PARENT SESSION
Oral Session #3: Plant Population Ecology. Presiding: N. Fetcher.
Monday, August 6, 2001. 8:00 AM to 11:30 AM. Hall of Ideas L&M.

Relative contributions of light conditions and Janzen-Connell processes to seedling survivorship in a Neotropical rainforest.

Vriesendorp, Corine¹, Kobe, Richard¹, ¹

ABSTRACT- Both the Janzen-Connell hypothesis and gap partitioning are widely cited as explanations for the maintenance of high levels of tree diversity in tropical forests. Rarely, however, are these mechanisms considered simultaneously. This study considers the relative contributions of resource availability and Janzen-Connell processes in determining survivorship of seedlings of Pentaclethra macroloba, a neotropical canopy dominant at the La Selva Biological Station. We monitored natural recruitment and survivorship of P. macroloba seedlings in a 1 x 200m² contiguous belt transect for 9 months. Using survival analysis and maximum likelihood methods, we characterized the mortality of P. macroloba seedlings as a function of (i) light availability, (ii) density of conspecific seedlings, and (iii) a neighborhood index of mature tree conspecifics. Initial results for the neighborhood index, incorporating both adult tree size and distance, were not significant, and over the range of seedling densities that we observed (1 - 8 seedlings / m²), there were only marginally significant effects of seedling density on P. macroloba mortality. In contrast to the Janzen-Connell factors, light conditions proved highly significantly in predicting survivorship.

KEY WORDS: janzen-connell hypothesis, tropical rainforest, seedling survivorship, maximum likelihood