Close association between grasshopper and plant communities in suburban secondary grasslands and the indicator value of grasshoppers for conservation

Semi-natural grasslands in Japan have decreased due to management abandonment and urbanization over the last 100 years, but they remain in suburban areas in addition to rural areas. Because suburban grasslands have various land-use histories and disturbance regimes, plant and herbivorous insect communities are likely to differ among grassland types. To identify grasslands with high conservation value, we conducted a comprehensive survey of grasshoppers and plants in 150 grasslands with 5 grassland types differing in land-use history and current management in northern Chiba prefecture, Japan. We then analyzed the association of the distributions of grasshopper and plant species compositions. Our results showed that grasshoppers were classified into habitat specialists and generalists. Three out of four habitat specialists were almost exclusively found in semi-natural grasslands and vacant lots, while habitat generalists were commonly observed at the cropland margins. This habitat specialist–generalist distribution gradient corresponded well to that found in plant communities, which was probably due to current disturbance regimes. We suggest that vacant lots as well as semi-natural grasslands have high conservation value for grassland organisms of various taxa in suburban areas, and grasshoppers are candidate indicator species for monitoring grassland environments.