OUR Ecological Footprint 1. 2. Ride bicycle; minimize car use.

Chapter 15: Dynamics of predator-prey interactions Lyunx = a cat but not = mt. Lion (closer to bobcat in size, action

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?

The jaws of snakes are adapted for grasping and swallowing large prey.

C41. 9 Rock python and gazelle. Can’t chew; must swallow whole C41.9 Rock python and gazelle. Can’t chew; must swallow whole. Long period of digestion.

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 K13.24 The value of flocking measured by distance at which they detected approach of a goshawk. Goshawk attack success is much reduced agains flocks Early detection if many eyes looking Group may mob predator Confuse predator by fleeing in all direcitons If in center, best chanc of not being eate\n. Figures 1A/B

Do crabs induce a structural defense (thicker shells) of mussels 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 is: independent var? control treatment? What could be: dependent var? Figure 2B Figure 2B

What is conclusion? Is shell thickness an inducible defense? Figure 2C

Prey have active adaptations for escaping their predators: chemical warfare! Bombadier beetle sprays noxious liquid at temp of boil water toward a predator.

Palatable prey avoid predators passively via crypsis.

Cryptic coloration - passive escape C53.5 camouflage: a canyon tree frog disappearing into granite

Unpalatable animals have warning coloration (aposematism) Unpalatable animals have warning coloration (aposematism). Predators learn from mistakes. C53.6 Poison arrow frog; skin produces noxious chemicals. Predators apparently learn to associate color with danger as soon as they touch frog’s skin. 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. 18

The fungus caused a rapid decline in this frog population. 19

Top-down control Tri-trophic predators interactions herbivores (prey) plants nutrients/light Bottom-up control Top-down: predators control herbivores Bottom up: plants (or nutirents that control plants) control herbivore (e.g. light or nutrients lower plant productivity which lowers herbivore producitify Also intraspecific competition may control herbivores; or other abioltic factors

Human activities have altered: 1) predator-prey relations 2) ‘top-down’ control

Do predators control prey abundance? If… then… K 13.11 Duck eggs hatching in ND from which striped skunks removed duirng hesting season Figure 6

Experimental removal of predator---> What happens to prey Experimental removal of predator---> What happens to prey? Cause-effect tested by experimentation. K13.12 Density of red kangaroos in Austrailia across border with dingo fence that prevents dingos (marsupial dog) from moving from S.A to sheep country of NSW. Kangaroos increases 166 X; emus increased 20X. Conclude that dingo predation limits the denisty of red kangaroos. What prevents dingos from going extinct in SA? Alternate prey to sustain when kangaroos in short supply.

Is there a response of this predator to an increase in its prey? Why? territorial K13.20 forest rodents and tawny owls in Poland. Red arrow = heavy crop from oak, maple, hornbean - triggered large increase in seed-eating rodents. Tawny owls maintain stable number on territories regardless of large change in prey abundance. Heavy seed 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? SS 15.8 Kestrels and voles during breeding. Curve did not reach horizontal level; no predator saturation. Type of curve underlying L-V equations Type 1 linear funcitonal response: predators take prey in proportion to their availability

***What type of functional response of wolves to moose? K13-17Type 11 fucntinonal response . Predation rate of wolves incresases with moose density, then appears to level off…need more data at higher densisites to resolve shape of relationsihip.

What type of functional response ***What type of functional response? Predators switch to different prey in response to fluctuations in prey density. Predators swtich to alternate prey in response to fluctuations in prey density. Water bug feeding on mayfly larvae; red line = no preference of mayfly larvae over other prey At low density - goes to other prey; at high density switches to mayfly disproportionately.

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? K 13.15 Density of wolves increass with moose density up to about 1 moose per km2 and them may reach a plateau. Wolves defend territories, which may restrict their numerical response to prey abundance Figure 11

Why didn’t top-down control limit spruce budworm devastation?

Is there a functional response. Numerical response ***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 K13.19 Warbler increased 12X in response to irruptionof spruce budworm in Canada. Showed both a functional (A) and numerical (B)response. C= combined (total) response As shown in C, an 8000 X increase in budworm reduced predator to an insignificant mortality agent. Threshold of prey density above which prey escape from being limited by predators.

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. 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.

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 Population cycles synchronized among species in a region. Periodic cycles with peaks separated by same number of years. Small mammal synchronized cycling, but dominated by varation in most common species, but other species tend to reach peak abundances more or less in synchrony with it. Figure 13

Other species may vary in their response to changes in the environment --> asynchronized cycles. Pop highs and lows don’t coincide closely, suggesting that they are governed by different factors. Four moth species in same haibtat fluctuate independently. Germany over 60 yrs. Figure 14

Predator and prey populations often increase and decrease in synchronized cycles. Which group lags the other?

Do prey control predators or vice versa? 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

Fence; no lynx Controls Extra food for hares Both

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. See Gotelli pg 161-2

Island (low predators) vs. mainland pops: Cycle continues; 2) Fluctuation less on island 45

Cycles have damped out with warmer temperatures. 46

How can these measles cycles be explained ***How can these measles cycles be explained? Who is predator and who is prey? Draw in the curve for the missing component. Measles = virus; must spread between living hosts…highly contagious.

Fluctuations in population density in a host-parasitoid system in the lab. Azuki bean weevil and wasp parasitoid kept for 120 cycles Krebs…pg 215

How stabilize predator-prey interactions? No sediment Sediment(hiding places) SS15.4 Paramecium and Didinium: R = K13.7 Gause’s testtube experiments A - oat w/o sediment; Didinium found all prey and ate, then starved to etinction B - oat with sediment; Didinium found all prey in clear, but then starved; some prey hid in refuge and took off after Didinium extinction C Immigration of P and D in oat without sediment; regular cycles Concluded: prey need refuge from predator stable system not from predator-prey interactions, but from outside force againsg the system.(immigration) Immigration Figure 19

Huffaker’s experiment to get predator-prey populations to persist without immigration. 2 mites = prey and predator

1) Oranges clumped---> what happened to cycle? Figure 20

2) Oranges dispersed randomly---> what happened to cycles? Why? 3) Spatial heterogeneity --->stable cycles. 120 spots; equilvalent of 6 oranges; added bariers to dispersal of predator (vasoline) and some pegs to faciliate parachuting of prey to new locations Figure 21