ECOLOGICAL SUCCESSION

ECOLOGICAL SUCCESSION

In the CSIR 2016 question, correct match of hypotheses to graph is:

The graph matching associates the rivet model with progressive loss of function, redundancy with an initial plateau, the idiosyncratic model with an irregular response, and the keystone model with an abrupt change after loss of an influential species. Those diagnostic curve shapes yield the stated mapping. Biodiversity–function hypotheses differ in how they assign ecological importance among species. Complementarity emphasizes distinct contributions, redundancy emphasizes overlap and compensation, rivet theory emphasizes cumulative weakening, keystone theory emphasizes particular influential species, and idiosyncrasy emphasizes context dependence. Real communities can display several patterns because functions differ and environmental conditions alter interactions. Richness alone therefore cannot identify mechanism; species traits, relative abundance, functional groups, and the order of species loss must also be considered. In this context, the keyed term, a-rivet, b-redundancy, c-idiosyncratic, d-keystone, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

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

View Details

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 through indirect effects. Functional groups summarize role overlap, while keystone effects identify unusually strong influence. Separating these dimensions explains why equal losses of richness can have very different ecological consequences and why conservation cannot rely solely on the number of species remaining. In this context, the keyed term, High richness, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause.

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

View Details

ECOLOGICAL SUCCESSION

What does 'functional group' imply in redundancy hypothesis?

A functional group comprises species that perform similar ecological roles, such as nitrogen fixation, grazing, pollination, or decomposition, even if they are not close relatives. In the redundancy hypothesis, overlap within such a group allows one species to compensate partly for loss of another. A functional relationship should be interpreted by asking whether change is gradual, buffered, abrupt, or irregular. Gradual loss is consistent with accumulating contributions; an initial plateau suggests compensation; an abrupt drop points to loss of a disproportionately important species; and an irregular curve indicates identity-dependent effects. These are conceptual expectations, not immutable laws. Different ecosystem processes—such as productivity, decomposition, pollination, or resistance—may follow different curves in the same community because they depend on different organisms and interactions. In this context, the keyed term, Same ecological role, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

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

View Details

ECOLOGICAL SUCCESSION

Which of the following best reflects competition for shared prey?

The stated key is scientifically inconsistent with the wording. Apparent competition occurs when two prey species share a predator, not when two consumers compete for shared prey. Competition for shared prey is ordinarily exploitative competition between predators, but that category is absent from the listed choices. Ecological interaction labels describe causal pathways rather than merely similar outcomes. Two organisms can decline together because they consume the same limiting resource, physically exclude one another, or are connected through a common predator. Experiments distinguish these cases by manipulating resources, access, or enemy abundance. Correct classification matters because coexistence mechanisms also differ: resource partitioning reduces exploitation, spatial separation may reduce interference, and enemy specialization can weaken apparent competition. In this context, the keyed term, Apparent, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

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

View Details

ECOLOGICAL SUCCESSION

Redundancy hypothesis implies function is maintained until:

The redundancy hypothesis groups species with overlapping ecological roles. Loss of one member may have little immediate effect because another can compensate, but function declines after losses remove enough members—or a uniquely important member—to cross the system's effective functional threshold. Biodiversity–function hypotheses differ in how they assign ecological importance among species. Complementarity emphasizes distinct contributions, redundancy emphasizes overlap and compensation, rivet theory emphasizes cumulative weakening, keystone theory emphasizes particular influential species, and idiosyncrasy emphasizes context dependence. Real communities can display several patterns because functions differ and environmental conditions alter interactions. Richness alone therefore cannot identify mechanism; species traits, relative abundance, functional groups, and the order of species loss must also be considered. In this context, the keyed term, Critical species are lost, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

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

View Details

ECOLOGICAL SUCCESSION

What’s a consequence of complementarity?

