Community Processes

Competition Theory

Competition Theory

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

Actually, competition operates on 2 levels:– Intraspecific competition.– Interspecific competition.

Which do you think is more important? In which case are resources most likely

to be limiting?

Competition Theory

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

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

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

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

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?

Henry Kaiser learned all about competition when he tried to break into the auto industry.

Competition Theory 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

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.

The became known as the competitive exclusion principle.

Competition Theory

Gause’s result was this:

– No two species can occupy the same niche at the same time.

What is a niche?– For want of a better definition, it is the total

of all resources used by a species.

Competition Theory

Now, think back to the burger restaurants: No two restaurants can occupy the same niche at the same time. Do they?

Competition Theory

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 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

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

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

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

What happens if the resource axis is multidimensional?

Clearly, organisms use a variety of resources, not just one.

We should be talking about a multi-dimensional niche.

Competition Theory

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

What happens if the resources are negatively dependent?

Competition Theory

Consider some additional examples:– Primates

• Chimps, Gorillas, Lemurs, and Orangutans.

– Penguins?

Competition Theory

Do we have any hard evidence for the existence of interspecific competition?

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

Consider eastern and western meadowlarks.

Body sizes in mammals in the north vs. the south.

Body proportions in mammals in the north vs. south.