Transcript Lecture #3 Competition & Niches

Lecture #3 Competition & Niches
Unit 9: Community Interactions
Competition - Ecological interaction
between two or more species that use the
same scarce resources.
Examples of resources organisms may
compete for
• Food
• Nesting sites
• Living space ( territory, home range)
• Light
• Water
• Mates
There are two types of competition
1) Intraspecific Competition- Competition that
occurs between members of the SAME
species.
Example- competition for territory between
rival wolf packs.
2) Interspecific Competition – Competition
that occurs between members of DIFFERENT
species.
Example- competition for newborn elk calves
between wolves, grizzly bear and coyotes
Most competitive interactions do not
involve fighting. Organisms often times
interact only by means of their effects on
the abundance of resources.
The barn swallow and little brown bat both
rely on the same food resource (flying
insects.) They hunt at different times
though. Why do you think they do this?
Answer: Competition between the two
species is reduced!
One way competition is reduced in nature
is by organisms utilizing their own niche.
Niche - the functional role (job) of a
particular species in an ecosystem.
• A niche includes when the organism eats,
where it lives, what it eats, the
temperature it prefers, when it mates,
how it finds a mate, etc.
• Every species has its own unique niche.
This is why ecosystems tend to be so
complex.
** Don’t confuse ‘niche’ with ‘habitat’,
which is the PLACE an organism lives.
The habitat of a organism is only PART
OF its niche.
• Sometimes, the niche of some organisms
overlap. If the resources that the
organisms share are in short supply, this
overlap will likely cause competition
between the organisms.
Example of a Niche - Cape May Warbler
The Cape May Warbler is a small insect
eating songbird spends its summers in the
northeastern United States and Canada.
• It nests in spruce trees at the tips of
the branches.
Fundamental Niche –The entire range of
conditions an organism is potentially able to
occupy within an ecosystem.
The fundamental
niche of the Cape
May Warbler
would include the
entire tree on
which it lives.
Feeding habits
The Cape May Warbler feeds at the tops
of the trees, even though the insects
that it eats are located throughout the
tree.
• They are only occupying a portion of
their fundamental niche.
Why? The Cape May Warbler shares
the tree that it lives in with other species
of birds.
• Robert MacArthur (Princeton
University) did a study on the feeding
habits of 5 species of Warblers.
• He found that all five species fed on
insects in the same spruce tree at the
same time.
How do the resources last?
Resource Partitioning!
Each species
occupies a different
part of the tree!
This reduces
competition & allows
all five species to
coexist.
Resource Partitioning for 5 species
of warblers
The realized niche is part of the
fundamental niche.
Realized Niche - The part of an
organism’s fundamental niche that a
species ultimately occupies.
• All five species had very similar
fundamental niches, yet used different
resources. They had different realized
niches.
What happens if two species are directly
competing for the same resources?
If two species are competing for the
same resource and one is slightly better
than the other; the result may be the
local extinction of the species less able to
obtain resources.
Competitive exclusion principle – the
local extinction of one species due to
competition.
Complete competitors cannot coexist
Human Impact
Human introduction of non-native species
to new environments, where some have
become invasive, has pushed many native
species towards extinction.
These ‘introductions’ have been both
accidental and intentional depending on
the non-native species in question.
Introduced (Alien) species- any organism
that was brought to an ecosystem where it
is not native as the result of human
actions
Invasive species- A species that takes
advantage of an unoccupied niche, or that
successfully out-competes native species.
• Invasive species have a negative effect on
ecosystems or negatively impact humans in
some way.
Invasive species may
grow exponentially if
they
1) Lack natural
enemies
2) Can occupy an
‘open niche’
3) Have ‘weedy’
characteristics.
Take 2 minutes to summarize what you
have learned by explaining how
competition may be reduced in nature,
what can happen if two species are
direct competitors and why introduced
species may cause ecosystem damage.