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Animal Behaviour - Education Scotland

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Social Behaviour
В© RZSS
Learning outcomes
To know definitions of and reasons for altruism and kin
selection, social behaviour in insects and the complexities
of primate behaviour.
Detailed learning outcomes
пЃ¬ Many animals live in social groups and have behaviours that are adapted to group living,
such as social hierarchy or cooperative hunting and defence.
(i) Altruism and kin selection
пЃ¬ An altruistic behaviour harms the donor individual but benefits the recipient. Reciprocal
altruism, where the roles later reverse, often occurs in social animals. The prisoners’
dilemma is a simple model.
пЃ¬ In cases where individuals are related (kin) there may be no requirement for the roles to
reverse. Instead, the behaviour benefits the donor in terms of a potential increased survival
of shared genes.
(ii) Social insects
пЃ¬ In the societies of insects such as bees, wasps, ants and termites, only some individuals
contribute reproductively. Most members of the colony are workers, who cooperate to raise
relatives.
(iii) Primate behaviour
пЃ¬ The long period of parental care in primates gives an opportunity to learn complex social
behaviours.
пЃ¬ To reduce unnecessary conflict, social primates use ritualistic display and appeasement
behaviours. Grooming, facial expression, body posture and sexual presentation are all
important in different species.
пЃ¬ In some monkeys and apes, alliances form between individuals. These are often used to
increase social status within the group.
пЃ¬ The complexity of social structure is related to ecological niche and taxonomic group.
Altruism and kin selection
пЃ¬ Some animals exhibit altruism.
Behaviour that reduces an individual's fitness
while increasing the fitness of another individual.
пЃ¬ Some altruistic acts can be explained in
terms of kin selection (altruistic behaviour
towards relatives).
An animal can increase the survival of genes like
its own by helping relatives.
Altruism and kin selection
пЃ¬ In reciprocal altruism, a favour may be
repaid later by the beneficiary or another
member of the social system.
This explains
altruistic acts by nonrelatives, eg vampire
bats sharing blood.
www.conservationcentre.org
пЃ¬ Naked mole rats also exhibit altruism/kin
selection.
The reproducing female (queen) mates with
one to three males (kings).
The rest of the colony consists of nonreproductive females and males, who care for
and protect the queen, kings and new
offspring.
Explaining cooperation as an
evolved adaptation
пЃ¬ How can natural selection favour a habit
of cooperation?
пЃ¬ The advantages of cooperative over
solitary action (cf. Dunbar,1988):
1.
2.
3.
4.
predator defence
resource defence
foraging/hunting efficiency
infant care.
Kin selection
пЃ¬ Individuals reduce their net lifetime production of
offspring in order to help their relatives
reproduce.
пЃ¬ Kin selection can lead to the extreme altruism of
the workers of some social insects.
пЃ¬ Even though the workers are sterile, they help
their siblings to survive and reproduce, passing
on by proxy the genes responsible for their
altruistic behaviour.
Hamilton’s law
 A preliminary explanation: Hamilton’s law
of inclusive fitness : rB > C
r = biological relatedness of giver and receiver
B = benefit to receiver (survival)
C = cost to give (1)
The net benefit minus the cost must be
greater than zero.
Hamilton’s law
Coefficients of relatedness table
Relationship
Coefficient (r)
Parent–offspring
0.5
Siblings
0.5
Half-siblings
0.25
Uncle/aunt–
niece/nephew
Grandparent–
grandchild
Cousins
0.25
0.25
0.125
Hamilton’s law
пЃ¬ How does this explain the evolution of altruism?
пЃ¬ A sister gives up her life for three of her siblings
(r = 0.5):
benefit = 0.5 Г— 3 = 1.5
cost = 1.0
(benefit – cost) = 1.5 – 1.0 = 0.5
Thus the sacrifice is a benefit that outweighs
costs and the gene for altruism could evolve
in a population.
Hamilton’s law
пЃ¬ Social insects such as termites, wasps and
bees are sisters.
