Behavioral Ecology - Exam 3

ZOO 425 Exam 3 - Spring 2025

game theory

the relative fitness of a strategy depends on all the game’s strategies

John Maynard Smith

adapted GT to ecology

GT

• formally describe the game rules

• formal mathematical description of the game strategies

• analytical solutions and simulations

Evolutionarily Stable Strategy (ESS)

a strategy that when adopted can’t be invaded by another strategy

Pure ESS

one strategy “wins”

mixed ESS

has more than 1 strategy “win”

aggression payoff matrix

• hawk strategy - always fight

• dove - never fight

• payoff of victory - V

• cost of lost fight - C

proportion of hawks

h = V/C

proportion of doves

(1-h)

hawk payoff

H = h(½ V - ½ C) + (1-h)V

dove payoff

D = h(0) + (1-h)V/2

equilibrium

H = D

change in V and C changes ESS and h at ESS

V>C = no dove invasion, always better to fight (pure ESS; low C)

C>V = hawk invasion (mixed ESS)

stable polymorphism

only has one strategy (can’t change)

mixed strategy

can choose the strategy and the probability of being agressive is h

GT and aggression predictions

1. the best strategy depends on all other strategies in the game

2. ESS doesn’t imply individuals are representative of the max payoff at equilibrium

3. the available strategies effect ESS

   1. new strategies change ESS

   2. V and C vary within the environment and within time

assessment

way individuals try to determine the cost of a potential fight with that individual

winner effects

a win increases the likelihood of another win

loser effects

a loss increases the likelihood of another loss

bystander effect

a bystander is more or less likely to fight if another individual loses or wins a fight the bystander watched

costs of sexual reproduction

• offspring only have ½ of your genes

• engaging in contests or competitions to find mates

• time and energy

• risk of predation, parasitism, or disease

benefits of sexual reproduction

• genetic variability

• brings together adaptive alleles or gene complexes

• reduces the load of deleterious mutations (avoids Muller’s Ratchet)

Muller’s Ratchet

asexual reproduction accumulates deleterious mutations and have more difficulty to purge mutations

ansiogamy

2 different types of gametes

sperm

small, mobile, cheap

eggs

larger, immobile, expensive

females should be choosy

because plenty of sperm to choose from to make up for high egg production costs

males should compete to fertilize limited eggs

because of a high success variance causing stronger sexual selection

intersexual selection

pressure between sexes

direct benefit

benefits to females

• ex. territory access, nuptial gifts (food), protection, offspring care

good genes

the genetic benefits to offspring based on mate selection to increase offspring fitness

• may cause runaway selection and passing on choices

honest indicator

a phenotypic trait that honestly indicates fitness; reproductive state can alter choices

example of honest indicator

immunity (MHC) and scents in humans

• females prefer the scent of males with a different MHC

• pregnant females (birth control hormones) prefer the scent of males with a similar MHC

intrasexual selection

pressures within sexes

sexual dimorphism

traits that differ between sexes within a species

mating system

the social system that describes how males and females come together to breed (social bonds)

breeding system

the genetic system that describes how males and females come together to breed (genetics)

components of mating systems

• number of partners

• timing and duration of associations

• male and female perspectives of costs and benefits

monogamy

• neither sex has the opportunity to monopolize the other

• each breeding adult is with one other breeding adult; male PC is essential and non-shareable for offspring success

frequency of monogamy in birds

with genetic tested, determined multiple fathers within nests

polygamy

• one sex is able to monopolize the other

• one sex has multiple partners

polygyny

1 male with multiple females

• strong male sexual selection

• little to no male PC

resource defense

one sex has access indirectly through monopolizing critical resources

female defense

males access females directly

male dominance

males display or compete for females who choose mates based on their status

explosive breeding assemblages

high mating sychronization

lek

expected when critical resources are abundant and widely dispersed or too unpredictable; too costly to be defendable

polygyny threshold

eventually the female’s cost of being with a male who is with many females becomes too high and it chooses a lower quality male

• IFD mate selection (fitness of high and low quality male are equal)

polyandry

1 female with multiple males

• female sexual selection

• little to no female PC

• typically when nest predation rates are high

resource defense

females control males indirectly by monopolizing critical resources

female access

female interactions with themselves limits male access

factors of parental care

• degree that parental care influences offspring survival

• number of times an adult can reproduce in a season or lifetime

  • trade-off of current PC and other activities (including future reproduction)

PC payoff matrix

• P - probability of offspring survival with a number of parents providing care

  • assumes P₀ < P₁ < P₂ and P₀ << P₁ ~ P₂ when there’s lots of food

• E_C - number of eggs a female lays if she cares for offspring

• E_D - number of eggs a female lays if she deserts offspring

  • E_D > E_C

• m - probability of a male who deserts will mate again

both desert (ESS1)

