The responses of different insect guilds to grassland degradation in northeastern China
Grassland insect diversity in many parts of the world is severely threatened by recent deterioration caused by global change and human activities. Insect species richness and abundance are likely sensitive to grassland degradation because of changes in vegetation structure and microclimates, and yet, our understanding of how diversity of insect community, particularly insect guilds responds to grassland degradation is still limited. Here, we conducted a field experiment to examine the responses of richness and abundance of total insects and different insect guilds along degraded levels (i.e., non-degraded, moderately, and severely degraded site) in meadow steppe at northeastern China. We found that higher species richness of total insects was detected in the moderately degraded sites, and there was no difference in abundance between the three sites. Furthermore, the responses of richness and abundance of each insect guild were significantly different. Hemiptera richness was significantly higher at moderately degraded sites, and Orthoptera richness was higher in severely degraded sites. Abundance of Hemiptera and Orthoptera increased with the increasing levels of degraded grasslands, but the abundance of Hymenoptera and Coleoptera decreased. Moreover, effect size of grassland degradation on Orthoptera abundance was larger from non-degraded to moderately degraded grassland; and larger effect size on Coleoptera abundance from moderately to severely degraded grassland. The different responses of insect guilds to grassland degradation are mainly attributed to changes in food and microclimate availability. In the light of convenience and operability, the finding from the study suggested that the abundance of an insect guild, rather than total insects and insect diversity seem to be a useful ecological indicator when assessing the levels of grassland degradation.