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Optimal theory The theory used to generate hypotheses about the adaptive value of characteristics which analyzes the costs and benefits of alternative.

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Presentation on theme: "Optimal theory The theory used to generate hypotheses about the adaptive value of characteristics which analyzes the costs and benefits of alternative."— Presentation transcript:

1 Optimal theory The theory used to generate hypotheses about the adaptive value of characteristics which analyzes the costs and benefits of alternative decisions in terms of their fitness payoffs Decision variable – behavioral options Currency – often related to fitness Constraints – intrinsic vs. extrinsic

2 Advantages Make assumption explicit Generate testable prediction Suggest new hypothesis if model does not fit Criticism Behavior may not always optimal

3 Optimal diet E 1 E 2 E 2 E 1 E 1 h 2 ----- > -----, if ----- > ------- => S 1 > -------- - h 1 h 1 h 2 h 2 S 1 +h 1 E 2 Always eat the most profitable prey type Include less profitable prey only if S 1 > (E 1 h 2 /E 2 ) - h1

4 Inclusion of the less profitable prey does not depend on its abundance, only on the abundance of the more profitable prey Specialist on prey 1 will switch and become generalist both suddenly and completely when prey 1 become rare

5 Multiple prey choice Rank all prey by profitability To decide whether to include a prey item when encounter, its profitability must exceed the net profitability of all higher ranking prey E 3 > (E 1 + E 2 )/(h 1 + s 1 + h 2 + s 2 )

6 Reasons for partial preference Discrimination error Lack of complete information Variation in predator or prey Simultaneous encounter of multiple prey Short term sampling rule for estimating encounter rate

7 Patch choice model When is the optimal time to leave a patch? e.g. hummingbird or bee visiting flowers Constraints Time spent searching in patches and traveling between patches are independent Perfect knowledge Energy gain in patches show diminishing gain

8 Marginal value theorem – patch residence time

9 Great tit Meal worm hidden in sawdust in pots hanging from trees Long and short travel time achieved by making lids hard or easy to remove Actual patch resident time ~ prediction

10 Central place foraging Starling travel between feeder and nest Load curve shows diminishing return because it becomes harder to probe as bill fills Observation fits MVT prediction

11 What if optimality fails Nutrients, predation, competition, risk of starvation, age, experience, etc. Consider currency other than profitability Efficiency, E gain /E spent

12 Nectar load of bee shows diminishing return because larger loads take more energy Fit maximize efficiency model but not maximize profitability Selection on hives favor efficiency

13 Foraging in a variable environment Immediate response Risk sensitive foraging Long-term response Topor or hibernation Fat storage Caching or hoarding agriculture

14 Risk sensitive foraging Choose to forage in constant or variable (unpredictable) environment Risk averse vs risk prone

15 Foraging in Juncos Two pans: one with a non-variable modest reward and the other with a variable but higher pay-off reward The birds that were non-energy limited chose the lower payoff pan over the higher payoff, but risky pan. When food was limited, they opted for the higher payoff but risky pan.

16 Why hoarding instead of fat storage Fat increase body mass and predation risk If food is super-abundant, not all can be stored as fat Large store provide food supply for a group over winter Can be more easily transferred to offspring

17 Anti-predator strategies making detection less likely egg-shell removal camouflage & cryptic behavior industrial melanism in moth Freezing removing evidence of presence broken-winged display

18 Cost of cryptic behavior Time lost for other activities Belding ’ s ground squirrels respond to alarm call: hiding in underground burrows = time not spent feeding Cost of time lost for feeding varies among individuals depending on their nutritional status. Well-fed individuals should have less to gain from additional feeding

19 Trinidadian guppies Males court most vigorously at moderate light intensity (low light, not visible to females; high light, too visible to predators) Small males court more vigorously, especially at high light intensity

20 making attack less likely physical and chemical repellents and weapons warning coloration & behavior bright color wings under dull color wings, big eye-spots hiss sound, inflation and increase body size, tail of rattlesnake, stripes and hand-stand of skunks mimicry

21 stotting--hypotheses alarm signal hypothesis social cohesion hypothesis confusion effect hypothesis pursuit-deterrent (un-profitability advertisement hypothesis) anti-ambush hypothesis handicap principle startle effect

22 making capture less likely vigilance, e.g. moth-bat misdirecting a predator's attack fleeing Cooperative defense vigilance selfish herd dilution effect group mobbing

23 Key prediction of selfish herd hypothesis Individuals should compete for access to safest spots in the herd Individuals in least safe spots in the herd should be safer than are solitary individuals e.g. blue-gill sunfish breeds in colony. Males compete for central territory which is preferred by females and lower in predation risk. Solitary males experiencing higher rate of infestation/predation than edge males

24 Cooperative defense: mobbing Hypothesis: If mobbing protects eggs and young, the degree of protection should be proportional to the intensity of the mobbing Test: placing eggs along a transect from inside to outside the border of the colony Results: mobbing rates increased toward center of colony and predation rate decreases as mobbing rates increased

25 Hypothesis: comparative method Related species nesting in habitats less vulnerable to terrestrial predation should not exhibit the behavior – kittiwake Unrelated species nesting in similar habitats should demonstrate mobbing – swallow, ground squirrels

26 Alarm call

27 Ideal free distribution Animal sequentially fill available habitat staring with best patches Assumption “ ideal ” by possessing perfect info about resource quality “ free ” to disperse appropriately Expectation – animals disperse to equalize energy intake or reproduction

28 Deviation from IFD 16/20 studies show too many in poor habitat or too few in rich habitat Perception error Differences in competitive ability Dominants exclude subordinates

29 Dominance – how? Resource holding potential - ability of control access to a resource Correlate w/ body size, experience, matrilineal relationship, fat reserves, prior success or failure, etc. Require recognition or status badge

30 Economics of territoriality Resource must be defendable Renewable, not ephemeral or super-abundant Benefit > cost of defense Energetic cost increase w/ # of intruders, territory size Benefit accrue by increasing energy intake rate, reducing energy cost and starvation risk

31 If nectar level increase from 2 to 3 ul per flower, the bird save 1.3 hr per day foraging time and save (1000x1.3) – (400x1.3) = 780 cal But the bird spent 0.28 hr per day defending and the cost of defending = (3000x0.28) – (400x0.28) = 728 cal  Economically defendable

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