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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 • • • • • • 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? • • • • 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