Are rare species maintained by stronger NDD? A still-unresolved problem

A central focus in ecology is identifying mechanisms that maintain species diversity, particularly the coexistence of rare and common species. Substantial empirical evidence shows that rare species experience stronger negative density dependence than common species. This result is inconsistent with classical competition theory, but it is supported by a more recent theoretical model which claims that stronger self-limitation in rare species promotes their coexistence with common species. We recently reanalyzed the Beverton-Holt model and showed that stronger self-limitation in rare species is not sufficient to maintain their coexistence with common species, and thus it does not contribute to enhancing species diversity. We propose that coexistence is better explained by an alternative mechanism based on phylogenetically determined plant-soil feedback between rare and common species. This mechanism shows that rare species fare well in the neighborhoods of phylogenetically distant heterospecifics, but perform poorly in the neighborhoods of conspecifics or close relatives. Common species do the exact opposite: they perform relatively well in their own neighborhoods, but poorly in others. This mechanism helps reconcile the coexistence of rare and common species.

 

Publications:

dos Anjos, L. and He, F. 2026. Strong self-limitation promotes the persistence of rare species: Comment. Ecology (in press).

Jiang, Y., Wang, Z.-H., Chu, C.-J., Kembel, S. and He, F. 2022. Phylogenetic dependence of plant–soil feedback promotes rare species in a subtropical forest. Journal of Ecology 110:1237-1246.

Fangliang He is a professor and the Canada Research Chair in Biodiversity and Landscape Modeling at the University of Alberta. He is an ecologist and statistician by training. He received his PhD from the University of Montreal 30 years ago, followed by a Master’s in Statistics from the University of Victoria. He was a research scientist with the Canadian Forest Service in Victoria, BC, before joining the University of Alberta in 2003. He loves to crunch numbers, which includes counting trees and species—both dead and alive—in our landscapes. His recent research focuses on coexistence theory.