Order of similarity between communities A, B, C is:
Similarity ordering compares the overlap in species composition for every pair of communities. The ranking A–B > B–C > A–C means A and B share the greatest fraction of their species, B and C share an intermediate fraction, and A and C are least alike. With presence–absence data, this may be tested using Jaccard similarity, C/(A + B − C), or Sørensen similarity, 2C/(A + B), where C denotes shared species. Both coefficients rise with overlap, although their numerical scales differ. Abundance data may instead use Bray–Curtis similarity, which also considers how evenly shared species are represent
Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation