Social Networks and Ecological Food Webs

I read an interesting recent article that discussed a digital “autopsy” of the social network Friendster. Friendster was the grandfather of the social network, preceding both MySpace and Facebook. At its peak it had over 100 million users and a $30 million buyout offer from Google (which they turned down). However, following some technical problems and a site redesign in 2009, the network suffered a catastrophic loss of traffic as users moved to other networks like Facebook.

In this “autopsy” the authors looked into the reasons behind Friendsters “death” and discussed two general reasons for the failure:

  1. The first factor is a cost-benefit ratio: when the costs, in terms of time and effort exerted by being a member of the social network are greater than the benefits obtained, the conditions are set for users to leave.
  2. This is where the network’s topology is important. If a huge number of people in the network have only two friends, then when one of them leaves, the other is left alone on the network and will likely exit as well. This results in a cascade of users leaving the network. However, if people have many friends on the network (many connections), the loss of a single friend is unlikely to result in their exit from the network and unlikely to trigger a cascade of exiting users.

The authors concluded that the “cause of death” was due to declining cost-benefit ratios experienced by users as a result of the technical problems and site redesign. However, it was exacerbated by the network structure.

So, the key point here is that the resilience of the network is determined by the number of connections that each person in the network has. So for any given network, the proportion of the network containing a certain number of friends fraction of the network with a certain number of friends with few connections can be a crucial indicator of the network’s overall resilience from cascades.

In ecology, food webs are “networks” that describe a biological community in terms of the interactions between consumers and resources. The interactions are modeled as connections between consumers and resources that relate to the represent the transfer of energy and matter between the two. The interactions are diagrammed as lines connecting the consumers and their resources – which could be predators and prey, herbivores and plants, plants and soil, etc.

What’s interesting about the Friendster article is its very strong parallel to ecological systems like food webs. Both social networks and food webs need many connections for stability and resilience. Like Friendster, food webs with few participants are highly vulnerable to collapse or sudden radical changes in their structure (called a “trophic cascade“), in which the loss or addition of one or more key participants effectively changes the entire food web by altering key links between network participants. (For example, it’s impossible to play the Kevin Bacon game if he were not part of the network).

For social networks, the key to stability is each person having many Friends so that the loss of any single friend from the network is buffered by the many connections that each person has with other friends. For food webs, stability comes from a similar structure: they need many participants in the food web (the network) to create many different pathways between resources. Having many participants requires preserving biodiversity. If the biodiversity of a system is altered too much by the loss of a top predator or the introduction of an invasive species, the “network” can change. When this happens, vital connections between species can be broken and other connections can arise when newly introduced species competes for the same resources that were formerly linked only to native species. If the network does not contain many participants and has few connections, even small changes in the network will have drastic effects – in the worst case, it can result in a trophic cascade, such as the one that “killed” Friendster.


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