#ecological diversity

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Different niches in same habitat exemplify:

“Resource partitioning” for different niches in same habitat exemplify. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. A niche is the multidimensional set of abiotic conditions, resources, and biotic relationships under which a population can persist. The fundamental niche reflects physiological and resource limits, while the realized niche is modified by competitors, consumers, mutualists, and dispersal barriers. The remaining alternatives—“Competitive exclusion”, “Complete competition”, “Charac

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

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BIODIVERSITY & IDH

Which value of Simpson’s Index (D) shows maximum diversity?

Using Simpson’s dominance definition, D = Σpᵢ², diversity is greatest when D is smallest. The index represents the probability that two randomly sampled individuals belong to the same species. As richness and evenness increase, that probability declines because individuals are spread among many taxa. A value of zero is the theoretical lower limit and therefore represents maximum diversity among the listed values. In a real finite community containing individuals, D ordinarily remains above zero; it approaches zero as the effective number of equally abundant species becomes very large. A value

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

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BIODIVERSITY & IDH

The number of different species in a community is called:

Species richness is the count of distinct species present in a defined community, area, or sample. A community containing twenty species has greater richness than one containing ten, regardless of how individuals are distributed among them. Evenness addresses that distribution: it is high when species have similar abundances and low when one or a few dominate. Dominance likewise concerns concentration of abundance, while an index combines selected components mathematically. Shannon and Simpson measures therefore can differ between communities that have identical richness but different evenness

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

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BIODIVERSITY & IDH

The diversity seen at regional level is:

Gamma diversity is the total diversity across a region or landscape that contains multiple local communities. It includes all species recorded when those communities are pooled and may be expressed as richness or as an effective diversity index. Alpha diversity describes diversity within a local habitat, while beta diversity captures differentiation or turnover among habitats. Under multiplicative partitioning, γ = α × β, so high regional diversity may result from species-rich local communities, strong compositional turnover, or both. For example, several forests with identical species lists c

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

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BIODIVERSITY & IDH

At high disturbance frequency, diversity is low due to:

Frequent or intense disturbance repeatedly removes biomass and interrupts population growth. Species that mature slowly, reproduce infrequently, or require stable habitat cannot complete their life cycles, leaving only disturbance-tolerant taxa, rapid colonizers, or organisms with resistant stages. This strong environmental filter reduces richness and often produces communities dominated by a few stress-tolerant forms. Under the intermediate disturbance hypothesis, diversity is therefore low at the high-disturbance end. “Generalist” may describe some survivors, but broad resource use is not th

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

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BIODIVERSITY & IDH

The IDH predicts highest diversity at:

The intermediate disturbance hypothesis predicts a hump-shaped relationship between disturbance and species diversity. At very low disturbance, strong competitors can monopolize limiting resources and exclude inferior competitors, reducing coexistence. At very high disturbance, mortality or biomass destruction occurs so frequently or intensely that only rapid colonizers and highly tolerant species persist. Intermediate disturbance can prevent complete competitive exclusion while allowing enough time for slower-growing species to establish, so early and late successional taxa coexist. Disturban

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

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BIODIVERSITY & IDH

Shannon-Weaver index (H’) accounts for:

Shannon–Weaver diversity is calculated as H′ = −Σpᵢ ln pᵢ. The number of terms reflects species richness, while the relative abundances pᵢ determine evenness. Adding species generally raises H′, and distributing individuals more equally raises it further. For a fixed richness S, the maximum is ln S when every species has pᵢ = 1/S. This permits Pielou evenness to be calculated as J′ = H′/ln S. The index can be interpreted as uncertainty in predicting the species identity of a randomly selected individual: many equally likely species create high uncertainty, whereas dominance makes identity pred

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

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BIODIVERSITY & IDH

What does Simpson’s index (D) value close to 1 indicate?

In the dominance convention, Simpson’s D = Σpᵢ² is the probability that two randomly selected individuals belong to the same species. A value close to 1 occurs when one species contains nearly all individuals. The community is then highly dominated, the identity of a sampled organism is predictable, and diversity is low. Maximum evenness would spread abundance among species, reduce each squared proportion, and drive D downward. Infinite or maximum diversity is therefore incompatible with D near 1. The notation requires care because some texts label 1 − D as “Simpson’s index”; that complementar

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

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BIODIVERSITY

What is the main advantage of using Simpson’s 1-D form?

The dominance form of Simpson’s index decreases as diversity rises, which often causes interpretive confusion: a numerically larger D means greater dominance and lower diversity. Transforming it to 1 − D reverses that direction. The resulting value is the probability that two individuals selected at random belong to different species, so larger values correspond directly to greater diversity. This intuitive direction is the principal advantage of the 1 − D form. It also remains bounded between 0 and 1, facilitating comparisons when methods and sampling are consistent. The transformation does n

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

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BIODIVERSITY

Gini-Simpson index is represented by:

Simpson’s dominance index D = Σpᵢ² measures the probability that two randomly selected individuals belong to the same species. Taking its complement gives 1 − D, the probability that the two individuals belong to different species. This complementary measure is called the Gini–Simpson index and increases with both richness and evenness. A community dominated by one species has D near 1 and 1 − D near 0; an increasingly even, species-rich community has smaller D and a Gini–Simpson value approaching 1. The alternatives 1/D and D represent the reciprocal Simpson index and dominance index, respect

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

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BIODIVERSITY

Which of the following about diversity components is incorrect?

Alpha, beta, and gamma diversity refer to different spatial scales. Alpha diversity is measured within a relatively homogeneous local habitat or community and may be represented by species richness or an index combining richness and evenness. Beta diversity quantifies differentiation among habitats, often as species turnover or as a multiplicative relation such as β = γ/α. Gamma diversity is the total diversity of the larger landscape or region containing those local communities. Consequently, describing alpha diversity as regional diversity reverses the established scale terminology. A forest

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

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