Evolution 3.5

Darwin’s Observations– Species have high reproductive rates but selection

pressures act to create a struggle for existence– There is variation in offspring, some better

adapted than other.– Those best adapted will survive longer and

therefore have an increased chance of passing on their favourable characteristics

– Fittest will survive– It is from Darwins observations that his theory of

Natural Selection was devised.

Gene Pools

• Gene Pool: all the genes in the population

Factors which affect the gene pool

ImmigrationEmmigrationNatural SelectionMutations

Genetic Drift

Genetic Drift: Allele frequency’s change over time (drift)Founder Effect: A small number of individuals colonise a new area.Bottleneck Effect: Where the population is reduced due to a catastrophic effect.

Fitness

• Fitness is the measure of how well suited an organism is to its environment.

The Species Concept• A species is a group of individuals which can interbreed to

produce fertile offspring.

Speciation is the process by which one or more new species are formed.

There are different types of speciationAllopatric: Occurs when species become geographically isolated.Sympatric: Occurs through ecologically isolating mechanisms. Eg

polyploidyPg 247 Biozone

Allopatric Speciation

Mainland Robin Chatham Island RobinPg 251 Biozone

Instantaneous speciation

• Eg Polyploidy in wheat

20 Chromosomes 40 Chromosomes

NZ Example- Manuka

Reproductive Isolating Mechanisms

These lead to speciationThese can bePrezygotic: before fertilisationPostzygotic: after fertilisation

Prezygotic Barriers

• Temporal- different breeding times• Behavioural- different courtship patterns• Structural- different reproductive structures• Gamete Incompatability- gametes cant fuse,

may have wrong enzymes etc.

Postzygotic Barriers

• Hybrid Invariability: even if fertilisation occurs the chromosome numbers may not match up and the zygote may not develop

• Hybrid sterility: They may reach maturity but be sterile eg Mules have 63 Chromosomes

• Hybrid disadvantage: Hybrids may be less likely to survive. (not to be confused with hybrid vigour)

Deme

• A local interbreeding population of a species.

Niche Differentiation

• Where species have very recently evolved from an existing species they will still have very similar adaptations and will strongly compete. This is where Gauses principle applies.

Character Displacement

• Where the ranges of these 2 species overlap the visible differences between the 2 species may become more pronounced. This is called Character displacement.

• Mate recognition?• Where the 2 species are geographically

separated they often remain very similar.

A Cline

A cline is a gradient of phenotypic character along a geographic variable such as latitude or altitude.

AB

C

D

E

A

C

D

Examples

• Salamanders on the east coast of USA

NZ Example- Ranunculus insignis

• Lobing in the leaf increases as we travel further south

NZ Example-Tomtits

• North Island tomtits have shorter tails and wings than south Island tom tits. This gradually happens as you travel down the country.

Ring Species

• A special type of cline where the demes(local populations) are arranged in a circle across the species range and the demes at the ends, although adjacent may be unable to interbreed.

• Pg 246 Biozone

A

B

C

D E

F

G

Types of evolution

• Divergent Evolution: Isolation of a population leads to reproductive barriers, eventually a new species forms.

Types of evolution

• Adaptive Radiation: Evolutionary diversification of related species into different environments or ways of life.

Types of evolution

• Convergent evolution: The independent evolution of similar features in unrelated species.

Eg Dolphins and sharksPg 259- 260 Biozone

Analogous Structures

• Same function and external appearance, but quite different origins.

Parallel evolution

• Some biologists argue that this is just convergent evolution.

• It is the development of similarities in separate but related evolutionary lineages.

Gradualism and Punctuated Equilibrum

• Pg 263 Biozone

Co- Evolution

• 2 species evolve together to form a mutually beneficial relationship. They may become dependant on one another for survival.

• Pg 261-2 Biozone

Summary of evolutionary types

Extinction

Major periods of extinction

• Pg 271 Biozone• Permian 225mya 90%marine

org• Cretaceous 65mya dinosaurs• Megafaunal 10,000ya mammals-

hunt• The 6th extinction present reef/

rainforest