Correct Response: D. Geographical isolation is when a physical barrier, such as a glacier, separates a population of organisms into multiple smaller populations and prevents gene flow between the smaller populations. The separated populations are subject to the selective pressures of their respective geographical locations and may evolve into distinct species through allopatric speciation. In character displacement (A) the differences among similar species are accentuated when they live in overlapping geographical regions. Competition for resources favors the selection of the traits in each species that allow each species to take advantage of different niches, resulting in reduced competition for resources. Punctuated equilibrium (B) is a model of evolution that proposes that species remain relatively stable over long periods and that evolution tends to happen in spurts. In adaptive radiation (C), a particular lineage evolves into many different species within a relatively short period of time after a change to the environment alters available resources and niches.
