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Lecture 4
Evolution and Life Histories
Principles of Ecology
Eben Goodale
College of Forestry, Guangxi University
Readings
• Up until now I have made reading notes for
each lecture.
• I will make one more of these for Tuesday
lecture (my wife presenting).
• It will be available Sunday night.
• After that, we will have 2 chapters of textbook
(ocassionally 1) per lecture.
Readings
• The textbook chapters will be available as .xps
files (10 pages per file).
• I will give out today pendrives with Chapters
9-12 (Apr 4, Apr 7 lectures).
• Please DO NOT give copies of these files to
anyone outside of class (technically illegal).
• I do not like distributing like this, but do so
because textbook not distributed in China,
and very expensive to buy privately.
Readings
• Please do readings before class, because it will
serve as a preparation for class.
• The exam material will, however, be directly
take from lectures, not the textbook.
• Before the exam, I will make a summary for
you on the concepts in the lectures that I will
test you on.
• Lecture PPTs will continue to be available
before class on Thursdays and Sundays.
Schedule
Lecture times:
Date
March 17
March 21
March 24
March 28
March 31
Topic
Introduction
The Physical Environment and the World’s Biomes
Will Include Comprehension Exam
Notes1
Notes2
Coping with Water, Temperature and Energy
Notes3
Evolution and Ecology; Life Histories
Notes4
Notes5
Avail on web
Sunday
Behavioral Ecology
MAY
APRIL
April 4
April 7
April 11
April 14
April 18
April 21
April 25
April 28
May2
Reading
Population Distribution, Abundance, Growth and Regulation 9, 10
Population Dynamics and Competition
Midterm Exam
Predation and Herbivory
Other Species Interactions
Holiday
The Nature and Change in Communities
Biogeography
Species Diversity; Ecosystem Productivity
11, 12
13
14, 15
16, 17
18
19, 20
May 5
Energy Flow, Food Webs and Nutrient Cycling
21, 22
May 9
May 12
Conservation Biology
Landscape and Global Ecology
23
24, 25
Review I
• We have been talking about how organisms
interact with their environment, obtaining water,
maintaining their temperature, and obtaining
energy.
• We have described features of organisms which
are “adapted（适应）” to their environment (fit
their environment due to evolution).
• We have described some examples of
“convergent evolution（趋同进化）”, where
different organisms in similar environments look
alike.
Today we talk more in depth about evolution
Today’s class
• Evolution
– Evolution as change
– Natural selection as mechanism of evolution
– Other mechanisms of evolution
– Speciation and evolutionary patterns
• Life histories
Evolution（进化） is change
• At the large time scale evolution is
modification (change) in living things over
time.
• Contrasted with creationism, which says that:
1)species were developed independently of
each other
2)species are fixed entities, they do not change
3)creation was recent
Evolution is change
Things that led Darwin to believe
in evolution:
•Fossils
•Vestigial（退化的） features
•Relations between
species
Vestigial features have lost their function,
like eyes on blind salamanders, or the
human tail bone.
Evolution is change
Things that led Darwin to
believe in evolution:
•Fossils
•Vestigial features
•Relations between
species
Galapagos “Darwin” finches…
The birds on different islands resemble
each other but also have differences.
Evolution is change
• Contrasted with creationism, which says that:
1)species were developed independently of
each other. Clear relationships among species.
2)species are fixed entities, they do not change.
Fossil animals, vestigial features.
3)creation was recent. Evidence of ancient earth.
Question: was Charles Darwin the first to postulate evolution?
Evolution is change
• At a small time scale, evolution is the change
in alleles（等位基因） (or change in gene
frequencies) in a population over generations.
• Example of allele controlling coat color, or
beak size.
An allele is an alternative version of a gene.
Natural selection is a mechanism
of evolution
• So how to explain evolution as the small time
scale in a population?
• Darwin postulated natural selection（自然选择）
as a mechanism of evolution (this was his novel
contribution).
• Let’s review the basic steps in the process.
Natural selection
What are the basic steps in this process:
1. Variation between individuals in traits
2. This variation is the trait is heritable（可继
承的）
3. In every generation, there are more
offspring produced than can survive.
