11-14 Lecture Notes
Transcript of 11-14 Lecture Notes
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Consumption (predation and herbivory)
I. How does predation affect prey populations?
Question: Do predators reduce prey populations below the level that can be su orted b available resources?
Predator removal experiments:
Wolves, cougars, coyotes removed from the Kaibab plateau 1907 1937
Start:
1920:
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Predator addition experiments: Restoring wolves to the Greater Yellowstone Ecosystem
o ves were ext rpatein the 1920s and
c o w s
elk are the main prey.
p e r 1 0 0
e s b o r n.
take home message?
C a l v
2. Create a hypothesis to explain the data.
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t
n v i g i l a
o p o r t i o
P
Distance to wolves km v i g i l a n t
o f t i m e
p o r t i o n
Wolves
Wolvesabsent present P r o
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II. How do prey respond to predators?
A. Standing defenses are always present
e.g. porcup ne qu s; camou age n ema e ac r s; chemical spray from skunks
Design an experiment to test the hypothesis that stingers are an effective standing defense in honeybees.
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B. Inducible defenses are produced in response to pre at on
e.g. blue crabs (predator) and mussels (prey)
Low predation in high i c k n e s s
tidal flow areas; highpredation in low tidal
s h e l l t h
v e r a g e
High
Lowpredation predation
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These data are correlational in nature, and there are otherreasonable inter retations besides induced defenses.
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Hypothesis: Mussels increase shell thickness andattachment stren th in res onse to evidence of redation.
An experimental test:
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III. How do predators affect communities of species?
A keystone species has an extraordinarily large impact on
e.g. Pisaster removal
experiments
h n e s s
c i e s r i c
Time (years)
S p
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Trophic cascades in the Greater Yellowstone Ecosystem
Hawks, owls,eagles Wolves
Coyotes
BeaverMooseElkRabbits Mice Deer
Grasses, forbs WillowAspen
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IV. Why is the world green?
H1: The top down hypothesis
H2: The poor nutrition hypothesis (Nlimitation) <
animals)
H3: The plant defense hypothesis
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Example: Nicotine as an inducible defense
yn es ze n roo s n response o a ac y er vores and transported to trichomes (leaf hairs)
Experiment: Study 3 populations of wild tobacco. For
many generations,
each
has
been
exposed
to
different
, , .
1. Grow individuals from each population in the same
environment. 2. Induce nicotine production in each (same stimulus).
3. Measure: number of seeds produced.
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NOTE: individuals from each population show about the same response to n uct on same n cot ne pro uct on .
Source population history Induced Control (not induced)
Low herbivory 4,494 6,047
Medium herbivory 5,314 7,335
, ,