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Transcript of Sociality and Social Behaviour. Level of Sociality Mating strategy Communication System Kin...
Sociality and Social Behaviour
Level of Sociality
Mating strategy
Communication System Kin Selection
Altruism
Predator Pressure
Resource Defence
Parental Care
Foraging Patterns
V.C. Wynne Edwards
Animal Dispersion in Relation to Social Behaviour(1962)
Reproductive restraint
Function of communal displays
Epidiectic display-allow animals to
assess their own numbers
Reproductive restraint
Epidiectic display
Assessment of population size
Reproductive restraint
Reproductive restraint- English Swift
Commonlylays 2 eggs perclutch
Can lay up to 5 eggs per clutch
Reproductive restraint- English Swift
Wynne Edwards- Courtship displays allow census of local population
Why the restraint?
- females lay fewer eggs than they are capable
Reproductive restraint- English Swift
Alternative explanation
Why the restraint?
Look at fledging success
Clutch size % fledging Mean/nest
2 82 1.64
3 45 1.35
Wynne Edwards
Group Selection
- animals will behave in such a fashion as to sacrifice personal benefit for the benefit of the group (altruism)
Difficult to explain genetically
A - a gene that promotes altruism
a - a gene that promotes selfishness
A - can’t spread - contains automatic selection against itself
Wynne Edwards
Difficult to explain genetically
A - a gene that promotes altruism
a - a gene that promotes selfishness
A - can’t spread - contains automatic selection against itself
p2 + 2pq + q2 = 1
Selection against any animal with’A’ = (1-s)
P2(1-s) + 2pq(1-s) + q2 = 1
Wynne Edwards
Group Selection
-reproductive restraint evolves if
Benefit to group of altruism
Reproductive advantage of being selfish
Group selection
Rabbits introduced to Australia - 24 in 1859
-1950 - about 1.5 billion
Control with myxoma
Group selection Rabbits and Myxoma
Facts/Assumptions
1. ‘Group’ = all the viruses in one rabbit
2. ‘virulence’ = lethality = r [reproductive rate]
3. Over time - virus has become less virulent
4. Transmission is by mosquitoes- so p[infection] is proportional to the lifespan of
the rabbit
Group selection Rabbits and Myxoma
Virulent form High reproduction(selfish)
Lower probability of transmission
Less virulent form
Low reproduction(altruistic)
Higher probability of transmission
Group selection Rabbits and Myxoma
Group selection argument
-less virulent = restrained reproduction = individual sacrificefor group survival
-more virulent = higher indvidual success = group extinction
Individual selection argument
- high ‘r’ x low transmission < lower ‘r’ x high transmission
Social BehaviourCosts and Benefits
Benefits1. Protection from physical factors - Aggregations
Social BehaviourCosts and Benefits
Benefits2. Protection against predators
a. Encounter Effect Grouped animalsare more difficult to find
Social BehaviourCosts and BenefitsBenefits2. Protection against predators
a. Encounter Effect
predicted
observed
Encounter rate
Colony size
Social BehaviourCosts and Benefits
Benefits2. Protection against predators
b. Dilution Effect
1:9 1:1000’s
How do groups form?Hamilton - Geometry for the selfish herd
Circular pond
Colony of frogs
Water snake
Colony of frogs
How do groups form?
Hamilton - Geometry for the selfish herd
At same time each day,snake appears and frogsgo to side of pond
Colony of frogs
How do groups form?
Hamilton - Geometry for the selfish herd
Frogs are given the opportunity to move.How???
Colony of frogs
Domain of danger
How do groups form?
Hamilton - Geometry for the selfish herd
Frogs are given the opportunity to move.How???
Colony of frogs
Domain of danger
Social BehaviourCosts and Benefits
Benefits3. Mate searching
Social BehaviourCosts and Benefits
Benefits4. Foraging success
Social BehaviourCosts and Benefits
Benefits5. Resource defense
Social BehaviourCosts and Benefits
Benefits6. Division of Labour
Termite Castes
Queen
WorkerKing
Alate
Soldier
Social BehaviourCosts and Benefits
Benefits7. Aiding relatives
Social BehaviourCosts and Benefits
Benefits8. Modifying the environment
Social BehaviourCosts and Benefits
Costs1. Increased competition
Number of aggressive acs
Colony size
Social BehaviourCosts and Benefits
Costs2. Increased disease and parasite rates
Lice/ nestling
Colony size
Social BehaviourCosts and Benefits
Costs3. Interference with reproduction
Social Behaviour-Why behave altruistically?
W.D. Hamilton - Kin Selection
Fitness has two components
Direct - gained through personal reproduction
Indirect - gained through reproduction of related individuals
INCLUSIVE FITNESS
Social Behaviour-Why behave altrustically?
Need to know the coefficient of relatedness
r = the probability that two individuals possess the same allele due to common ancestry
Parent/offspring 0.5Full siblings 0.5Half siblings 0.25Cousins 0.125[Aunt/Uncle]/[Niece/Nephew] 0.25Grandparent/grandchild 0.25
Social Behaviour-Why behave altrustically?
Hamilton’s rule
Altruism will spread if
B/C > 1/r
B = benefit to recipient of altruist’s helpC = cost to altruistr = coefficient of relatedness
Social Behaviour-Why behave altrustically?
Examples??
Florida Scrub Jay
Social Behaviour-Why behave altrustically?
Social Behaviour-Why behave altrustically?
Typical Group
Breeding Pair
Helpers
Social Behaviour-Why behave altrustically?
Reproductive success - benefits to breeding pair
1.62 young /nest
2.20 young /nest
Helpers(any number)
Social Behaviour-Why behave altrustically?
Reproductive success - benefits to helper
1.94 young /nest
One Helper
Helper success = 1.94 - 1.62 = 0.32 x .5 (for relatedness)
= 0.16
Social Behaviour-Why behave altrustically?
Helper success = 1.94 - 1.62 = 0.32 x .5 (for relatedness)
= 0.16
From previous slide:
Novice breeder success = 1.02 / nest x 0.5 = 0.51
Social Behaviour-Why behave altrustically?
Helper success = 0.16
From previous slide:
Novice breeder success = 0.51
Why sacrifice 2/3 of your own success by being a helper?
Other costs in being a novice breeder1. Survivorship2. Being forced to marginal territories3. Greater chance of taking over home territory