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4.2: Interactions
among Organisms
When two species use the same resource,
they participate in a biological interaction
called competition.
Competition occurs for resources in short
supply – food, nesting sites, living space,
light, mineral nutrients, and water.
To understand competition, you need to
understand the “day-to-day” activities of
organisms.
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habitat is the
place a plant or
animal lives
An earthworm’s
habitat is
SOIL!
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niche is an organism’s
total way of life
can be thought of as its
“job” for the
ecosystem
includes what it eats
and what eats it!
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competitive exclusion principle: no two
species can occupy exactly the same niche
in exactly the same habitat at exactly the
same time
direct competition between different
species always produces a winner and a
loser with the losing species dying out
instead of competing for similar resources,
species usually divide them
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three species of
warblers all live in the
same trees and feed
on insects
one species feeds on
high branches,
another on low
branches & the third
feeds in the middle
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Some relationships between organisms
are not “healthy” for both.
Predation is the act of one organism
killing another for food.
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herbivory: special type of predation
where plants are preyed upon by
herbivores
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keystone species: one special species
that directly or indirectly affects the survival
of many other species
loss of the keystone species can cause
dramatic changes in the health of the
whole ecosystem
tends to be a top predator but can also be
an important food source for many other
organisms
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Which is the
keystone species?
What would happen if
the wolf population
was removed?
The deer population would explode, causing the
plant population to crash. This will cause the
insects to drop which will cause the rodent
population to crash then the snake population to
crash….
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Symbiotic Species
In symbiosis, two or more species live
together in a close, long-term association.
Symbiotic relationships can:
~ benefit one organism and harm the other
~ benefit both organisms
~ benefit one organism and leave the other
unaffected
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Parasitism
symbiotic relationship where one organism
feeds on & usually lives on/in another
(usually larger) organism
lamprey parasitizing a trout
tapeworm from human intestine
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Parasites do not usually kill their prey
(known as the host) because they
depend on the host for food and a place
to live.
flea bites on a human
engorged deer tick attached to
back of a toddler's head
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Mutualism
symbiotic relationship in which both
species benefit
Bee gets food (pollen) from
flower while the flower gets
it’s pollen spread to other
plants to continue the
species.
Bird removes bugs from the
alligator’s mouth for food while
the alligator gets parasites
removed from it’s teeth.
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How is this an example of mutualism?
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Commensalism
symbiotic relationship in which one species
benefits & the other is neither harmed
nor helped
A titan triggerfish creates feeding
opportunities for smaller fish by
moving large rocks too big for
them to shift themselves.
Smaller plants use larger trees as a
way to climb up and reach the sun
they need to survive.
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So…
How well do YOU know interactions
among organisms?
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