пЃ¬ Bees die once they have stung in defence of a
colony – this benefits all and fits with Hamilton’s
law.
Complex social organisation
hinges on complex signaling
пЃ¬ In behavioural ecology a signal is a form of
communication that causes a change in
behaviour in another animal.
пЃ¬ Social behaviour depends on signalling:
п‚Ў sounds
п‚Ў scents
п‚Ў displays
п‚Ў touches.
Signalling in bees
пЃ¬ Honeybees perform dances that seem to
communicate the direction and distance of
nectar to other members of the colony.
пЃ¬ The round dance indicates that food is nearby, in
an unspecified direction.
пЃ¬ The waggle dance probably indicates both
distance and direction of food.
Other examples of sociable insects:
пЃ¬ termites
пЃ¬ ants.
Agonistic behaviour
пЃ¬ The logic of fighting is decidedly suspect in
most cases.
пЃ¬ One animal is going to win and the other will
lose.
пЃ¬ The loser has gained nothing, and may well
have sustained disastrous injury.
пЃ¬ Relatively minor injury is likely to have fatal
consequences by preventing capture of prey or
allowing a predator to catch an individual with,
for example, a slight muscle strain.
пЃ¬ Even the winner may be damaged, and must
balance the risk of injury with the potential
gain in food, territory or mating success.
пЃ¬ Threat displays allow animals to assess the
likelihood of winning or losing before actually
taking the risk of battle.
пЃ¬ Agonistic behaviour is social behaviour
consisting of threats and combat that settles
disputes between individuals in a population.
пЃ¬ Rituals involving agonistic behaviour often
resolve confrontations between competitors.
пЃ¬ Agonistic behaviour can directly affect an
individual's evolutionary fitness.
пЃ¬ The victor often gains first or exclusive access
to mates, food, etc.
пЃ¬ Threat displays usually involve displaying
either strength or weaponry to the full.
пЃ¬ This is usually enough for the smaller or
weaker to realise that further conflict would
be pointless.
пЃ¬ Retreat is a very important feature of conflicts.
пЃ¬ In artificial situations where retreat is not a
possibility, it is very common for threat displays
to lead to vicious and often fatal fighting.
пЃ¬ Overcrowded domestic animals are a ready
example, where battery hens have to have their
beaks removed and intensively reared pigs have
their canine teeth pulled out at birth to avoid
injuries.
Appeasement
пЃ¬ In natural situations where retreat is not a
possibility (young birds are often the targets
of redirected aggression and escape is not
really an option), behaviours which can
reduce the aggressive motivation without
retreat may be of greater value.
Appeasement gestures fall into two groups:
• One type inhibits attack by arousing a
conflicting tendency in the attacker, eg
postures reminiscent of sexual activity and
behaviours normally associated with young
animals
В© RZSS
• The second type relies on demonstrating the exact
opposite of threat behaviour, eg bared teeth, face
to face, hackles raised all constitute threat in most
dog-like species, whilst wide open mouth, head and
hackles down, and a sideways-on position are
appeasing gestures.
Dominance hierarchies are
maintained by agonistic behaviour
пЃ¬ Many animals live in social groups
maintained by agonistic behaviours.
пЃ¬ Dominance hierarchy is the ranking of
individuals based on social interactions.
Chickens establish a �pecking order’
пЃ¬ Resources are often partitioned based on the
dominance hierarchy.
Dominance hierarchies and reconciliation
behaviour in chimpanzees
пЃ¬ Dr Jane Goodall is
one of the world's
best-known
biologists.
пЃ¬ She has studied the
behaviour of
chimpanzees in their
natural habitat, in
East Africa, since the
early 1960s.
В© The Jane Goodall Institute/Hugo Van Lawick
 Dr Goodall’s research indicates that dominance
hierarchies and reconciliation behaviours are
integral parts of the lives of many primates, for
example a chimpanzee that has threatened
another member of its group may use a hand
gesture to invite reconciliation.
В© RZSS
Acknowledgements
пЃ¬ Thanks to R. Purdie at Sanquhar Academy for
use of some materials.
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