Plant and herbivorous insect diversity loss are greater than null model expectations due to land-use changes in agro-ecosystems

The effect of land-use changes on plant diversity is an important issue, as plant diversity is vital to maintaining of threatened insect diversity in agro-ecosystems. Although many studies have examined patterns of a few threatened species, few studies have examined a large number of threatened species while comparing organisms of different trophic levels. Observed and expected community assembly patterns of common and threatened species should be evaluated along land-use gradients in agro-ecosystems, using species richness and red list indicator (RLI). This study examined local and regional diversity of plants and herbivorous insects among abandoned, traditional, and intensified land-use types in semi-natural grasslands and compared observed and expected values via null model analysis. This study showed that the richness and RLI of plants and herbivorous insects were maintained in the traditional land-use. However threatened plants and herbivorous insects at sites of land abandonment and intensified use were significant lower than null model expectations. Although, plant richness, rather than RLI, was responsible for maintaining richness and the RLIs of herbivorous insects, plant richness did not linearly correlate with plant RLIs. Threatened plants did not depend on plant richness, it will be vital to identify and conserve unique environments for diversity of plants and herbivores. In conclusion, we should reintroduce traditional land-use practices in intensified use and abandoned grasslands. National and local governmental support for the appropriate management of semi-natural grasslands is beneficial for biodiversity conservation at both the local (e.g., present study area) and national (Japanese) levels.