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
Immigration
Emmigration
Natural Selection
Mutations
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 speciation
Allopatric: Occurs when species become geographically
isolated.
Sympatric: Occurs through ecologically isolating mechanisms.
Eg polyploidy
Pg 247 Biozone
Allopatric Speciation
Mainland Robin
Pg 251 Biozone
Chatham Island Robin
Instantaneous speciation
• Eg Polyploidy in wheat
20 Chromosomes
40 Chromosomes
NZ Example- Manuka
Reproductive Isolating Mechanisms
These lead to speciation
These can be
Prezygotic: before fertilisation
Postzygotic: 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.
A
A
B
C
C
D
D
E
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
D
E
C
F
B
A
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 sharks
Pg 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
Cretaceous
Megafaunal
The 6th extinction
225mya
65mya
10,000ya
present
90%marine org
dinosaurs
mammals-hunt
reef/ rainforest