Download The evolution of cooperation in an ecological context

how does cooperation evolve?
cooperation => group
evolution => natural selection
=> mechanism of evolution of cooperation is group selection
factors determining strength of group selection
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local fitness effects
genes which give the individual higher fitness are selected
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genetic structure
groups are defined by the sharing genetic structure, i.e.
cooperation
evolution of altruism by group selection
(Pepper & Smuts 2000)
investigate the effects of
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varying ecology
group selection + kin interaction VS group selection – kin
interaction
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alarm calling VS restrained feeding
agent-based model
world
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2D wrap around lattice
agents
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plant
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forager
model continued
plant behaviour
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linear
grow
linear
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logistic
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●
be consumed
logistic
model continued
forager behaviour
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movement
same as sugarscape with vision = 1 and can move into any of 8 cells
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death
same as sugarscape with forager lifetime = infinity
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reproduction
reproduce asexually when energy >= fertility threshold
parent energy -= child initial energy
child born in cell closest to parent
model continued
cooperation
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alarm calling
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feeding restraint
model continued
targeted individual
Range around it in which foragers will give alarm calls
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
model continued
Restrained feeders consumption = 0.5 * plant energy
Unrestrained feeders consumption = 0.99 * plant energy
50%
plant
size
99%
model continued
model continued
patch gap width
patch width
uniform environment
(one plant per cell)
patch width = 529
gap width = 0
alarm-caller
non-caller
pure population
mixed population
uniform environment
(one plant per cell)
patch width = 529
gap width = 0
restraint feeding
non-restraint feeding
pure population
mixed population
discussion of results
(pure population)
who cares
tells us nothing about between-group selection since there is
only one group
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
variable environment
(mixed population)
population = 0.5 * alarm caller + 0.5 * non-alarm caller
variable environment
(mixed population)
population = 0.5 * restraint feeder + 0.5 * non-restraint feeder
discussion of results
(mixed population)
local fitness effects
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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
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)
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
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
variable environment
(mixed population + absence of kin assortment)
alarm calling never evolved in any of the 100 runs BUT
restraint feeding did
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)
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)
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
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
discussion of results continued
(mixed population + absence of kin assortment)
genetic structure continued
however restraint feeders were selected when patch width low and gapwidth 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
summary
evolution of cooperation
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favored by group-selection
diminshed by within-group selection
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evolution of cooperation is dependent on
ecological patchiness
small patches and large gaps stabilise
degree of migration
strong vs weak altruism
critique
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kin selection
there was no kin discrimination rule but the rule is defined in biology
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reproduction
reproduction was asexual and the offspring were the genetic clones of their
parents whereas the rules of genetics are well established
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movement
movement rule had vision of 1 which made migration difficult if not
impossible
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
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death
foragers lived forever, a more realistic life expectancy was given in
sugarscape
●
simple
not a very sophisticated model
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