Interactive effects of large herbivores and plant diversity on insect abundance in a meadow steppe in China

Abstract

The structure and dynamics of insect community in grasslands can be influenced by grazing management via altered characteristics of plant community. However, attempts to better understand the complex relationships among plants, insects, and large herbivores is still hampered largely by the interactive effects of plants, insects, and large grazers on each other. In this study, we test the hypothesis that the effect of large herbivores on insect abundance is grazer species-specific and pre-grazing plant diversity-dependent using an experiment with manipulating four grazing treatments (i.e., control, cattle, goats, and sheep) at low, intermediate, and high plant diversity levels in a meadow steppe at northeast in China. We show that grazing significantly increased the abundance of the entire insect community. The abundance of each insect order responded differently to grazing treatments, with higher abundance of Orthoptera and Homoptera under sheep grazing, enhanced abundance of Coleoptera and Diptera under cattle grazing, and reduced Hemiptera abundance, but greater abundance of Lepidoptera under goats grazing. Thus different treatments profoundly changed insect taxonomic composition. The six most dominant species (Euchorthippus unicolor, Aelia nasuta, Trigonotylus ruficornis, Curculionidae sp., Coccinula quatuordecimpustulata, and Cicadellidae sp.) responded differently to grazing by large herbivores, with either increased or decreased its abundance. The effects of grazing on insect abundance were driven by their differential responsive mechanisms for vegetation. More importantly, the effects of grazing on insect abundance at both order- and species-levels potentially depended on plant diversity levels of pre-grazing. Our results suggest that different herbivore species should be used in the background of different plant communities for better conservation of insect community in managed grassland.