The latest issue of Journal of Ecology includes a Special Feature guest edited by Ignasi Bartomeus and Oscar Godoy. Below, Ignasi and Oscar tell us more about the inspiration behind their Special Feature and how they went about putting it all together.
Why a special issue on biotic controls of plant coexistence?
The quick answer is that although there are clear theoretical expectations that biotic interactions should influence the determinants of species coexistence through competitive interactions, very few empirical tests were available to date. This revelation came to us during the AEET-MEDECOS meeting in Seville, where we attended several talks showing, for instance, that pollinator assemblages of common and rare plant species differ, or that generalist herbivores attack more heavily abundant species.
All these talks described beautifully crafted datasets full of natural history, but none of them connected these multi-trophic patterns with their consequences for species demography and therefore changes in community dynamics. We wondered why this was and arrived at the conclusion that there is a disconnect between theorists and empiricists that needed to be bridged. While there is strong theoretical development on mechanisms promoting species coexistence, validating this theory has proven challenging.
The gist of coexistence theory
Coexistence theory explains that the way two species interact allows coexistence at local scales only if their niche differences overcome fitness differences (Chesson, 2000; 2003). Niche differences cause intraspecific competition to exceed interspecific competition, and promote stabilizing effects by buffering species against extinction when they drop to low relative abundance. Niche differences are thought to arise when species use different resources, or are being used differently by their consumers. Hence, when two species use the same resource and are predated in exactly the same way (i.e. niche differences are zero), coexistence is not possible, and differences in competitive ability determine the superior competitor.
We can connect these simple theoretical concepts to conducted experiments, for example, rare plant pollinators may follow mechanisms related to niche differences; however, generalist herbivores targeting a common species would mostly follow a mechanism related to the competitive ability of the dominant plant. Interestingly, biotic interactions can act simultaneously on niche and fitness differences therefore we have the expectation that both mutualistic and antagonistic interactions can potentially either promote or reduce coexistence. But which of these two mechanisms is more prevalent in nature?
A collection of interactions
With this idea in mind, we contacted a worldwide set of authors working on different systems ranging from herbivory and pollination, to seed predation and nitrogen fixing mutualists, and challenged them to answer the same question: How do biotic interactions shape species coexistence in your system?
Take a look at our Special Feature if you are curious about the results. Start first with our editorial, which introduces species niche and fitness concepts, how they were integrated into coexistence theory, and will put the findings of these new papers into context. If you are interested in the most recent updates of the theory developed by Peter Chesson, read his paper reviewing and updating novel theoretical findings on mechanisms of maintenance of species diversity with special emphasis on biotic interactions and multi-species assemblages. Not full yet? Then, keep reading through the further 9 experimental and observational studies answering our core question with state-of-the-art experimental designs and modeling techniques.
We hope you enjoy reading this special feature as much as we did organizing it.
Ignasi Bartomeus and Oscar Godoy
Read the full special feature online: Biotic controls of plant coexistence