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Am. beech Sugar maple Axis Sun to shade Tradeoff Allocation of Energy: vertical or horizontal Prey size/speed In capture techniques mass vs speed Micro-habitats.

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Presentation on theme: "Am. beech Sugar maple Axis Sun to shade Tradeoff Allocation of Energy: vertical or horizontal Prey size/speed In capture techniques mass vs speed Micro-habitats."— Presentation transcript:

1 Am. beech Sugar maple Axis Sun to shade Tradeoff Allocation of Energy: vertical or horizontal Prey size/speed In capture techniques mass vs speed Micro-habitats in spruce trees Time allocation; adaptation to parts of the tree Patch quality Cream-skimmers must get to patches first, or monopolize access Lion Cheetah G. pyramidumG. allenbyii Blackburnian BTGW

2 HW #3 (25 points): Mechanisms of Coexistence Due March 20 th. See Website Next week: Mutualisms; Mark McGinley March 20-22: Communities and Food Webs; Travis Hinkelman Exam II: Post-LV competition up to spring break MARCH 29th 77% turned in 2 HWs 45% 0 or 1 HW

3 Effect * of species 1 on species Effect of species 2 on species 1 COMPETITION MUTUALISM PREDATION * On per capita growth rate X

4 Predation – species interaction where one party benefits (predator) and one is hurt (prey) - behaviorally: diet choice, patch use - community level: How does predation contribute to species diversity ? - population impacts: how predators control and/or regulate prey numbers (or vice versa) Lethal approach – predators kill their prey Fear approach – predators scare their prey

5 type I - linear type II - satiation # prey consumed density of prey (N) Predators have two responses to their prey: (1)Numerical response -  predators with  prey (2)Functional response – predator consumption changes with prey density type III

6 Predator-prey models 1  N = r(K-N) -  (N)P N  t K 1  P =  (N)N  - d P  t  = conversion of consumed prey into new predators d = predator death rate  (N) = predator functional response rate of prey consumption by an individual predator as a function of prey density. logistic growth mortality from predators mortality birth via consumption of prey

7 What does it mean for the prey isocline to be humped? What does it mean for the predator isocline to be a vertical line? P N Pred (-) Pred (+) Prey (+) Prey (-) K

8 What does it mean for the prey isocline to be humped? safety in #’s limits to growth What does it mean for the predator isocline to be a vertical line? P N  no interactions among predators

9 Predator-prey Isoclines: per capita growth rates = 0 P N Region of neg. DD: damped oscillations (stable) Region of pos. DD: expanding oscillations (unstable) Apex of isocline: stable limit cycle (neither expands nor dampens)

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13 P N Region of pos. DD: expanding oscillations (unstable)

14 Unstable dynamics leads to population eruptions, particularly among insects Eucalyptus psyllid Spruce budworm Pine beauty moth Viburnum whitefly

15 How do you stabilize unstable predator-prey interactions? (Huffaker’s 1958 experiments) prey predator Simple environments lead to simple outcomes -- EXTINCTION

16 So, create complex environments including barriers to predator dispersal and cycles emerge – illustrates the importance of REFUGES

17 Physical Refugia – Predators do not have access to prey

18 Behavioral Refugia – Predators and prey not together in time and space * * * * * *

19 P N Refugia work by reducing predator efficiency & go from unstable to stable Low N* = efficient predator High N* = inefficient predator

20 What NOT to do – the Paradox of Enrichment K mule deer mountain lion mule deer K KK’ stable EQ unstable EQ (1) Productivity goes into building new predators NOT prey (2) Instability increases (3) Populations go extinct  Feed deer (increases K to K’) N* P*

21 Summary: (1)Predator-prey interactions contain inherent time lags that result in population cycles (2) These cycles can be stable, unstable, or neutrally stable (3) Relatively efficient predators lead to unstable cycles and extinction (4) Complex environments and refuges can stabilize predator-prey interactions (5) Enriching the prey population is not a viable strategy, rather it destabilizes interactions and leads to population extinction

22 The Ecology of FEAR

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24 Fear in the South African Landscape – Augrabies NP Rock Hyrax

25 The view away from the Kopje -

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27 Comparison of the lethal and fear approaches Lethal - predators kill their prey - Population density driven systems - Brownian motion behavior of pred/prey Fear - predators scare their prey - Fear driven systems: fierce predators and fearful prey - Sophisticated game of stealth and fear L W L W W W WL

28 K The Catch-22 of the lethal approach Efficient predators lead to highly unstable predator- prey interactions Inefficient predators lead to extinction of the predator in variable environments KK

29 K The Catch-22 of the lethal approach Inefficient predators lead to extinction of the predator in variable environments KK

30 Incorporating the Ecology of Fear (Brown et al. 1999) Prey are apprehensive – i.e., they engage in vigilance behavior M Fear (i.e., predation risk) = (prey have perfect info) (k + bu*) Fear: -  w/likelihood of encountering a predator, M -  w/predator’s lethality, 1/k -  w/effectiveness of vigilance, b -  w/level of vigilance, u* # pred, #prey, feeding opportunities

31 Tradeoff: Too much vigilance  miss out on valuable feeding opportunities Too little vigilance  likely killed by a predator Shift the hump in the prey’s isocline. Still safety in #s, but reduced high N reduces its effectiveness Bend down the predator’s isocline. Predator’s have reduced efficiency because more predators results in greater vigilance in the prey making them harder to catch  Interference or Behavioral Resource Depression

32 Implications: (1)Greater stability in predator-prey interactions – no Catch-22, and reduce the Paradox of Enrichment (2) Territoriality in fierce predators may function to protect the catchability of the prey – avoid the “wayward” Mnt. Lion stumbling into your territory (3) Behavior (e.g., vigilance) is a leading indicator of ecological change

33 Wolves, elk, and bison in Yellowstone: reestablishing the “Landscape of Fear” (Laundre et al – Can J. Zool. 79:1401) Wolves reintroduced into the Lamar Valley of Yellowstone in

34 This now becomes a familiar scene – wohoo!!!

35 ...while time spent foraging declines Vigilance in female elk w/calves increases…

36 Similarly for bison, however, males and females w/o calves no show behavioral shift

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38 1997 versus 2001

39 Three kinds of evidence: - The changes are much faster than could occur from elk mortality - Reduced herbivory is restricted to risky habitats - Elk have exhibited behavioral changes consistent with an Ecology of Fear Hypothesis: (1) favor areas with good visibility & escape structures (scat) (2) increased vigilance and less feeding These changes have left physiological evidence

40 Cottonwood trees need wolves in order to establish their populations as does willow and aspen.

41 O. Schmitz et al Control no spiders GH Plants lethal spiders non-lethal spiders if spiders have (-) on grasshoppers Experimental demonstrations of non-lethal effect of predators

42 20% 29% Most of the decrease in grasshoppers is due to ‘non-lethal’ effects

43 How do grasshoppers die with non-lethal spiders? Shift in daily activity to safer (from predators) but high stress Exposure to Sun & Heat w/spiders w/o

44 Do we see an increase in plant biomass? Its less clear there is an effect on plants

45 Broad Conclusions: Predators have at least two general effects on prey: lethal and non-lethal Predators kill prey and are also involved in a sophisticated game of stealth and fear Incorporating behavior (Fear) has important consequences for pred-prey interactions ….”Ignore Behavior at your peril”

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48 Raptors Lemmings Moss Raptors Voles Roots Are lemmings and voles predators or prey ??


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