Community Processes
Competition Theory
Competition Theory
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Competition is the cornerstone of
Darwin’s view of nature.
If resources are limiting, we expect
some individuals to be better at getting
available resources than others.
What happens to the individuals that are
better at getting resources?
Competition Theory
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Actually, competition operates on 2
levels:
– Intraspecific competition.
– Interspecific competition.
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Which do you think is more important?
In which case are resources most likely
to be limiting?
Competition Theory
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In reality, most of our competition theory
in biology comes from the world of
business.
Consider 2 fast food restaurants, like
Burger King and MacDonalds.
– Are the restaurants competing for some
resource?
– Are they doing exactly the same thing?
Competition Theory
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Both restaurants serve fast food.
Both restaurants cater to the lunch and
high-school crowds.
Both restaurants installed ‘kiddie parks.’
Both restaurants modify their menus in
response to consumer demands.
Both restaurants advertise heavily.
Competition Theory
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Are the 2 restaurants identical? Do they
attempt to carve out different consumer
niches? Can you identify a difference in
the customer base of the 2 chains?
Now consider Hardee’s. How does this
restaurant stack up?
What is going on here?
Competition Theory
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How do you get rich in business?
Henry Kaiser (Industrialist, ship builder,
autos, aluminum, electronics, steel,
dams, health insurance etc.) siad: Find
a need and fill it.
What is the implication? Find
something that other businesses are not
doing, and do that.
Competition Theory
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Imagine you wanted to start a chain of
fast food restaurants.
– Would you try to mimic MacDonalds or
Burger King, because their formula works,
or would you try something unique and
different?
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Henry Kaiser learned all about
competition when he tried to break into
the auto industry.
Competition Theory
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In a biological sense, the first real
demonstration of competition theory
was performed by Gause in the 1930’s.
Gause used 2 species of Paramecium.
– When the first species was grown alone in
a petri dish, it showed logistic population
growth.
– When the second species was grown
alone in a petri dish, it too showed logistic
population growth.
Competition Theory
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However:
– When both species were grown together in
the same petri dish, one species grow
logistically (although with a reduced growth
rate) while the second species grew
logistically at first, but then crashed.
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The became known as the competitive
exclusion principle.
Competition Theory
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Gause’s result was this:
– No two species can occupy the same
niche at the same time.
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What is a niche?
– For want of a better definition, it is the total
of all resources used by a species.
Competition Theory
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Now, think back to the burger
restaurants: No two restaurants can
occupy the same niche at the same
time. Do they?
Competition Theory
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There is a flip side to Gause’s work:
– Gause added crushed glass to the bottom
of his petri dish, and started cultures of
both species of Paramecium.
– This time, both species were able to
coexist. Why? They were now able to
sub-divide the ‘habitat.’
Competition Theory
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Notice, there is at least one requirement
that is very important: RESOURCES
MUST BE LIMITING.
With the paramecia, extinction occurred
after resources became depleted.
Without limiting resources, there is no
competition.
As an example, consider coyotes and
wolves.
Competition Theory
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The range of the wolf has contracted
over the last 200 years, while that of the
coyote has expanded dramatically.
30 years ago, the coyote was a rare
sight in LA. Now it is the most common
road-kill on LA freeways.
What happened?
Competition Theory
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To aid our thinking, we need a
conceptual model:
– Resource availability curves
– Resource utilization curves
– Resource / Niche overlap
– Niche width
Competition Theory: conceptual
model.
Competition Theory
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Consider foxes:
– Do arctic foxes and grey foxes use the
same resources?
– Do they use the same resources in the
same way?
– Are their niches different?
• Temporal differences?
• Spatial differences?
Competition Theory
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What happens if the resource axis is
multidimensional?
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Clearly, organisms use a variety of
resources, not just one.
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We should be talking about a multidimensional niche.
Competition Theory
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It is important to know if the various
resource axes are dependent or
independent.
If the resource axes are independent,
then there will be overlap as expected.
If the resources are positively
dependent, there will not be overlap.
Competition Theory
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What happens if the resources are
negatively dependent?
Competition Theory
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Consider some additional examples:
– Primates
• Chimps, Gorillas, Lemurs, and Orangutans.
– Penguins?
Competition Theory
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Do we have any hard evidence for the
existence of interspecific competition?
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We have data about clinal variation.
– A cline is a change in some aspect of an
organisms physiology or morphology, over
some distance.
Clinal Variation
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Consider eastern and western
meadowlarks.
Body sizes in mammals in the north vs.
the south.
Body proportions in mammals in the
north vs. south.