Transcript Predation and competition

Penguin Predation and
Competition
Jean Pennycook
www.penguinscience.com
The formation of a food web in an ecosystem is based
on predation and competition.
Some food web definitions
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.
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.
When Emperor and Adélie Penguins adapted to the
environment of Antarctica they pretty much got the place
to themselves. However there are a few other animals that
live here 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.
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.
Skuas are very clever and
aggressive predators.
Penguin view of a Skua.
Skuas have their own
chicks to feed, and they
have to guard them from
other skuas, which would
eat them as they would a
penguin chick!
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.
For more information on the Southern Ocean food web go to www.lastocean.com
Weddell seals haul out on
the ice in early October to
give birth to their pups. The
Skuas hang around the
seal breeding area and
feed off the afterbirth from
the seals.
Weddell seal pup, less than a day old
with it’s mother.
Seal afterbirth, rich in nutrients.
The Skuas will make short work
of this.
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.
Leopard Seals eat Adélie Penguins. They hang around the sea ice
edge and wait for the penguins to enter or jump out of the water.
A leopard seal waiting for
a penguin to go into the
water
An adult leopard seal.
Notice the large mouth
and sharp teeth.
Picture courtesy: Kirstin Lundquist
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.
Click the picture to watch the Orcas looking for food in the ice crack.
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!
We can tell when the Minke whales are in the area.
If there are no whales, the penguins feed their chicks krill. We
can tell because the food passed to chicks is pink. When the
whales arrive in the area, the penguins switch to fish which is
silver. This is because it is easier for the whales (and the
penguins) to catch krill than it is for them to catch fish.
An adult feeding krill to its chick
An adult feeding fish to its chick
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.
Because Adélie penguins are only found in Antarctica and the Antarctic
Treaty protects all life on this continent, man is no longer a threat to
these engaging and beautiful creatures. In the early years of Antarctic
exploration, explorers would build their huts near the penguin colonies
because, like the penguins, the humans need easy access to the sea.
The humans also find an easy supply of eggs and meat.
In the 19th and early 20th century penguins,
especially King Penguins, were killed and then boiled
for their fat. Man no longer kills penguins for this
reason and these birds have rebounded in numbers.
Most of the 18 species of penguins (most live away
from Antarctica), however, are on the endangered list
because humans have depleted their prey.
For more information about Adélie Penguins go to www.penguinscience.com
Other Powerpoint presentations for you classroom:
Introduction to the Polar regions, Why is Antarctica so cold?
Introduction to Adélie Penguins, Adélie Penguins march into the classroom
Penguin Adaptations, This is a harsh continent
Adélie Penguin Behavior, Good manners are always in style
Penguin Predation and Competition, Life is tough for an Adélie Penguin
Adélie Penguins Cope with Global Climate Change
Did You Know, How researchers know what they know
Penguin Quandaries, Can you answer these mysteries
Fun pictures about Adélie Penguin
Go to www.penguinscience.com The education page.