Here come old flat top
He come groovin’ up slowly
He got joo joo eyeball
Come together
Lennon  & Mccartney

We have been working on the applications of random matrix theory to ecology for four years. By now, it is quite clear that the most important challenge ahead is to extend the theory to the case of structured networks (as described here). A new study we just published is a first step in this direction:

 Stefano Allesina, Jacopo Grilli, György Barabás, Si Tang, Johnatan Aljadeff & Amos Maritan
Predicting the stability of large structured food webs
Nature Communications, 2015

In this work, we studied community matrices produced according to the cascade model, in which “big fish eat little fish”. These matrices look like this:

eyeballmatwhere the red squares represent negative coefficients (effects of predators on prey), and the blue ones positive coefficients (effects of prey on predators). These matrices produce a peculiar spectrum, suggestive of an “eyeball”:


In the paper, we derive simple, analytical results that allow us to approximate the spectrum (and hence the stability) of the eyeball.

 I wrote an R package that performs the analysis described in the paper, and published it on github.

PS: Despite the quote from the Beatles above, all I could listen to while writing the paper was Pink Floyd. Maybe because I remember another eyeball I saw a long time ago