Main Points. 1) Metabolism and allometries continued

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1 Main Points 1) Metabolism and allometries continued 2) Optimal Foraging Theory -- key assumptions -- example: heritability of foraging behavior in ground squirrels -- diet choice -- example: dietary specialization in sea otters -- example: CSI special mammal edition -- when to stop eating Terms: search time, handling time, optimal foraging theory, marginal value theorem, patch Pre-reading: Monday 15 October = NA Wednesday 17 October = Emlen and Oring 1

2 Metabolism and body size Energy-equivalence rule = energy consumed by populations of co-occurring species tends to be equivalent. This is because allometries between body size and metabolic rate, and body size and population density cancel out. metabolism of population body mass (g) 2

3 Metabolism and body size Trade-offs between body size, metabolism, and fitness Small individuals/species -- high mass-specific metabolic rates -- fast conversion of energy into offspring, compared to ability to obtain energy 1.8 g Etruscan shrew 2.0 g bumblebee bat 3.0 g African pygmy mouse (right) 3

4 Metabolism and body size Trade-offs between body size, metabolism, and fitness Large individuals/species -- low mass-specific metabolic rates -- slow conversion of energy into offspring, compared to ability to obtain energy 700 kg polar bear 1500 kg gaur 3500 kg bush elephant 4

5 An optimal body size? = smallest mammal on landmass = largest mammal on landmass Brown et al

6 An optimal body size? Brown et al

7 An optimal body size? Brown et al

8 An optimal body size? Brown et al

9 Basics of Foraging 9

10 Basics of Foraging Two components of foraging 10

11 Basics of Foraging Two components of foraging -- searching/finding = search time 11

12 Basics of Foraging Two components of foraging -- searching/finding = search time -- subduing/pursuit/digesting = handling time 12

13 Optimal Foraging Theory Optimal Foraging = processes through which animals maximize energy acquired per unit time, energy, and risk involved in finding food. Key assumption: natural selection favors animals that maximize energy gain; there are two ways that this can occur: -- through learning -- through inheritance of optimally foraging parents 13

14 Optimal Foraging Theory Test of OFT assumption: -- calculated optimal diet of adult female Columbian ground squirrels, based on plant availability 14

15 Optimal Foraging Theory Test of OFT assumption: -- calculated optimal diet of adult female Columbian ground squirrels, based on plant availability -- calculated differences between observed diet (what squirrels actually ate) against calculations of the optimal diet 15

16 Optimal Foraging Theory Test of OFT assumption: -- calculated optimal diet of adult female Columbian ground squirrels, based on plant availability -- calculated differences between observed diet (what squirrels actually ate) against calculations of the optimal diet -- compared kids differences to mom s differences 16

17 Optimal Foraging Theory Kid s deviation from prediction Ritchie Mom s deviation from prediction

18 Optimal Foraging Theory Kid s deviation from prediction Ritchie Mom s deviation from prediction

19 Optimal Foraging Theory Discussion Q: From the graph below, what can we conclude about if and how foraging behavior is transferred from mom to kids? Hint: think in terms of learning versus inheritance. If foraging behavior were entirely learned (or entirely inherited), would these graphs look different? How? Kid s deviation from prediction Ritchie Mom s deviation from prediction

20 Optimal Foraging Theory Two decisions required of optimal foragers 20

21 Optimal Foraging Theory Two decisions required of optimal foragers 1. what do I include in my diet? (diet choice) 2. when do I leave a patch? (the marginal value of patches) 21

22 Diet Choice What do I include in my diet? Should depend on: -- ease of searching (finding) and handling (subduing/pursuing/digesting) 22

23 Diet Choice Reintroduced Sea Otters otter density prey density -- site 1 = sea otters close to carrying capacity; resources limiting -- site 2 = sea otters recently reintroduced; resources abundant food intake site 1 site 2 Tinker et al

24 Diet Choice Reintroduced Sea Otters otter density prey density -- site 1 = sea otters close to carrying capacity; resources limiting -- site 2 = sea otters recently reintroduced; resources abundant food intake site 1 site 2 Tinker et al

25 Diet Choice Reintroduced Sea Otters otter density prey density -- site 1 = sea otters close to carrying capacity; resources limiting -- site 2 = sea otters recently reintroduced; resources abundant food intake site 1 site 2 Tinker et al

26 Diet Choice Reintroduced Sea Otters otter density site 1 site 2 site 1 site 2 food intake prey density site 1 site 2 Tinker et al

27 Diet Choice What do I include in my diet? Should depend on: -- ease of searching (finding) and handling (subduing/pursuing/digesting) prey -- forager s state (i.e. how desperate am I)? 27

28 Diet Choice the Man-Eaters of Tsavo In 1898, between humans killed by lions in southern Kenya while constructing Kenya-Uganda railway. 28

29 Diet Choice the Man-Eaters of Tsavo Both individuals were shot and donated to Chicago Field Museum in 1898, where they currently are on display. 29

30 Diet Choice the Man-Eaters of Tsavo bone collagen (years) hair keratin (months) 30 Yeakel et al

31 Diet Choice the Man-Eaters of Tsavo bone collagen (years) hair keratin (months) 31 Yeakel et al

32 Optimal Foraging Theory Two decisions required of optimal foragers 1. what do I include in my diet? 2. when do I leave a patch? 32

33 Optimal Foraging Theory Marginal Value Theorem = an animal should remain in a patch until the energy gain from that patch has declined to the average gain for the habitat. 33

34 The Marginal Value Theorem Examples of patches 34

35 Giving-Up Times and Patch Quitting Rules What factors should influence when I quit foraging in a patch? -- risk of starvation -- risk of predation -- lots of missed opportunities 35

36 Giving-Up Times and Patch Quitting Rules Marginal Value Theorem: What factors should influence when I quit foraging in a patch? MVT makes three testable predictions Foragers will stay (i.e., eat) longer 1) in a more profitable patch 2) when travel time between patches is high 36

37 The Marginal Value Theorem Time to next patch Time spent in patch 37

38 The Marginal Value Theorem Time to next patch Time spent in patch 38

39 The Marginal Value Theorem Time to next patch Time spent in patch 39

40 The Marginal Value Theorem Time to next patch Time spent in patch 40

41 The Marginal Value Theorem short time to next patch long time to next patch total energy gain Time to next patch Time spent in patch 41

42 Giving-Up Times and Patch Quitting Rules Marginal Value Theorem: What factors in the environment influence when I should leave a patch? MVT makes three testable predictions Foragers will stay (i.e., eat) longer 1) in a more profitable patch 2) when travel time between patches is high 3) when the environment, in general, is of low quality 42