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

• Activity Number: 377
• Type: Contributed
• Date/Time: Wednesday, August 11, 2004 : 2:00 PM to 3:50 PM
• Sponsor: Section on Statistics and the Environment
• Author(s): Glenn Hofmann*+
• Companies: Household International
• Keywords: bounded domain ; bounded null models ; mid-domain effect ; competition ; gap-partitioning ; rain forest

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. 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 which used range-size criteria to constrain random placement of species optima within the domain. The null model assumes that proximity to domain boundaries depresses species density through its influence on range size. This mathematical phenomenon, known as the mid-domain effect in studies of geographic gradients, has not previously been applied to resource gradients. It concurs surprisingly well with our data.