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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 decisions in terms of their fitness payoffs
Decision variable – behavioral options
Currency – often related to fitness
Constraints – intrinsic vs. extrinsic
Advantages
Make assumption explicit
Generate testable prediction
Suggest new hypothesis if model does not fit
Criticism
Behavior may not always optimal
Optimal diet E1 E2 E2 E1 E1h2
----- > ----- , if ----- > ------- => S1 > -------- - h1
h1 h2 h2 S1+h1 E2
Always eat the most profitable prey type
Include less profitable prey only if S1 > (E1h2/E2) - h1
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
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
E3 > (E1 + E2)/(h1 + s1 + h2 + s2)
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
Patch choice modelWhen 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
Marginal value theorem – patch residence time
Great titMeal 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
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
What if optimality failsNutrients, predation, competition, risk of starvation, age, experience, etc.
Consider currency other than profitability
Efficiency, Egain/Espent
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
Foraging in a variable environment
Immediate responseRisk sensitive foraging
Long-term responseTopor or hibernation
Fat storage
Caching or hoarding
agriculture
Risk sensitive foraging
Choose to forage in constant or variable (unpredictable) environment
Risk averse vs risk prone
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.
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
Anti-predator strategies making detection less likely
egg-shell removalcamouflage & cryptic behaviorindustrial melanism in mothFreezingremoving evidence of presencebroken-winged display
Cost of cryptic behaviorTime 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
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
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
stotting--hypotheses alarm signal hypothesissocial cohesion hypothesisconfusion effect hypothesispursuit-deterrent (un-profitability advertisement hypothesis)anti-ambush hypothesishandicap principlestartle effect
making capture less likelyvigilance, e.g. moth-bat
misdirecting a predator's attack
fleeing
Cooperative defense
vigilance
selfish herd
dilution effect
group mobbing
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
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
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
Alarm call
Ideal free distributionAnimal 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
Deviation from IFD16/20 studies show too many in poor habitat or too few in rich habitat
Perception error
Differences in competitive abilityDominants exclude subordinates
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
Economics of territorialityResource 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
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