1. Divergence & adaptive radiation

2. Divergence
Occurs when two or more species result from a common ancestor – typically this is by allopatric speciation when two populations become geographically isolated.
Difference selection pressures in the different environments result in 2 populations diverging as different phenotypes are selected for to meet the demands of the new environment.
The populations may diverge enough (accumulation of different alleles in the gene pool) that reproductive isolation (hence speciation) results.

3. Adaptive radiation A type of divergent evolution.
Involves rapid evolution of a large number of species from an ancestral group to occupy a variety of different ecological niches that may have become available suddenly.
EG – members of an ancestral species move into new environments. They may out-compete and displace other species, or habitats may become available through a catastrophic event (dinosaur extinctions allowed mammals to occupy vacant niches). Populations are subject to new selection pressures and new adaptations evolve. Geo iso may occur. Accumulation of new alleles in the isolated gene pools result in reproductive isolation and therefore new species form.

4. Adaptive radiation
May result from a sudden decrease of competition which can happen in two ways:
Evolution of some new structure, physiology or behaviour enabling exploitation of a different aspect of habitat.
Geographical isolation from competitors or predators.
EG – Displayed in the evolution of Australian marsupials, with many different species evolving to fill a diversity of niches from a common ancestor.

5. Homologous structures
Important source of evidence for divergence and adaptive radiation.
Features that are similar in structure and origin but different in function.
Similarity indicates common ancestor, while difference in function indicates adaptation to different selection pressures in different environments.
EG – Pentadactyl limb – consists of same 5 groups of bones that have been modified, according to function in modern vertebrate species. Forelimbs and hindlimbs may be used in different ways, but their basic anatomical structure is the same.

6. Adaptive radiation in NZ
Read the examples scanned onto the blog.

7. Convergent evolution
Occurs when two or more unrelated species evolve to resemble each other as a result of being subject to similar selection pressures.
This results in analogous structures – different evolutionary origins that appear very similar because they carry out the same or very similar functions.
EG – wings of birds and insects, Australian marsuials and other placental animals (mole, anteater etc) Rodents and rabbits are only distantly related but both have incisors that wear into a chisel shape.
Resemblances are always superficial. A dolphin is more similar to a bat and a rabbit than to a shark.
Convergence is purely phenotypic, being confined only to certain body features linked to adaptation to a particular niche. At the genetic level, all evolutionary pathways diverge.

8. Parallel evolution
Occurs when two or more related groups evolve along similar lines independently.
EG – Flightlessness has occurred independently in a number of NZ chafer beetles all of which are found in the South Island.
There is no clear cut distinction between convergence and parallel evolution since the degree of relatedness between the evolutionary starting points may vary from extremely close to very distant.
The closer the evolutionary starting points, the more convergence intergrades with parallelism.

9. Co-evolution
A reciprocal evolutionary change where a change in a feature of one species acts as selection pressure for change in a feature of another unrelated species.
Both species have a strong ecological relationship with eachother.
EG – evolutionary change in the structure of a plant may act as selection pressure to bring evolutionary change in a herbivore that eats that plant. This change on the herbivore then acts as a selection pressure for a change in the plant to reduce being eaten. And so on.
See examples scanned in from the blog 