The roles of beetles and flies in yak dung removal in an alpine meadow of eastern Qinghai-Tibetan Plateau

Flies and beetles are 2 major functional invertebrate groups responsible for dung removal and nutrient cycling in many alpine pastures. In order to determine the effect of the 2 groups on dung removal rate, as well as the associated mechanisms, we conducted a two-factor, two-level factorial-designed experiment in an alpine meadow of eastern Qinghai-Tibetan Plateau. Four treatments were included: (A) flies excluded, beetles included; (B) beetles excluded, flies included; (C) both flies and beetles excluded; and (D) both flies and beetles included, each having 45 replicates of artificial dung pats (17 cm in diameter; ca. 248 g in dry weight). We examined dung quality, removal rates, and abundance and biomass of macro-soil faunas within the dung 9 times (5 replicates sampled each time) during the experimental period of 32 d. Both beetles and flies (maggots), as well as the interaction between the 2 groups, markedly affected the dung removal rates. The total dry weight loss of the dung during the experiment was 167.6 g and 127.5 g on average for the beetle and fly groups, respectively. The removal rate in terms of both dung weight and organic matter loss was significantly greater for the beetles than the flies, which was principally because the consumption rate was lower and the resident time was shorter for fly maggots than for the beetles. The coexistence of the 2 species increased dung removal synergistically on the first sampling day and additively between the 2(nd) and the 5(th) day. However, after the 8(th) day of the experiment, the coexistence effect was negative, such that the dung loss of treatment D was comparable to treatment A but significantly greater than treatment B. The synergistic control might be due to the mediating effect of predator beetles on the relative abundance of coprophagous beetles and maggots, and the negative effect of the functional group diversity was because of the overwhelming competitive advantage of the beetles over fly maggots. In conclusion, although both fly and beetle species may significantly contribute to dung removal, the effect of the interaction between flies and beetles appears to depend on dung age (the sampling timing) in the alpine meadow.