Download Predators and Food Webs Direct vs. Indirect Effects Keystone

Direct vs. Indirect Effects
Predators and Food Webs
Direct effect- a change in the phenotype
or abundance of a species mediated
by
y an interaction with another species.
p
I. Direct vs. Indirect Effects
II. Keystone predators
Indirect effect- a change in the phenotype
or abundance of a species caused by
a species it does not interact with
directly.
III. What controls food webs?
Keystone Predators
What controls food webs?
A keystone species is one whose impact on its
community or ecosystem is disproportionately
large relative to its abundance.
Mitella
Pisaster
Mytilus
Top down control- food webs are
controlled by the negative impacts of
predators on p
p
prey
y ((demand driven).
)
Bottom up control- food webs are
controlled by the availability of prey for
predators (supply driven).
Nucella
[Source: Paine 1966, Am. Nat. 100: 65-75]
Why is the world green?
Where have all the fish gone?
[Source: Hairston et al. 1960, Am. Nat. 94: 421-425]
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[Source: Estes et al. 1998,
Science 282: 473-476]
2