• E_DP₀ > E_CP₁ or female will care

• E_DP₀(1+m) > E_DP₁ or male will care

female deserts and male cares (ESS2)

• E_DP₀ > E_CP₁ or female will care

• E_DP₁ > E_DP₀(1+m) or male will desert

female cares and male deserts (ESS3)

• E_CP₁ > E_DP₀ or female deserts

• E_CP₁(1+m) > E_CP₂ or male cares

both care (ESS4)

• E_CP₂ > E_DP₁ or female deserts

• E_CP₂ > E_CP₁(1+m) or male deserts

Extra-Pair Copulation (EPC)

breeding outside of a monogamous mating system

• polygynous breeding system and monogamous mating system

female EPC benefits

• increased offspring genetic diversity

• increased fertilization

• decreased likelihood of female harassment or offspring infantilization

• trading up

trading up

females getting the best of both PC (from mating pair) and genetic quality (from breeding pair)

female EPC costs

• partner retaliation

• disease, parasite transmission, predation

• uncertain quality of extra-pair (less assessment)

• risk of injury

male EPC benefits

• increased offspring production

male EPC costs

• sperm depletion

• disease, parasites, predation

• injury by extra-pair’s mating partner

• increased risk of cuckoldry

• dissolution of social bonds

Extra-Pair Paternity (EPP)

proportions of copulations by EPC; less likely with increased PC

classic female choice

choice of mate made pre-insemination

• ex. courtship, nuptial gifts, territory quality

courtship behaviors

provides opportunity for assessment and comparing male phenotypes

cryptic female choice

mate choice made post-insemination, choice of high quality sperm

• ex. sperm train, fowl sperm ejection to prevent insemination by subdominant males

mate guarding

male only cares about guarding when the other bird is male and their mate is fertile

• don’t waste time or energy when female isn’t reproducing

• pre-insemination

sperm compeition

• head start (ex. locking, plugging)

• displace or remove other sperm

• change frequency of copulation

• change sperm investments (ex. strategic investments)

locking

• benefits - physical guarding is more effective

• costs - time and energy not used for other activities

plugging

• benefits - time and energy available for other activities

• costs - not as effective as locking (plug can be removed)

strategic sperm investments

• increased investment with presence of other males

• female mating status - priority over insemination order or quantity

• female size

• future opportunities (ex. sperm depletion, coolidge effect)

sperm depletion

high dominance males have increased initial copulations, but decreased with increased number of copulations

coolidge effect

males exhibit renewed interest in mating when a new female is introduced

• reserved sperm for new female, not depleted

alternative strategies

each individual has a specific phenotype and strategy that doesn’t change in their lifetime

• frequency-dependent selection determines proportion of strategies

• ex. Coho Salmon - hooknose (fight) and jack (sneak)

  • each strategy works best when it’s rare

conditional strategies

behavioral assessments of individual status causes individual to choose their strategy

• relative fitnesses ≠ and the individual chooses the strategy with the higher fitness

• depends on individual’s status

• switchpoint - = fitness between strategies

sequential hermaphroditism

changing sex

protogynous hermaphrodite

female changes to male

protandrous hermaphrodite

male changes to female

changing environmental conditions

changes in environmental conditions = changes in strategy fitnesses = change in equilibriums = change in strategy frequencies

mutualism

benefits both parties immediately

kin selection

the evolution of characteristics that favor the survival (and reproduction) of close relatives of the affected individual

Hamilton and Haldane

kin selection important figures

direct fitness

genes contributed by an individual via personal reproduction in the bodies of surviving offspring (the individual’s offspring)

indirect fitness

genes contributed by an individual via survival in the bodies of offspring of a related individual (a relative’s offspring)

coefficient of relatedness (r)

the pathway that connects focal individuals

• (pathway form individuals)^{number of path} + (individual pathways)^{number of paths} = r

Hamilton’s Rule

r(benefit_recipiant) > cost_altruist

• rB > C

alarm calls

• who calls - females (sometypes/rarely males)

  • typically with female PC and not male

• who are called to - offspring and sometimes other kin

Emlen and Oring 1977

describes different mating systems based on the ability to monopolize mates within different spatial and temporal ecological conditions

Gross 1996

describes alternative strategies, mixed strategies, and conditional strategies and describes developmentally fixed or plastic alternative

• alternative - genetic polymorphisms with equal fitness with frequency-dependent selection

• mixed - theoretical strategy of a mix of strategy tactics

• conditional - choice of strategy based on individual status, environmental status, and density of strategies

  • switchpoint

• developmentally fixed - hormones play a roll in pre-adult to determine phenotype, but don’t change as adults

• developmentally plastic - hormones play a roll in adults changing tactics, hormones play a roll in adulthood