4. Individuals with traits that fit the
environment well survive and reproduce.
5. More individuals in the next generation will
have the favored trait.
An important distinction:
phenotype vs. genotype
•
•
•
•
We see that the first ingredient for
natural selection is variation, and we
note that if variation is hereditary,
natural selection will occur.
BUT not all variation is genetic. Some of
how an organism appears (its
phenotype（表现型）) is
environmental. Think of a large,
spreading tree in a good sunny place,
compared to one in the middle of a
forest.
We should keep in mind that
phenotypic plasticity（表现型可塑性）
can explain variation among individuals.
What human examples can you think of?
This book
tells story
of identical
twins separated
at birth
Natural selection in action
Darwin’s Finches
Images from: Freeman and Herron (2001)
Natural selection in action
Peter and Rosemary Grant
Daphne Major
Beak of the Finch
1995
By J. Weiner
Natural selection in action
1. Variation between individuals in traits
Images from: Freeman and Herron (2001)
Natural selection in action
2. This variation is heritable
Images from: Freeman and Herron (2001)
Natural selection in action
3. In every generation, there are more offspring
produced than can survive.
# Birds
1975
1979
# Seeds
Images from: Freeman and Herron (2001)
Natural selection in action
4. Individuals with
traits that fit the
environment well
survive and
reproduce.
5. More individuals in
the next
generation will
have the favored
trait.
Characteristic
of seeds
Images from: Freeman and Herron (2001)
Large seeds
Small seeds
Natural selection in action
4. Individuals with
traits（特质）
that fit the
environment well
survive and
reproduce.
5. More individuals in
the next
generation will
have the favored
trait.
Images from: Freeman and Herron (2001)
1976
1978
Review: using another example,
explain how evolution occurred
Weight
of sheep
Horn length
1975
2005
Year
What Darwin didn’t know: genetics
and mutations.
Wild type
• We now know that
genetic information
is encoded in DNA.
• Mistakes in DNA
copying make
mutations（突变）,
which create
variation.
The simplest kind of mutation:
a point mutation where one
nucleotide replaced by another.
mRNA
A
G
U
A A G U U U G G C U A A
5
Protein
3
Lys
Met
Phe
Gly
Amino end
Stop
Carboxyl end
Base-pair substitution
No effect on amino acid sequence
U instead of C
A U G
A
A G
U
Lys
Met
U G
Phe
Missense
A
U
G U U
Gly
A
A
Stop
A instead of G
U G
A A
G U
U U
A G U U
A
A
Lysand Francis
Phe
Ser
James Met
Watson
Crick,Stop
1953
Nonsense
U instead of A
A
U G
Met
U
A G U
Stop
U
U
G G
C U
A
A
What Darwin didn’t know: genetics
and mutations.
• Mutations can also be
larger: like the deletion
of entire parts of a
chromosome.
• In addition to mutation,
recombination（重
组）, which occurs
during sexual
reproduction, also
produces variation
Mutation as an evolutionary force
• Mutation and recombination produce
variation among individuals, the first
ingredients for natural selection.
• Mutation can also be thought of as a
mechanism of evolution because it creates
new alleles.
Another evolutionary force: genetic drift
Before
After
Genetic drift（基因漂变） is the change in the
frequency of alleles in a population over time through
random events
Genetic drift
Genetic drift is
more important
factor in small
populations than
large ones.
Demonstration of
Genetic drift in simulation:
http://sites.sinauer.com/ec
ology3e/problem06.html
Cheetahs
are an example
of a small population
One example of genetic drift is when a species gets very rare
“Bottleneck”
Or when a small group of individuals starts a new colony
Another evolutionary force: gene flow
• Gene flow（基因流） is when alleles move
between populations.
• Because it tend to make populations more
similar to each other, it acts to slow evolution.
Summary of evolutionary forces
• Natural selection: increases frequency of
advantageous alleles.
• Mutation: creates new alleles.
• Genetic drift: change in frequency of alleles,
can lose to loss of alleles in small populations.
• Gene flow: movement of alleles between
populations. Tends to decrease changes in
alleles.
