• The process by which many species evolve from a common ancestor is known as adaptive radiation

• The Original Common ancestor was under intense competition from other species and is unable to exploit the full range of ecological niches.

Stages of adaptive radiation

Stage 1

New population forms in environment lacking competition and is able to exploit the range of ecological niches.

A niche is a description of an organisms lifestyle and is best understood as its type of feeding e.g. predator, herbivore, parasite etc

Adaptive Radiation

Stage 2

Reduced selection pressures allow population to increase in number.

Stage 3

Individuals with novel features (alleles) move into new ecological niches in order to reduce competition.

Stage 4

Natural Selection combined with barriers (mainly ecological) result in many sub-populations forming from the original.

Stage 5

Sub-populations evolve into many species adapted to wide range of environments.

Examples of adaptive radiation include :-

Darwin’s finches :-

Marsupials in Australia see fig. 19.2 p 140 and table 19.1

Their different shaped mouth parts allow them to eat different foodstuffs

Cichlids in lake Malawi

Honeycreeper found in Hawaii

• Evidence for adaptive radiation is shown by homologous structures.

• Homologous structures are structures which have similar anatomy but may have different functions –

Homologous structures

• Homologous structures show divergent evolution where common features have been adapted for different functions

Thigh

Lower leg

Ankle

Upper arm

Forearm

Wrist

Hand Foot

Pentadactyl Limb

Convergent evolution is the process by which features of differing origins are adapted form similar functions

Convergent Evolution

e.g. Wings of bats, birds and insects

the jointed legs of insects and vertebrates;

tail fin of fish, whale and lobster eyes of the vertebrates and squid and octopus