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#community diversity

3 public questions tagged with this topic.

BIODIVERSITY

What does a higher Simpson’s D value indicate?

A high value of Simpson’s dominance index D = Σpᵢ² indicates that abundance is concentrated in one or a few species. Since D is also the probability that two randomly chosen individuals belong to the same species, strong dominance makes this probability large and ecological diversity low. If all species are similarly abundant, each pᵢ is smaller, the squared terms shrink, and D declines. Species richness also tends to reduce D when additional species contribute appreciable abundance. Thus a high D does not imply high diversity or equal abundance, and it says nothing directly about turnover amo

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

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BIODIVERSITY

Which of the following is a community-level measure of diversity?

Gamma diversity is the total diversity of a region or landscape containing multiple local communities. It is therefore a regional-level measure, not a community-level one. Within a single community, alpha diversity can be described through species richness, evenness, or composite indices such as Shannon or Simpson diversity. Both “evenness” and “species richness” among the alternatives are legitimate community-level attributes: richness counts species, whereas evenness describes how equally individuals are distributed among them. Beta diversity then captures turnover between communities, and g

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

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BIODIVERSITY

The value of Shannon’s index (H) increases with:

Shannon diversity is H′ = −Σpᵢ ln pᵢ, where pᵢ is the proportional abundance of each species. The index increases when more species are added and when individuals are distributed more evenly among the species already present. A rare species contributes relatively little because its pᵢ is small, while a strongly dominant species lowers overall uncertainty: a randomly chosen individual becomes easier to predict. For a fixed richness S, H′ reaches its maximum when every species has abundance 1/S, giving H′max = ln S. Evenness can therefore be expressed as J′ = H′/ln S. Dominance and unevenness mo

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

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