Scientists have learned that the size of groups of primates is not random. There is a preferred group size.
Excluding humans, primates are mammals that have two arms and two legs, with the ability to climb trees (with most having five digits on each limb and an opposable thumb). Primates have large brains, and forward-facing eyes. Primates include apes, monkeys, lemurs, tarsiers, and lorises.
Susanne Shultz at the University of Manchester in the United Kingdom, and her research colleagues, compared group sizes in 215 primate species.
The researchers found that the average number in a group varied between species but was always clustered around five distinct sizes.
The preferred group sizes were: 3, 5, 15, 30 and 50.
The smallest group of 3 had two adults and one baby.
Larger groups tended to be one male with many females, or many males and females together.
A group with many males and few females were rare. A group with one female with many males was also rare.
Species of primates that live in open areas form the largest groups, perhaps to defend themselves against predators.
Species of primates that live in trees in thick forests prefer medium-sized groups, perhaps because large groups would be difficult to coordinate and manage.
Therefore zoologically, primates have a preferred group size, according to their species.
(Biology Letters, DOI: 10.1098/rsbl.2017.0490)
Photographer: Martina Nicolls
Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM