Triadic closure in the animal kingdom
https://www.deccanherald.com/content/500949/hyenas-their-own-facebook-algorithm.html
Hyenas are carnivorous animals which live and hunt in groups called clans. Some members of such clans can spend their entire lifespan (~19 years) in the same clan. As such, the societal structure of such clans and the relationship between their members is a topic of interest. Even in networks of non-human organisms, we can still observe concepts relevant to the networks we use to describe human interactions, namely triadic closure, and weak and strong ties.
It was observed by scientists from the University of Tennessee that hyenas tend to rely on friends, and when additional friends were needed, say, to improve success at hunting, they were more likely to bond with a friend of a friend, rather than a completely unfamiliar hyena. A member of the team, Amiyaal Ilany, suggested that there was an evolutionary advantage to such behavior, as “[cohesive] clusters can facilitate efficient cooperation and hence [maximize] fitness, and so our study shows that hyenas exploit this advantage”. More relevant to those of us in this course is the fact that this is an example of triadic closure, if we represent a clan’s societal structure as a graph, with strong ties between every pair of hyenas which are friends with one another. We now consider a mechanism for triadic closure to occur under this model.
Consider hyenas A and C, which are not friends with each other, but are both friends with a 3rd hyena B. To hunt larger prey, 3 hyenas may be needed, in which case it is likely that B would invite some subset of its friends, which could include A and C on a given day. As this could occur multiple times over the relatively long lifespan of a hyena, it is likely that A and C will eventually recognize and trust each other as competent hunters and trustworthy when it comes to sharing the spoils of the hunt. And also due to the time A and C will spend with one another hunting prey, A and C will be likely to become friends, forming a strong tie between the two, under our model, and form a tie of some strength between one another.
One other topic of interest could be the clustering coefficient of such societies, as a function of the size of prey a given clan primarily hunts. One can imagine a clan which primarily hunts larger prey would have more incentive to send out larger groups of hyenas for each hunting trip. This would give more opportunities for triadic closure to occur by the mechanism above, which means that for every node N in the graph representing the clan G, for each pair of friends sharing a strong tie with N, (N’, N”), one can expect the edge (N’, N”) to be added to E(G) within a short span of time (relative to the lifespan/average residence time of a hyena in V(G)), which implies that more pairs of friends of each node N in V(G) will themselves be friends, increasing the clustering coefficient. It follows by similar reasoning that in a clan which prefers hunting prey which only require 1-2 hyenas to hunt (observe that for the mechanism above to take place, at least 3 hyenas must be in the same hunting team), then one might expect to observe a lower clustering coefficient in such clans.