ka6: social behaviour

• Many animals live in social groups and have behaviours that are adapted to group living such as social hierarchy, cooperative hunting and social defence.
• Social hierarchy


  A rank order within a group of animals consisting of a dominant and subordinate members
• Dominant


  Members of a social hierarchy that are at the top of the rank order
• Subordinate


  Members of a social hierarchy that are at the bottom of the rank order
• Aggressive behaviour

  Determines social hierarchy
• Ritualistic (threat) displays

  Carried out by dominant individuals in a social hierarchy to maintain their status
• Appeasement behaviour

  Carried out by subordinate animals in a social hierarchy to reduce conflict
• Social hierarchy examples

  • Pecking order in birds
  • Hierarchies in wolves
• Social hierarchies increase the chances of the dominant animal’s favourable genes being passed on to offspring
• Animals often form alliances in social hierarchies to increase their social status within the group
• Cooperative hunting increases hunting success of predatory groups.  When a kill is achieved all members of the group obtain food.  By working together, the animals are able to tackle larger prey and as a result gain more food than by hunting alone and less energy is used per individual

   

  Cooperative hunting benefits the subordinate animals as well as the dominant leader of the group, as the subordinate animal may gain more food than by foraging alone.
• Social defence strategies

  Increase the chance of survival
• Social defence strategies

  • Individuals can watch for predators whilst others can forage for food
  • Among a flock of birds there are many eyes to look out for predators and their movement as a group makes it harder for predators to pick out one animal from the rest
• Specialised formations


  Groups adopt specialised formations when under attack protecting their young
• Staying together as a large group many types of animals rely on the principle of ‘safety in numbers’ as a means of defence
• Staying together as a large group or herd many animals are protected from predators
• An altruistic behaviour harms the donor individual but benefits the recipient.  This unselfish behaviour is called altruism.  Behaviour that appears to be altruistic can be common between a donor and a recipient if they are related (kin)

   

  There are two possible explanations for altruistic behaviour:

  • Reciprocal altruism.
  • Kin selection.

   
• Reciprocal altruism often occurs in social animals. It involves one individual, at some cost to itself, giving help to another provided that there is a prospect of the favour being returned at a later date when the role of donor and recipient are reversed.  For example, apes grooming to remove parasites.
• Two suspects (X and Y) are jointly charged with a crime they did commit
• The police have insufficient evidence to convict them for the crime
• They do have enough evidence to convict them both with a minor offence
• If X remains silent and Y testifies against X, X will serve 8 years and Y will go free
• If X testifies against Y and Y remains silent, X will go free and Y will serve 8 years
• If both X and Y remain silent, they will each serve 1 year for the minor offence
• If both X and Y testify against each other, they will each serve 4 years
• A self-interested decision (i.e. testifying against accomplice) leads to best personal outcome but worst mutual outcome
• If they trust each other and cooperate (i.e. both remain silent) it results in the best mutual outcome
• The donor sacrifices their own safety or chance to reproduce to ensure the survival of others.  The donor will only do this if the recipients are close relatives (kin) because related individuals possess shared genes. 

   

  The donor will benefit as there is an increased chance of shared genes surviving in the recipient’s offspring or future offspring.
• Complex patterns of social behaviour have evolved in some insect societies such as termites, ants, bees and wasps
• Close co-operation occurs between the individuals in caring for the young
• Division of labour in insect societies

  • A few fertile members contribute reproductively (queens and drones)
  • Many sterile members (workers) co-operate with close relatives to raise relatives. This increases the survival of shared genes
  • Workers defend the hive, collect pollen, carry out waggle dances to show the direction of food
• Colony of honey bees

  • One female queen who is mother to all bees
  • Thousands of female workers maintain and defend the hive to ensure the survival of the closely related offspring
  • Hundreds of male drones to reproduce with the queen
• Primates

  Mammals with large brain size, binocular vision (i.e. two eyes positioned at front of head) and opposable thumbs
• Primates

  • Lemurs
  • Monkeys
  • Apes
  • Humans
• Primates

  • Produce a small number of young and take great care of them
  • During the long period of parental care many opportunities arise for young primates to learn complex social behaviours essential for their survival
• Young primates


  • Learn complex behaviours that support the social hierarchy as they reduce unnecessary conflict
  • Reduce energy waste and impact negatively on survival of the species
• To reduce unnecessary conflict social primates communicate using ritualistic displays and appeasement behaviours
• Grooming

  Example of reciprocal altruism and used to build friendships
• Sexual presentation


  Used by females to appease dominant male
• These behaviours can differ between primate species