Main Points. Test #1 Thursday 1 October minutes for questions on Test #1 Tuesday 29 September.

Transcription

1 Main Points 1) Predation as a driver of ecological communities -- experiments in ecology -- top-down vs bottom-up regulation of populations -- example: apparent competition in northern ungulates -- example: an application of apparent competition and predator swamping in conserving a declining ungulate 2) Density- vs behaviorally-mediated interactions -- the composite hypothesis of trophic cascades -- example: trophic cascades and woody-plant regeneration in the GYE -- example: top-down control does not always result in trophic cascades Pre-reading: Tuesday 29 September = Young et al Thursday 1 October = NA Test #1 Thursday 1 October minutes for questions on Test #1 Tuesday 29 September. Thursday 24 Sep (today) = HW #1 ed to Jake as a.doc by 5pm. There will be no confirmation of receipt, so please save a copy of your that you send. Terms: functional response, predator swamping, press experiment, pulse experiment, natural experiment, top-down regulation, bottom-up regulation, trophic cascade 1

2 Density-dependent population growth # kids surviving / ind population size 2

3 Density-dependent population growth # kids surviving / ind Density-Dependent Factors 1) Competition 2) Disease/Parasites 3) Predation population size 3

4 Functional responses of predators Functional Response: the response of a predator to the abundance of prey. 4

5 Functional responses of predators Functional Response: the response of a predator to the abundance of prey. Involves the question Does the number of prey an individual predator eats depend on that prey s abundance? Deals with changes in predator behavior (not predator numbers). 5

6 Functional responses of predators Functional Response: the response of a predator to the abundance of prey. # prey consumed by predator prey abundance Type 1 Functional Response the number of prey consumed increases without limit with increasing prey abundance. 6

7 Functional responses of predators Functional Response: the response of a predator to the abundance of prey. # prey consumed by predator prey abundance Type 2 Functional Response The number of prey consumed rises at first, then levels off. 7

8 Discussion Q: what would cause a predator to exhibit behavior consistent with a type 2 (versus type 1) functional response? # prey consumed by predator prey abundance 8

9 Functional responses of predators Predator swamping: an anti-predator strategy whereby the probability of an individual being eaten decreases with numbers. 9

10 Functional responses of predators Prey switching: predators switch between different species of prey when alternative sources of prey are abundant, reducing pressure on the prey population. # prey consumed by predator prey abundance Type 3 Functional Response The number of prey consumed increases with increasing prey abundance, then levels off. 10

11 Experiments in conservation biology Experiment = a test under controlled conditions made to examine the validity of a hypothesis. 11

12 Experiments in conservation biology Experiment = a test under controlled conditions made to examine the validity of a hypothesis. Pulse experiment = manipulation is applied once, then the response of the system (e.g., abundance, distribution, diversity) is measured. 12

13 Experiments in conservation biology Experiment = a test under controlled conditions made to examine the validity of a hypothesis. Press experiment = manipulation is applied continually, then the response of the system (e.g., abundance, distribution, diversity) is measured. 13

14 Experiments in conservation biology Experiment = a test under controlled conditions made to examine the validity of a hypothesis. Natural experiment = an observational study in which a manipulation is applied by nature, rather than by experimenters. 14

15 Top-down versus bottom-up control 15

16 Top-down versus bottom-up control 16

17 Top-down versus bottom-up control = (predators not poached) = (predators poached) = (predators not poached) 17

18 Top-down versus bottom-up control = (predators not poached) = (predators poached) = (predators not poached) Sinclair et al

19 Top-down versus bottom-up control = (predators not poached) = (predators poached) = (predators not poached) Sinclair et al

20 Top-down versus bottom-up control = (predators not poached) = (predators poached) = (predators not poached) Sinclair et al

21 Prey switching and prey preferences From Wittmer et al

22 Prey switching and prey preferences caribou show evidence of an Allee effect, implying that food isn t limiting. 22

23 Prey switching and prey preferences? 23

24 Prey switching and prey preferences _ 24

25 Prey switching and prey preferences Apparent competition: indirect negative interaction incurred by one (or more) prey species because of a shared predator. _ 25

26 Discussion Q: Why does the dashed arrow only point to the caribou? In other words, why don t moose experience more predation because of caribou? _ 26

