Transcript 14 Predator-prey 2010

Ecological footprints of some
nations already exceed available
ecological capacity.
Our ecological ‘footprint’…
1)
Before lecture on Tuesday,
take the quiz on www.myfootprint.org.
Insert your result in the top of the lecture outline,
as shown on the LO (cut out the one shown), and
bring the lecture outline to class.
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
•
•
•
•
•
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Group living
Induced structural defense
Chemical defense
Cryptic coloration
Aposematism
Mimicry
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…
Top-down control
predators
Tri-trophic
interactions
herbivores (prey)
plants
nutrients/light
Bottom-up control
Do predators control prey abundance?
If…
then…
Figure 6
Is there a response of this predator to an
increase in its prey? Why or why not?
Heavy
seed crop
in 89
territorial
Figure 7
Human activities have altered:
1) predator-prey relations
2) ‘top-down’ control
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.
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
Population cycles synchronized among
species in a region. Periodic cycles with
peaks separated by same number of years.
Figure 13
Cycles have damped out with warmer
temperatures.
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?
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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.
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