Penguin Predation and Competition
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.
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
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.
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
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.
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.