Social behaviour Chapter 9*

Social Behaviour

Social organizations:

• Solitary

• Pairs

• Family groups

• Herds/Flocks

• Complex societies

Complex societies/Eusociality, social organisation

• The highest level of social organization

• Overlapping generations within a colony of adults

• Division of labour into a caste system:

  • Single reproductive female (queen)

  • Sterile workers

  • Drones (male)

  • Soldiers

• Cooperative care of brood

Costs and benefits of living in a group

Costs:

• Greater conspicuousness

  • Easier to see a big group of animals

• Competition

  • Food sharing

  • Dominance disputes

• Disease transmission

• Reduced reproductive fitness

  • Infidelity

  • Inbreeding

  • Infanticide

Benefits:

• Reduced predation risks

  • “Many eyes” effect

  • Confusion by blending in

• Information sharing

• More reliable access to mate

• Increased success in accessing food

  • Ability to take down larger pray

  • Ability to mob larger predators of kills

• Shared rearing of offspring

• Energy conservation

  • I.e. huddling together

The selfish herd*

• A theory based on the assumption that predation risk is not evenly distributed across positions within a group

• Individuals within a population attempt to reduce their predation risk by putting other conspecifics between themselves and predators

Edge effect

• Higher exposure to predation risk at the edge of a group

• Creates competition for good positions

• Consider motivation vs. risk (e.g. hunger)

• Part of the selfish herd theory

• Position is affected by: social status, age, health, food motivation, reproductive status

Domain of danger

A key element in the theory is the domain of danger, the area of ground in which every point is nearer to a particular individual than to any other individual

Social networks

• Animal social networks are descriptions of social structures

• Networks consist of nodes connected by edges

• Consists of nodes and edges

Centrality, social networks

A measure of an individual’s structural importance in a group based on its network position

Degree centrality, social networks

• Based on the number of direct edges an animal has

• An animal with more edges (degree node) will have more influence on those around it and possibly on the whole network (e.g. disease transmission)

Direct edges, social networks

A focal individuals immediate connections

Indirect edges, social networks

A focal individuals connections with individuals through other individuals

Bridges, social networks

Some individuals (nodes) serve as bridges in or between networks (node B)

Dominance

• A social relationship reducing conflicts

• Determines priority access to contested resources

  • mating opportunities, food, shelter

• Not a personality trait, rank can change

• Only applicable within a species

Signals and dominance

• Can provide information about rank or fighting ability and helps in the establishment of dominance hierarchies

• Can signal dominance, individual identity and fighting ability

A few examples of how rank is earned:

• Signals

• Age (birds born in succession)

• Inherited rank

Affiliative

Relating to forming social and emotional relationships with others, or to the feeling of wanting to form these relationships

Tit for tat*

Kin selection*

Cooperative breeding*

Hamilton’s rule*