Topic: Keystone Species
and Trophic Cascades
What is a "keystone?"
Which stone do you think is the most important?
What is a "keystone?"
Keystone Species= A species
on which other species in an
ecosystem largely depend, such
that if it were removed the
ecosystem would change
drastically.
Example: Otters
Example of a Keystone Species: Bees
· Bees pollinate plants, which is key to plant survival.
· As plants get pollinated, they produce fruit, which other
species rely on heavily.
· It is thought that Albert Einstein predicted that if bees
disappear from our planet, man would only have 4
years left to live.
Example of a Keystone Species: Fig Tree
· During parts of the year the Fig tree is the only tree
producing fruit, which many species rely on for survival.
· Once the tree dies, the hollow trunk provides a habitat for
thousands of organisms (reptiles, birds, invertebrates)
What is a trophic
cascade?
A trophic cascade occurs
when predators limit the
density or behavior of
their prey and thereby
enhance the survival of
the next lower trophic
level.
Who do you think is a
keystone species in
this food web?
Based on the number
of arrows, the mouse
plays a large role in
this community.
If the mouse population
died off, who would be
affected?
(Trophic Cascade)
X
Think of a trophic cascade like a domino
effect- once one organism is affected
everyone else gets affected too!
Why are wolves in Yellowstone National
Park so important?
https://www.youtube.com/watch?v=ysa5OBhXz-Q&t=18s
https://www.youtube.com/watch?v=ysa5OBhXz-Q&t=18s
Opinion: Do you think humans
are a keystone species?
https://www.youtube.com/watch?v=guh7i7tHeZk
https://www.youtube.com/watch?v=guh7i7tHeZk
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