#species colonization

Biogeography

A new and empty island initially has:

“High immigration and low extinction” for a new and empty island initially has. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. 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. The remaining alternatives—“High extinction and low immigration”, “Low immigration and high extinction”, “Both high immigration and high extinction”—refer to different states, processes, or scales and therefore do not express the same causal relationship. At equilibrium, species identities can continue to turn over even when richness is approximately stable. The model predicts a balance of rates, not an absence of colonization or extinction. 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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Island

The 'source pool' refers to:

“Mainland or nearby habitat” for the 'source pool' refers to. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. At equilibrium, species identities can continue to turn over even when richness is approximately stable. The model predicts a balance of rates, not an absence of colonization or extinction. The remaining alternatives—“Island itself”, “Island vegetation”, “Predation pressures”—refer to different states, processes, or scales and therefore do not express the same causal relationship. 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. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors. 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: The Theory of Island Biogeography, MacArthur & Wilson, Ch. 2-4

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Island

Factors primarily influencing colonization rates on islands:

“Distance from mainland” for factors primarily influencing colonization rates on islands. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. 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. The remaining alternatives—“Island shape”, “Island vegetation”, “Island altitude”—refer to different states, processes, or scales and therefore do not express the same causal relationship. At equilibrium, species identities can continue to turn over even when richness is approximately stable. The model predicts a balance of rates, not an absence of colonization or extinction. 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: The Theory of Island Biogeography, MacArthur & Wilson, Ch. 2-4

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SUCCESSION

Which model suggests that any species can colonize and persist without help from others?

In the tolerance model of succession, any species capable of reaching a site may establish without needing earlier residents to improve the environment. Early and late species can therefore colonize independently, but later-successional species eventually dominate because they tolerate lower resource levels, live longer, or compete more effectively under conditions such as shade. Their success is not caused by facilitation; neither is establishment necessarily blocked by incumbents. Facilitation instead requires pioneers to create conditions needed by successors. Inhibition gives residents a negative priority effect, making later establishment difficult until the first occupants die or are disturbed. The phrase “persist without help” captures tolerance only if it means colonization does not depend on previous species. It should not imply that every colonist remains forever: competitive replacement is central to the model. Dispersal still matters because a tolerant species cannot establish if it never arrives. Thus, independent establishment combined with eventual replacement according to life-history and competitive traits explains why tolerance is the appropriate successional mechanism.

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

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