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.
Darwin's finches or Galapagos finches. Darwin, 184...
English: Black smoker at a mid-ocean ridge hydroth...
English: Adaptive radiation in the charicinidaeTh 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
_nch
large cactus
_nch
small ground
_nch
vegetarian
_nch
tree
_nches
ground
_nches
insect-eating species
seed-eating species
C08-F08-OB11USB
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...