The scaling of social interactions across animal species

Luis E C Rocha,Koen Schoors,Matthew Smith,Jan Ryckebusch

doi:10.1038/s41598-021-92025-1

Abstract

Social animals self-organise to create groups to increase protection against predators and productivity. One-to-one interactions are the building blocks of these emergent social structures and may correspond to friendship, grooming, communication, among other social relations. These structures should be robust to failures and provide efficient communication to compensate the costs of forming and maintaining the social contacts but the specific purpose of each social interaction regulates the evolution of the respective social networks. We collate 611 animal social networks and show that the number of social contacts E scales with group size N as a super-linear power-law E=CN^beta for various species of animals, including humans, other mammals and non-mammals. We identify that the power-law exponent beta varies according to the social function of the interactions as beta = 1+a/4, with a approx {1,2,3,4}. By fitting a multi-layer model to our data, we observe that the cost to cross social groups also varies according to social function. Relatively low costs are observed for physical contact, grooming and group membership which lead to small groups with high and constant social clustering. Offline friendship has similar patterns while online friendship shows weak social structures. The intermediate case of spatial proximity (with beta =1.5 and clustering dependency on network size quantitatively similar to friendship) suggests that proximity interactions may be as relevant for the spread of infectious diseases as for social processes like friendship.

Highlights

Social animals self-organise to create groups to increase protection against predators and productivity
Correlations between social interactions, as for example dominance and physical contact, friendship ties maintained through communication, or the intertwined relation between trust and spatial proximity, reveal the complexity of social phenomena and suggest that common principles may underlie the formation of social ties
The network size varies across species and social interactions because of experimental settings, characteristics and limitations of the study populations, e.g. the observation capacity of researchers, cost of technical devices, free-range vs. confined animals, online platforms, or animals living in small groups

Summary

Introduction

Social animals self-organise to create groups to increase protection against predators and productivity. The cost to establish and maintain social contacts in small groups is relatively low but increases in larger g roups[7]. Research on urban systems shows that human societies organise in groups (e.g. cities) to optimise resources like infra-structure and to increase intellectual, social and economic outputs[16,17]. These observations lead us to hypothesise that across species and social contexts, the number of social contacts E scales with group size N as E = CNβ , where C and β are positive constants

Methods

Results

Conclusion