Complementarity raises ecosystem function when species differ in resource use, timing, rooting depth, microhabitat, or facilitative effects. As richness increases, these distinct contributions accumulate, enabling more complete resource capture or mutually beneficial interactions than a single species could achieve. 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 through indirect effects. Functional groups summarize role overlap, while keystone effects identify unusually strong influence. Separating these dimensions explains why equal losses of richness can have very different ecological consequences and why conservation cannot rely solely on the number of species remaining. In this context, the keyed term, Accumulated function increase, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

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

View Details

ECOLOGICAL SUCCESSION

In interference competition, interaction occurs:

Interference competition involves direct actions that reduce another individual's access to resources or habitat. Aggression, territorial exclusion, overgrowth, and allelopathic chemicals are examples; exploitative competition is indirect because competitors interact only through depletion of a shared resource. Ecological interaction labels describe causal pathways rather than merely similar outcomes. Two organisms can decline together because they consume the same limiting resource, physically exclude one another, or are connected through a common predator. Experiments distinguish these cases by manipulating resources, access, or enemy abundance. Correct classification matters because coexistence mechanisms also differ: resource partitioning reduces exploitation, spatial separation may reduce interference, and enemy specialization can weaken apparent competition. In this context, the keyed term, Directly among individuals, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

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

View Details

ECOLOGICAL SUCCESSION

Which component is used to derive Pielou’s evenness index?

Pielou's evenness is calculated as J = H′/ln(S), where H′ is Shannon entropy and S is species richness. Dividing observed Shannon diversity by its maximum possible value at that richness isolates how uniformly individuals are apportioned among species. Community indices compress abundance data, so their assumptions and mathematical conventions must remain explicit. Shannon entropy gives weight to both common and uncommon species, Simpson measures are more strongly influenced by dominant species, and Sørensen similarity usually uses presence–absence overlap. Equal abundance provides useful benchmarks: Shannon reaches ln(S) and Pielou reaches one. These properties allow the numbers to be interpreted biologically rather than treated as isolated arithmetic results. In this context, the keyed term, Shannon’s H, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

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

View Details

ECOLOGICAL SUCCESSION

Evenness index close to 0 implies:

Pielou-type evenness near zero means individuals are distributed very unequally among species. One or a few species account for most observations while the remainder are rare; equal abundances would instead drive the standardized index toward its upper limit of one. Diversity has separable richness and evenness components. Shannon entropy rises when species number increases or abundances become more equal, while Pielou evenness scales Shannon entropy against the maximum possible value for that richness. Simpson measures emphasize the probability that sampled individuals belong to the same or different species, depending on convention. Every calculation therefore requires explicit relative abundances and a stated formula; comparing values produced under different conventions can reverse interpretation. In this context, the keyed term, Dominance by few species, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

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

View Details

ECOLOGICAL SUCCESSION

A community with dominant species influencing function supports:

When a dominant or exceptionally influential species controls much of an ecosystem process, the pattern fits the keystone view. Functional output then depends more on the presence of that species than on species number alone, and its removal can cause a disproportionate change. 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 through indirect effects. Functional groups summarize role overlap, while keystone effects identify unusually strong influence. Separating these dimensions explains why equal losses of richness can have very different ecological consequences and why conservation cannot rely solely on the number of species remaining. In this context, the keyed term, Keystone, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

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

View Details

ECOLOGICAL SUCCESSION

Idiosyncratic hypothesis curve is:

The idiosyncratic hypothesis predicts no consistent, smooth relationship between species richness and ecosystem function. Effects depend on the particular identity, traits, and interactions of species lost or gained, so the response can rise, fall, or remain unchanged in an irregular and context-dependent way. A functional relationship should be interpreted by asking whether change is gradual, buffered, abrupt, or irregular. Gradual loss is consistent with accumulating contributions; an initial plateau suggests compensation; an abrupt drop points to loss of a disproportionately important species; and an irregular curve indicates identity-dependent effects. These are conceptual expectations, not immutable laws. Different ecosystem processes—such as productivity, decomposition, pollination, or resistance—may follow different curves in the same community because they depend on different organisms and interactions. In this context, the keyed term, Unpredictable, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

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

View Details

ECOLOGICAL SUCCESSION

In the keystone hypothesis, function is lost:

The keystone hypothesis predicts that ecosystem or community function depends disproportionately on one or a few influential species. Removing such a species can trigger an abrupt functional decline even when total richness changes only slightly, because numerous interactions or regulatory effects depend on that species. Ecosystem function can respond to diversity through niche partitioning, facilitation, insurance, or a sampling effect. Niche differences allow more complete resource use, asynchronous responses stabilize aggregate output, and high richness increases the chance of including a strongly productive species. Functional redundancy can buffer initial losses, but compensation is rarely unlimited because species differ in response traits and performance under stress. Consequently, both response shape and species identity are needed to distinguish among competing biodiversity hypotheses. In this context, the keyed term, Immediately after key species loss, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.

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

View Details