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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.
