Ecology Ch. 14 Competition Model Experiments

What are pairwise interactions?

Interactions between pair of organisms

What are the 7 pair wise interactions?

Predation (+, — )

herbivory (+, —)

parasitism (+, —)

competition ( —, —)

amensalism (—, 0)

commensalism (+, 0)

mutualism (+, +)

What type of pairwise interactions is competition?

A (negative, negative) interaction that occurs when organisms of the same of different species compete over a common resource that is in short supply.

What are the six types of competition?

Intraspecific-within species

Interspecific- between species

Exploitative is indirect — species simply consume or deplete a shared resource, and the effect on competitors happens through the resource itself. (possible test question)

Interference is direct — one organism actively prevents another from accessing a resource, regardless of how abundant that resource is.

symmetric- equal impact on both competitors

asymmetric - unequal impact on competitors

NOT EXCLUSIVE

What are traits of competitoin?

Intraspecific competition is stronger than interspecific competition

Competition is mostly asymmetric

What is the niche concept?

Grinnell’s (1917) definition - Role of the organisms in the community

Hutchinson (1957) - tolerance range for environmental variation

Fundamental niche- activity range for all tolerance variables

Realized Niche- includes biotic factors

What is niche overlap?

Occurs when two niche’s of individuals overlap. If overlap is a limiting resource, competition occurs.

Bird 1 has more overlap

Bird 2 has more range

Bird 1 will be more affected by the niche overlap if Bird 2 can outcompete Bird 1.

What is the competition exclusion principle?

Proposed by Gause in 1934.

It states that two species or populations cannot inhabit the same niche because one will consistently out-compete the other. Dominant competitor will drive weaker competitor to extinction

Coexistence requires different niches

When the two individuals that feed on the same thing in different ways are bred together, one of them is driven to extinction. (Being driven to extinction is an important part of competitive exclusion)

What is the difference between competition and amensalism?

What is Tansley’s Bedstraw experiment?

G. sylvestre and G saxatile ( two species of bedstraw would only grow on specific soil)

One would only be found on basic soil, while one would only be found on acidic soil.

Even when the other plant was transplanted, it would slowly return to being only one type of plant.

Example of competitive exclusion principle.

What is the environmental impact on competition?

What is the Connell 1961 experiment?

Both of them want to be in the lower intertidal area, but Semibalanus and Cthalmalus don’t overlap

Semibalanus is found in the lower intertidal area while Cthamalus was found in the higher intertidal area.

Regardless of manipulation, Balanus competitively excludes Cthamalus.

Cthamalus has a tolerance refuge from Balamus because it has has higher desiccation resistance

How is Chipmunk distribution on mountains an example of the competitive exclusion principle?

What are the ways species coexist?

niche partitioning/character displacement

Predators can suppress dominant competitors

Disturbance- reset

Competitive networks

What is niche partitioning?

Occupy different parts of a niche

Niche partitioning occurs through adaptive radiation, favored by evolution, divergence.

How does a predator suppressing a dominant competitor allow coexistence in a niche?

What is disturbance?

like physical disruption that resets competitive hierarchies before exclusion completes, maintaining diversity.

What are competitive networks?

In hierarchical/transitive communities, an external force is needed to maintain diversity.

But in non-transitive competitive networks (A beats B, B beats C, C beats A), diversity can be maintained internally without any outside intervention.

Picture equal transitive community

What happens when everyone has roughly equal competitive ability?