“Multispecies coexistence without diffuse competition; or why phylogenetic signal and trait clustering weakens coexistence”

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Simon Maccracken Stump

How competitive interactions are affected when species have different effects on one another

A tropical tree on Barro Colorado Island, Panama, one of whose leaves has been damaged by a leaf-mining insect. Part of this paper analyzes a model based on tropical forests and how tree diversity is affected by pests.
(Credit: Simon Maccracken Stump)

Most species compete with a mix of close competitors and distant competitors. What factors determine the structure of competitive interactions is hotly debated (for example, do related species compete more?). However, what is not clear is whether this structure matters for the community as a whole. Is a community where species have a mix of strong and weak competitors more stable than one where each species competes equally, and are there other emergent effects?

Simon Stump, a research associate at Michigan State University’s W. K.. Kellogg Biological Station, developed a simple theoretical model to tackle this question. Inspired by work in tropical forests, the model examines how trees can coexist either by using different parts of habitat, or by having different natural enemies. He demonstrates that the structure of competition can have three community-level effects: one that alters how stable a community is overall, and two that alter which species are the dominant competitors. He examines how these three effects play out differently in several different communities.

According to this model, the presence of some strong competitors and some weak competitors will alter community dynamics in two ways. First, many species will be equally competitive, because there will often be a trade-off between having many strong competitors in a good niche and having few strong competitors in a poor niche. Second, such communities will be more fragile than expected; the model gives methods for measuring this effect. Read the Article