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​Which one of the following is INCORRECT regarding Hill numbers (q), a family of diversity indices?​
Question

Which one of the following is INCORRECT regarding Hill numbers (q), a family of diversity indices?

A.

As q increases, the index puts increasing weight on the most common species in the assemblage, with the contribution of rare species gradually reducing in the summation.

B.

As q increases, the index puts increasing weight on the rare species in the assemblage, with the contribution of common species gradually reducing in the summation.

C.

As q increases, the diversity index decreases, unless all species are equally abundant.

D.

Once q 5, Hill numbers rapidly converge to the inverse of the relative abundance of the most common species.

Correct option is B

Hill numbers (also called the effective number of species) provide a unifying framework for measuring diversity. They are parameterized by an order q, which determines the sensitivity of the diversity measure to species abundance.

  • When q = 0, Hill number equals species richness (all species weighted equally).

  • When q = 1, Hill number corresponds to the exponential of Shannon entropy (weights species proportional to their abundance).

  • When q = 2, it relates to the inverse of Simpson’s index, giving more weight to common species.

  • As q increases, more weight is given to common species, and rare species are downweighted.

  • Conversely, lower q values (closer to 0) emphasize rare species.

Therefore:

  • Statement (1) is correct: As q increases, the diversity measure emphasizes dominant species.

  • Statement (3) is correct: Increasing q tends to decrease the diversity index, especially if species are not equally abundant.

  • Statement (4) is correct: For q ≥ 5, the Hill number becomes very close to the inverse of the most abundant species’ relative abundance.

  • Statement (2) is INCORRECT: It falsely claims that increasing q emphasizes rare species, which is the opposite of the correct trend.

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