PARENT SESSION
Contributed Oral Session 142: Biodiversity and Nitrogen
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal

Intraspecific variation in plant competitive ability: Species trait or environmental consequence?

Lamb, Eric^*,1, Cahill, James¹, ¹ Department of Biological Sciences, Edmonton, Alberta, Canada

ABSTRACT- Many models make predictions relating variation in plant species competitive ability to environmental and community parameters, and the relative competitive ability of species is thought to be important in structuring plant communities. However, beneath the variation in competitive ability among species is often very high variation in competitive ability within species. The causes of this intraspecific variation are poorly known, but have consequences for efforts to invoke competition as a cause in ecology (e.g. invasion success). This study was designed to quantify the intraspecific variation in competitive response ability along environmental and compositional gradients and with fertilization. Twelve species were studied in a native grassland using a field experiment. Pairs of established plants of each species were located and the neighbours were removed from around one plant. Half of the pairs received nitrogen fertilization, and environmental and community parameters were measured around all pairs. We found large between- and within-species variation in competitive response ability. Nitrogen addition altered the competitive ability of five species (3 increased and 2 declined). The potential growth rate of plants varied between locations, and this influenced the competitive ability of four species (competitive ability increased with growth rate for 1 species and declined for 3). Much of the remaining within-species variation (30-90% of total variation) could be explained as a response to community and environmental parameters such as above- and belowground biomass and diversity. This research has two major implications. First, the growth-rate dependence of competitive ability within a species means that any experimentally derived competitive hierarchy is likely to be contingent on the growth rates of the plants studied, even within species. Second, the species-specific responses to environmental conditions demonstrate that competitive response ability should not be viewed as a fixed trait, but rather as the average of a range of integrated and plastic responses by a plant to its environment.

Key words: plant ecology, competition, community structure, grassland ecology