.