#biological invasions

SPECIES

Which statement describes the biotic resistance hypothesis correctly?

“Species-rich communities resist invasions better” for which statement describes the biotic resistance hypothesis correctly. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. The inference is strongest when the relevant variables, spatial boundary, and time scale are explicit. Context can alter the magnitude of an effect without changing the definition of the focal concept. The remaining alternatives—“Low biodiversity resists invasive species”, “Species-poor communities resist invasions better”, “High biodiversity always leads to invasions”—refer to different states, processes, or scales and therefore do not express the same causal relationship. A sound explanation connects the stated pattern to a causal pathway and distinguishes it from alternatives that describe different levels of organization or different ecological processes. The cited framing is therefore most useful when treated as a conditional biological claim, with assumptions about scale and environmental context kept explicit.

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

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SPECIES

Which hypothesis suggests invasive species thrive due to lack of natural enemies?

“Enemy release hypothesis” for which hypothesis suggests invasive species thrive due to lack of natural enemies. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Species management must identify the demographic stage and ecological process that most strongly limits population growth. Prevention, early detection, removal, habitat manipulation, and biological control act at different points in an invasion or recovery trajectory. The remaining alternatives—“Novel weapons hypothesis”, “Empty niche hypothesis”, “Biotic resistance hypothesis”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Effective control reduces propagule pressure or population growth without causing unacceptable non-target effects. Repeated monitoring is necessary because seed banks, dormant stages, recolonization, and density-dependent compensation can reverse short-term gains. 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: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation

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Species Control

Characteristic generally NOT true for invasive species:

The keyed exception is “Less likely to invade species-rich ecosystems.” In the context of characteristic generally not true for invasive species, that statement differs from the governing ecological pattern and must be evaluated against the mechanism rather than accepted from wording alone. Species management must identify the demographic stage and ecological process that most strongly limits population growth. Prevention, early detection, removal, habitat manipulation, and biological control act at different points in an invasion or recovery trajectory. The remaining alternatives—“Greater phenotypic plasticity”, “High dispersal ability”, “High competitive ability”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Effective control reduces propagule pressure or population growth without causing unacceptable non-target effects. Repeated monitoring is necessary because seed banks, dormant stages, recolonization, and density-dependent compensation can reverse short-term gains. 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: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 21

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Types of Species

Which hypothesis explains invasive species' success due to lack of natural enemies?

“Enemy release hypothesis” for which hypothesis explains invasive species' success due to lack of natural enemies. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Management outcomes depend on scale and context: suppressing abundance at one site does not guarantee regional eradication when dispersal reconnects treated and untreated populations. The remaining alternatives—“Novel weapons hypothesis”, “Empty niche hypothesis”, “Propagule pressure hypothesis”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Species management must identify the demographic stage and ecological process that most strongly limits population growth. Prevention, early detection, removal, habitat manipulation, and biological control act at different points in an invasion or recovery trajectory. 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: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation

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