Download Predator and Prey - SD43 Teacher Sites

Summit 2015
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https://m.youtube.com/watch?v=ffcyVpqn9n
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The formation of a food web in an ecosystem is based
on predation and competition.
Predation: when one species eats another species.
Even top predators and large animals like lions and
whales are vulnerable to predation when they are
young.
Predator – organism that does the eating
Prey: the species that is eaten.
Competition: when two species use the same food
source. Sometimes one organism will out-compete
another, forcing the less successful organism to leave
the ecosystem or switch to another food source.
Competition: When two species compete,
their niches overlap
Competitive exclusion principle – no two
species can occupy exactly the same
ecological niche for very long
Both species suffer harm
Migration or predation will ultimately
occur
5. Population Size
To ponder: What effects the size of a population?
population grows
Decrease in predators
plenty of food
food shortage
Predators
Food
POPULATION SIZE
overcrowding
Disease
increased aggression
/ competition for
resources
increase in
predators
population
falls
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Predators may capture prey by:
 Walking
 Swimming
 Flying
 Pursuit and ambush
 Camouflage
 Chemical warfare
9. Predator Adaptations – General
Predators have adaptations to catch and consume their prey.
birds of prey have
keen eyesight and
sharp beaks and
talons
camouflage
allows predators
to blend in with
their
surroundings
treefrogs have
special pads on
their feet so
they can cling to
vertical surfaces
venomous snakes have
poisonous venom to
subdue their prey
kingsnakes
are
immune to
the venom
of
venomous
snakes
https://m.youtube.com/watch?v=_IWw8
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Prey may avoid
capture by
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
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Camouflage
Chemical warfare
Warning coloration
Mimicry
Deceptive looks
Deceptive
behavior
8. Prey Adaptations – General
Prey have adaptations to detect and prevent being eaten by
predators.
venomous coral snake
mimicry
speed &
keen senses
camouflage
warning
colors &
patterns
scarlet kingsnake
11. Predator & Prey adaptations Eyes
The eyes of predators face forwards. This gives them good
depth perception allowing them to judge distances well. Can
focus on a single point.
The eyes of prey are located on the side of the head. This
allows them to see to the side and rear while eating, without
moving their head. Some prey have almost 360° vision.
12. The Lynx and the Snowshoe
hare
This is the most common example of the predator prey
relationship.
15. Predator–prey graph
There are always more prey than predators.
The prey always increases before the predators do.
To do: Explain why the predator increases after the prey.
16. Predator–prey graph
This population data comes from fur trapping records.
How are the populations linked?
17. Predator–prey graph
estimated population size
(thousands)
How does the lynx population depend on the number of
snowshoe hares?
snowshoe
150
Take a closer
hare
look at this part
lynx
of the graph.
100
50
0
1800
1820
1840
1860
time (year)
1880
1900
18. Predator–prey graph section
Why does the peak for the lynx population always come after
the peak for the number of snowshoe hares?
snowshoe
hare
lynx
estimated population size
(thousands)
150
100
For the populations
to survive, there
will always be more
hares than lynxes.
50
0
1850
1855
1860
time (year)
1865
19. Predator–prey cycle
Predator and prey population sizes follow a cycle.
What happens if the prey population increases?
normal prey population
prey population
prey population
increases
increases
predator
population
decreases
as less food
prey population decreases
because of more predators
predator
population
increases
as more food
20. Predator–prey cycle
Predator and prey population sizes follow a cycle.
What happens if the prey population decreases?
normal prey population
prey population
prey population
decreases
decreases
predator
population
decreases
as less food
prey population increases
because of less predators
predator
population
increases
as more food
21. Plenary
The population of any species is normally limited by the
amount of food available.
If the population of the prey increases, then so will the
predators
population of the _______.
However, as the population of predators increases, the
decreases
number of prey _______.
Eg.
•More grass means more ______.
rabbits
•More rabbits means more foxes
_____
•But more foxes means less
______.
rabbits
•Eventually, less rabbits will
mean ____
less foxes again.
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A population of predators cannot increase
unless there is enough prey.
At the same time, the predators tend to keep
the population of prey from increasing.
As a result there is usually a balance similar to
a teeter-totter with more prey or predators at
different times.
Here are are a few other animals that live in Antarctica and
which compete for food or are predators of Adélie
Penguins.
Leopard
Seals
Minke
whales
Weddell
and
Crabeater
Seals
South
Polar Skua
South Polar Skuas look like large seagulls, to which they are
related. They eat fish mostly, but also penguin eggs and
chicks. When seals come out onto the ice to bear their pups,
the Skuas hang around to eat the after birth. These opportunist
eaters are the scavengers of Antarctica.
HOW THEY ACT AS PREDATORS:
Mated pairs of skuas work together to steal penguin eggs and chicks. One bird
will distract the adult penguin on the nest and the other will sneak from the
other side to grab the prize.
The penguins will not leave
the nest. So, a skua often will
fly or walk around a penguin
quickly to get it off balance
and expose the egg or chick. It
works most of the time for one
but not both eggs.
Weddell seals do not eat penguins, but they do eat the same
food that penguins do: Antarctic silver fish. For the time
being there is enough for everyone, but as commercial
fishing starts to deplete the Southern Ocean of fish, the
delicate food web may get out of balance and competition for
food between these species may become much more
important.
Crab eater seals do not prey on penguins, but do eat the same
important prey item: krill. Like Weddell seals, for now this food
source is plentiful, but things may change as the commercial fishing
in the Southern Ocean continues to increase.
Whales
The two common whales in the Ross Sea area are the Minke and the
Orca (killer whales). The Orcas have difficulty out-maneuvering the
penguins in the water (penguins too quick) and Adélie Penguins are
too small to spend energy in catching. Orcas go after the large Antarctic
toothfish which live under the ice close to the bottom of the ocean.
These Orcas are feeding along the ice
edge where they can dive under the ice
and search for the toothfish.
Minke Whales.
These whales feed on small fish and krill (shrimp) by taking in huge
gulps and then sieving the water through the baleen in their mouths.
These whales do not feed on penguins but because Adélies eat the
same prey, they are competitors. Each Minke whale eats as much as
2000 penguins in a day!
Adelie Diet Composition
100%
80%
60%
Fish
40%
Krill
20%
Squid
0%
Oct
Nov
Dec
Jan
Feb
Month
Look at the graphs on
the left. Notice that as
the whales appear in
the area Dec and Jan,
the diet of the penguins
changes to fish.
Number of Whales
Number of whales sited
35
30
25
20
Number of Whales
15
10
5
0
Oct
Nov
Dec
Jan
Feb
As the whales leave in
Feb the diet changes
back to krill.
https://m.youtube.com/watch?v=Ls2Q55
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