How many species would coexist in a random ecosystem? 

Nov 2, 2018
By Carlos A. Serván

In an ecological community with random interactions, a large number of species is likely to coexist.

Credit: Carlos A. Serván

Carlos A. Serván leads a paper in Nature Ecology & Evolution to answer this question

Put a large number of species together such that each of them can interactly freely with the others—as it would happen if one were to open all the cages of a zoo. If we come back after a number of years, how many of the original species will we encounter? In a new paper José, Jacopo, Kent, Stefano and myself explore this question by analyzing communities following Lotka-Volterra dynamics parameterized with interaction coefficients and growth rates sampled from random distributions. We were able to derive the full distribution of the number of coexisting species and show how this distribution is influenced by parameters dictating the way species interact with each other, such as the network structure of the community. Turns out that, although constructing a community in which all species coexist is extremely difficult—and gets harder as the number of species increases—, one can easily observe communities containing a large fraction of the original species by letting the dynamics of the community unfold.