Sociality and Social Behaviour. Level of Sociality Mating strategy Communication System Kin Selection Altruism Predator Pressure Resource Defence Parental

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


Epidiectic display

Assessment of population size


Reproductive restraint- English Swift

Commonlylays 2 eggs perclutch

Can lay up to 5 eggs per clutch


Wynne Edwards- Courtship displays allow census of local population

Why the restraint?

- females lay fewer eggs than they are capable


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


Virulent form High reproduction(selfish)

Lower probability of transmission

Less virulent form

Low reproduction(altruistic)

Higher probability of transmission


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


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


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?


Frogs are given the opportunity to move.How???

Colony of frogs

Domain of danger

How do groups form?


Frogs are given the opportunity to move.How???

Colony of frogs

Domain of danger


Benefits3. Mate searching


Benefits4. Foraging success


Benefits5. Resource defense


Benefits6. Division of Labour

Termite Castes

Queen

WorkerKing

Alate

Soldier


Benefits7. Aiding relatives


Benefits8. Modifying the environment


Costs1. Increased competition

Number of aggressive acs

Colony size


Costs2. Increased disease and parasite rates

Lice/ nestling

Colony size


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


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


Examples??

Florida Scrub Jay



Typical Group

Breeding Pair

Helpers


Reproductive success - benefits to breeding pair

1.62 young /nest

2.20 young /nest

Helpers(any number)


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


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


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

Documents

Sociality and Social Behaviour. Level of Sociality Mating strategy Communication System Kin Selection Altruism Predator Pressure Resource Defence Parental