coefficient of biotic similarity

The coefficient of biotic similarity is a measure used in biogeography to quantify the resemblance between different geographic regions based on their shared species. It is calculated using Jaccard's coefficient, represented by the equation:1

(s = c / (a + b + c))

where:
* s is the coefficient of similarity
* c is the number of taxa shared between two areas
* a is the number of taxa unique to the first area
* b is the number of taxa unique to the second area

A higher coefficient indicates greater similarity between the regions. This method helps in defining biogeographic regions by comparing the species composition of different areas.1