“Who are the people in your
neighborhood?”
Interactions between
organisms
Roles in Ecosystems
Niche = The “job” of an organism in an ecosystem
Described using
Where organism
lives/carries out “job”
Some words:
habitat, biome, etc.
How organism obtains
fuel (food)
Some words:
Producer and Consumer,
autotroph and heterotroph,
herbivore and carnivore,
predator or scavenger, etc…
For Example
• The Waterstrider – top-water predator of
small animals on the surface of the water
Types of Interactions
There are several different ways organisms
can interact.
Predation
• A trophic (feeding)
relationship where
one organism eats
another, killing it.
• Other trophic
relationships are
herbivory and
detritivory
Consuming
dead organisms
Hawk photo from: http://www.flickr.com/photos/jurvetson/226587515/
Consuming
plants
Competition
The struggle for
limited resources
Carrying capacity = The maximum number of
organisms that can be supported by
available resources
Competition
When populations rise over carrying capacity (increase in
population or decrease in resources)  more competition
Interspecific = between 2 different species
Intraspecific = between same species
Symbiosis
Living together
When 2 different species live in a close,
inter-dependent relationship.
At least one member of the pair benefits.
Symbiosis
Mutualism: When both organisms
benefit; What most people think of as
“symbiosis”.
e.g. Lichens, coral
Commensalism: One benefits by eating
unused food, the other is unaffected
e.g. gut bacteria, remora and sharks
Parasitism: One benefits the other is
harmed (not killed)
e.g. tapeworm, ticks
Altruism
One organism helps
another organism but
gets no benefit, risks
harm or is harmed in
doing so
Being “nice”
Common in some birds
Can be intraspecific or
interspecific
Beware of
anthropomorphisms!
Fairy wren photo:
http://commons.wikimedia.org/wiki/File:Superb_fairy_wrens_mark_2.jpg
Let’s look for some
interactions!
Yep……….
It’s
Lab time!