PREDATOR & PREY RELATIONSHIPS-ANSWER KEY
Name:________
Date:__________
DEFITINIONS
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.
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.
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
PREDATORS
 Predators may capture prey by:
 Walking
 Swimming
 Flying
 Pursuit and ambush
 Camouflage
 Chemical warfare
Predators have adaptations to catch and consume their prey.
PREY
 Prey may avoid capture by
 Camouflage
 Chemical warfare
 Warning coloration
 Mimicry Deceptive looks
 Deceptive behavior
Prey have adaptations to detect and prevent being eaten by predators.
PREDATOR AND 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.
THE LYNX AND THE SNOWSHOE HARE
There are always more prey than predators.
The prey always increases before the predators do
What happens in the prey population increases?
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What happens if the prey population decreases?
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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
predators.
However, as the population of predators increases, the number of prey
decreases.
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.
EXAMPLES of predator and prey relationships in Antarctica
These are 4 different species that interact with the Adelie penguins (compete for
food or act as predators).
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.
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
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 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!