Network visualization of the Estero de Punta Banda food web (Kevin Lafferty)

Interest in food webs, the networks of who eats whom in an ecosystem, has exploded in recent years, and it is beginning to bring with it a mountain of data – so much data, in fact, that ecologists can now ask not just how food webs are structured, but also how those structures depend on sample size, physical location, climate, or other characteristics of the habitat.

In theory, they can answer those questions. The trouble, says SFI Omidyar Fellow Joshua Grochow, is that most scientists don’t really have the right mathematical tools to answer them rigorously, a problem that he, SFI Vice President for Science Jennifer Dunne, and colleagues are addressing during a working group at SFI February 29- March 1.

“The datasets of food webs really cry out for better analysis, to do comparison and interpolation,” Grochow says, to see how food webs’ structures depend on something as simple as latitude or something more complex, such as the introduction of parasites.

Right now, network science offers only somewhat crude and ad hoc ways to answer questions like that, largely because it offers mostly simple measures of food web structure – for example, the number of species each organism eats, how many feeding links away each animal is from primary producers, and how many species are omnivores, cannibals, or herbivores.

“It turns out that rigorous comparison of network structure across datasets is a very challenging, non-straightforward, problem,” Dunne says. Grochow and Dunne hope to develop more sophisticated analysis approaches.

One idea is to compare the frequency of different sized motifs – smaller structures that show up repeatedly within a larger network – across different food webs, though that’s just one possibility; analysis has been done of three-node motifs in food webs, but not larger motif sets. 

By bringing together rich databases from ecology and rigorous new thinking from computer science, Grochow and Dunne say, they will be better prepared to search for general patterns in food webs as well as the underlying mechanisms that drive observed ecological organization.

Read more about the Feb. 29–March 1, 2016 working group "Comparing ecological networks along gradients."