Download Lecture 3 Evolutionary rescue and Evolution 101

This lecture
• What is evolution, and how does it work?
• Why might evolution matter for species’
responses to climate change?
• How can we predict whether evolution will
occur?
What is Evolution?
Any change across successive generations in the
genetic makeup of biological populations.
What is Evolution?
Any change across successive generations in the
genetic makeup of biological populations.
Biston betularia
Darwin’s Logic
Fact 1: Every species would
increase exponentially if all
offspring survived.
Fact 2: Most populations
are relatively stable.
Fact 3: Natural resources
are limited.
Darwin’s Logic
Fact 1: Every species would
increase exponentially if all
offspring survived.
Fact 2: Most populations
are relatively stable.
Fact 3: Natural resources
are limited.
Inference 1: Since more individuals are produced than can be supported by the
available resources, there must be a ‘struggle for existence.’
Inference 2: Survival is not random, but depends in part on the hereditary
constitution of surviving individuals. This unequal survival constitutes the
process of natural selection
Darwin’s Logic
Fact 1: Every species would
increase exponentially if all
offspring survived.
Fact 2: Most populations
are relatively stable.
Fact 3: Natural resources
are limited.
Inference 1: Since more individuals are produced than can be supported by the
available resources, there must be a ‘struggle for existence.’
Inference 2: Survival is not random, but depends in part on the hereditary
constitution of surviving individuals. This unequal survival constitutes the
process of natural selection
Fact 4: No two individuals are
exactly the same; populations
have enormous variability
Fact 5: Much of this variation is
heritable.
Darwin’s Logic
Fact 1: Every species would
increase exponentially if all
offspring survived.
Fact 2: Most populations
are relatively stable.
Fact 3: Natural resources
are limited.
Inference 1: Since more individuals are produced than can be supported by the
available resources, there must be a ‘struggle for existence.’
Inference 2: Survival is not random, but depends in part on the hereditary
constitution of surviving individuals. This unequal survival constitutes the
process of natural selection
Fact 4: No two individuals are
exactly the same; populations
have enormous variability
Fact 5: Much of this variation is
heritable.
Inference 3: Over the generations, the process of natural selection will
lead to a continuing gradual change of populations, that is, to evolution.
Demographic effects of adaptation: a thought experiment
N t+1=Nt+0.2*Nt(100-Nt/100)
generation 1
New stressor kills 50% per generation
N t+1=Nt+0.2*Nt(100-Nt/100) – 0.5Nt
generation 2
New stressor kills 50% per generation
N t+1=Nt+0.2*Nt(100-Nt/100) – 0.5Nt
generation 3
New stressor kills 50% per generation
N t+1=Nt+0.2*Nt(100-Nt/100) – 0.5Nt
generation 4
New stressor kills 50% per generation
N t+1=Nt+0.2*Nt(100-Nt/100) – 0.5Nt
generation 5
New stressor kills 50% per generation
N t+1=Nt+0.2*Nt(100-Nt/100) – 0.5Nt
generation 6
New stressor kills 50% per generation
N t+1=Nt+0.2*Nt(100-Nt/100) – 0.5Nt
generation 7
New stressor kills 50% per generation
N t+1=Nt+0.2*Nt(100-Nt/100) – 0.5Nt
generation 7
New stressor kills 50% per generation
N t+1=Nt+0.2*Nt(100-Nt/100) – 0.5Nt
generation 8
New stressor kills 50% per generation
N t+1=Nt+0.2*Nt(100-Nt/100) – 0.5Nt
generation 9
N t+1=Nt+0.2*Nt(100-Nt/100) – 0.5Nt
generation 10
What if there is genetic variation?
Without
variation
Without genetic variation
With genetic variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5N
100
90
Population size
80
With
variation
70
60
50
40
30
20
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5NS
10
0
1 2 3 4 5 6 7 8 9 10
Generation
resistant
susceptible
generation 1
What if there is genetic variation?
Without
variation
Without genetic variation
With genetic variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5N
100
90
With
variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5NS
Population size
80
70
60
50
40
30
20
10
0
1 2 3 4 5 6 7 8 9 10
Generation
generation 2
What if there is genetic variation?
Without
variation
Without genetic variation
With genetic variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5N
100
90
With
variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5NS
Population size
80
70
60
50
40
30
20
10
0
1 2 3 4 5 6 7 8 9 10
Generation
What if there is genetic variation?
Without
variation
Without genetic variation
With genetic variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5N
100
90
With
variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5NS
Population size
80
70
60
50
40
30
20
10
0
1 2 3 4 5 6 7 8 9 10
Generation
What if there is genetic variation?
Without
variation
Without genetic variation
With genetic variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5N
100
90
With
variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5NS
Population size
80
70
60
50
40
30
20
10
0
1 2 3 4 5 6 7 8 9 10
Generation
What if there is genetic variation?
Without
variation
Without genetic variation
With genetic variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5N
100
90
With
variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5NS
Population size
80
70
60
50
40
30
20
10
0
1 2 3 4 5 6 7 8 9 10
Generation
What if there is genetic variation?
Without
variation
Without genetic variation
With genetic variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5N
100
90
With
variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5NS
Population size
80
70
60
50
40
30
20
10
0
1 2 3 4 5 6 7 8 9 10
Generation
What if there is genetic variation?
Without
variation
Without genetic variation
With genetic variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5N
100
90
With
variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5NS
Population size
80
70
60
50
40
30
20
10
0
1 2 3 4 5 6 7 8 9 10
Generation
What if there is genetic variation?
Without
variation
Without genetic variation
With genetic variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5N
100
90
With
variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5NS
Population size
80
70
60
50
40
30
20
10
0
1 2 3 4 5 6 7 8 9 10
Generation
What if there is genetic variation?
Without
variation
Without genetic variation
With genetic variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5N
100
90
With
variation
N t+1=Nt+0.2*Nt(k-Nt/k)-0.5NS
Population size
80
70
60
50
40
30
20
10
0
1 2 3 4 5 6 7 8 9 10
Generation
Evolutionary rescue occurs when a
population survives because of
evolution, when it would otherwise
have gone extinct
A central goal of this class is to understand how,
and under what circumstances evolutionary rescue
could occur in the context of climate change
What is Evolution?
Any change across successive generations in the
genetic makeup of biological populations.
Year one
Drift
Natural selection
Year two
Natural Selection
Differential reproduction or survival causes some genotypes to
increase in frequency, others to decrease
Evolution is a change in the genetic makeup of a population, but
natural selection acts on phenotypes.