#ecological theory

Biogeography Complete

According to the theory, species diversity is balanced between:

“Immigration and extinction” for according to the theory, species diversity is balanced between. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Island biogeography explains species richness as a dynamic balance between immigration and extinction. Immigration generally declines as an island fills with species, whereas extinction rises as more species divide finite area and maintain smaller populations. The remaining alternatives—“Competition and predation”, “Mutation and drift”, “Abiotic and biotic factors”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Larger islands usually support more habitats and larger populations, lowering extinction risk; less isolated islands receive colonists more readily and may experience rescue effects. These mechanisms also apply to habitat fragments that function as ecological islands. This distinction matters because similar surface patterns can arise through different mechanisms, whereas ecological prediction depends on identifying the mechanism that actually changes rates.

Ref: Biogeography, Lomolino et al., 5th Ed., Ch. 5-8

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Biogeography

According to the theory, species diversity on islands is:

“Dynamic and balanced” for according to the theory, species diversity on islands is. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Island biogeography explains species richness as a dynamic balance between immigration and extinction. Immigration generally declines as an island fills with species, whereas extinction rises as more species divide finite area and maintain smaller populations. The remaining alternatives—“Fixed and constant”, “Decreasing continually”, “Increasing continually”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Larger islands usually support more habitats and larger populations, lowering extinction risk; less isolated islands receive colonists more readily and may experience rescue effects. These mechanisms also apply to habitat fragments that function as ecological islands. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.

Ref: Biogeography, Lomolino et al., 5th Ed., Ch. 1-4

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Habitat Niche

Hutchinson's niche concept considers a niche as:

“Multi-dimensional” for hutchinson's niche concept considers a niche as. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Niche differentiation reduces overlap by separating species along resource, space, or time axes. Such partitioning can stabilize coexistence when each species performs relatively better under the conditions it uses most strongly. The remaining alternatives—“Single-dimensional”, “Two-dimensional”, “Only spatial”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Habitat describes where an organism occurs; niche additionally describes how it obtains resources and affects or responds to other organisms. Distribution therefore provides evidence about a niche but is not identical to it. The cited framing is therefore most useful when treated as a conditional biological claim, with assumptions about scale and environmental context kept explicit. Linking the wording to measurable consequences for fitness, abundance, or flux gives the conclusion its scientific meaning and prevents a purely mnemonic interpretation.

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

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Habitat Niche

The niche concept was modernized by:

“G.E. Hutchinson” for the niche concept was modernized by. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Habitat describes where an organism occurs; niche additionally describes how it obtains resources and affects or responds to other organisms. Distribution therefore provides evidence about a niche but is not identical to it. The remaining alternatives—“Charles Darwin”, “Robert MacArthur”, “Thomas Smith”—refer to different states, processes, or scales and therefore do not express the same causal relationship. 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 cited framing is therefore most useful when treated as a conditional biological claim, with assumptions about scale and environmental context kept explicit.

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

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Extinction Topic

The extinction vortex involves:

“Synergistic interactions among genetic, demographic, and environmental factors” for the extinction vortex involves. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Human-driven habitat conversion, exploitation, introduced enemies, pollution, and climate change often interact rather than acting independently. Traits such as slow reproduction or ecological specialization can magnify vulnerability. The remaining alternatives—“Only biotic factors”, “Independent extinction drivers”, “Climate change only”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Extinction risk rises when abundance, geographic range, or genetic variation becomes small because demographic chance, environmental fluctuations, inbreeding, and rare catastrophes then have disproportionate effects. Correlated losses among subpopulations further weaken regional persistence. Linking the wording to measurable consequences for fitness, abundance, or flux gives the conclusion its scientific meaning and prevents a purely mnemonic interpretation. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.

Ref: Conservation Biology, Primack & Sher, 6th Ed., Ch. 7

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Extinction Topic

The extinction vortex was first described by:

“Gilpin and Soulé” for the extinction vortex was first described by. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. The mechanism should be evaluated across both local and global scales. Local disappearance can be reversed by recolonization, whereas global extinction is irreversible and requires the loss of every surviving population. The remaining alternatives—“Darwin and Wallace”, “Frankham and Soulé”, “Stephens and Bradshaw”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Human-driven habitat conversion, exploitation, introduced enemies, pollution, and climate change often interact rather than acting independently. Traits such as slow reproduction or ecological specialization can magnify vulnerability. Linking the wording to measurable consequences for fitness, abundance, or flux gives the conclusion its scientific meaning and prevents a purely mnemonic interpretation. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.

Ref: Conservation Biology, Primack & Sher, 6th Ed., Ch. 7

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Predator Prey Model

If a predator prefers prey1 regardless of prey2 abundance, it is due to:

In the optimal diet model, prey are ranked by expected energetic return per unit handling time, E/h. If E1/h1 exceeds E2/h2, prey 1 is the higher-ranked item and should be accepted whenever encountered. This profitability difference explains a persistent preference, but the phrase “regardless of prey2 abundance” reflects an additional prediction: acceptance of a lower-ranked prey generally depends on encounter rates with the more profitable prey, not on how abundant the lower-ranked prey itself is. When prey 1 is sufficiently common, a predator can reject prey 2 and spend search time seeking prey 1; when prey 1 becomes rare, including prey 2 may increase average gain. A long handling time for prey 2 could contribute to its lower ratio but is not the complete criterion because energy content also matters. Equal profitability would not predict a consistent ranking. Thus, the inequality correctly identifies prey 1 as more profitable, while prey 1 encounter rate determines whether strict specialization remains advantageous.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 14

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Predator Prey Model

A predator will prefer prey type P1 over P2 if:

Optimal diet theory ranks prey by profitability, usually E_i/h_i, where E_i is usable energy from prey type i and h_i is handling time. Prey type P1 ranks above P2 when E1/th1 exceeds E2/th2, because each unit of post-encounter time devoted to P1 yields more energy. The ratio, not the sum or product of energy and handling time, captures energetic return rate. A predator encountering the higher-ranked type should accept it under the basic model. Whether it also accepts the lower-ranked type depends mainly on the encounter rate with higher-ranked prey: abundant P1 can make rejecting P2 worthwhile, whereas rare P1 raises search costs and favors a broader diet. Abundance of P2 itself does not directly determine acceptance after encounter in the classic contingency model. Real choices can incorporate nutrients, capture probability, toxins, and risk, but these can be represented by adjusting expected gain or effective handling cost. The inequality therefore states a ranking rule rather than a complete prediction of diet composition.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 14

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BIODIVERSITY

According to ecological theory, maximum services are delivered when:

Ecosystem services are most reliably sustained when multiple species make substantial contributions rather than when function is concentrated in one dominant species. Even contribution raises functional evenness: different taxa participate in production, decomposition, pollination, nutrient retention, or trophic regulation, reducing dependence on a single vulnerable contributor. It can also strengthen the “insurance effect,” because species respond differently to drought, disease, or disturbance; decline of one contributor may be offset by another. This does not mean every species performs an identical role or contributes exactly the same amount. Complementarity among distinct functional traits may be more important than numerical equality, and some keystone species have disproportionate effects. Functional redundancy can buffer loss, but redundancy alone does not guarantee maximum service if redundant species all respond similarly to stress. Communities composed entirely of predators or mutualists are trophically unrealistic and omit processes needed for complete ecosystem functioning. Among the alternatives, even contribution best captures broad participation and low dominance. The general principle is that service delivery depends on abundance distribution, functional identity, and complementarity together, so evenness supports stability without implying that species are ecologically interchangeable.

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

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