Only one of these mechanisms of evolution leads to adaptation.
Which is it?
Only natural selection creates
adaptations
• Adaptation is the match
of an organism to its
environment.
• A great example is the
story of the Soapberry
Bugs.
The length of beak of soapberry
bugs in different populations
There are limit to adaptations
• There needs to be the variation
for natural selection to work with.
• The history of animals limits their
possibilities. For example,
mammals that return to the sea
(dolphins) can’t just evolve the
ability to breathe under water.
• Gene flow often acts against
adaptation.
• The environment is itself
changing… so there’s a “moving
target”.
Nor can a panda immediately
evolve an opposable thumb.
What does natural selection
lead to?
What kind of selection was our bird example? Our sheep example?
Stabilizing（稳定性） selection
• Idea of trade-offs
www.kellymannophotogra
phy.com/
Size of babies
Low birth weight
often higher risk
of infection
High birth weight
complications at birth
Disruptive selection
www.blackwellpublishing.com
Back to Darwin’s finches …
what would happen if two
types of seeds were available…
very large and very small?
This kind of natural selection is rare and may
lead to speciation…
T. B. Smith, Nature, 1987
Speciation
• Speciation（物种形成）
can occur when:
– Two populations become
isolated
– Each population
undergoes evolution,
usually through natural
selection.
– When they meet again
they do not reproduce.
Speciation
• Often occurs because
these two populations
are in different places
(allopatric speciation
（区域种化）), but
can occur in same
place (sympatric
speciation（同域物种
形成）) in some
circumstances.
Famous example of
sympatric evolution, where
one population of apple
fly adapted to new invasive
tree species
Speciation
Each type of cross-bill has its
own call type (so they can
Recognize each other)
Assortative mating
How does Benkman (2003) hypothesize that speciation is occuring?
A phylogenetic (= evolutionary) tree
shows history of speciation and extinction
This recent example of
whale evolution similar to
ideas Darwin proposed in
his notebooks in the 1850’s
Story of life includes periods of mass
extinction, followed by adaptive radiations
• In history of earth, 5
mass extinction（大量
消亡） events may
have removed many
species.
• Adaptive radiations
（适应辐射） are
Adaptive radiations occur when
when a group of
organisms give rise to a new niche opens up after
many species in a short extinction (mammals after
dinosaurs), or a new place is
time
colonized (Hawaii is formed by
volcanos)
Evolution and ecology and linked
together
• Take for example, the case of
predator and prey, an
ecological relationship.
• Over time predators become
more efficient at catching prey
through natural selection.
• But at the same time, prey
become more efficient at
escaping predators!
• Ecology at one instance a
product of ever-changing
“coevolutionary（共同进化）
armsrace”.
Evolution and ecology and linked
together
• Ecology also influences
evolution:
• Take care for instance the
soapberry bugs.
• New environments (different
trees) make different kinds
of beaks adaptive.
• Leads to two different kinds
of populations and
eventually speciation.
• Ecological change has lead
to evolution.
Today’s class
• Evolution
– Evolution as change
– Natural selection as mechanism of evolution
– Other mechanisms of evolution
– Speciation and evolutionary patterns
• Life histories（生活史）
The case study of Nemo
We all know that movie’s
are not realistic… but did
you know that in real life
Nemo’s father probably
would have changed sex
and turned into a female?
Sequential （连续地）
hermaphroditism（雌雄
同体）
The diversity and complexity of
lifecycles
Release egg and sperm
Colony of identical
polyps
Polyp reproduces
asexually
Note :
•Sexual / Asexual
life phases
•Metamorphosis（变形）
Estimated 80% of
animal species undergo
Small larva floating at sea
Metamorphosis into attached polyp
The diversity and complexity of
lifecycles
Even more strange
(to humans) because
Haploid（单一的） life
stages are
multicellular.
Basic question: to be sexual or not?
• Advantages asexual
Basic question: to be sexual or not?
Advantages sexual
•Sexual reproduction
increases genetic
variability (new
combinations of genes,
recombination)
•Evidence from C.
elegans worms
Life history
• The study of life history
looks at the timing of
how organisms grow,
develop, reproduce and
survive until death.
