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

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What are predator adaptations to exploit prey?

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

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Do crabs induce a structural defense (thicker shells) of mussels?

How would you test thishypothesis?

Figure 2A

What is:independent var?control treatment?

What could be:dependent var?

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Figure 2B

Figure 2B

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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-resourceInteraction. E.g. a fungus that kills forgsIs spreading rapidly.

The fungus caused a rapid decline in thisfrog population.

Top-down control Tri-trophic predators interactions

herbivores (prey)

plants

nutrients/light Bottom-up control

Human activities have altered:1) predator-prey relations2) ‘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?

territorial Heavyseed crop in 89

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 responseto 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. Which type of response, functional or numerical, is made by individual warblers?

4. 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 hare-lynx 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

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ControlsFence;no lynx

Extra food

for hares Both

• What is conclusion?

• Do predation, food, or a combination of both factors control the hare-lynx cycle?

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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-preypopulations 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