Species Interactions. Fitness: the relative contribution to the gene pool in the next generation

Species Interactions

Species Interactions

Fitness: the relative contribution to the gene pool in the next generation

Species InteractionsChange in Fitness as a Result of the Interaction

+ net gain of fitness

0 no net change of fitness

- net loss of fitness

Fitness: the relative contribution to the gene pool in the next generation

Species InteractionsSpecies A Species B

- -

- +

0 0

+ +

Competition

Predation

Neutralism

Mutualism

Change in Fitness as a Result of the Interaction

+ net gain of fitness

0 no net change of fitness

- net loss of fitness

Fitness: the relative contribution to the gene pool in the next generation

Competition - / -

Experiments by Russian ecologist Gause in 1934 examined two closely related species of protozoans. When cultured on a constant food source separately, both reached carrying capacity. When cultured together, P. aurelia proved to be a better competator and drove P. caudatum to extinction.

Competition - / -

Competition - / -

Two possible outcomes to competition:

•Competitive exclusion = extinction

•Niche partitioning = coexistence

Competition - / -

Two possible outcomes to competition:

1.Competitive exclusion = extinction (one species dominates)

2. Niche partitioning = coexistence (species have slightly different niches)

Therefore, many species may coexist and still use similar resources in a similar way, if they can specialize in their ecosystem.

Predation + / -

virus

Various types:

Carnivores, Herbivores, Omnivores, Parasites, Parasitoids

Pepis sp.

Predation + / -

Ecologically, there seems to be a trade-off between competitive ability

and the ability to escape predators.

STRATEGY FOR SURVIVALCompetitive Ability R

esistance to

Predation

Predation + / -

What do you see? How do you interpret this graph?

STRATEGY FOR SURVIVALCompetitive Ability R

esistance to

Predation

Predation + / -

What is Species A good at in its ecosystem? What is this species not as

good at?

STRATEGY FOR SURVIVALCompetitive Ability R

esistance to

Predation

Species A

Predation + / -

STRATEGY FOR SURVIVALCompetitive Ability R

esistance to

Predation

Species ASpecies B

What is the strategy for Species B?

Analogy: It is very difficult to be good at everything. But, using different strategies (different

niches) you can still be good at the “game.”

Neutralism 0 / 0

Neutralism 0 / 0

It is important to remember that this is not the absence of interaction.

Neutralism 0 / 0

Where neutralism becomes more important is when examining larger numbers of species interactions in a bounded community.

Example: Tide pool communities. Though their members interact frequently, many neither benefit nor cost one another.

Studies suggest that 5% or less show significant correlations in abundance, for example.

Mutualism + / +

Atta cephalotes

Interactions in a tropical ecosystemEciton burchelli

What types of interactions are present in the army ant situation? Write them in your notebook and explain your

thinking.

Now it is your turn to form analogies.

In your notebook, come up with analogies for ecological community interactions using

your own neighborhood community or school.

Explain and draw a quick picture illustrating

competition, predation, neutralism and mutualism.