Transcript Slide 1

Tinbergen’s Four Questions
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Causation
Ontogeny
Survival value
Evolution
Four questions in modern jargon
• Causation: neural, hormonal, perceptual
and cognitive mechanisms mediating
behavior
• Ontogeny: development and learning
• Survival value: adaptation and adaptive
significance
• Evolution: historical patterns by which
behavior evolve
Wilson’s view of Animal Behavior
• Ethology: taxonomic character
(Lorenz), ritualization (Huxley),
comparative studies
(Tinbergen).
• Sociobiology: shifted emphasis
away from 3 of 4 questions.
• We will concentrate on two of
Tinbergen’s four questions:
survival value (adaptation) and
evolution (historical patterns).
• We will also consider the
advantages of integrating all
four questions.
• Profound historical distinctions between early
ethology and comparative psychology have
been recently bridged by shared interest in
communication and social behaviour, and
research from physiology and applied areas.
• Although we reiterate the rise of sexual selection
and mating behaviour as prominent areas of
research, we also show that interest in
mechanism and development has proven
particularly resilient over the years.
Adaptations and Such
• Adaptive: An aspect of the phenotype that
on average enhances the inclusive fitness.
• Adaptation: An aspect of the phenotype
that has evolved to fill its current function.
• G.C. Williams: “adaptation is a special
and onerous concept that should be used
only where it is really necessary” (1966,
Adaptation and Natural Selection, p 4)
Studying Adaptive Function
• The Behavior of Animals, Chs 1, 9, 13
• Fit by design: The design of the animal matches
its function so well, there is a strong argument
for adaptation.
• Optimality: To what degree does behavior fit the
predictions of a mechanism needed to fulfill a
specific function.
• Game Theory: Do animals behave in a
frequency-dependent manner to maximize
fitness.
Fit by design
Orchid-Moth pollinator
• Darwin wrote a book on
the “contrivances by
which orchids are
pollinated”.
• The Madagascar orchid,
Angraecum sequipedale
has an 11 inch long
nectar receptacle.
• Darwin predicted a moth
with a tongue that long.
• 40 years later the moth
Xanthopan morgannii
was discovered.
Bat Pollinators
• Many bat species pollinate flowers but
there is no evidence of a match between
bat morhphology and flower parts.
• Anoura fistulata is a glossophagine bat in
the Andes of Ecuador
•
Nature, 2006, 444, 701.
Bat Pollinators
• Many bat species pollinate flowers but
there is no evidence of a match between
bat morhphology and flower parts.
• Anoura fistulata is a glossophagine bat in
the Andes of Ecuador
•
Nature, 2006, 444, 701.
• Do flowers evolve to enhance bat
detections?
•
Nature 1999, 398, 759.
Glossophaga commissarisi
Mucuna holtonii
• Is the vexillum a signal to the bats?
• Is the vexillum a signal to the bats?
• When the vexillum is covered with a plastic bag
the flower is less likely to be pollinates
(evidenced by the exploded keel): 21% vs 88 %
• Is it an odor, visual, or
echolocation cue?
• Stuff vexillum with
cotton, so it looks and
smells the same but
gives a different echo
it is less likely to be
fertilized: 17% vs 66%
• Is it an odor, visual, or
echolocation cue?
• Stuff vexillum with
cotton, so it looks and
smells the same but
gives a different echo
it is less likely to be
fertilized: 17% vs 66%
• The vexillum provides
both a conspicuous signal
and one that is
directional.
• This is true if the echo
hits the fronts of the
vexillum or if it is rotated
by 30 dgrees.
• Other congeners that are
pollinated by
megachiropterns do not
have a raised and convex
vexillum.
Optimal Foraging
• MacArthur & Pianka
(1966) began optimal
foraging theory with
questions of how
animals used
resources in a patchy
environment.
• One of first intros of
animal behavior into
ecology
Optimal Foraging: Building the Model
• Should an animal consume all prey items
encountered or reject the less profitable?
• Step 1: Specify alternatives. After
encounter with prey item X should it be
consumed or searching continue?
• Step 2: Fitness currency or proxy. E/T.
Optimal Foraging: Building the Model
• Step 3: Specify constraints.
– Energy (E) can only be acquired after a
certain handling time (H)
– Prey is encountered randomly during search
(S) at some rate (λ)
– Predator knows encounter rate, identifies prey
without error, can not search and eat, search
efficiency and speed remain constant
Testing the model: Step 1
• Formulate Predictions
• Maximize E/T
• Compare specialist versus generalist, E1 is
more profitable
• For generalist:
– E = S(λ1E1 + λ2E2)
– T = S + S(λ1H1 + λ2H2)
– E/T = S(λ1E1 + λ2E2) / S + S(λ1H1 + λ2H2)
• For specialist: E/T = Sλ1E1 / S + Sλ1H1
Testing the model: Step 1
• Formulate Predictions
• Maximize E/T
• Compare specialist versus generalist, E1 is
more profitable
• For generalist:
– E = S(λ1E1 + λ2E2)
– T = S + S(λ1H1 + λ2H2)
– E/T = S(λ1E1 + λ2E2) / S + S(λ1H1 + λ2H2)
• For specialist: E/T = Sλ1E1 / S + Sλ1H1
• Be a specialist when E/Tspec > E/Tgen:
Sλ1E1 / S + Sλ1H1 > S(λ1E1 + λ2E2) / S +
S(λ1H1 + λ2H2)
or
(E1H2 / E2 ) - H1 > 1/λ1
• A specialist is favored when the encounter
rate with prey 1 increases and thus 1/λ1 gets
smaller.
• A generalist when:
1/λ1 > (E1H2 / E2 ) - H1
• As the encounter rate with the more
profitable prey decreases and thus 1/λ1
becomes larger, generalists are favored.
• Relative abundance of prey does not affect
choice, only encounter rate with more
profitable prey. More abundant prey 1, more
likely prey 2 gets dropped out of diet.
• Duration of search time (S) has no effect.
Testing the Model: Step 2
• Experimentation
• Great tits could view meal worms of 2 sizes passing on a
conveyer belt, λ with each prey is varied.
• Once a prey is taken, bird must fly to its perch to eat,
could not handle and search at the same time.
• All H is the same.
• Prey density and proportion of both the large (L) and
small (S) prey are varied
• Equal λ, low densities predicts generalist foraging.
• > λ for L prey → specialist
• Maintain λL increase λS,, λL = λS → specialist
• Maintain λL increase λS,, λS = 2λL → specialist
• Relative prey abundance is unimportant, only the
encounter rate with more profitable prey.
• Prey density and proportion of both the large (L) and
small (S) prey are varied
• Equal λ, low densities predicts generalist foraging.
• > λ for L prey → specialist
• Maintain λL increase λS,, λL = λS → specialist
• Maintain λL increase λS,, λS = 2λL → specialist
• Relative prey abundance is unimportant, only the
encounter rate with more profitable prey.
• Prey density and proportion of both the large (L) and
small (S) prey are varied
• Equal λ, low densities predicts generalist foraging.
• > λ for L prey → specialist
• Maintain λL increase λS,, λL = λS → specialist
• Maintain λL increase λS,, λS = 2λL → specialist
• Relative prey abundance is unimportant, only the
encounter rate with more profitable prey.
• Prey density and proportion of both the large (L) and
small (S) prey are varied
• Equal λ, low densities predicts generalist foraging.
• > λ for L prey → specialist
• Maintain λL increase λS,, λL = λS → specialist
• Maintain λL increase λS,, λS = 2λL → specialist
• Relative prey abundance is unimportant, only the
encounter rate with more profitable prey.