Light Availability and Juvenile Tree Distributions in a Temperate Rain Forest: Why Do Different Species Coexist on the Same Resources?

• Activity Number: 107
• Type: Contributed
• Date/Time: Monday, August 8, 2005 : 8:30 AM to 10:20 AM
• Sponsor: Section on Statistics and the Environment
• Author(s): Glenn Hofmann*+ and Chris Lusk and Robin Chazdon
• Companies: Household International and University of Concepcion and University of Connecticut
• Keywords: rain forest ; light availability ; resource gradient ; mid-domain effect ; ranks

Abstract

Ecologists have proposed that tree species may coexist by specializing on light environments associated with forest gaps of different sizes. Remarkably few studies, however, have actually examined juvenile tree distributions along light availability gradients. Here, we describe distributions of juvenile trees in relation to canopy openness in a temperate rainforest and test the hypothesis that competitive sorting causes coexisting species to overlap less in light environment occupancy than would be expected by chance. Average overlap of species' interquartile ranges on the canopy openness gradient was tested against a bounded domain null model of community structure that used range-size criteria to constrain random placement of species optima within the domain. The null model assumes proximity to domain boundaries depresses species density through their influence on range size. This mathematical phenomenon, known as the middomain effect in studies of geographic gradients, has not previously been applied to resource gradients. It concurs surprisingly well with our data.