10 public questions tagged with this topic.
Species with a Type II survivorship curve, such as birds, experience a constant mortality rate at all life stages.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Interactions - Predation and Herbivory
“Narrow niche and limited environmental tolerance” for specialists species are more prone to extinction due to. 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—“Broad niche”, “High reproductive rates”, “Generalist diet”—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. 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: Concepts and Applications, Molles, 9th Ed., Ch. 13
“Interspecific competition” for realized niches generally become smaller than fundamental niches because of. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. 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 remaining alternatives—“Genetic drift”, “Natural selection”, “Population growth”—refer to different states, processes, or scales and therefore do not express the same causal relationship. 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. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 13
The rescue effect occurs when immigrants enter a small, declining local population and reduce its probability of extinction. New arrivals add individuals directly, can increase reproduction by supplying mates, and may restore genetic variation or reduce inbreeding. The patch remains occupied throughout; immigration “rescues” it before abundance reaches zero. This differs from recolonization, which establishes a population in a patch after local extinction has already occurred. In metapopulation models, both processes depend on connectivity, but they affect occupancy in different ways: rescue lowers the local extinction rate, whereas recolonization raises the colonization rate of empty patches. Predator control and resource reallocation are management actions, not the defining mechanism. Increased reproduction may contribute after immigrants arrive, but immigration is the causal link between patches. Very high connectivity can also synchronize populations or spread disease, so more dispersal is not always beneficial. The rescue effect is strongest when donor populations provide migrants and the recipient patch remains suitable enough for those migrants to survive and reproduce.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 9
An Allee effect occurs when individual performance declines as a population becomes very small or sparse. Individuals may struggle to find mates, cooperate in defense, modify habitat, or avoid inbreeding. Consequently, per-capita fitness rises with density over the low-density range. This positive density dependence is the reverse of the crowding effects emphasized in ordinary logistic regulation. At low density, ordinary competition weakens, but an Allee effect can reverse the expected advantage of rarity. At high density, resource depletion and social interference usually lower performance. Considering both ranges shows why population growth can have thresholds, stable equilibria, or overshoots instead of following a single simple trajectory. The key idea is the direction of the trade-off or feedback, because that direction determines the population-level outcome. Field evidence should therefore be compared with the model assumptions before extending the conclusion to every species, habitat, or time period. Interpreting the example at the appropriate population scale keeps the causal mechanism distinct from a simple correlation or an absolute rule.
Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 5
“Generalist species” for which of the following is least associated with extinction risk. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. 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. The remaining alternatives—“Narrow niche width”, “Top predator status”, “Habitat fragmentation”—refer to different states, processes, or scales and therefore do not express the same causal relationship. 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 cited framing is therefore most useful when treated as a conditional biological claim, with assumptions about scale and environmental context kept explicit.
Ref: Conservation Biology, Primack & Sher, 6th Ed., Ch. 7
“Increases extinction risk” for high population size variability. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. 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. The remaining alternatives—“Reduces extinction risk”, “Maintains stability”, “Is unrelated to extinction”—refer to different states, processes, or scales and therefore do not express the same causal relationship. 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. This distinction matters because similar surface patterns can arise through different mechanisms, whereas ecological prediction depends on identifying the mechanism that actually changes rates. The cited framing is therefore most useful when treated as a conditional biological claim, with assumptions about scale and environmental context kept explicit.
Ref: Conservation Biology, Primack & Sher, 6th Ed., Ch. 7
“High” for reproductive ability reduces extinction risk when it is. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. 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. The remaining alternatives—“Cyclic”, “Low”, “Delayed”—refer to different states, processes, or scales and therefore do not express the same causal relationship. 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. 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
“Species are top predators and hence rare” for high trophic status implies. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. 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. The remaining alternatives—“Species consume only plants”, “Organisms are decomposers”, “Species are at the bottom of the food chain”—refer to different states, processes, or scales and therefore do not express the same causal relationship. 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. Linking the wording to measurable consequences for fitness, abundance, or flux gives the conclusion its scientific meaning and prevents a purely mnemonic interpretation.
Ref: Conservation Biology, Primack & Sher, 6th Ed., Ch. 7
Eurythermal species tolerate a broad range of environmental temperatures. Their proteins, membranes, metabolic regulation, stress responses, and behaviour remain functional across wider thermal limits than those of stenothermal species. This breadth allows survival through seasonal fluctuations, movement among contrasting microhabitats, or occupation of geographically variable environments. It does not mean performance is equally high at every temperature. A tolerance curve still contains an optimum, zones of stress, and lethal lower and upper boundaries; eurythermal simply means those boundaries are relatively far apart. Reproduction only in summer describes a seasonal schedule, not thermal breadth. Migration and hibernation are possible strategies for avoiding unfavourable conditions, but neither is required in a species that tolerates them directly. Acclimatization may shift thermal performance within an individual’s plastic capacity, while evolutionary adaptation can alter the population’s range over generations. Thermal tolerance can also differ among eggs, larvae, and adults, so the most sensitive stage may set distribution limits. A broad tolerance often aids widespread species and biological invaders, although dispersal, moisture, food, and biotic interactions still constrain where they actually occur.
Ref: Evolutionary Analysis, Herron & Freeman, 5th Ed., Ch. 10
