In animal behaviour, group augmentation occurs when animals living in a group behave so as to increase the group's size. Such behaviour could be selected for if larger groups increase the survival chances of the individuals in the group; therefore individuals could be selected to help raise other animals' offspring (alloparental care) or perform other cooperative acts, even helping unrelated individuals.
The meerkat Suricata suricatta is one species where group augmentation is suspected to be an important driver of cooperative behaviour.
References
Group augmentation Wikipedia(Text) CC BY-SA