Size-distance relationships reveal the importance, or lack thereof, of competition among understory plants in an old-growth deciduous forest

Abstract

In this study, I applied the little-used method of size-distance relationships to the ecological problem of species coexistence by investigating competitive interactions in an old-growth deciduous forest understory community, with the specific objectives to (1) explore and critically assess the method and (2) test the predictions of niche and neutral theory regarding the intensity of intra- versus interspecific competition. No fatal flaws were detected in the method, but the mechanisms of species coexistence in this community remain unclear, as the finding that intraspecific competition is less intense than interspecific competition was inconsistent with the predictions of both niche and neutral theory. More importantly, though, size-distance relationships revealed that competition is less important than expected, which suggests that asking what enables species coexistence may have been an inappropriate line of inquiry to begin with, given that the coexistence question itself is based on assumptions about competition that were not justified in this community. I, therefore, advise ecologists to reassess the approach to the study of natural diversity by rethinking both the questions posed and the methods used.