• Stress on trade-offs
（物质交换）. For
example, early
reproduction often
means low survival.
When first
reproduce?
How many
offspring?
Size of
offspring?
How long
survive?
Trade-off I: size of offspring
Trade-off: the bigger your offspring, the less you can have of them.
For plants:
For animals:
Advantages of being BIG
• Bigger organisms have
fewer predators bigger
than they are.
• Big seeds, eggs have
more resources to
sustain when very
young
Seedling
height
An extreme in
large offspring:
the kiwi Seed size
Bigger seed, better chance
of surviving, growing
Advantages of being small
• Small things can disperse
farther
– Think small wind-blown
seeds of weedy plant.
– Or young fish that is so
small it has little resistance
to waterflow and disperses
widely
• Small things can also
undergo dormancy（休
眠）, and wait until
conditions are good to
grow.
Trade-off II: age when first reproduce
Trade-off: the more investment in reproduction early,
the less survival.
It takes a lot of energy just to find mates (fly example)
In addition, any that puts a lot of energy into reproduction has less
resources for its own growth and survival (tree example)
Trade-off II: age when first reproduce
Trade-off: the more investment in reproduction early,
the less survival.
From Santos and Nakagawa 2012
In birds, individuals with increased clutches
Survive the winter less well.
Trade-off II: age when first reproduce
• Extreme lifecycle called
semelparous（只生一胎
的） (reproduce only
once): annual plants,
insects…also bamboo,
salmon (“big-bang”).
• Only once but big
numbers.
• In contrast humans,
perrenial plants are
iteroparous（多繁殖
的）.
• Reproduce repeatedly but
not large numbers at any
one time.
Advantages of short, long life
Advantages short life
Get in, get out of new area
Think weedy plants
Advantages long life
Stick around, but face
The growing competition
r vs. K selection
• Putting together these
trade-offs, we see two
different strategies as
extremes on a continuum:
• “r species（R-选择物种）”:
short-lived species that
make many, highly
dispersible young. Think of
a weed.
• These species go to a
disturbed environment
(plowed ground), grow
quickly, reproduce, and
leave (are out-competed).
r vs. K selection
• “K species（K-选择物种）
”: long-lived species that
have only a few, large
offspring at a time, invest
in each of them.
• These species live in
mature (undisturbed)
environments which are
competitive (like a high
canopy forest).
• Hence, life histories are
influenced by ecological
stability
Note: we will understand why these species are called ‘r’ and ‘K’ when
we talk about population growth.
Explaining the clownfish strange
system
• Clownfish live in anemones, stinging
stationary animals, and are immune
to the sting.
• Tiny young are planktonic and
disperse widely
• Larger fish find anemones, which can
support several fish; the group of
fish at one anemone are not related.
• There’s a strong hierarchy among
these fish: the biggest fish is the
breeding female, second biggest
breeding male, others are sexually
immature.
• If breeding female dies, male
changes sex and becomes female.
Explaining the clownfish strange
system
What could explain this
strange system?
• Predation on reef very
high, so small fish leave.
• Large fish able to invest
more in eggs (the larger
gamete), so the largest
fish are female.
• Why do smaller fish wait
their turn?
Homework
• Go over lecture notes again (Lecture 4).
• By Sunday night, lecture 5 with notes available
on internet; read over.
• http://sites.sinauer.com/ecology3e/problem0
6.html This is the problem we looked at in
class today.
• Reading for lecture 5: Petrie 4 on sexual
selection in peacocks.
Key concepts
• Evolution is the modification
of living things over time, and
change in gene frequencies in
a population.
• Natural selection is the only
mechanism of evolution that
produces adaptation, a fit
between organism and
environment. But there are
other mechanisms of
evolution: mutations, genetic
drift and gene flow.
• Speciation and extinction
describe patterns of life over
long timescales.
• Life histories describe the
timing of birth, reproduction
and death; in many organisms
they involve transitions
between different life stages.
• The environment where an
organism lives influence its life
histories: stable environments
favor long-lived organisms that
invest heavily in a few
offspring, whereas quicklychanging environments favor
short-lived organisms with
many small offspring.