how does cooperation evolve?
DESCRIPTION
how does cooperation evolve?. cooperation => group evolution => natural selection => mechanism of evolution of cooperation is group selection. factors determining strength of group selection. local fitness effects genes which give the individual higher fitness are selected - PowerPoint PPT PresentationTRANSCRIPT
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how does cooperation evolve?
cooperation => group
evolution => natural selection
=> mechanism of evolution of cooperation is group selection
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factors determining strength of group selection
● local fitness effects
genes which give the individual higher fitness are selected
● genetic structure groups are defined by the sharing genetic structure, i.e. cooperation
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investigate the effects of
● varying ecology
● group selection + kin interaction VS group selection – kin interaction
● alarm calling VS restrained feeding
evolution of altruism by group selection(Pepper & Smuts 2000)
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agent-based model
world
● 2D wrap around lattice
agents
● plant
● forager
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model continued
plant behaviour
● grow
●linear
●logistic
● be consumed
linear
logistic
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model continued
forager behaviour
● movement
same as sugarscape with vision = 1 and can move into any of 8 cells
● death
same as sugarscape with forager lifetime = infinity
● reproduction
reproduce asexually when energy >= fertility threshold
parent energy -= child initial energy
child born in cell closest to parent
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model continued
cooperation
● alarm calling
● feeding restraint
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model continued
targeted individual
Range around it in which foragers will give alarm calls
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model continued
forager has 0.02 probability of being targeted
alarm callers will respond if within 5 cells of targeted forager
probability of kill = 1 / ( n + 1 )where n is the number of alarm callers
targeted forager can not make an alarm call
kill population = alarm callers + targeted forager
a random forager is chosen from the kill population
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model continued
50%
99%
plantsize
Restrained feeders consumption = 0.5 * plant energy
Unrestrained feeders consumption = 0.99 * plant energy
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model continued
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model continued
patch width
patch gap width
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pure population mixed population
uniform environment(one plant per cell)
patch width = 529
gap width = 0
alarm-caller
non-caller
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uniform environment(one plant per cell)
patch width = 529
gap width = 0
pure population mixed population
restraint feeding
non-restraint feeding
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discussion of results(pure population)
who cares
tells us nothing about between-group selection since there is only one group
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discussion of results(mixed population)
local fitness effects
● group selection ignores suboptimisation problem within cooperative group (Heylighen 1997) fitness(non-cooperators) > fitness(cooperators)
genetic structure
● cooperative systems eroded from within by genetic competition (Campbell 1983)
mixed population => non-cooperative genes selected => local fitness and genetic structure effects not strong enough for group selection to occur
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variable environment(mixed population)
population = 0.5 * alarm caller + 0.5 * non-alarm caller
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variable environment(mixed population)
population = 0.5 * restraint feeder + 0.5 * non-restraint feeder
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discussion of results(mixed population)
local fitness effects
● population size must be small (Futuyma 1986)
small patch width + high gap width => many small population groups
groups a
#(cooperators) >> #(non-cooperators)
groups b
all other groups fit into groups b
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discussion of results(mixed population)
local fitness effects continued
● altruistic group has higher fitness due to synergy of cooperation (Heylighen 1997)
fitness(groups a) > fitness(group b)
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discussion of results continued(mixed population)
genetic structure
● there can not be significant gene flow (Futuyma 1986, Goldstein & Zimmerman 2000)
● migration rates must be implausibly low (Ridley 1993)
low patch size + high gap width + low vision
=> low probability of migration => gene flow
=> reduced probability of non-cooperator infiltration of groups a
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discussion of results continued(mixed population)
genetic variance continued
● successful groups must be able to export their local productivity from the local area (Wilson et al 1992)
patch full => steady emigration
fitness(cooperator) > (non-cooperator) => higher probability of successful colonisation for cooperators than non-cooperations
difficulty of migration => infiltration of non-cooperators low
=> local fitness and genetic structure effects are strong enough in some scenarios for group-selection => cooperation evolves
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variable environment(mixed population + absence of kin assortment)
alarm calling never evolved in any of the 100 runs BUTrestraint feeding did
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discussion of results(mixed population + absence of kin assortment)
local fitness
● alarm calling can only spread if foragers are heavily recompensated by others increasing their fitness relative to themselves (Wilson 1979, 1980)
recompensation comes through spatial association to cooperators
cooperators <=> kin
spatial association was removed largely by randomising birth locations
fitness(alarm callers) < fitness(population)
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discussion of results(mixed population + absence of kin assortment)
local fitness continued
however,
feeding restraint conferred benefits as well as costs on the bearer
=> fitness(restraint feeders) > fitness(alarm-callers)
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discussion of results continued(mixed population + absence of kin assortment)
genetic structure
● kin selection increases genetic selection between-groups and decreases it within-groups (Smith 1964)
spatial association <=> kin discrimination
randomised birth starting location
=> kin selection was not operating
=> selection between-groups was reduced
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discussion of results continued(mixed population + absence of kin assortment)
genetic structure continued
migration rates must be implausibly low (Ridley 1993)
there can not be significant gene flow (Futuyma 1986, Goldstein & Zimmerman 2000)
random birth locations => mixed population => gene flow
=> non-cooperators selected over cooperatots
=> local fitness effects and genetic structure are not enough for between-group selection to occur for alarm callers
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discussion of results continued(mixed population + absence of kin assortment)
genetic structure continued
however restraint feeders were selected when patch width low and gap-width high
small group size => restraint feeder becomes an increasing proportion of the acts recipients
=> kin selection was not needed
=> local fitness effects and genetic structure were strong enough for the evolution of feeding restraint
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summary
evolution of cooperation
● favored by group-selection
diminshed by within-group selection
● evolution of cooperation is dependent on
ecological patchiness
small patches and large gaps stabilise
degree of migration
strong vs weak altruism
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critique
● kin selection
there was no kin discrimination rule but the rule is defined in biology
● reproduction
reproduction was asexual and the offspring were the genetic clones of their parents whereas the rules of genetics are well established
● movement
movement rule had vision of 1 which made migration difficult if not impossible
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critique continued
● model parameters
the starting population size was 40 which is small
the size of the world was not given, the assumption is x = y = 527 which is small
● death
foragers lived forever, a more realistic life expectancy was given in sugarscape
● simple
not a very sophisticated model
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references
d. j. Futuyma, evolution biology, 1986
t. h. Goldsmith, w. f. Zimmerman, biology, evolution, and human nature, 2000
f. heylighen, http://pespmc1.vub.ac.be/COOPGEVO.html, genetic scenarios for evolving cooperation, 1997
j. w. Pepper, b. b. Smuts, the evolution of cooperation in an ecological context: an agent-based model, 2000
m. Ridley, evolution, 1993