PARENT SESSION
Oral Session #33: Biodiversity and Ecosystem Function: Nutrients, soils, microbes.
Presiding: K. Brown
Tuesday, August 6. 8:00 AM to 11:30 AM. Grand Ballroom Central, Radisson.

Competition theory modified by stoichiometric ecosystem properties.

Daufresne, Tanguy^*,1, Hedin, Lars¹, ¹ Department of Ecology and Evolutionary Biology, Princeton, New Jersey

ABSTRACT- Theoretical approaches of plant competition have highlighted the principle of competitive exclusion, and the fact that the coexistence of two plant species depends on different nutrient requirements. Such approaches generally assume chemostat input-output dynamics, although our empirical knowledge of natural ecosystems show that this is an oversimplification, and that different ecosystems display very different functional controls of inputs, outputs, and recycling. Here, we present a series of non-chemostat models of plant-nutrient dynamics, which show that the chemostat assumption leads to an incomplete view of the phenomenon. Our model is stoichiometrically explicit and takes into account recycling and different mechanisms of nutrient loss. We find that stoichiometric differences in plant nutrient uptake only have limited effect on competition and coexistence once the assumption of chemostat dynamics is relaxed. In contrast, competitive outcomes and the conditions of coexistence are strongly influenced by mechanisms and nutrient ratios of losses from the ecosystem, two parameters that vary widely among different ecosystem types. Thus, the conditions of coexistence not only depend on the nutrient requirements of each plant, but also on how each plant affects the losses of each nutrient. We will discuss the relevance of these results to both terrestrial and aquatic ecosystems.

KEY WORDS: stoichiometry, nutrient loss, competition, coexistence