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Sociality and Social Behaviour

Sociality and Social Behaviour. Communication System. Kin Selection. Mating strategy. Foraging Patterns. Altruism. Level of Sociality. Predator Pressure. Parental Care. Resource Defence. V.C. Wynne Edwards. Animal Dispersion in Relation to Social Behaviour (1962).

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Sociality and Social Behaviour

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  1. Sociality and Social Behaviour

  2. Communication System Kin Selection Mating strategy Foraging Patterns Altruism Level of Sociality Predator Pressure Parental Care Resource Defence

  3. V.C. Wynne Edwards Animal Dispersion in Relation to Social Behaviour (1962)

  4. Reproductive restraint Function of communal displays Epidiectic display -allow animals to assess their own numbers

  5. Reproductive restraint Epidiectic display Assessment of population size Reproductive restraint

  6. Reproductive restraint - English Swift Commonly lays 2 eggs per clutch Can lay up to 5 eggs per clutch

  7. Reproductive restraint - English Swift Why the restraint? Wynne Edwards - Courtship displays allow census of local population - females lay fewer eggs than they are capable

  8. Reproductive restraint - English Swift Why the restraint? Alternative explanation Look at fledging success Clutch size % fledging Mean/nest 2 82 1.64 3 45 1.35

  9. 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

  10. Wynne Edwards Difficult to explain genetically A - a gene that promotes altruism a - a gene that promotes selfishness p2 + 2pq + q2= 1 Selection against any animal with’A’ = (1-s) P2(1-s) + 2pq(1-s) + q2= 1 A - can’t spread - contains automatic selection against itself

  11. Wynne Edwards Group Selection -reproductive restraint evolves if Benefit to group of altruism Reproductive advantage of being selfish

  12. Group selection Rabbits introduced to Australia - 24 in 1859 -1950 - about 1.5 billion Control with myxoma

  13. 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

  14. Group selection Rabbits and Myxoma Virulent form High reproduction (selfish) Lower probability of transmission Less virulent form Low reproduction (altruistic) Higher probability of transmission

  15. Group selection Rabbits and Myxoma Group selection argument • less virulent = restrained reproduction = individual sacrifice • for group survival • more virulent = higher indvidual success = group extinction Individual selection argument - high ‘r’ x low transmission < lower ‘r’ x high transmission

  16. Social BehaviourCosts and Benefits Benefits 1. Protection from physical factors - Aggregations

  17. Social BehaviourCosts and Benefits Benefits 2. Protection against predators Grouped animals are more difficult to find a. Encounter Effect

  18. Social BehaviourCosts and Benefits Benefits 2. Protection against predators a. Encounter Effect predicted Encounter rate observed Colony size

  19. Social BehaviourCosts and Benefits Benefits 2. Protection against predators b. Dilution Effect 1:9 1:1000’s

  20. How do groups form? Hamilton - Geometry for the selfish herd Circular pond Colony of frogs Colony of frogs Water snake

  21. How do groups form? Hamilton - Geometry for the selfish herd At same time each day, snake appears and frogs go to side of pond Colony of frogs

  22. How do groups form? Hamilton - Geometry for the selfish herd Frogs are given the opportunity to move. How??? Colony of frogs Domain of danger

  23. How do groups form? Hamilton - Geometry for the selfish herd Frogs are given the opportunity to move. How??? Colony of frogs Domain of danger

  24. Social BehaviourCosts and Benefits Benefits 3. Mate searching

  25. Social BehaviourCosts and Benefits Benefits 4. Foraging success

  26. Social BehaviourCosts and Benefits Benefits 5. Resource defense

  27. Social BehaviourCosts and Benefits Benefits 6. Division of Labour Soldier Alate Termite Castes Queen King Worker

  28. Social BehaviourCosts and Benefits Benefits 7. Aiding relatives

  29. Social BehaviourCosts and Benefits Benefits 8. Modifying the environment

  30. Social BehaviourCosts and Benefits Costs 1. Increased competition Number of aggressive acs Colony size

  31. Social BehaviourCosts and Benefits Costs 2. Increased disease and parasite rates Lice/ nestling Colony size

  32. Social BehaviourCosts and Benefits Costs 3. Interference with reproduction

  33. 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

  34. 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 0.5 Full siblings 0.5 Half siblings 0.25 Cousins 0.125 [Aunt/Uncle]/[Niece/Nephew] 0.25 Grandparent/grandchild 0.25

  35. Social Behaviour-Why behave altrustically? Hamilton’s rule Altruism will spread if B/C > 1/r B = benefit to recipient of altruist’s help C = cost to altruist r = coefficient of relatedness

  36. Social Behaviour-Why behave altrustically? Examples?? Florida Scrub Jay

  37. Social Behaviour-Why behave altrustically?

  38. Social Behaviour-Why behave altrustically? Typical Group Breeding Pair Helpers

  39. Social Behaviour-Why behave altrustically? Reproductive success - benefits to breeding pair 1.62 young /nest 2.20 young /nest Helpers (any number)

  40. 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

  41. Social Behaviour-Why behave altrustically? From previous slide: Helper success = 1.94 - 1.62 = 0.32 x .5 (for relatedness) = 0.16 Novice breeder success = 1.02 / nest x 0.5 = 0.51

  42. Social Behaviour-Why behave altrustically? From previous slide: Helper success = 0.16 Novice breeder success = 0.51 Why sacrifice 2/3 of your own success by being a helper? Other costs in being a novice breeder 1. Survivorship 2. Being forced to marginal territories 3. Greater chance of taking over home territory

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