#community ecology

Niche CD RP CEP

Which is NOT a mechanism for species coexistence?

Stable coexistence requires mechanisms that reduce average interspecific competition or create stabilizing advantages when a species becomes rare. Niche differentiation and complementarity achieve this by allowing species to use different resources, places, or times, thereby limiting direct overlap. If the number of independently limiting resources or niche dimensions is sufficiently large relative to competitors, classical resource-competition theory can also permit coexistence, though the wording given is simplified. Niche overlap, by itself, is not a coexistence mechanism; it indicates shar

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 13

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BIODIVERSITY & IDH

Which community type will have lowest Simpson’s index value (D)?

For Simpson's concentration index D, commonly written as the sum of squared species proportions, values become smallest when abundance is spread evenly across species. Squaring makes large proportions contribute disproportionately, so a dominant species raises D strongly. Equal abundance minimizes the sum for a fixed number of species and indicates low concentration and high diversity. This interpretation depends on using D itself; transformed versions such as 1-D or 1/D reverse the direction of comparison. High richness combined with low evenness can still produce substantial concentration, a

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

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BIODIVERSITY & IDH

A community with high evenness and richness will have:

Species richness supplies the number of different taxa, while evenness describes how uniformly individuals are distributed among them. A community high in both components has many possible species identities and little numerical dominance, producing high values of composite diversity measures. Shannon H′ rises with richness and reaches its maximum for a fixed richness when all species are equally abundant. Simpson dominance D becomes low under even abundance, while its complement 1 − D becomes high. Thus “low Simpson index” could be misleading: it is true only for the dominance form D, not for

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

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BIODIVERSITY

In species-area curves, which relation is NOT valid?

A species–area relationship specifically links the number of species S to sampled area A, commonly expressed as S = cAᶻ or, after logarithmic transformation, log S = log c + z log A. The curve rises because larger areas include more individuals and habitats, but its slope typically diminishes on arithmetic axes. “Richness versus area” directly represents this relationship. Prey killed versus prey density instead describes a predator functional response, while photosynthesis versus light describes physiological resource saturation. Tree richness versus evapotranspiration is an environment–diver

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

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ECOLOGICAL SUCCESSION

What increases the chance of dominant species being present?

Greater species richness increases the sampling probability that a highly productive or otherwise dominant species is included in a community. This selection effect can raise measured ecosystem function even without every species contributing a unique mechanism, because diverse assemblages draw more species from the regional pool. Species richness counts taxa but does not show their abundance, traits, or interaction strengths. Dominant species may control bulk process rates, rare species may provide specialized functions or future insurance, and predators can restructure whole food webs throug

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20

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