Download 14 Predator-prey 2009

OUR Ecological Footprint
1.
2.
Chapter 15: Dynamics of
predator-prey interactions
Objectives
• Adaptations of predators
• Prey deterrents to predation
• Do predators limit prey?
• Functional / numerical responses of
predators to prey density
• Predator-prey synchronized cycles
• How stabilize predator-prey interactions?
• Laboratory studies of refugia/spatial heterogeneity
What are predator adaptations to exploit prey?
x
The jaws of snakes are adapted for grasping
and swallowing large prey.
Predators vary in size relative to their prey.
Prey deterrents to predation
•
•
•
•
•
•
Group living
Induced structural defense
Chemical defense
Cryptic coloration
Aposematism
Mimicry
*** What’s central ?
•*** What’s main
conclusion?
Figures 1A/B
nd a
ressor
picture.
Do crabs induce a
structural defense (thicker
shells) of mussels?
How would you test this
hypothesis?
Figure 2A
What is:
independent var?
control treatment?
What could be:
dependent var?
Figure 2B
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Figure 2B
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
What is conclusion? Is shell thickness an
inducible defense?
Figure 2C
Prey have active adaptations for escaping
their predators: chemical warfare!
Palatable prey avoid predators passively
via crypsis.
Cryptic coloration - passive escape
Unpalatable animals have warning
coloration (aposematism). Predators learn
from mistakes.
Figure 3
Warning is even greater in groups…
Disease: another type of consumer-resource
Interaction. E.g. a fungus that kills forgs
Is spreading rapidly.
The fungus caused a rapid decline in this
frog population.
Top-down control
predators
Tri-trophic
interactions
herbivores (prey)
plants
nutrients/light
Bottom-up control
Human activities have altered:
1) predator-prey relations
2) ‘top-down’ control
Do predators control prey abundance?
If…
then…
Figure 6
Experimental removal of predator--->
What happens to prey?
Cause-effect tested by experimentation.
Is there a response of this predator to an
increase in its prey? Why?
Heavy
seed crop
in 89
territorial
Figure 7
Individual predators exhibit 3 types of
functional responses to increasing prey
density.
Functional response: A change in rate of
capture of prey by an individual predator
as prey density changes.
• Type I: Capture directly proportional
to prey density
• Type II: Capture levels off at high prey
density (predator satiation)
• Type III: as Type II, but is also low at low
prey density
•
1) heterogeneous habitat---> hiding places
•
2) lack of learned search behavior
•
3) switching to alternative prey
***What type of functional response of
kestrels to vole density?
***What type of functional response of
wolves to moose?
***What type of functional response?
Predators switch to different prey in response
to fluctuations in prey density.
Switching to alternative prey occurs only
when preferred prey density falls to low level.
Predator satiation of individual predators,
then numerical response in population size of
predator via population growth or
immigration.
Figure 10
Is this a numerical or functional response
of wolves to moose?
Figure 11
Why didn’t top-down control limit
spruce budworm devastation?
***Is there a functional response?
Numerical response? What is the total
response of warblers to spruce budworm
abundance? Does the warbler control its
prey?
Figure 12A
B
C
Sample Exam ?
Birds, especially warblers, are primary
predators of the insect spruce budworm,
an invading pest of boreal forests. The
ability of the predators to control these
prey during a huge outbreak of the
budworm was monitored.
1) Warblers showed a Type II functional
response to increasing prey density.
Illustrate this response in Fig. A. Explain
the shape of the predator’s response.
2) Warblers also show a numerical response
to increasing prey density. Illustrate this
response in Fig. B.
3.
4.
Which type of response, functional or numerical, is made
by individual warblers?
Fig. C shows the population response of the warblers to
increasing prey density. Were the predators able to
control these prey? Explain.
Population cycles synchronized among
species in a region. Periodic cycles with
peaks separated by same number of years.
Figure 13
Other species may vary in their response
to changes in the environment -->
asynchronized cycles.
Figure 14
Predator and prey populations often increase
and decrease in synchronized cycles.
Which group lags the other?
•
•
•
•
Predators eat prey--->reduce prey numbers
Predators go hungry---> their numbers drop
Few prey do better--->prey numbers rise
Predators have more food---> their numbers
rise.
• Do prey control predators or vice versa?
• What other factor could explain prey cycles?
Question: What factors control the harelynx population cycle?
• Hypothesis: Predation, food availability to
prey, or a combination of those two factors
controls the cycle.
• Null Hypothesis: They do NOT control the
cycle.
• Experimental Design??
• Prediction: Hare populations in at least one
type of manipulated plot will be higher than
mean population in control plots.
• Prediction of null H: Hare populations will
be the same in all of the plots.
Figure 16
Fence;
no lynx
Controls
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Extra food
for hares
Both
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
• What is conclusion?
• Do predation, food, or a combination of both
factors control the hare-lynx cycle?
Figure 17
The lynx-hare story update…alternative
explanations.
Island (low predators) vs. mainland pops:
1) Cycle continues;
2) Fluctuation less on island
Cycles have damped out with warmer
temperatures.
***How can these measles cycles be
explained?
Who is predator and who is prey? Draw in
the curve for the missing component.
Fluctuations in population density in a
host-parasitoid system in the lab.
How stabilize predator-prey interactions?
No
sediment
Sediment
(hiding
places)
Immigration
Figure 19
Huffaker’s experiment to get predator-prey
populations to persist without immigration.
1) Oranges clumped--->
what happened to cycle?
Figure 20
2) Oranges dispersed randomly--->
what happened to cycles? Why?
3) Spatial heterogeneity --->stable cycles.
Figure 21