Summit 2015

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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 SIZE Food plenty of food population grows food shortage population falls Diseaseovercrowding increased aggression / competition for resources increase in predators Decrease in predators Predators

 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 venomous snakes have poisonous venom to subdue their prey camouflage allows predators to blend in with their surroundings kingsnakes are immune to the venom of venomous snakes treefrogs have special pads on their feet so they can cling to vertical surfaces

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 Prey may avoid capture by  Camouflage  Chemical warfare  Warning coloration  Mimicry  Deceptive looks  Deceptive behavior

camouflage mimicry venomous coral snake scarlet kingsnake speed & keen senses warning colors & patterns 8. Prey Adaptations – General Prey have adaptations to detect and prevent being eaten by predators.

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 How does the lynx population depend on the number of snowshoe hares? 0 50 estimated population size (thousands) lynx snowshoe hare time (year) Take a closer look at this part of the graph.

18. Predator–prey graph section Why does the peak for the lynx population always come after the peak for the number of snowshoe hares? 0 50 estimated population size (thousands) lynx snowshoe hare time (year) For the populations to survive, there will always be more hares than lynxes.

Predator and prey population sizes follow a cycle. What happens if the prey population increases? normal prey population prey population increases prey population increases predator population increases as more food predator population decreases as less food prey population decreases because of more predators 19. Predator–prey cycle

Predator and prey population sizes follow a cycle. What happens if the prey population decreases? normal prey population 20. Predator–prey cycle prey population increases because of less predators prey population decreases predator population increases as more food predator population decreases as less food prey population decreases

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 population of the _______. However, as the population of predators increases, the number of prey _______. 21. Plenary Eg. More grass means more ______. More rabbits means more _____ But more foxes means less ______. Eventually, less rabbits will mean ____ foxes again. predators decreases rabbits foxes rabbits less

 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 Weddell and Crabeater Seals Minke whales 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!

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.

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