Lecture 13: Feb 12 Predators and foraging PT.1
What is an adaptation?
● A heritable trait/ phenotype that:
○ Spread in the past 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
● Benefits> needs to outweigh cost for traits to be adaptation
● Better than existing alternative traits/ phenotypes
Descent with Modification
● Any 2 species can be traced back to a common ancestor
● Differences & similarities between them are the result of adaptation
● The more recent their common ancestor, the more similar they are
● The more similar their environment, the more similar they are
Homology vs. Analogy
● Homology = similarities due to common ancestry
○ Bat with a wing, whale with slipper = same bone structure
○ seal & penguin = have flippers , serve similar function
● Analogy = similarities due to similar environment/ function
Not all Traits are Adaptive
● Genetic mutation are randomly
○ N. Selection can only work with the genes that exist = cannot create certain
genes or traits (evolution is not a directed process )
● Environmental change, so some traits that are used to adaptive may no long be so
○ Become ‘neutral’ that will be selected against
● Some are costly but are genetically linked to other traits that provide benefits
○ ‘By products’
Mobbing behaviour of Colonial, ground-nesting Gulls
● Many birds will ‘mob’ predators - harass predators to drive them away
● Can protect eggs and chichs (reproductive success)
● While mobbing is often effective, takes time and energy , can lead to death of the
‘mobber’
STUDY: Black headed gulls in Netherlands
● Hypothesis: mobbing behaviour distracts predators, reducing the chance that predators
will find the mobber’s offspring
● Experiment: placed 10 chicken eggs, one every 10 meters, from inside of colon to
outside of colony (did this multiple times in different colonies)
● Is Mobbing an adaptation?
○ Result: data partially supported hypothesis
, ○ Invokes N. selection which produces a change in gene frequency within
population overtime
○ He did not measure whether mobbing affects gene frequency
○ Fitness (or reproductive success) isn’t just making eggs.
■ A fitness benefit is not realized until an animal’s offspring reproduce
Measuring fitness
● Scientist accept certain fitness-related ‘proxies’ (correlates of fitness) without measuring
fitness directly
● Researchers will often look at variables that are prob correlated to fitness - number of
surviving young, success in territory defense, amount of food procured
● Measures are imperfect correlation
The Comparative Method
● Another way to determine whether a trait is adaptive is to look at species that face
different or similar selection pressures
● Closely-related species with different selection pressures = might reveal divergent
evolution
● distantly -related species with similar selected pressure = convergent evolution (exp.
Independent evolution of the same trait )
○ Increase the prob that the behavior is adaptive
● Currently: 50 species of gulls ( ground nesting vs. cliff-nesting )
● Genetic techniques allow is to construct evolutionary trees based on DNA similarities
● Phylogeny: the simplest is usually correct , parsimony explanation
Prediction: if mobbing by ground-nesting gulls is an adaptation to predation, then gull species
whose eggs are at low risk of predation should show less mobbing behaviour
Cliff-nesting Gulls
● Fewer nest predators
○ Small mammals, predatory birds
○ Fewer benefits of mobbing
● Size of adults is reduced
○ More vulnerable to predator attack
○ Increased costs of mobbing
● Little mobbing behaviour = divergent evolution - suggest that mobbing is adaptive
(support the hypothesis)
● Benefits: predators like mice can’t reach them , predation is reduced , mobbing
behaviour = reduced
○ Cost higher than benefits
Convergent Evolution in Mobbing
● Many species that breed in groups (colonies) face the problem of having many nests and
young visible to predators
, ● Many such birds (exp. Colonial swallows) show mobbing behaviour
● So do colonial ground squirrels
Lecture 14: Feb 22 Predators & Foraging pt.2
Camouflaged Moths
● Peppered moth
○ Melanic form was once rare, then became common and then became less
common
● Classic Study: PLaced both forms on dark trees trucks and light trees trunks to see
which one gets eaten more quickly
○ Species does not sit on trunks . Sits below limb joints - it is a behavioural
adaptation
○ Another factor: pinned or limb joint , pollution or not
○ Have strong selection pressure vs. not
○ interaction : 3 variation , the answer depends on the morph, pollution or perch
site
Aposematism - Darwinian Puzzle
● Monarch Butterflies = emerges as a butterfly but before was a caterpillar eats a certain
milkweed that is poisonous = coloration prevents others from eating them, warning
coloration
Stotting by Gazelles
● Thomson’s gazelle: jump when they see a cheetah, when cased they leap several feet
into air and flare white rump patch at the predatory= stotting
● HYPOTHESIS:
○ tried to avoid being ambushed by other cheetah (isn’t supported)
○ It is an alarm Signal to warn others
○ Social Cohesion = group together in protection in large numbers =
communicating
○ Attack Deterrence = jumping around confuses the cheetah and doesn’t know
which one to follow/chase (supported)
● Cheetahs abandon hunts more often when gazelles stot
● Honest Signal - resistant to cheating , higher they can jump = shows that it is healthy
○ Trusted by cheetahs (they don’t waste their time and energy)
What is an adaptation?
