The Mutualistic Niche: Mycorrhizal Symbiosis and Community Dynamics

Abstract

The niche is generally viewed in terms of species' intrinsic physiological potential and limitations due to competition. Although DNA sequencing has revealed the ubiquity of beneficial microbial symbioses, the role of mutualisms in shaping species niches is not broadly recognized. In this review, I use a widespread terrestrial mutualism, the ectomycorrhizal symbiosis, to help develop the mutualistic niche concept. Using contemporary niche theory, I show how mycorrhizal symbioses expand environmental ranges (requirement niche) and influence resource use (impact niche) for both plants and fungi. Simple niche models for competition between resource specialists and generalists also predict a range of ecological phenomena, from unexpected monodominance by some tropical trees to the functional biogeography of mycorrhizal symbiosis. A niche-based view of mutualism may also help explain stability of mutualisms even in the absence of clear benefits. The niche is a central concept in ecology, and better integration of mutualism will more accurately reflect the positive interactions experienced by nearly all species.