adaptation and anti-predator behavior chapter 6. why adaptation and anti-predation fact – death is...
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Adaptation and Anti-predator Behavior
Chapter 6
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Why adaptation and anti-predation
Fact – death is bad for fitness
So selection to avoid predation will be intense.
As a result, MANY many anti-predatory behaviors have evolved.
But how did they evolve?
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Adaptationist’s approach
Currently the main idea behind behavioral ecology
HistoricallyEthology (study of instinctual behavior in Europe)
Evolutionary ecology (study of evolution in U.S.A.)
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Adaptation’s approachAlso called the cost-benefit approachChoose a behavior of interestAssume the behavior has an adaptive
advantageie. behavior has been favored by natural selectionie. behavior conveys a net advantage on an
animal speciesConstruct a hypothesis about the nature of the
adaptation.Or hypotheses about the selective forces that
produced the behaviorOr hypothesis of “evolutionary design”.
Evolution does not have blueprints
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Adaptation’s approach
Test the hypothesisGenerate testable predictions
ie. predictions that can be falsifiable
Based on outcome of test, modify the hypothesis and test again
Note – the assumption of adaptation is never under examination
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Definition
Adaptation
A heritable trait that either spread because of natural selection and has been maintained by selection to the present or is currently spreading relative to alternative traits because of natural selection.
In either case, the trait confers an advantage to those individuals that possess it, which can be translated into greater reproductive success and fitness.
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Example in Action
Mobbing behavior by black-headed gulls
Why do an activity that expends valuable energy and time, and could result in injury or death?
Does the fitness benefit (+ effect on producing offspring) outweigh the fitness cost (- effect on genetic success)?
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Black-headed gulls
Gulls are observed to mob (attack) any possible predator that enters their nesting grounds.
Why attack?To protect yourselfTo protect your young
Costs to attacking?Could get injuredCould be killed and eaten by predator
Cost of not attacking?Young get eaten (- reproductive success)
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Test the hypothesisHans Kruuk tested the predator
distraction theory.
Placed 10 eggs, 1 per 10m, along a transect from outside to inside a gull nesting colony.
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Comparative Method for Testing
Testing predictions about evolution of a trait by looking at other species.
We have already done this:Infanticide in lions and monkeys
Anti-bat behavior in moths
We start with an ancestral trait for a group, and see where novel difference have arisen.
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Determining character states
What is ancestral?
Generally a trait contained by the majority of the group.
Idea that all gulls came from a common gull-like ancestor.
Behavior nesting site.
Most gulls nest on the ground, but a few nest on cliffs.
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Which is more likely?
Occam’s Razor – simpler explanation is most likely correct. (parsimony).
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Divergent evolution
Why is a behavior present in most of a group, but not all?
There needs to be a change in the selection pressure for some to promote the success of the new trait.
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Kittiwakes have clawed feet to hold onto ledges.
Ledges provide protection from predators of all kinds (mammalian, reptilian, and avian).
Reduced predation pressure has resulted in reduced or zero mobbing behavior.
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Convergent Evolution
Evolution of similar traits by groups that are not evolutionary related but share similar habitats.
If mobbing occurs in colonial, ground-nesting gulls, then other colonial breeders under predation threats may mob as well.
This is seen in other bird species, like most sparrows.Some sparrow species are cliff dwelling species, and do not
mob predators.
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Types of Evolution
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Predation Rules the World
Examples and Explanations of Anti-predatory Behavior
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Types of anti-predatory behavior
Decreasing detection by predators
Preventing attack or capture during an encounter with a predator
Behavior once captured
Chemical Defenses
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1. Decreasing detection by predators
Major adaptations
Camouflage – matching the background
Behavioral implications
Remain motionless – freezing in presence of possible threat
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Behavioral implications
Remain motionless – “freezing” in presence of possible threat.
Choose proper locationSeems to be the case – animals “realize” their
coloration and match background.
Alter color to match backgroundLizard (chameleon)Cephalopod (squid and octopus)Fish (flounder)Sunfish and bluegill – takes 2-3 weeks
Cover certain color cells with other cells
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Seek Concealment
Stay in dense vegetation
Common in small animalsAmazon leaf-carrying fish
Song birds moving within brush or cover
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Removing evidence of presence
Tinbergen’s egg shell experimentsBirds remove egg shell from nest after young
hatch.Avoid detection by predators
CaterpillarsChickadees learn that damaged leaves have
caterpillarsA “clever” caterpillar eats around the edge to
make leaf look undamagedAnti-predatory behavior
trim edges, clip damaged leaves, leave leaf during the day
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Clever Caterpillarsand Chickadees
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2. Preventing Attack or CaptureWhen to initiate escape?
