Effects of grazing on macro-moth assemblages in two different biomes in Mongolia

Abstract

Intensive land use, e.g. pastoralism, decreases biodiversity and leads to homogenization of habitats. However, the effect of land-use changes differs under varying climatic conditions. Thus, it is essential to study how land use affects biodiversity on a large scale. Moreover, species respond differently to environmental changes depending on whether they are specialists or generalists. We studied macro-moths in Mongolian pastures under two different grazing regimes (grazed and less grazed plots) in ten study sites that belong to two distinct biomes along a large-scale latitudinal gradient from desert to steppe. We explored 1) how livestock grazing affects macro moth diversity, species composition, and species richness, 2) how specialist and generalist moths respond to grazing in desert (Desert and xeric shrublands) and grassland (Temperate grasslands, savannas & shrublands). Moths are sensitive to environmental changes and suitable bioindicators. We also revealed a) indicators of grazing and b) indicators representative for certain sections of the latitudinal gradient. Totally, we recorded 80 species in the desert and 202 species in grassland in 2018 and 2019, which were DNA barcoded. In the desert, grazing did not affect macro-moth diversity, whereas grassland was negatively affected. However, not all moth families showed the same response to grazing. Species diversity, species richness, and abundance of Erebidae, Geometridae, and Noctuidae were significantly higher in the less grazed plots. Further, species dissimilarity between grazed and less grazed plots was mainly due to species replacement rather than species loss. In the desert, the species richness of both specialist and generalist moths did not differ between grazed and less grazed plots; in contrast, in grassland, the species richness of both groups was higher in less grazed plots. We found two indicator species of grazing in the desert: Hyles chuvilini in less grazed, and Cucullia splendida in grazed pasture. In grassland, we found ten indicator species exclusively for less grazed pastures: Catarhoe cuculata, Euxoa ochrogaster, Lacanobia thalassina, Megalycinia strictaria, Mythimna comma, Polia bombycina, Rhyacia simulans, Sideridis kitti, Sideridis egena, and Smerinthus caecus. These indicator species can be used as references for habitat quality and for moths' dispersal due to climate change in future studies. Among the environmental variables, plant species richness, altitude, and livestock number were the most important variables. Species composition of high altitudes in the desert was distinct, and higher species richness in this area indicated that high altitudes could serve as a refuge area during global warming and should receive conservation management.