Dung beetles and nutrient cycling in a dryland environment

Insects are involved in the biogeochemical cycles of multiple elements and influence soil fertility. In particular, soil insects and the functions that they support can affect the response of terrestrial ecosystems to environmental changes. We experimentally studied the role of dung beetles as recyclers of cow dung in drylands of the Central Monte in mid-western Argentina; and we extrapolated these results to ecosystem impact in a grazing field, considering the dung beetle's abundance in summer. We conducted experiments with four species of dung beetles (Sulcophanaeus imperator, Eucranium arachnoides, Digitonthophagus gazella and Malagoniella puncticollis), and quantified their abundance on the field. Dung beetles incorporated nitrogen, ammonium, and phosphorous to the soil, but this activity varied substantially among species. The highest quantity of organic matter, nitrogen and phosphate was incorporated to the soil by S. imperator, one of the larger beetle studied. While the per capita effect of S. imperator is superior to other species studied, the impact on the ecosystem of the invasive D. gazella might be superior due to their major abundance in grazing fields. Our results highlight the importance of considering both components, per capita effect and abundance, to estimate with more reliability the relative importance of dung beetle species. Given that the effect of dung beetles on nutrient cycling is variable among species, and their abundance is variable in space, it is important to conserve beetle diversity in order to maximize their beneficial impacts on soils. Therefore, dung beetle effect on soil might be crucial in drylands to mitigate the nitrogen losses caused by grazing.