Download Ecosystem Interactions and Populations

Ecosystem Interactions and
Populations
Interactions and Populations
All populations of species in an ecosystem
strive for survival
 What do you think populations need in
order to survive?
 Resources: food, water, safe shelter
 But there are many factors that affect a
population’s survival
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Biotic and Abiotic Interactions
Biotic Interactions: Interactions between
living things.
 Example: How would a flower and a bee
interact? How would a moose and a
parasite interact?
 Abiotic Interactions: Interactions between
living and non-living things
 Example: How would a deer be affected
by a dry and hot weather?
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Biotic Interactions
There are three main ways in which
organisms in communities interact with
each other.
1) Competition: interactions between two or
more organisms
competing for the
same resource
in a given habitat.
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Biotic Interactions
2) Predation: the act of one organism eating
another organism in order to obtain food.
Prey animals adapt in order to avoid being
eaten. Ex. Camouflage or the ability to run
very fast.
- Mimicracy: one species that looks like
another species.
Biotic Interactions
3) Symbiosis: a close interaction between
two different species where one species
lives in, on, or near another species.
Three types of Symbiosis:
a) Mutualism
b) Commensalism
c) Parasitism
What do you think each of these mean?
Biotic Interactions
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Mutualism – both species benefit from the partnership.
Ex: the boxer crab carries around anemones in its claws.
The anemone protects the boxer crab from predators,
and the anemone eats scraps of food that the boxer crab
drops.
Commensalism – one species benefits from another
species, but that species gets no harm or benefit from it.
Ex. A bird building a nest in a tree (tree doesn’t suffer)
Parasitism – one species benefits at the expense of
another. Ex. Leach or a tick sucking blood from an
animal.
SEE PAGE 47 for MORE EXAMPLES
Which type of Symbiosis?
1
2
3
Which type of Symbiosis?
Image 1 – parasitic tick on a dog
 Image 2 - As buffalo eats grass, the
egrets (birds) eat the insects that they stir
up. The buffalo is unaffected.
 Image 3 – The bee feeds from the flower’s
nectar, but it also helps cross-pollenate
the flower so it can reproduce.
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Birth of an Ecosystem:
Surtsey, Iceland
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Read pp. 36-37
Characteristics of Populations
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Populations are always reproducing.
As there are more and more of an organism in
one given area, they each get a smaller share of
the total resources in that area.
Equilibrium – when the number of births in a
population equals the number of deaths. (No
growth or shrinkage of the population)
Carrying capacity – The maximum number of
individuals that an ecosystem can support
without reducing its ability to support future
generations of the same species.
Equilibrium and Carrying
Capacity
• In this graph, the rabbit population has achieved equilibrium, and
the population remains constantly below the ecosystem’s carrying
capacity
• However, populations in ecosystems often goes in cycles.
Snowshoe Hare and Lynx
Populations
Predator-Prey relationship
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Snowshoe hares are prey for the lynx
As the population of hares increases, the lynx have more
food, so their population increases.
This results in fewer snowshoe hares, because the lynx
eat the hares.
Because there are so many lynx eating hares, the hares
numbers decrease.
There is now a food shortage for the lynx, so the weaker
lynx will become malnourished, some will die – resulting
in a smaller lynx population.
Since there are less lynx, the hares population begins to
increase again.
This cycle will repeat itself
Carrying Capacity
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Look at the snowshoe
hare population.
Which number seems
to be the most common
“peak”?
About 6000
Therefore, 6000 is their
carrying capacity.
If they go over 6000,
more lynx will come
along and eat them,
causing their
population to dip low
again
Carrying Capacity
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Look at the lynx
population
Which number seems to
be the most common
peak?
About 4000
Therefore, 4000 is their
carrying capacity.
If they go over 4000,
there is too much
competition and they run
out of food.
Their population
consequently dips
Predator-Prey relationships
If an ecosystem gets overpopulated, this
will exceed the carrying capacity.
 Predator-Prey relationships are one way to
ensure that ecosystems do not get
overpopulated with one species. It’s a
natural form of population control.
 If there is too much prey, there will be
more predators to eat them
 If there are too many predators, they will
compete and run out of prey
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Limiting Factors
Limiting Factors
Limiting factors are any environmental
factor that prevents an increase in the
number of organisms.
 Biotic Limiting Factors
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Competition among organisms for resources,
presence of predators, reliance on other
organisms for survival, presence of disease.
Abiotic Limiting Factors
Amount of sunlight, water, soil, air.
 Natural disturbances – storms, fires, drought
 Humans: e.g. logging
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Limiting Factors
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Limiting Factors is what affects the ecosystem’s
carrying capacity
This can cause a population to increase and
decrease over the years
A population cannot continue to survive over the
its carrying capacity. This is unsustainable. If
there are no more resources, the future
generation can’t survive.
Do you think this concept applies to humans
too? Give an example.
When a population cannot
survive
In a sustainable ecosystem, populations
reach their carrying capacity and can
continue to survive indefinitely
 However, limiting factors can wipe out an
entire population of a species in a
ecosystem. Humans are largely
responsible for this.
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What happens to a population
that can’t survive?
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In a case of a major disturbance, a
population can go to ZERO in an
ecosystem. This happens 2 ways:
Extirpation: If a population cannot survive in
one ecosystem, but it may continue to survive
in another ecosystem.
 Extinction: If a population is extirpated from
one ecosystem and cannot survive in any
other ecosystem, it ceases to exist. The
species is gone forever.
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Examples
Extirpated: Bison
Extinct: Golden toad
Homework
Page 42 Questions 1 – 3
 Page 46 Questions 2 -8 (graph not
necessary for #8)
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