Transcript General Ecology

General Ecology
Basic Principles
Basic Principles
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Definition of principle / law:
– Hypothesis
– Theory
– Law
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How do we test hypotheses?
– Support or falsification?
– Consequences of a wrong decision
Scientific Method
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Science is a process of conjecture and
refutation.
– Each time we make a decision about a
conjecture, we might be wrong.
– Consider the definitions of the following
words: Truth, Fact, Reality, Belief, and
Proof.
– Now, as an example, consider how a bat
views the world.
What are the basic principles of
Ecology?
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Laws of physics and chemistry.
– Laws of thermodynamics
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Evolution via natural selection.
– Definition of evolution:
– Organic evolution is defined as a change in
allele frequencies over time.
Some examples of evolution
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The peppered moth in England.
Kangaroo rats in California
domestic dogs
People
– Diabetes
– Skin color
– Height???
How does evolution work?
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Darwin’s observations:
– There is variation amongst organisms.
– That variation is heritable.
– Some forms of variation are better than
others.
– Those organisms with the better forms of
variation survive longer, and produce more
offspring.
How does evolution work?
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What is the consequence of these
observations?
– Changes in allele frequencies over time.
Important point!
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Notice, we did not use the idea “survival
of the fittest.”
– This idea was used to justify ‘social
darwinism’ earlier this century.
– What we as ecologists mean by ‘fittest’ is
not the same as what the general public
thinks.
– Fitness refers to production and survival of
progeny.
Another important point!
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Evolution is not theory, it is law
(principle). This does not mean it is
true, it means that the hypothesis has
been tested extensively, and never
falsified.
The veracity of evolution says nothing
about the existence of a supreme being.
Forms of natural selection
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Stabilising selection.
– Here, the extremes
of the phenotyps
distribution are
selected against,
while the center of
the phenotype
distribution is
selected for.
Forms of natural selection
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Directional selection
– Here, one end of the
phenotype
distribution is
selected for, while
the other end is
selected against.
The result is a shift in
the phenotype
distribution.
Forms of natural selection:
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Disruptive selection
– Here, both extremes
of the phenotype
distribution are
selected for, while
the middle of the
phenotype
distribution is
selected against.
Forms of natural selection
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Sexual selection
– Here, members of one sex select specific
characteristics in the opposite sex.
– Consider the secondary sexual
characteristics in humans, colors in birds,
sexual size dimorphism in mammals,
dewlaps in Anoles, reverse sexual size
dimorphism, etc.
– Sexual selection is important because the
resource is limiting.
Forms of natural selection
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Kin selection
– We often observe behaviors that are
difficult to interpret. For example, green
woodhoopoes remain at the natal nest and
help their parents rather than establish
their own nests.
– Prairie dogs give alarm calls to warn of
coyotes.
Forms of natural selection
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Kin selection cont.
– These patterns make sense only in the
context of inclusive fitness.
– There are examples from humans:
• who is most likely to rush into a burning house
to save a child?
• Does altruism exist, or can it be explained as a
selfish act?
Forms of natural selection
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Group selection
– This idea is derived from a book by V. C.
Wynn-Edwards back in the early 60’s.
Wynn-Edwards was trying to explain the
fact that few organisms overpopulate their
habitats (except humans apparently). He
suggested that lemmings committed
suicide by going over the cliffs of Dover,
for the good of the species.
Forms of natural selection
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Group selection cont.
– Walt Disney picked up on this, and
produced a film for his weekly ‘Wonderful
World of Disney’ back in the 60’s. It has
become an urban legend that lemmings
commit suicide. They do not. How did
Disney film the mass suicide?
Forms of natural selection
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At what level does natural selection
operate?
– Allele?
– Chromosome?
– Cell?
– Organism?
– Population?
– Species?
How does speciation occur?
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Natural selection is only the mechanism
by which most evolution occurs. In
order to understand the history of life on
earth, we must understand how
speciation works.
We need: some form of reproductive
isolation.
Reproductive isolation
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Behavioral
Temporal
Morphological
Social
Geographic
Speciation
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Once there is reproductive isolation,
there must be selection which produced
different phenotypes/genotypes in the 2
groups. Thus, if the groups again
become sympatric, there will not be
gene flow.
A species is a group of individuals that
is reproductively isolated from other
such groups. Obviously, there are
problems with this definition.
Consider some examples:
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Rasenkreise of salamanders and pocket
mice.
K-rats in California
Domestic dogs.
Humans?
Even though we rarely (note, I did not
use never) observe speciation, it clearly
happens.
More examples
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Convergence in design
– hedge hogs, porcupines, and echidnas.
– Whales & dolphins, penguins, and tuna
(note: the writers of the Bible did not
realize whales were mammals - neither do
most people).
Pilot whale (porpoise)
Killer Whales
False killer whales
Emperor Penguins
If speciation occurs, what can we
say about the history of life?
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Consider the homologies between
organisms. For example: limb structure
in vertebrates; circulation in fish,
amphibians, reptiles, mammals, and
birds; distribution of sebaceous glands
in vertebrates; heterochrony in humans
and chimps. What is the ultimate
homology? The genetic code.
Now, are we biased in any way?
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Of course.
– Gradualism: the idea that all evolutionary
change is slow and stately.
– Progressivism: the idea that evolution
leads to some pinacle or perfect form
(presumably us).
– Determinism: the idea that our fates are
predetermined.
Evolutionary biases
– Adaptationism: the idea that we are
perfectly adapted to our environment.
– Consider the panda, consider your pinky or
your baby toe, or consider your ear lobes.