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 rather than a universal law, but its defining prediction is highest diversity under intermediate disturbance, not at either extreme. This reasoning connects organismal behavior with broader ecological consequences. A mechanism that changes encounter rates, resource use, or reproductive success can scale up to alter population trajectories and the structure of species interactions. The alternatives can be separated by asking what changes for each participant and which process causes that change. That approach is more reliable than treating familiar examples as fixed labels, because many interactions shift with environmental context.

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, and merely having few individuals does not determine D unless their allocation among species is known. Ecological categories are simplified models, yet they remain valuable when their assumptions are stated. The selected description captures the dominant net effect, while real systems may vary with density, habitat, life stage, and environmental conditions. This reasoning connects organismal behavior with broader ecological consequences. A mechanism that changes encounter rates, resource use, or reproductive success can scale up to alter population trajectories and the structure of species interactions.

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 abundance therefore represents the upper limit of the evenness component of diversity. The relevant evidence concerns process rather than wording alone. Linking the described pattern to energetic returns, fitness consequences, or receiver responses makes the inference biologically coherent and distinguishes it from the competing alternatives. Ecological categories are simplified models, yet they remain valuable when their assumptions are stated. The selected description captures the dominant net effect, while real systems may vary with density, habitat, life stage, and environmental conditions.

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. Ecads therefore need not become sterile or genetically diverse when conditions are standardized. At population level, this mechanism can influence abundance, coexistence, and evolutionary selection. Separating immediate individual effects from longer-term community outcomes gives the selected concept a clearer ecological meaning and avoids relying only on memorized terminology. The relevant evidence concerns process rather than wording alone. Linking the described pattern to energetic returns, fitness consequences, or receiver responses makes the inference biologically coherent and distinguishes it from the competing alternatives.

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. Mechanistic reasoning is essential here: classifications should follow measurable consequences for survival, reproduction, resource acquisition, or detection. Context can modify interaction strength, but it does not erase the defining contrast among the alternatives presented. At population level, this mechanism can influence abundance, coexistence, and evolutionary selection. Separating immediate individual effects from longer-term community outcomes gives the selected concept a clearer ecological meaning and avoids relying only on memorized terminology.

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 between-community component. Turnover should be distinguished from nestedness. Two sites may differ because one contains a subset of the other, producing richness loss without true species replacement; modern beta-diversity analyses can separate these components. Environmental filtering, dispersal limitation, geographic distance, disturbance, and historical barriers all generate turnover. For conservation, high beta diversity means that protecting a single species-rich site may fail to capture many regional species, so multiple compositionally distinct habitats are needed. The concept therefore links local assemblages to regional gamma diversity by quantifying how rapidly membership changes across space or time.

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 invasion, and impose stressful microclimates. Nevertheless, the defining idea is mixed membership plus potential unique boundary species. A biome is a very large climatic vegetation unit, an ecotype is a genetically differentiated local population, and a clone is a set of genetically identical organisms; none denotes a community boundary. Ecotones may be sharp or broad and can shift with succession, hydrology, climate, or land use. Their mixed composition makes them important for studying species turnover and landscape connectivity, while their sensitivity to environmental change can make them useful ecological indicators.

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 valid point is that alpha is assessed at the single-habitat scale, not that every single habitat has more species than every region. Beta diversity describes change among local habitats, while gamma diversity pools them across the region. A local community may have high alpha diversity because it contains many evenly represented species, yet regional gamma will ordinarily be at least as large in richness terms because it includes the union of local species. The keyed choice should thus be understood as identifying the scale of alpha diversity, with the comparative adjective treated as a flaw in the stem rather than a literal cross-scale ranking.

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 of one indicates complete dominance by a single species. This direction reverses for the complementary Gini–Simpson index, 1 − D, where values near one indicate high diversity, and for the reciprocal 1/D, where larger numbers indicate more effective species. The formula must therefore accompany the name “Simpson’s index.” The keyed zero assumes the dominance convention consistently used in these rows. Interpreting the scale probabilistically prevents memorization errors: low same-species draw probability means high diversity, whereas high same-species draw probability means low diversity.

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. Richness estimates depend strongly on sampling effort, area, season, detectability, and taxonomic resolution. Rarefaction or standardized coverage is often used to compare samples of unequal size, and unseen-species estimators can account for taxa likely missed. Richness also has no information about species identity: two communities may each contain ten species yet share none, producing equal richness but high beta diversity. Despite these limitations, it is the simplest and most intuitive biodiversity component and forms the basis of species–area curves, local alpha-diversity comparisons, and regional conservation inventories.

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 can have high alpha but relatively low beta, limiting gamma. Conversely, individually modest sites can collectively yield high gamma if each contains different specialists. Delta diversity is sometimes used for turnover over broader biogeographic gradients, but it is not the standard term for pooled regional diversity. Defining spatial grain and extent is important because “regional” depends on study design: the same forest could be gamma scale for quadrat sampling but alpha scale in a continental analysis. Gamma remains the appropriate component whenever the aim is to summarize diversity over the full set of local habitats under consideration.

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 therefore not the defining feature of an ecocline. Neither sudden diversity loss nor invasion is required; diversity may rise, fall, or peak along the gradient depending on turnover, productivity, stress, and overlap. Ecoclines can be studied with transects and ordination, which reveal how abundances track environmental axes. Individual species may have different optima and tolerance curves, so whole-community composition changes through overlapping responses rather than all taxa switching at one point. The concept emphasizes continuity and gradient-driven replacement, linking species-level tolerance to landscape patterns of beta diversity.

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

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