11-14 Lecture Notes

7/30/2019 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

, ,

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11-14 Lecture Notes