Differential sensitivity: Focused competition, phylogenetic relatedness, and community structure

Background/Question/Methods As indicated by the co-occurrence of closely related species in a world-wide survey of woody plants, the coexistence of similar species accounts for an average of 30% of species diversity within communities, yet the coexistence and relative abundance of similar species is a continuing ecological conundrum. Classic niche theory dictates that when co-occurring species have similar requirements, the better competitor will exclude the other(s) from the community; coexistence of similar species is a transient phenomenon occurring en route to extinction of the poorer competitor(s). Alternatively, neutral theory posits that species are ecologically interchangeable, with coexistence controlled primarily by chance. Using close phylogenetic relatedness as an objective measure of similarity, we previously demonstrated that neither theory explained the relative abundances of co-occurring pairs of similar tree species in a species-rich tropical forest.

Results/Conclusions We show that the stable, focused competition of a temporal niche dynamic provides a significant fit to the distribution of fractional abundances (pairwise relative abundances) observed in this forest. An earlier report of independent evidence of temporal dynamics in this community supports our results, and our model identifies additional criteria for field tests of differential sensitivity (DS) temporal dynamics.