Transcript Keystone species

Yellowstone National Park
Wolf Case Study
Wyoming’s Yellowstone
Species Interactions may
cause trophic cascades
 Trophic
cascade: changes in one level will
create changes in other trophic levels.

Trophic Levels:
tertiary
consumers
5
secondary
consumers
5000
primary
consumers
500,000
producers
5,000,000

Tertiary Consumer
 Secondary
Consumer

Primary Consumer

Primary Producer
/plants
Food Web in Yellowstone
 The
wolves eat
moose, pronghorn,
mule deer, elk,
bison, and bighorn
sheep.
 They
share these
prey (food) with
other predators like:
coyotes, mountain
lions, and grizzly
and black bears.
The wolves are a keystone species
Keystone
species: they have an
unusually large effect on the
ecosystem.
In 1926 unrestricted hunting had
eliminated the wolves from the park
community.
In 1920 An annual census of elk was
initiated by park managers.
Intervening in nature
From
1920-1968 the park service
selectively killed elk herds so they
wouldn’t go over caring capacity.
In 1968 they stopped because of
public pressure.
Once the killing stopped the elk
population rapidly increased.
Effects of the increase in Elk
 The
elk eat aspen trees and once their
population took off there were no more
young trees.
 The elk also severely browsed (ate)
streamside willows and this didn’t allow
beavers to eat or make dams.

The absence of beavers dams made less
biodiversity because of loss of this habitat.
Everywhere
else there
were no elk, there were
tree populations which
told scientists it was due to
the elk that trees were
becoming depleted.
Bring Back the Wolves
 In
1995 after the wolves had been gone
for 70 years, park managers decided to
bring some to the park again.
 They had noticed that in the Lamar
Valley, where they brought back the
wolves that the tree problem began to go
away and other things also became more
established.
Lamar Valley in Yellowstone



Once the wolves were back the elk there avoided the
aspen groves where wolves could easily attack them.
This allowed the tree population to increase and also
allowed the beaver colonies to increase from one in
1996 to seven in 2003.
These beavers where then able to make dams and
mini ecosystems for all other creatures that rely on
them.
The
presence of this one
predator effected many trophic
levels of the ecosystem.
Cause and Effect for Yellowstone
Main Cause:
Effect/ Cause
Effect/ Cause
Effect/ Cause
Effect/ Cause
1926 Hunting
Of wolves kills
them all off
Effect/ Cause
Overall Effect: Loss of Biodiversity in Yellowstone
Conclusion Questions
1. Define what a keystone species is and give an
example of one and why it is one?
2. Explain a trophic cascade?
3. Summarize what this case study was about?
Analyze the data to help make your summary more
in depth.
4. Compare and contrast this case study with the wolf
and deer case study you did before.