Extra Credit: due Thursday 28 September at 5pm as a.doc ed to Jake. Help session Tuesday 26 September.

Transcription

1 Main Points 1) Functional responses of predators -- prey switching and prey preferences -- Example: removing protected populations to save an endangered species -- apparent competition and the decline of species of conservation concern -- Example: apparent competition between caribou and moose -- Example: using cattle to conserve (yet another) declining antelope 2) Trophic interactions -- the composite hypothesis of trophic cascades -- Example: trophic cascades and woody-plant regeneration in the GYE 3) Help sesh for homework Pre-reading: Thursday NA Tuesday NA Field Trip: Thursday 28 September. Meet 920 sharp outside Berry Center entrance on Lewis. If you need Jake to contact your professor from an earlier class, let him know. Presentation #1 Groups: must meet with Jake before 3 October. Extra Credit: due Thursday 28 September at 5pm as a.doc ed to Jake. Help session Tuesday 26 September. Test #1: Tuesday 3 October Terms: functional response, prey switching, apparent competition, trophic cascade 1

2 Functional Responses Functional Response: the response of a predator to the abundance of prey. 2

3 Functional Responses 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). 3

4 # prey consumed by predator Functional Responses Functional Response: the response of a predator to the abundance of prey. Type 1 Functional Response the number of prey consumed increases without limit with increasing prey abundance. prey abundance 4

5 # prey consumed by predator Functional Responses Functional Response: the response of a predator to the abundance of prey. Type 2 Functional Response The number of prey consumed rises steeply at first, then levels off. prey abundance 5

6 # prey consumed by predator Discussion Q: what would cause a predator to exhibit behavior consistent with a type 2 (versus type 1) functional response? prey abundance 6

7 # prey consumed by predator Functional Responses Prey switching: predators switch between different species of prey when alternative sources of prey are abundant, reducing pressure on the prey population. Type 3 Functional Response The number of prey consumed increases with increasing prey abundance, then levels off as prey switching occurs. prey abundance 7

8 Functional Responses of Predators and Allee effects of Prey 8

9 Functional Responses of Predators and Allee effects of Prey Courchamp et al Science. 9

10 Prey Switching and Prey Preferences Wittmer et al Oecologia. 10

11 Prey Switching and Prey Preferences caribou show evidence of an Allee effect, implying that food isn t limiting. Wittmer et al Oecologia. 11

12 Prey Switching and Prey Preferences? 12

13 Prey Switching and Prey Preferences _ 13

14 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? _ 14

15 Prey Switching and Prey Preferences Apparent competition: indirect negative interaction incurred by one (or more) prey species because of a shared predator. _ 15

16 Prey Switching and Prey Preferences Serrouya et al Peer J. 16

17 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. 17

18 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 18

19 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

20 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

21 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

22 Lions selectively kill hartebeest

23 Experimental removal of lions

24 0 0 S a F a S c treatments (lions, no lions) x 3 years ( ) 0 S sa S a S a S c S sa F a

25 Lions suppress hartebeest populations λ = λ =

26 Lions drive an Allee effect Hartebeest exhibit inverse density-dependence in the presence of lions, and negative density-dependence where lions have been experimentally removed.

27 How have hartebeest coexisted with lions for thousands of years? Historical baseline Pre-1950s Lethal control of lions 1950s-mid 1980s Restoration of lions 1980s-present

28 How have hartebeest coexisted with lions for thousands of years? Historical baseline Pre-1950s Lethal control of lions + Fire suppression 1950s-mid 1980s Restoration of lions + Fire suppression + Tree encroachment mid 1980s-present?

29 Lion and hartebeest numbers are correlated negatively

30 +

31 Number of prey consumed per predator Functional responses and spatial refuges Type II Prey density

32 Number of prey consumed per predator Proportion of prey population eaten Functional responses and spatial refuges Type II Type II Prey density Prey Density

33 Number of prey consumed per predator Proportion of prey population eaten Number of prey consumed per predator Proportion of prey population eaten Functional responses and spatial refuges Type II Type II Type III Type III Prey density Prey Density

34 Functional responses and spatial refuges

35 Functional responses and spatial refuges

36 Glade creation experiment In 2010, constructed bomas standardized for the following: cattle m diameter -- active for 1 month

37 Glade creation experiment After 3 years, zebra were attracted to glades (β = 1.02 ± 0.69 CI) After 3 years, hartebeest avoided glades (β = ± 0.95 CI) zebra + experimental glades hartebeest + experimental glades

38 Predators, Livestock Production, and Apparent Competition 38

39 Glades tripled mortality due to lion predation for hartebeest No glade in territory Glade in territory Constructed frailty models for hartebeest survival Odds = 2.969, S.E. = 0.232, P < 0.001

40 Blacktail Creek YNP, 1996 Blacktail Creek YNP,

41 Density Vs. Behaviorally-Mediated Interactions Trophic cascade = indirect, positive effect of predators on plants routed through herbivores + 41

42 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 A Deceptively Simple Looking Meta-Hypothesis meta-hypothesis carnivore herbivore producer

44 A Deceptively Simple Looking Meta-Hypothesis meta-hypothesis hypothesis 1 carnivore carnivore herbivore herbivore producer

45 A Deceptively Simple Looking Meta-Hypothesis meta-hypothesis hypothesis 1 hypothesis 2 carnivore carnivore herbivore herbivore herbivore producer producer

46 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

47 47

48 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