BIODIVERSITY & IDH

BIODIVERSITY & IDH

Which combination correctly describes IDH?

The intermediate disturbance hypothesis proposes a hump-shaped relationship between disturbance intensity or frequency and local diversity. With little disturbance, strong competitors may exclude weaker species and reduce coexistence. Severe or very frequent disturbance removes many organisms, especially slow-growing or disturbance-sensitive taxa, leaving only a limited tolerant set. At intermediate levels, competitive exclusion is interrupted without eliminating most populations, allowing colonizers, tolerant species, and superior competitors to coexist. The hypothesis is context dependent ra

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

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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

In species evenness, diversity is maximum when:

Maximum evenness occurs when every species contributes the same proportion of individuals to the community. Under that distribution, randomly sampled individuals are least likely to be concentrated in a single taxon, so uncertainty of species identity is high and dominance is low. If one species becomes disproportionately abundant, evenness and most diversity measures decline even though richness may remain unchanged. Low richness concerns the number of species, not equality among their abundances, while random spatial placement does not guarantee an even abundance distribution. Equal abundanc

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

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BIODIVERSITY & IDH

Ecads when kept in same environment become:

Ecads are environmentally induced forms within a species, not genetically fixed races. Different conditions can produce contrasting body size, pigmentation, leaf form, or physiology through phenotypic plasticity. When those individuals are transferred to a common environment, the environmental cues become similar and their phenotypes tend to converge, making them morphologically similar. This common-garden logic distinguishes plastic responses from inherited differentiation: persistent differences would suggest genetic divergence, whereas disappearing differences indicate environmental control

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

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BIODIVERSITY & IDH

Diversity due to differences in abundance of species is called:

Evenness measures how uniformly individuals are distributed among the species present. Two communities may contain the same number of species yet differ greatly in diversity if one is dominated by a single species while the other has comparable abundances throughout. Richness counts species without considering their relative numbers, whereas dominance emphasizes concentration in one or a few taxa. Turnover instead describes compositional change across places or times. Thus abundance differences are captured specifically by evenness, an essential component of indices such as Shannon diversity.

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

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BIODIVERSITY & IDH

What represents species turnover?

Beta diversity represents species turnover among communities, habitats, or sites. It is high when local assemblages share few species and low when they are compositionally similar. Pairwise turnover can be measured with dissimilarity coefficients such as 1 minus Jaccard or Sørensen similarity, while regional multiplicative partitioning uses β = γ/α. Alpha diversity describes diversity within one local community, and gamma diversity is the pooled diversity across the wider region. Delta diversity is sometimes applied to turnover across larger geographic gradients, but beta is the standard betwe

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

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BIODIVERSITY & IDH

Which zone is characterized by species from two ecosystems and additional unique species?

An ecotone is the transition zone between two neighbouring ecosystems or communities. Because environmental conditions and resources overlap, it can contain species from both adjoining systems as well as edge specialists that occur mainly in the transition. This combination can produce the edge effect—locally elevated richness, abundance, or interaction intensity. Examples include a forest–grassland margin, an estuary between river and sea, or a marsh–upland boundary. Elevated diversity is not inevitable: abrupt human-created edges may exclude interior specialists, increase predation or invasi

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

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BIODIVERSITY & IDH

Which of the following shows greater alpha diversity?

Alpha diversity is defined within a single local habitat or community. Among the scale descriptions given, “single habitat” is therefore the appropriate unit for an alpha-diversity measurement. An ecosystem may contain several habitat types, multiple communities explicitly span a broader comparison, and a whole region corresponds to gamma diversity. The wording “greater alpha diversity” is imprecise because a spatial category alone does not guarantee a larger numerical value; actual richness and abundance data are needed to decide which specific habitat is most diverse. The scientifically vali

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

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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

Ecocline represents:

An ecocline is a gradual change in species composition or community structure along a continuous environmental gradient. Moving from low to high elevation, dry to wet soil, or low to high salinity may progressively replace species according to their physiological tolerances and competitive abilities. Boundaries are diffuse because the underlying environmental variable changes continuously. An ecotone, by contrast, is often described as a more recognizable transition zone between adjacent communities, although the two terms sometimes overlap in ecological usage. A sharp ecosystem boundary is th

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

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