Social networking in the Columbian ground squirrel, Spermophilus columbianus

Networks are collections of units that potentially interact as a system. Electronic power grids, human societies, the Internet, food webs and metabolic pathways are examples of networks that have emergent properties that allow all vertices (viz. individuals, components, species, etc.) to be linked by a short chain of intermediate vertices. My field observations on a colony of 65 free-ranging Columbian ground squirrels suggest that their society also exhibits these characteristics via social interaction. On average, any dyad of squirrels in the colony can be connected via amicable interaction with three intermediate individuals. The connectivity of individuals (viz. the number of individuals to which an individual is directly connected) decays following a scale-free power law distribution. Individuals that have similar age, reproductive status and number of associates (viz. the number of individuals to which the individual is connected via social interaction) interact amicably with each other more than other squirrels. The network is robust to the removal of random individuals. However, simulated removal of individuals that are connected to many other squirrels increases the number of intermediates between two random individuals and fragments the network into smaller clusters when removals exceed 10% of the individuals in the colony. Thus, certain individuals appear to play more central roles than others in the cohesion of the network. My results reinforce previous studies showing that network theory can be used to determine the roles played by individuals in the cohesion of animal societies, thus providing a framework for studying sociality across species.