The Daily Bulletin

Please join the Biology Department and the Great Lakes Center for the seminar “The Null Matters: Using Realistic Models of Dispersal Resolves the Janzen-Connell Paradox,” presented by Jeffrey Lake, associate professor of environmental science at Siena Heights University, on Monday, March 18, at 3:00 p.m. in Science and Mathematics Complex 151. Attendees are welcome to enjoy coffee and cookies during the seminar.

Abstract
Proposed mechanisms of species coexistence in spatially structured plant communities are many; evidence supporting or effectively eliminating competing hypotheses has been less than convincing. One of these key hypotheses is that of conspecific negativity density dependence (CNDD), often known as the Janzen-Connell hypothesis. In spite of convincing theoretical evidence and logical consistency of this argument, studies of spatial distribution of trees in forests quite consistently have found spatial clumping of species, not the overdispersion one would expect if CNDD were driving forest structure and coexistence. Dr. Lake's research team analyzed the spatial distribution of trees in the tropical forest of Barro Colorado Island, Panama (BCI), relative to expected distribution under various null dispersal models. Once they moved from assuming a fully random uniform model of seed dispersal to realistic models parameterized from observed seed dispersal, they found overdispersal/repulsion of conspecifics in most species. This work demonstrates a key role for CNDD in structuring a tropical forests, and reminds us of the critical importance of selecting our null model correctly.