4.2 – Niches and Community Interactions
WHAT IS A NICHE?
 Niche - the range of conditions in which a species lives
and the way the species obtains what it needs to survive
and reproduce.
TOLERANCE
Tolerance - ability to survive and reproduce under a
range of environmental circumstances.
Every organisms has a tolerance range.
COMPETITION
 Occurs when organisms attempt to use the same limited
resource in the same place at the same time.
THE COMPETITIVE EXCLUSION
PRINCIPLE
 Direct competition between different species generally
produces a winner and a loser.
 Losing species dies out.
 In the the experiment shown in the graph, two species of
paramecia (P. aurelia and P. caudatum).
 Grown separately and together.
COMPETITION AND PREDATION ARE T WO
IMPORTANT WAYS IN
WHICH ORGANISMS INTERACT.
Intraspecific
competition - occurring
within one species
Interspecific
competition - occurring
between species
DIVIDING RESOURCES
 Instead of competing for
similar resources, species
usually divide them.
 Example: the three species
of North American
warblers shown all live in
the same trees and feed on
insects.
PREDATOR-PREY RELATIONSHIPS
 Interaction where one animal captures and feeds on
another animal
 This graph shows changes in predator and prey
populations over time.
SYMBIOSIS
 Any relationship where two species live closely together.
There are three major types of
symbiotic relationships.
– Mutualism : Both organisms benefit!! (+,+)
– Commensalism: One organism benefits, the
other is unharmed (+,O)
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.
• Parasitism: One organism benefits, the other is
harmed (+, -)
+
Parasitism
_
Hornworm
caterpillar
The host hornworm
will eventually die as
its organs are
consumed
by wasp larvae.
_
Organism is not affected
+
Braconid
wasp
Braconid larvae
feed on their
host and
release
themselves
shortly before
reaching
the pupae
stage of
development.
Organism benefits
Parasitism meet their needs as:
Ectoparasites (such as leeches)
Endoparasites (such as hookworms)