Lecture 9: Social Behaviour

Question 1

Costs of group living:

Answer 1

• more competition for resources (e.g. food, mates)
• more conspicuous to predators
• susceptible to parasites (incl. brood parasites) & disease
• conspecifics may kill offspring

Question 2

benefits of group living:

Answer 2

• improved foraging efficiency
• less chance of being predated (dilution and confusion effects)
• improved defence of resources from non-group members
• communal care of offspring

Question 3

Costs of group living in cliff swallows;

Answer 3

• they breed in colonies & suffer from a blood-sucking parasitic bug
• more bugs per nest in larger colonies
• the more bugs a chick has on it, the slower it grows

Question 4

experiment to look into whether ‘do bugs cause chicks to grow slower?’ with cliff swallowed

Answer 4

Mary & Charles Brown fumigated half the nests in a colony to see whether this improved chick growth.

IT DID, providing evidence to infer causation

Question 5

Benefits of group living in guillemots

Answer 5

• they breed at higher densities than any other bird, up to 70 individuals/m2.
• WHY? what is the adaptive significance of breeding in such close proximity?
• -> breeding success increases with group density, = more neighbours = greater safety from predatory gulls

Question 6

animal lifestyles types:

Answer 6

• solaritary like moose

- social bird groups described

Question 7

why do guillemots allopreen or groom each other?

Answer 7

• reduce parasite burden?
• reduces stress (important in these tightly packed conditions)
• build relationships that reduce local competition

Question 8

how does unselfish behaviour evolve?

Answer 8

individuals can gain fitness through success of relatives. Can drive altuirstic behaviour. Bill (william) Hamiltons theory of kin selection/inclusive behaviour

Question 9

Thatch-building in sociable weavers: how many birds live together

Answer 9

500 birds in huge communal nests

Question 10

Thatch-building in sociable weavers: is thatch building costly?

Answer 10

yes. it requires time & effort

Question 11

Thatch-building in sociable weavers: possible fitness benefits of direct (selfish) nests

Answer 11

• own nesting success
• avoiding punishment
• mate attraction

Question 12

Thatch-building in sociable weavers: possible fitness benefits of indirect (altruistic) nests

Answer 12

-relatives’ nesting success

Question 13

Thatch-building in sociable weavers: if for OWN NESTING SUCCESS ONLY

Answer 13

it would be unstable, because each individual would nebefit more by letting the others work harder

Question 14

Thatch-building in sociable weavers: if to AVOID PUNISHMENT

Answer 14

most individuals would build & punish those that didn’t. However, most individuals did not build and weren’t punished

Question 15

Thatch-building in sociable weavers: if to ATTRACT MALES

Answer 15

should beamingly done by young, unpaired birds, but most builders were older birds

Question 16

Thatch-building in sociable weavers: if for RELATIVES NESTING SUCCESS

Answer 16

males should contribute more, because they are more closely related to fellow members of their colony

Question 17

Thatch-building in sociable weavers: TRUE RESULT:

Answer 17

89% of thatch built by males. Also, males were more likely to build when they were more closely related to their neighbours.

Supports role for INDIRECT BENEFITS in driving thatch-building behaviour.

Sociable weavers gain some direct benefits from thatch-building. However, this is not enough to drive the behaviour alone, because it would favour freeloaders who gained the benefits without doing the work. Individuals with close relatives as neighbours gain both direct and indirect benefits, and so are more likely to invest in building.
== indirect kin-selected benefits are likely to have been important in the evolution of thatch-building.

Question 18

most benefits associated with group living are

Answer 18

selfish ones, to its own adv, promoting on genes into next generation

Question 19

example of altruistic behaviour:

Answer 19

• group living birds, failed own breeding attempt as lost eggs/chick will help others out, as allo parents
• many other organisms show complex and unselfish behaviours - grooming, feeding others offspring etc

Question 20

if natural selection favours individuals that survive bested have most surviving young, how can a behaviour involve which helps others have more young at cost of helper own chances

Answer 20

in 1960s william hamilton, realised individuals can pass their genes onto next generation indirectly through relatives as well as through their own. = KIN SELECTION

Question 21

probability of parent & offspring sharing a gene

Answer 21

known as COEFFICIENT OF RELATEDNESS (r) & = 0.5 (50%)

Question 22

brothers and sisters probability of sharing same gene is

Answer 22

also coefficient of relatedness = 0.5

Question 23

what is INDIVIDUAL or DIRECT selection =

Answer 23

a behavioural act favoured by selection that involves parents and offspring (fitness gain via personal reproduction = direct fitness)

Question 24

what is KIN SELECTION or INDIRECT selection

Answer 24

a behavioural act favoured due to it beneficial effect on non-descendant kin
(fitness gain via helping non-descendant kin = indirect fitness )

Question 25

an individuals total contribution of evens to the next generation - those conferred directly plus indirectly - is its

Answer 25

INCLUSIVE FITNESS

why we find animals living in group, tend to be groups of related individuals

Question 26

under what conditions should “altruism” be selected for?

Answer 26

rB>C 
where 
B= benefits 
C = costs 
r = coefficient of relatedness