OUR Ecological Footprint Recycle; pay tax for it. 2.

This week lab: Due: Homework 9: Pop. Problem Set Start: SDP-2 Read paper about project Xerox Abstract/Intro for group members + TA Complete Proposal WS 1 in lab To be returned by TA: Draft 1 SDP1 Following week’s lab: Due: Draft 2 SDP1

Chapter 18: Dynamics of predator-prey interactions

Objectives Predator-prey synchronized cycles How stabilize predator-prey interactions Laboratory studies of spatial heterogeneity Functional / numerical responses of predators to prey

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 total response of the warblers to increasing prey density. Were the predators able to control these prey? Explain. (On all three figures, the x axis label is: No. of insects/0.9m2 leaves Fig. A: y axis = No. of insects/stomach Fig B: y axis = No. nesting pairs/100 acres Fig C: y axis = Mortality due to predators (%). The curve in Fig. C goes sharply up at low density and slowly falls as density increases.

Predator and prey populations often increase and decrease in synchronized cycles; predators lag prey.

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?

Question: What factors control the hare- lynx population cycle? Hypothesis: Predation, food availability, 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.

Controls Fence; no lynx Extra food for hares Both

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

The lynx-hare story update…alternative explanations.

***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? ---with prey refuge and/or immigration No sediment Sediment Immigration

Huffaker’s experiment to get predator-prey populations to persist without immigration.

1) Oranges clumped---> no stable cycles and extinction of prey

2) Oranges dispersed randomly---> predators slow to find prey--->prey survived longer. 3) Spatial heterogeneity --->stable cycles.

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 predation via population growth or immigration.

Numerical response of wolves to moose

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?

Objectives Predator-prey synchronized cycles How stabilize predator-prey interactions? Laboratory studies of spatial heterogeneity Functional / numerical responses of predators to prey

Vocabulary

Ch 19 Competition

Objectives Types of competition Types of resources Intraspecific competition and D-D regulation Plants Animals

Sample exam ? The figure below illustrates the distribution of two species of buttercups along a transect across ridge (high land) and furrow (low valley) grassland. 1.In one sentence summarize the results. 2.Provide two alternative hypotheses (If…then) for the observed pattern. 3.Draw or describe one complete experiment that would test both hypotheses. 4.What specific results from the experiment would provide support for your hypothesis 1 above?

Figure for preceding ? F R F R F Distance along transcect (m) No. of plants Sp 1 peaks on furrow (F) Sp 2 peaks on ridge (R )

Competition : Use or defense of a limiting resource that reduces the availability of that resource to other individuals.

***What are types of resources? Plants Abiotic Biotic Animals Abiotic Biotic (A condition is NOT a resource.)

For sessile animals, space is an important resource. For most plants, space is not considered a resource.

Consequences of competition: 1)Superior competitor persists at lower resource levels. 2)Limits resources for growth, l x, m x. 3)D-D regulation of births, deaths---> 4) Population growth rate slows.

Superior competitors can persist at lower resource levels.

Types of competition : Exploitation vs. interference Intraspecific vs. interspecific If interspecific, closely related vs. distantly related

Competition may occur through exploitation (indirect) of shared resources or (direct) interference (individuals defend resources actively). exploit interfere

***Predict: Is intra- or interspecific competition greater? Why? Do closely or distantly related species compete more? Why?

Limiting Resource: If resource is scarce relative to demand. Renewable resource: constantly regenerated e.g. prey, nutrients Non-renewable resource: occur in fixed amounts and can be fully re-used e.g. space, hiding places

Liebig’s Law of the Minimum: Populations are limited by the single resource that is most scarce. A population increases until the supply of the limiting resource is insufficient; then growth stops. Applies to resources that do NOT interact to determine population growth rate. How realistic is this ‘Law’?

***Do these results support the Law of the Minimum? Explain.

N and P act synergistically to promote growth.

Intraspecific competition + Density-dependent population regulation Negative plant responses: Growth Reproduction Survival

1) Density-dependence in plants decreases growth. Size hierarchy develops. ***What is the evolutionary consequence of a size hierarchy? What is one assumption?

2) Density-dependence decreases some components of reproduction (size at birth).

3) Density-dependence increases mortality. Intraspecific competition causes “self- thinning”. Biomass (g)

Logistic growth model Intraspecific Competition results in decelerating growth rate

Law of constant yield: *** What are 2 conclusions? N

Intraspecific competition + density- dependent population regulation Negative animal responses: Growth Time to sexual maturity Birth rate Death rate

Density-dependent regulation (via intraspecific competition) of growth. *** Summarize 2 conclusions.

Density-dependent regulation of time to reach sexual maturity. ***Does age or weight determine sexual maturity? Explain.

Density-dependent regulation of birth rate

Higher density (> competition) leads to lower birth rate and (probably) lower population growth.

Objectives Types of competition Types of resources Intraspecific competition and D-D regulation Plants Animals