#coexistence

CEP RP CD

Ecologically similar species coexist if:

“Significant niche differences arise” for ecologically similar species coexist if. 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—“Niches identical”, “Complete competition”, “Identical resources”—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. 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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Niche CD RP CEP

Niche overlap implies:

Niche overlap means that two species share some portion of resource use or environmental requirements. Greater overlap can increase the potential for competition when the shared resource is limiting, but overlap may be partial rather than identical. Identical resource use represents the extreme of complete overlap, not the general meaning of the term. Species can overlap on one axis, such as food type, while differing on another, such as feeding time or microhabitat. Conversely, measured overlap does not prove competition if resources are abundant. Completely separate niches imply zero overlap, and abiotic interactions do not describe resource sharing between species. None of the listed choices states “shared or partly shared resource use,” so the keyed wording is scientifically too strong even though it is the nearest available choice. Quantitative indices such as Pianka’s measure overlap on a continuum from none to complete identity. Interpreting those indices requires information on resource availability and fitness effects. The accepted principle is therefore common use of at least part of niche space, with competition contingent on limitation and the absence of sufficient partitioning.

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

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Predator Prey Model

Which situation favors stable coexistence?

A predator with multiple prey can persist by switching toward whichever prey is relatively abundant, reducing pressure on a prey species when it becomes rare. This frequency-dependent switching can provide each prey a low-density refuge and dampen extreme consumer–resource cycles. A broader resource base also prevents immediate predator starvation when one prey declines, although persistent predator subsidy can instead create apparent competition and harm a rare focal prey. Stability therefore depends on switching strength, functional responses, and whether prey fluctuations are synchronized. Rapid prey reproduction alone does not guarantee coexistence; it may support recovery, but delayed density dependence can amplify oscillations. Lack of predator territory has no consistently stabilizing effect, and isolated prey may escape predation locally but do not by themselves establish dynamical coexistence. Among the alternatives, multiple prey provide the clearest mechanism for buffering food availability and distributing predation. The conclusion is conditional rather than universal: generalist predators stabilize coexistence most effectively when they preferentially attack common prey instead of maintaining heavy pressure on a declining species.

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

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Predator Prey Model

Predators are unable to drive prey to extinction if:

A limited predator carrying capacity prevents predator numbers from increasing without bound as prey become rare. If predator survival and reproduction depend strongly on the focal prey, declining prey reduces the resource base, causing predator decline before every prey individual can be removed. Refuges, handling constraints, territoriality, and alternative food webs may further permit persistence. This negative feedback can protect prey from extinction: low prey density supports fewer predators, reducing total predation pressure. Density-independent predator growth would remove that stabilizing response and could intensify prey loss. Mimicry may reduce capture probability for particular prey but is not the general condition described, while an absent prey population is already extinct. The statement is not an absolute law—predators introduced to naïve, spatially restricted prey can cause extinction, especially if predators are subsidized by alternative prey. In the intended single-resource system, however, resource-limited predator carrying capacity creates a numerical response that weakens predation as prey decline, favoring coexistence rather than complete elimination.

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

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