27 Prey switching and prey preferences Apparent competition has been implicated in the declines of many species of conservation concern. Typically involves either introduction of a novel primary prey (that subsidizes predators), habitat alteration, or both. 27

28 Predators, Livestock Production, and Apparent Competition Laikipia District consists of ~10,000 km 2 managed jointly for cattle production and tourism no formal protection; entirely voluntary highest abundances of wildlife anywhere in Kenya 28

29 Predators, Livestock Production, and Apparent Competition Observation 1: plains zebra and cattle have not declined over a 20-year time period; their numbers are controlled by rainfall From Georgiadis et al

30 Predators, Livestock Production, and Apparent Competition Observation 2: some antelopes have declined concurrently with a shift in ranchers attitudes towards predators hartebeest waterbuck common eland buffalo From Georgiadis et al

31 Predators, Livestock Production, and Apparent Competition Observation 3: zebra prefer to graze in areas where cattle recently have been corralled day 2 day 1 day 28 day

32 Predators, Livestock Production, and Apparent Competition Question 1: by changing where zebra occur, can cattle be used to shift hunting behavior of lions? 32

33 Predators, Livestock Production, and Apparent Competition # prey consumed by predator prey abundance Type 2 Functional Response The number of prey consumed rises at first, then levels off. 33

34 Predators, Livestock Production, and Apparent Competition # prey consumed by predator prey abundance Type 3 Functional Response The number of prey consumed increases with increasing prey abundance, then levels off. 34

35 Predators, Livestock Production, and Apparent Competition Question 2: can cattle be used to pull lions away from hartebeest and other declining ungulates? 35

36 Predators, Livestock Production, and Apparent Competition hartebeest population growth is consistent with an Allee effect, and Type II functional response of predators 36

37 Predators, Livestock Production, and Apparent Competition hartebeest population growth seems limited by lions, and not other predators 37

38 Predators, Livestock Production, and Apparent Competition 38

39 Predators, Livestock Production, and Apparent Competition 39

40 If this works, why would it work? 40

41 Blacktail Creek YNP, 1996 Blacktail Creek YNP,

42 Density Vs. Behaviorally-Mediated Interactions Trophic cascade = indirect, positive effect of predators on plants routed through herbivores + 42

43 Discussion Q: Marris described a debate in the literature concerning wolves, elk, and woody plants (aspen and willows) in the GYE. What does this debate concern? What evidence exists in favor of each side? + 43

44 A deceptively simple looking meta-hypothesis meta-hypothesis carnivore herbivore producer

45 A deceptively simple looking meta-hypothesis meta-hypothesis hypothesis 1 carnivore carnivore herbivore herbivore producer

46 A deceptively simple looking meta-hypothesis meta-hypothesis hypothesis 1 hypothesis 2 carnivore carnivore herbivore herbivore herbivore producer producer

47 A deceptively simple looking meta-hypothesis meta-hypothesis hypothesis 1 hypothesis 2 hypothesis 3* carnivore carnivore carnivore herbivore herbivore herbivore producer producer producer * by itself, this positive association between producers and carnivores often is taken as evidence for a trophic cascade

48 Density Vs. Behaviorally-Mediated Interactions Ripple and Beschta presented data showing that: 1) wolves increased in the GYE between Ripple and Beschta

49 Density Vs. Behaviorally-Mediated Interactions Ripple and Beschta presented data showing that: 1) wolves increased in the GYE between ) elk decreased in the GYE between Ripple and Beschta

50 Density Vs. Behaviorally-Mediated Interactions Ripple and Beschta presented data showing that: 1) wolves increased in the GYE between ) elk decreased in the GYE between ) browsing decreased, and aspen height increased, especially in risky areas between Ripple and Beschta

51 Density Vs. Behaviorally-Mediated Interactions 51

52 Density Vs. Behaviorally-Mediated Interactions The wolf population appears to be near saturation, controlled currently by intraspecific competition for territories Kauffman et al

53 Density Vs. Behaviorally-Mediated Interactions 53

54 Density Vs. Behaviorally-Mediated Interactions rapid re-occupation of the Northern Range with persistent beaver colonies, especially along Slough Creek, occurred because Tyers of the Gallatin National Forest released 129 beavers in drainages north of the park. Smith and Tyers, 2008, p