Which taxon, what index we should measure for maximizing total γ-biodiversity in Japan?
Conservation planning will be efficient and effective if the biological hotspots could easily be identified. However, there are controversies over the congruence among multi-taxa and also over the indices for measuring the importance of hotspots. Disagreements among taxa and indices become serious when the spatial resolution gets finer as in the national or regional survey while the congruence among taxa are often observed for some degree in global scale analyses. Here we use extraordinary rich records of three popular taxonomic groups, odonates (dragonflies and damselflies), butterflies and vascular plants that were compiled in the fine grid cells (ca. 10km x 10km) in Japan. Three indices, richness, rarity and complementarity were compared. We aimed to analyze which taxon and what index will be the best to prioritize the conservation sites by drawing the species accumulation curve against the conservation area.
When we tested each taxonomic group individually, the complementarity index, which maximizes the β-biodiversity among sites, always provided the best conservation strategy with the smallest area and for all taxonomic groups. It was also true when we use the complementarity index of single taxon for maximizing the total γ-biodiversity but the rarity index of single taxon sometimes works better than the complementarity index. The performance of the richness index was the worst among three and even worse than the random selection. When we test the surrogacy of the taxonomic groups, vascular plants performed the best for representing the other species. It was because vascular plants have the largest number of species than the other two and contain lots of rare species which only have been found in a single cell. The region with many rare and endemic species will have high conservation priority especially when we do not have exhaustive lists for the target groups.