● A heritable trait/ phenotype that:
○ Spread in the past 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
● Benefits> needs to outweigh cost for traits to be adaptation
● Better than existing alternative traits/ phenotypes
Descent with Modification
● Any 2 species can be traced back to a common ancestor
● Differences & similarities between them are the result of adaptation
● The more recent their common ancestor, the more similar they are
● The more similar their environment, the more similar they are
Homology vs. Analogy
● Homology = similarities due to common ancestry
○ Bat with a wing, whale with slipper = same bone structure
○ seal & penguin = have flippers , serve similar function
● Analogy = similarities due to similar environment/ function
Not all Traits are Adaptive
● Genetic mutation are randomly
○ N. Selection can only work with the genes that exist = cannot create certain
genes or traits (evolution is not a directed process )
● Environmental change, so some traits that are used to adaptive may no long be so
○ Become ‘neutral’ that will be selected against
● Some are costly but are genetically linked to other traits that provide benefits
○ ‘By products’
Mobbing behaviour of Colonial, ground-nesting Gulls
● Many birds will ‘mob’ predators - harass predators to drive them away
● Can protect eggs and chichs (reproductive success)
● While mobbing is often effective, takes time and energy , can lead to death of the
‘mobber’
STUDY: Black headed gulls in Netherlands
● Hypothesis: mobbing behaviour distracts predators, reducing the chance that predators
will find the mobber’s offspring
● Experiment: placed 10 chicken eggs, one every 10 meters, from inside of colon to
outside of colony (did this multiple times in different colonies)
● Is Mobbing an adaptation?
○ Result: data partially supported hypothesis
, ○ Invokes N. selection which produces a change in gene frequency within
population overtime
○ He did not measure whether mobbing affects gene frequency
○ Fitness (or reproductive success) isn’t just making eggs.
■ A fitness benefit is not realized until an animal’s offspring reproduce
Measuring fitness
● Scientist accept certain fitness-related ‘proxies’ (correlates of fitness) without measuring
fitness directly
● Researchers will often look at variables that are prob correlated to fitness - number of
surviving young, success in territory defense, amount of food procured
● Measures are imperfect correlation
The Comparative Method
● Another way to determine whether a trait is adaptive is to look at species that face
different or similar selection pressures
● Closely-related species with different selection pressures = might reveal divergent
evolution
● distantly -related species with similar selected pressure = convergent evolution (exp.
Independent evolution of the same trait )
○ Increase the prob that the behavior is adaptive
● Currently: 50 species of gulls ( ground nesting vs. cliff-nesting )
● Genetic techniques allow is to construct evolutionary trees based on DNA similarities
● Phylogeny: the simplest is usually correct , parsimony explanation
Prediction: if mobbing by ground-nesting gulls is an adaptation to predation, then gull species
whose eggs are at low risk of predation should show less mobbing behaviour
Cliff-nesting Gulls
● Fewer nest predators
○ Small mammals, predatory birds
○ Fewer benefits of mobbing
● Size of adults is reduced
○ More vulnerable to predator attack
○ Increased costs of mobbing
● Little mobbing behaviour = divergent evolution - suggest that mobbing is adaptive
(support the hypothesis)
● Benefits: predators like mice can’t reach them , predation is reduced , mobbing
behaviour = reduced
○ Cost higher than benefits
Convergent Evolution in Mobbing
● Many species that breed in groups (colonies) face the problem of having many nests and
young visible to predators
, ● Many such birds (exp. Colonial swallows) show mobbing behaviour
● So do colonial ground squirrels
Lecture 14: Feb 22 Predators & Foraging pt.2
Camouflaged Moths
● Peppered moth
○ Melanic form was once rare, then became common and then became less
common
● Classic Study: PLaced both forms on dark trees trucks and light trees trunks to see
which one gets eaten more quickly
○ Species does not sit on trunks . Sits below limb joints - it is a behavioural
adaptation
○ Another factor: pinned or limb joint , pollution or not
○ Have strong selection pressure vs. not
○ interaction : 3 variation , the answer depends on the morph, pollution or perch
site
Aposematism - Darwinian Puzzle
● Monarch Butterflies = emerges as a butterfly but before was a caterpillar eats a certain
milkweed that is poisonous = coloration prevents others from eating them, warning
coloration
Stotting by Gazelles
● Thomson’s gazelle: jump when they see a cheetah, when cased they leap several feet
into air and flare white rump patch at the predatory= stotting
● HYPOTHESIS:
○ tried to avoid being ambushed by other cheetah (isn’t supported)
○ It is an alarm Signal to warn others
○ Social Cohesion = group together in protection in large numbers =
communicating
○ Attack Deterrence = jumping around confuses the cheetah and doesn’t know
which one to follow/chase (supported)
● Cheetahs abandon hunts more often when gazelles stot
● Honest Signal - resistant to cheating , higher they can jump = shows that it is healthy
○ Trusted by cheetahs (they don’t waste their time and energy)
