Data and code for lower bound of rare species ratio of European freshwater macroinvertebrates

The phrase "Rare species are common" is widely recognized, but quantifying how common rare species are—specifically, their ratio—remains an area requiring further exploration. In this study, we present an analysis using community data of European freshwater macroinvertebrates to establish a lower bound for the ratio of rare species. By leveraging the Hill numbers framework, where "q = 0" estimates the total number of rare and common species and "q = 1" estimates the number of common species, we calculated the lower bound of the rare species ratio as 1 - (the ratio of common species number to the observed species richness). Our analysis included data from 19,649 communities (site-year pairs) with species counts exceeding three, yielding an average rare species ratio of 67.75%, with the 10th and 90th percentiles being 47.16% and 85.33%, respectively. Recognizing that community surveys often underrepresent rare species, we acknowledge that the observed species count is an underestimate of the total species richness. Consequently, we stress that our calculated ratio is a lower bound, indicating that rare species are likely even more common than our findings suggest.