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#community similarity

3 public questions tagged with this topic.

BIODIVERSITY

Which one is used to assess similarity between two communities?

Sørensen’s coefficient compares the composition of two communities using shared species. For presence–absence data it is commonly calculated as Cₛ = 2c/(a + b), where a and b are the numbers of species in the two communities and c is the number occurring in both. The coefficient ranges from 0, indicating no shared species, to 1, indicating identical species lists. Because shared species are weighted twice, the numerator corresponds to their contribution to both lists. It is useful for comparing sites, seasons, successional stages, or treatment plots and is closely related to beta diversity: lo

Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation

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BIODIVERSITY

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

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BIODIVERSITY

Which pair of communities has the highest similarity using Sorenson’s coefficient?

Sørensen similarity for presence–absence data is 2c/(a+b), where c is the number of shared species and a and b are the richnesses of the two communities. Counting shared taxa in the source dataset makes communities A and C the pair with the largest coefficient. Alpha diversity describes composition within a community, whereas pairwise similarity compares composition between communities. Abundance-based indices require relative frequencies; incidence-based coefficients require shared and unshared taxa. High richness does not guarantee high evenness, and high diversity within two sites does not

Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation

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