Triadic Closure in Food Webs
Food webs are fairly straightforward. Nodes are organisms (animals, plants, etc.), and edges indicate “consumption.” If two nodes are connected, then one organism eats the other. Generally, food webs can be organized into tiers, these tiers being producers and primary, secondary, and tertiary consumers (leaving out decomposers). Primary consumers are carnivores that eat other carnivores, secondary consumers eat herbivores, and primary consumers eat producers, which are mostly plants.
I found food webs while looking for contexts in which triadic closure might be less common. In social networks, triadic closure is fairly common because friends of friends are likely to at least know each other. In food webs, triadic closure is much less common because it can only happen when an organism fits into two tiers. For example, in the network below, the hawk is taking on two roles in the food web: secondary consumer and tertiary consumer. Thus the hawk shares prey with the snake, but also eats the snake. There is therefore triadic closure between hawks, snakes, and rodents. The scarcity of triadic closure in food webs stems in part from its tiered structure, because most organisms interact with only the tiers directly above and below them. Without ties within their own tier or to tiers two or more levels away, there is no way to consistently make triangles. This logic can be applied to other networks as well, and I am curious as to whether a similar phenomenon could be observed in the social networks of strongly enforced caste systems. This might also help explain a lack of empathy or understanding between social classes.
From: http://emnrcd.org/wp-content/uploads/2014/08/Wildlife-Post-Field-Trip-Curriculum.pdf