Organisms competing for contested resources like nutrients, light, and space play an important role in biodiversity. A recent paper co-authored by incoming SFI Omidyar Fellow Jacopo Grilli finds that the number of competitors may matter.

“The authors’ model potentially offers a better understanding than that provided by previous models of how diverse communities are maintained in nature, where it has often been hard to explain the high levels of biodiversity observed,” writes former SFI Omidyar Fellow James O’Dwyer (University of Illinois), in a review of the paper.

Think of two saplings seeking to exploit the advantages of light streaming through a new opening in the forest canopy. One will emerge the winner in this simple pairwise contest.

But add a third sapling and predicting a winner is far less straightforward, like predicting who will win in a three-person game of rock-scissors-paper. Rock smashes scissors, but while paper covers rock, it also answers to scissors.

Now imagine the game with hundreds or thousands of different competitive moves. In their model, Grilli and co-authors did just that. They also made their competition a bit “noisy” by allowinging non-standard outcomes every so often (this time, scissors cuts rock) — much like in nature, where many factors, from soil chemistry to hungry insects, can make outcomes less predictable.

As they tweaked the model’s parameters by allowing new species to enter the system, for example — they were able to probe the dynamics of competition and diversity in new ways.

Their analysis proffers, among other insights, that higher-order interactions — those involving multiple competitors — may play a significant role in stabilizing an ecological system.

“The jury is still out on whether this is the right way to describe ecological competition,” says O’Dwyer, “but these results suggest these higher-order interactions are something to look for in real systems, and the model at least makes it more tractable to study these effects.”

The intersection of Grilli and O’Dwyer’s work — and their common SFI pedigree — is no coincidence. Both are ecologists with backgrounds in physics. About five years ago, Grilli read one of O’Dwyer’s papers and was drawn in by its physics-inspired approach — one Grilli had already been thinking about. Grilli had not heard of SFI, but his interest in O’Dwyer’s paper eventually led to his application for the Fellowship.

“It’s nice to see two generations of Omidya Fellows constructively building on and challenging each other’s work, and, in doing so, pushing complexity science in ecology forward,” says SFI Professor Jessica Flack. “It speaks to the strength of this unique postdoctoral fellowship.”

Grilli’s paper and O’Dwyer’s review were published Aug. 10 in Nature. 

 

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