Diffusion of constructed resources and specialism promotes facilitation in spatial systems

Sessile organisms contend with locally limiting nutrients and neighbours. Increases in nutrient concentration due to niche construction and diffusion of resources change the interaction sign between neighbours usually thought to compete for resources. We investigate conditions under which the positive effect of niche construction outweighs the negative effect of resource consumption. Following the design of facilitation experiments, we model two patches connected by resource flows, and ask whether the presence of a niche constructor in one patch eases the colonisation of the other. Niche constructors positively affect neighbouring organisms when their niches are sufficiently differentiated, and when the constructed resource diffuses more than the non-constructed resource. Our work proposes mechanisms for the emergence of facilitation, which is increasingly recognised as a key process structuring plant and microbial communities. We discuss the implications for the spatial structure of communities and their functioning, including in an agricultural context.