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14.2 Community
Interactions

when organisms live together in an ecological
community they interact constantly.

Three types of interactions
– Competition
– Predation
– Symbiosis
Competition- competing
for resources

occurs due to a limited
number of resources
– Intraspecific competition
– Interspecific competition


Resource- any
necessity of life. water,
nutrients, light, food.
Competitive
exclusion principleno two species can
occupy the same niche
in the same habitat at
the same time
Predation



Predation- when
an organism
captures and feeds
on another
organism.
Predator- hunter
Prey- hunted
Symbiosis
Symbiosis- any relationship where
two species live closely together.
 (3 types)

– Mutualism
– Commensalism
– Parasitism
Symbiosis

Mutualism- both
species benefit
from a relationship.

Lichens (fungus
and Algae)
One example is the lichens, little non-descript patches of stuff you see growing on rocks and tree bark.
This is a symbiosis, consisting of a fungus and an alga. The fungus provides a protective home for the
algae, and gathers mineral nutrients from rainwater and from dissolving the rock underneath. The alga
gathers energy from the sun. There are thousands of species of lichen in the world; actually thousands
of species of fungi with just a few species of algae which can form a partnership with almost any of
them.
Symbiosis

Commensalism –
One member of a
symbiotic
relationship benefits
and the other is
neither helped or
harmed

Ex. Holes used by
bluebirds in a tree
were chiseled out by
woodpeckers after it
has been abandoned
Ø
Human Our eyelashes
are home to tiny mites
that feast on oil
secretions and dead
skin. Without harming
us, up to 20 mites may
be living in one eyelash
follicle.
Commensalism
Ø Organism is not affected
+
+
Organism benefits
Demodicids Eyelash
mites find all they need to
survive in the tiny follicles
of eyelashes. Magnified
here 225 times, these
creatures measure 0.4
mm in length and can be
seen only with a
microscope.
Symbiosis


Parasitism- One
creature benefits
and one creature is
harmed
Ex tapeworm.
Feeds in a humans
intestines absorbing
his/her nutrients.
+
Parasitism
+
_
Hornworm
caterpillar
The host hornworm
will eventually die as
its organs are
consumed
by wasp larvae.
_
Organism is affected
+
Braconid
wasp
Braconid larvae
feed on their
host and
release
themselves
shortly before
reaching
the pupae
stage of
development.
Organism benefits
Relationships: Symbiosis = Living Together
a) commensalism
b) mutualism
c) parasitism
Identify these relationships