PREDATOR AND PREYSummit 2015

https://m.youtube.com/watch?v=ffcyVpqn9ng

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 SizeTo ponder: What effects the size of a population?

POPULATION SIZE

Food

plenty of food

population grows

food shortage

population fallsDiseaseovercrowding

increased aggression / competition for resources

increase in predators

Decrease in predators

Predators

Most Consumer Species Feed on Live Organisms of Other Species Predators may capture prey by:

Walking Swimming Flying Pursuit and ambush Camouflage Chemical warfare

9. Predator Adaptations – GeneralPredators 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 preycamouflage 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

 https://m.youtube.com/watch?v=_IWw8Ruz8Uo

Most Consumer Species Feed on Live Organisms of Other Species Prey may avoid

capture by Camouflage Chemical

warfare Warning

coloration Mimicry Deceptive looks Deceptive

behavior

camouflage

mimicryvenomous coral snake

scarlet kingsnake

speed & keen senses

warning colors & patterns

8. Prey Adaptations – GeneralPrey 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 graphThere 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 graphThis population data comes from fur trapping records. How are the populations linked?

17. Predator–prey graphHow does the lynx population depend on the number of snowshoe hares?

0

50

esti

mat

ed p

op

ula

tio

n s

ize

(th

ou

san

ds)

1800 1820 1840 1860 1880 1900

100

150

lynx

snowshoe hare

time (year)

Take a closer look at this part

of the graph.

18. Predator–prey graph sectionWhy does the peak for the lynx population always come after the peak for the number of snowshoe hares?

0

50

esti

mat

ed p

op

ula

tio

n s

ize

(th

ou

san

ds)

1850 1855 1860 1865

100

150

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 populationprey population

increasesprey population

increases

predator population increases

as more food

predator population decreases

as less foodprey population decreasesbecause 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 increasesbecause of less predators

prey population decreases

predator population increases

as more food

predator population decreases

as less food

prey populationdecreases

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

rabbitsfoxes

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.

MORE EXAMPLES OF PREDATOR & PREY RELATIONSHIPS IN

ANTARCTICA……..

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!

0%

20%

40%

60%

80%

100%

Oct Nov Dec Jan Feb

Month

Adelie Diet Composition

Fish

Krill

Squid

Number of Whales

0

5

10

15

20

25

30

35

Oct Nov Dec Jan Feb

Nu

mb

er o

f w

hal

es s

ited

Number of Whales

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.

https://m.youtube.com/watch?v=Ls2Q55OOVHA