Decide when or whether you need to initiate escape
Escape can be costly in time and energy.
Ex. Lizard flight initiation distancesWhen warm, will allow threat
to get closer
Main tactic is actually cryptic coloration and stillness, run only when believed discovered.
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Pursuit deterrence signalAn honest signal of ability to
escape.“I can run away…don’t even
bother.”
Ex. Stotting in gazellesJumps really high
Hypothesis 1 – signal to other gazellesAlarmGroup formation
Hypothesis 2 – Pursuit-deterrence signal
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Stotting and Signals
Observations: stotting observed in solitary gazellesAlso flash white hind quarters to predator
Predator generally abandons chase when stotting (3/4 of the time).
White-tail deer in North America also stott and flash tail to say “Hi, I see you.”
Tail wagging in lizards also the same signal.
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Protean Behavior
Extremely erratic behavior during escape
Random turns and reversals (zig zag)
This is common in many animals, occurs when you are about to get caught.
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6.15 Cryptic coloration depends on background selection
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Misdirecting Attacks
False heads
Fish have false eye spots
Tail loss in lizardsAbility to jettison tail to escape capture. Can re-
grow it later.
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Distraction Displays
Attempt to look injured to lure predator away from young.
Generally in shorebirds (Killdeer)
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Intimidation Displays
Look bigger and meaner than you are.
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Startling Displays
Deter attack
Gain time for escapeEx. Moth eye spots
Gives them time to escape
Toad w/ 2 black spots that blow up when threatened
Caterpillars that can inflate and look like a snake
Fly wings that resemble spider legs
Birds will fly right at the predator as a last resort (Hans Solo maneuver)
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Startling Displays
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Predator Inspection Behavior
Approach predator
A form of pursuit deterrence in some cases.
Lets the predator know its been seen
May also get info on the predatorIdentity of predator
Identify state of predator (whether its hunting or not)
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3. Behavior Once Captured
Fight back
Fear screams upon captureWarns others (relatives) when self dies
Might startle predator (not effective)
Get help
Attract other predators. Why???
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Behavior Once Captured
Other predators might fight over you, giving you a chance for escape.Best studied in birds.
Play DeadPredator might let go
May ignore prey
“Tonic immobility” – going limp and play dead.
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4. Chemical Defenses
“Slime and Goo” defensesBlack widow spiderSalamandersTermites (part of gooey head blows up)
Noxious defensesSkunksPoison skin (frogs and toads)Stinging insects (bees and ants)Monarch butterflies (toxin from plants)
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Chemical Defenses
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Deception – Batesian mimicsAposematically colored animals that are
not toxicBee-fly mimics
Acoustical mimicBurrowing owls can make a rattle sound
like an rattlesnake.
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Social Defenses
Group intimidation of predatorsMuskox and buffaloSome moth and sawfly larvae practice group vomiting
Improved predator detection in groupsExtremely common benefit to grouping in vertebratesIn a group – there are more eyes looking for predators
Assumption : a detector has to be able to warn others of attack through either alarm call or behavioral change
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Many-eyes effect%
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Group Size
Vigilance – time spent alert
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Effect of many eyesVigilance goes down as group size increases
Time spent foraging therefore goes up as group size increases
Even though individuals are less vigilant, the group has a high collective vigilance.Only works if everyone in groups will get the
warning.
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Vigilance against hawks
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Selfish herd effect
Animals seek the safest position within a group
Safest location is in the center, all else equal.
Dominate individuals are commonly in the center (largest)
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Examples of selfish herdsEx. Schools of fish
Cost of protection – food is less plentifulIncreased competition for foodHungry individuals are on the outside or edge of
the group
Ex. PenguinsIf a seal is attacking, the dominate penguins in
the center push others off the ice to feed the seal.
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Dilution of risk (numerical dilution)
When an attack is successful, what is the probability of being killed.
The probability of death = 1/N (group size).
Dilution effect may favor synchrony in reproduction in colonial animals
Pro
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eath
Group Size
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Mass Reproduction/Hatching
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Mobbing Predators
Ground squirrel mob rattle snakes
Benefit – pursuit deterrence signal
Moves predator along
Teaches offspring what threats to live are.
Ex. Songbirds