BIOS 3010: Ecology Lecture 8: Predator foraging & prey defense. 2. Predation: 3. Predator diet breadth and preference:

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1 BIOS 3010: Ecology Lecture 8: Predator foraging & prey defense 1. Lecture Summary: What is predation? Predator diet breadth. Preference & switching. Optimal foraging. Marginal value theorem. Functional responses. Interference. Spatial distribution. Ideal free distribution. Bernard D Abrera at M F Batesian mimicry in Papilio dardanus Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 1 2. Predation: Predation is the ecological process that describes the nature and dynamics of the interaction between prey defense and predator foraging. Defense against predators can also influence prey foraging behavior as shown in Figs 9.18 & Here we will consider the nature of this interaction behaviorally in an evolutionary context and in the next lecture we will consider the dynamics of prey-predator interactions Remember Hutchinson's ecological theater and the evolutionary play Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 2 3. Predator diet breadth and preference: Food preference: Monophagous: Often specialists that feed on a single prey type Oligophagous Polyphagous: Often generalists that attack many prey types. Preference is defined as: The proportion of a food type in an animal's diet being higher than its proportion in the environment. Table 9.1 and Fig ranked profitability according to energy return per unit handling time. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 3 1

2 4. Switching diet: Food items eaten disproportionately when common & ignored when rare (Fig. 9.15). Predators also learn from experience. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 4 5. Optimal foraging: To obtain food a predator must expend time and energy to search for prey and then handle it: Pursuing, subduing, accepting and consuming. Optimal forager should balance costs and benefits of searching and handling to maximize its overall rate of intake. Diets tend to be more generalist in unproductive environments where prey items are relatively rare, but specialist when prey are common and easy to find (Fig. 9.17). Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 5 6. The marginal value theorem: Optimal patch residence time is defined in terms of the rate of energy extraction at the moment of departure (the marginal value of the patch) see Fig An optimal forager is assumed to maximize its overall intake of a prey resource during foraging bouts moving from patch to patch. The currency to be maximized is energy and the problem is how to do this without leaving a patch too soon or staying too long. See Fig for an example. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 6 2

3 7. Functional responses: Relationship between predator consumption rate and prey density: Holling classified three basic types of functional response: Type 1: linear rise of consumption rate with prey density to a maximum level e.g. filter feeders such as Daphnia (Fig. 10.8) or baleen whales. Type 2: commonest; consumption rate rises at decelerating rate with prey density to plateau (Fig. 10.9): Search time decreases & handling time increases with increasing prey density until all predator time is spent handling prey which sets the level of the curve maximum. Type 3: S-shaped (sigmoidal) with accelerating consumption at low prey densities (Fig ): Much like switching (shows the effect of learning, often through search image formation). Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 7 8. Mutual interference among consumers: Increases in predator density lead to intraspecific competition because of mutual interference which depresses overall feeding rates because searching efficiency is reduced: -m is the slope of searching efficiency that decreases with increasing consumer density and represents a coefficient of interference in Fig Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 8 9. Predators and patchily distributed prey: Prey (food items) are usually patchily distributed (whether random, aggregated or regular) and patches vary in quality or quantity of food. So predators may show a density-dependent aggregative response to prey density as in Fig. 9.11, thus: 1) Predators spend most time in patches with highest prey density 2) Most predators occur in patches with highest prey density 3) Prey in highest density patches are therefore most vulnerable to predation and prey in low density patches are least vulnerable. 1) and 2) can be true, but some examples show inverse density dependence or density independence as in Fig ) may not be true because prey often aggregate for defense and so predator aggregative responses may not increase the proportion of prey attacked. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 9 3

4 10. Predators and patchily distributed prey: Huffaker s oranges: Patchiness can also stabilize prey-predator interactions as Huffaker showed in his famous experiment with mites playing hideand-seek among oranges (Fig ) that generated both spatial and temporal habitat heterogeneity. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide The ideal free distribution : Some conflict exists between the aggregative response and mutual interference. Initially high density food patches are attractive but as more predators aggregate they interfere more and so the patch is less profitable. Hence the ideal free distribution - consumers are ideal in their assessment of patch profitability and they are free to move from patch to patch according to profitability (Fig. 9.27a) and patches should eventually be equally profitable if consumers are equal (9.27b). Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 11 Figure 9.18: Seasonal changes in predicted habitat profitability & actual foraging by bluegill sunfish. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 12 4

5 Figure 9.19: Effect of largemouth bass on bluegill foraging location Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 13 Table 9.1 (3 rd ed.): Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 14 Figure 9.14: Prey profitability and selection by crabs and wagtails Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 15 5

6 Figure 9.17: Optimal diet choice in bluegills & great tits with predictions of Charnov s (1976) optimal diet model. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 16 Figure 10.8: Type 1 functional response - Daphnia filtering yeast. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 17 Figure 10.9: Type 2 functional response - damselflies eating Daphnia & bank voles eating willow shoots Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 18 6

7 Figure 10.10: Type 3 functional responses for (a) shrews & mice eating sawfly cocoons, (b, d) flies eating sugar drops, (c, e) wasps attacking aphids. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 19 Figure 9.10 (3 rd ed.): Mutual interference among (a) Encarsia wasps and (b) predatory mites. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 20 Figure 9.11 (3 rd ed.): Aggregative responses in (a) parasitoid wasp, (b) coccinellid larvae, (c) redshank, (d) woodpigeons. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 21 7

8 Figure 9.20: Percent parasitism in the field showing (a, c) direct density dependence, (b) inverse density dependence, (d, e) density independence Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 22 Figure 10.16: Eotetranychus (a) orangefeeding mite dynamics Eotetranychus, (b) single oscillations caused by predatory mite, (c) oscillations sustained by habitat patchiness Eotetranychus Typhlodromus Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 23 Figure 9.22: The marginal value theorem. Staying time predictions based on rates of energy extraction and cumulative energy extraction with time spent in patches of food. Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 24 8

9 Figure 9.23: Experimental test of the marginal value theorem with caged great tits. +energy costs Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 25 Figure 9.27: Ideal free distribution in 33 ducks fed bread at 2:1 profitability Dr. S. Malcolm BIOS 3010: Ecology Lecture 8: slide 26 9