Bever's conceptual model of plant-soil feedbacks predicts coexistence between two plant species under strong competition or under dominance by one plant on another. In addition, feedbacks could also lead to competitive oscillations. Here we present a fairly complete analysis of Bever's model using a graphical method that reveals all possible invasion scenarios and the dynamics that follow. Our graphical method can be useful for the analysis of similar models that use the Lotka-Volterra competition equations as part of their formulation.

Results/Conclusions

(1) As a consequence of density dependence, Bever's interaction coefficient does not unequivocaly indicate the net direction of the feedback effects, positive or negative. We propose a more appropriate alternative. (2) Oscillations only take place under net negative feedback, and alternative stable coexistence states only under net positive feedback. (3) Stable coexistence can be turned unstable due to oscillations induced by negative feedbacks, which in turn could degenerate into high amplitude cycles and the extinction of one species.