Download Lecture Nine: Community Interactions

Lecture Nine: Community Interactions
The various species in an ecosystem do not live in a vaccuum! They have evolved over the
millennia in response to pressures from both the environment and from other species with which
they live and interact.
SYMBIOSIS - "living together" This term refers to the members of two different species (i.e.,
two populations) having some sort of ecological interaction that affects both populations. Here
are some of the theoretical types of interactions which can evolve over many generations.
When two species evolve in response to each other's activities, the process is known as
coevolution.
"+" means that the population benefits from the interaction
"-" means that the population is harmed by the interaction
"0" means that the population is not affected by the interaction
type of interaction
mutualism
EXAMPLES:
pop'n A
pop'n B
+
+
nature of effect
obligatory; both populations benefit
protocooperation
EXAMPLES:
+
+
NOT obligatory; both pop'ns benefit
competition
EXAMPLES:
-
-
populations inhibit one another
neutralism
EXAMPLES:
0
0
populations don't affect one another
predation
EXAMPLES:
+
-
predator (A) kills & consumes prey (B)
parasitism
+
-
parasite (A) exploits the host (B), but
does not kill it outright
parasitoidism
EXAMPLES:
+
-
parasitoid (A) eventually kills host (B)
commensalism
+
0
commensal (A) benefits; host (B) not
affected
-
0
A inhibited; B unaffected
EXAMPLES:
EXAMPLES:
amensalism
EXAMPLES:
Ecological niche - Defined by the species, this is everything that an organism eats,
where it nests, sleeps, forages, etc. In short, everything that defines its natural history.
Two species can never occupy exactly the same ecological niche, or one will eventually
become extinct. However, the niches of different species may overlap to some degree.
When this happens, interspecific (i.e., between species) competition occurs.
Keystone species - species on which many other populations ultimately depend for
survival.
EXAMPLES:
Indicator species - a species whose population density allows humans to gauge the
health of an entire ecosystem
EXAMPLES:
Native species - a species found in the place where it naturally evolved. Native
populations often have complex and delicately-balanced interactions with one another
that can be disrupted by the introduction of exotic species.
EXAMPLES:
Exotic species - a species living in a place where it did not originally evolved. These
are often introduced by humans into ecosystems where they do not naturally belong.
Some exotic species introduced into new environments are much better able than native
species to compete for resources, and they can sometimes displace native species.
This can have very profound effects on the other native species which used to rely on a
native species driven extinct (or to great scarcity) by an invasive exotic.
EXAMPLES:
Taking a closer look at some of the results of predation:
Crypsis - camouflaging coloration
Aposematism - warning coloration (poisonous or venomous species)
Mimicry - a species has evolved the superficial appearance of something else
Batesian Mimicry - a harmless mimic looks like a poisonous model.
Mullerian Mimicry - several poisonous/distasteful species resemble one another.
There's a difference between these:
poisonous – toxic when eaten or touched
venomous – delivers toxin with some sort of apparatus, such as a fang, or stinger.