Contemporary niche theory is a structuring framework in the understanding of species coexistence, species distribution, ecosystem functioning, and the feedback between organisms and their environment. It highlights the dichotomy between the requirement niche, the sensitivity of a population to its environment, and the impact niche, the way this population in turn modifies its environment. Initially developed in the context of resource competition, extensions such as the inclusion of shared predation under the term `apparent-competition’ have broadened the scope of the theory.
Yet, a more general framework of contemporary niche theory that also includes positive interactions, such as facilitation and mutualism, is still missing. Such a need is reinforced by the recently expanding interest for positive interactions within plant communities. Building on recent advances on the subject, this presentation is an attempt to lay down the theoretical premises of such a niche theory of positive interactions. These ideas will be illustrated through a model of coexistence between nitrogen-fixing and non-fixing plant species competing for nitrogen and phosphorous.
Results/Conclusions
After defining what we mean by `positive interactions’, we first address the niche of a single species subject to positive interactions through the example of a nitrogen-fixing plant. We show how the requirement and impact niches can be combined graphically to obtain another niche dichotomy, Holt’s invasion and persistence niche. The mismatch between the latter two niches indicates the existence of alternative stable states between species’ presence and absence.
Second, we study how accounting for a second species can affects the niche of the first species. We show that the presence of the second species can either extend both the invasion and persistence niche of the first species, or only extend the invasion niche of the first species.
Finally, we discuss the validity of difference metrics of niche overlap in the context of two-species coexistence involving positive interactions.
To conclude, this study shows that extending contemporary niche theory to account for positive interactions can lead to new and broader niche concepts, and help us understanding how positive interactions shape ecological communities.