PARENT SESSION
Oral Session 18: Ecological Theory I: Modeling.
Presiding: R Zabel
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room F 152.

Null-model analysis of morphological dispersion for size-related correlates of species competitive ability in old-field vegetation.

Cunningham, John¹, Schamp, Brandon^*,1, Aarssen, Lonnie¹, ¹ Queen's University, Kingston, Ontario, Canada

ABSTRACT- Plant species competitive ability is thought to be largely driven by components of plant size (i.e. potential height, maximum or mean potential biomass, basal spread). If interspecific competition is both driven by size related traits, and important in developing community structure, these traits should demonstrate predictable dispersion within plant communities. The only analysis of the dispersion of these traits thus far examined only one scale, and used a fixed quadrat size. It has been demonstrated that the number of individuals that occupy a given fixed quadrat size varies in relation to the size of those individuals and/or species. This study investigates dispersion of size related traits for plant species using three quadrat sizes of fixed ramet number: 500 ramets, 250 ramets, 100 ramets. Our null model tests the prediction that for a given mean trait value, variation in that trait (CoV, GINI, Lorenz Asymmetry Coefficient) will either be significantly smaller (i.e. underdispersed), not significantly different, or significantly greater (i.e. overdispersed) than observed for randomly generated quadrats (proportionally sampled from species pool). A Size-Advantage Hypothesis predicts underdispersion of size-related traits, while no significant dispersion suggests assembly independent of species size, and overdispersion suggests size-related niche separation. At the 500 ramet scale, 27% of quadrats showed significant overdispersion of species potential height and biomass while 73% of quadrats showed no significant dispersion. At the 250 ramet scale, 34% of quadrats showed significant overdispersion of potential height and biomass, 61% of quadrats showed no significant dispersion, and 5% showed significant underdispersion. At the 100 ramet scale, 31% of quadrats showed significant overdispersion, 55% showed no significant dispersion, and 14% of quadrats showed significant underdispersion.

Key words: null-model, species size, morphological dispersion, competitive ability