Abstract
With the new global goal to achieve a recovery of biodiversity by 2030, the measurement and quantitative evaluation of biodiversity has become an important topic. In this study, we developed a method to evaluate the degree of habitat quality at a given site based on records of indicator species selected by focusing on the “nestedness” of the species assemblage. We used data from the Monitoring Site 1000 Satoyama Surveys conducted throughout Japan. In selecting indicator species, we verified that there is nestedness in the species composition, and then selected indicator species based on their frequency of occurrence throughout Japan. Candidates were selected based on criteria such as the strength of their relationship to the total number of species, their range of distribution, and the balance of ecosystem types. Finally, we selected 54 plant species, 37 bird species, and 22 butterfly species through expert judging by specialists from each taxon. The validation test using datasets from different study sites showed significant positive correlations between the number of indicator species and total number of species at each study site, as well as between the rarity index (expressed as the average of the inverse of its national frequency of occurrence of each indicator species) and the number of endangered species. However, the explanatory power of the selected indicator species to the total number of species and endangered species did not differ significantly from the average value when indicator species were selected randomly. Although these indicator species are not the best set for assessing biodiversity quantitatively, we were able to develop a method to assess the ecological status of each site, which can be used over a relatively large geographic range and ecosystem types, and with less effort and expertise than conventional methods that survey all species. This metric can also be used to identify important conservation areas within a region and to monitor protected areas and other effective area-based conservation measures (OECM), which will contribute to the realization of Nature Positive on a regional basis.
