Stably coexisting communities deliver higher ecosystem multifunctionality

Linking the processes determining species coexistence and effects of
biodiversity on ecosystem functioning is important for a mechanistic
understanding of how species loss impacts ecosystems. There are good
theoretical reasons to expect stably coexisting communities to deliver
higher ecosystem functioning, as niche differences should promote
coexistence and complementarity, however, there is still little empirical
evidence to demonstrate this relationship. We present a novel experimental
approach to tackle this question, in which we first measured interaction
coefficients and intrinsic growth rates for 12 grassland species and used
population models to estimate coexistence5. We then assembled 48
three-species communities, predicted to differ in their degree of
coexistence and measured seven above and belowground functions. Here we
extend findings demonstrating that biodiversity increases
multifunctionality to show that amongst communities with the same initial
diversity, multifunctionality is higher when all the species are predicted
to coexist. Decomposing coexistence into the influence of niche and
fitness differences showed that multifunctionality was high in niche
differentiated communities but also in those with a single highly
competitive species. We further examined the effect of indirect
interactions, which provide an alternative mechanism of coexistence in
multispecies communities, and found that they also provided an alternative
route to high multifunctionality. Our results point the way to a
unification of coexistence and biodiversity theory and to a more
mechanistic understanding of the functional effects of biodiversity
change.