In Yale University’s Environment 360, science writer Carl Zimmer outlines how some ecologists are applying network theory to understand the “small-world” networks that form and sustain ecosystems. Zimmer relates how the “Six Degrees of Kevin Bacon” idea of intimate linkages can be used to understand how different animal and plant species relate to each other.
Zimmer writes that the six degrees of Kevin Bacon became a sensation in the 1990’s. The idea is that every actor is less than six steps away from the actor Kevin Bacon. Scientists created a Web site, The Oracle of Bacon, which analyzes connections between 1.6 million actors. “It reveals that all actors in Hollywood are connected to Bacon on average of 2.95 steps.” Furthermore, there is a sub-set of 1,000 actors that are linked to the rest of Hollywood by less than three links — these are the set of highly connected actors who form nodes.
This relationship is seen in other human systems. Albert-Laszlo Barabasi, author of “Linked: How Everything Is Connected to Everything Else,” argues that the World Wide Web is organized in similar fashion. There are major nodes (Google, New York Times.com, etc) that receive the bulk of links, which actually makes the whole network more efficient. “These hubs shorten the path between all nodes in the entire network.”
Now, some scientists are exploring how these theories relate to ecosystems and can be used to preserve natural systems. While there are different species (oak trees, bees, rats) and these play different roles (predator, prey, pollinator, pollinated), depending on their position in the ecosystem, “nature is arranged in networks made up of links between species.”
For example, some species with fewer connections to other species are more vulnerable. “Most plants, for instance, depend on animals of one sort or another to spread their pollen. In some cases, scientists have discovered exquisitely co-evolved partners that specialize only on one another.” These types of partnerships, which are ”specialized,” make some plant species more vulnerable to extinction if one partner declines. More generalized partnerships (species that have partnerships with multiple species) may be more resilient.
Zimmer says a “field of wildflowers is like Hollywood.” The elite subset of 1,000 actors in Hollywood is much like the set of generalists that form nodes and multiple partnerships across species. One researcher, Jordia Bascompte at the Spanish Research Council, found that this “small-world” natural network fosters more biodiversity than other kinds of networks.
Bascompte also analyzed marine ecosystems in the Caribbean and discovered fish form inter-connected “modules” around sharks. Zimmer writes: “The Caribbean network is thus organized around sharks, with each species a highly connected hub in its particular module. That arrangement means that overfishing sharks could have an even bigger effect on marine ecosystems than ecologists have previously realized.” If sharks decline, in other words, other fish species bloom, which could lead to changes in the underlying ecosystem structure, or eventual ecosystem collapse.
Scientists hope to use this information to determine how overfishing, deforestation, and invasive species affect existing natural networks and preserve fragile ecosystems. Using these concepts, Zimmer argues, scientists can understand how pesticides and pollutants that impact plant life end up having a direct effect on large predators like bears or sharks. The effects ripple through the natural networks.
Also, check out a recent special report from The Economist on the growth of social networks.
Image credit: How Stuff Works.com
