Practice question

The keyed exception is “Mainland continents.” In the context of which is not considered an island according to island biogeography theory, that statement differs from the governing ecological pattern and must be evaluated against the mechanism rather than accepted from wording alone. 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—“Oceanic islands”, “Peaks of mountains”, “Isolated springs in deserts”—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.