52 Social Organisation

Key Idea: In social groups, members of the group interact regularly. Social species organise themselves in a way that divides resources and roles between group members. All behaviour has its roots in an individual's underlying genetic programme, but these innate behaviours are often modified by learning through experience, particularly social interactions. The behavioural adaptations of organisms contribute to their fitness (survival and successful reproduction) and so are the products of natural selection. Many animals live in cooperative groups for all or part of their lives. Structured social species are those where individuals live together in an organised fashion and can be divided into eusocial and presocial groups. Social groups divide resources and activities between them and are mutually dependent.

Eusocial animals

Eusocial animals are those in which a single female produces the offspring and non-reproductive individuals care for the young. They have the highest form of social organisation. Individuals are divided into different castes with specific roles. In most cases, a queen produces all the young and members of the group are normally directly related to the queen. Non-reproductive members of the group may be involved in care of the young, foraging, or defence of the nest site. Examples include ants, honey bees, termites, and naked mole rats.

3D

Termite queen Worker

Soldier

USDA, PD

Presocial animals

Presocial animals exhibit more than just sexual interactions with members of the same species, but do not have all of the characteristic of eusocial animals. They may live in large groups based around a single breeding pair and relatives (e.g. aunts/older siblings) may help raise the young. These groups often form hierarchies where the breeding pair are the most dominant. There may also be separate hierarchies for male and female group members. Examples include canine species that live in packs (e.g. wolves), many primates, and some birds. The number of males in a social group varies between species. In equines, a single stallion controls a group of mares. Young males are driven away when they are old enough. In elephants, the group is led by a matriarch, and the herd relies on her to make decisions in a crisis.

Female elephants and their offspring form small groups lead by the oldest female (the matriarch). Adult male elephants only visit the group during the reproductive season.

1. What is the difference between eusocial and presocial groups?

2. Describe the organisation of a eusocial animal group:

3. In eusocial animals, worker and soldier castes never breed but are normally all genetically related. How might their contribution to the group help pass their own genes to the next generation?

4. Elephant herds are led by a single matriarch and consist of her daughters and their calves. The matriarch leads the herd to feeding and watering grounds. How does living as a group help the survival of the herd once the matriarch dies?