​Which one of the following statements is NOT correct?​

Correct option is C

Explanation-

Option A -  "Both alpha and gamma diversities measure the presence and abundance of species in a community." - CORRECT
Alpha diversity measures how many species are in one habitat or community, and sometimes also considers how abundant each species is.
Gamma diversity measures the overall number of species in a larger region that includes multiple habitats.
So yes, both measure species richness, and when using indices like Shannon Index or Simpson Index, they also consider abundance.

Option B - "Gamma diversity can be expressed as the product of alpha and beta diversities across sites." - CORRECT
Mathematically, the relationship is:

$$\gamma = \alpha \times \beta$$

This is Whittaker's multiplicative model.

Option C - "Gamma diversity is the sum of alpha diversities for a set of sites." - INCORRECT
Let’s say we have 3 sites:
                    Site A: 5 species
                    Site B: 6 species
                    Site C: 4 species
Sum of alpha diversities = 5 + 6 + 4 = 15
If 3 species are common to all, the actual gamma diversity (unique species across region) might be only 10, not 15.
So, summing alpha diversities can overestimate gamma diversity.
It ignores shared species and beta diversity (species turnover).

Option D - "Gamma diversity can be expressed as the sum of alpha and beta diversities across sites." - CORRECT
This is based on the additive model:

                                                $$\gamma = \alpha + \beta$$

This is an alternative to Whittaker’s model, especially useful in certain statistical contexts.​​

Since option C is the only incorrect statement among all the other options that makes it a correct answer

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