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Common relationships among various species within
natural communities.
Population – group of individuals of the same species
living in the same area, potentially interacting
Community – group of populations of different species
living in the same area, potentially interacting
What are some ecological interactions?
Why are ecological interactions important?
Interactions can affect distribution and abundance.
Interactions can influence evolution.
Think about how the following interactions can affect
distribution, abundance, and evolution.
Types of ecological interactions
competition
predation (predator/prey)
arasitism (parasite/host)
mutualism
commensalism
symbiosis
Competition – two species share a requirement for a
limited resource  reduces fitness of one or both species
Predation – one species feeds on another  enhances
fitness of predator but reduces fitness of prey
Parasitism – one species feeds on another  enhances
fitness of parasite but reduces fitness of host
Mutualism – two species provide resources or services
to each other  enhances fitness of both species
Commensalism – one species receives a benefit from
another species  enhances fitness of one species; no
effect on fitness of the other species
Symbiosis – two species live together  can include
parasitism, mutualism, and commensalism
Organizing ecological interactions
effect on species 1
+
effect on
species 2
+
mutualism
0
commensalism
-
predation
herbivory
parasitism
0
-
commensalism
predation
herbivory
parasitism
competition
competition
competition