Adpative Radiation

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Adaptive Radiation

Adaptive radiation occurs when a single species evolves into a number of distinct but

closely related species. Each new species fi lls a diff erent ecological niche. Th is process

usually occurs when a variety of new resources become available-resources that are

not being used by other species.

Consider the example of Darwin's fi nches (Figure 1). Here, a group of 13 species

that live in the Galapagos Islands evolved from a single species. Let us assume that the

original species of fi nch living on the mainland of South America had a medium-sized

bill ideally suited to feed on certain medium-sized seeds. Individuals born with slightly

smaller bills might have been better at eating smaller seeds, but they might have faced

stiff competition from other bird species that were already specialized in feeding on the

smaller seeds. Finches eating larger seeds would also face similar competition.

Th e result

adaptive radiation the relatively rapid

evolution of a single species into many

new species, fi lling a variety of formerly

empty ecological niches

mangrove _nch

warbler _nch

woodpecker _nch

large tree _nch

medium tree _nch

small tree _nch

large ground _nch

sharp-beaked _nch

cactus _nch

medium ground


large cactus


small ground








insect-eating species

seed-eating species


Figure 1 Thirteen species of Darwin's fi nches are the result of recent adaptive radiation and fi ll

many different ecological niches. Genetic evidence shows they all evolved from a single common

ancestor species.

NEL 8.3

was stabilizing selection on the mainland fi nches to stay in their specialized ecological

niche. An entirely diff erent fate awaited individuals of this fi nch species once they

reached the Galapagos Islands (Figure 2). Instead of hundreds of other species of...