Competition among simulated plant species in a toy local vegetation model

Abstract

Kleidon and Mooney (2000) used a trait-based simulation of plants in the global environment to argue that the tropics maintain more biodiversity because a greater variety of strategies of allocation of functional parts, such as leaves and roots, lead to viable physiologies in those regions. However, they did not account for competition for resources, which often leads to competitive exclusion and thus to low diversity of plant types. Here we sought to revisit Kleidon and Mooney’s study by simplifying their modelling approach in a local mid-latitude temperate environment but including explicit competition for water. We hypothesized that competition would reduce potential biodiversity. We first explored the viability of 1000 randomly assigned strategies of allocation to roots, leaves and storage in this environment. After identifying individual plants that can survive in the local ecosystem, we investigated whether pairs of these viable species can stably co-exist in a 20 year simulation when competing for water. The toy model, though highly idealized, leads to plausible growth curves for isolated plants, although simulated plants are smaller and slower growing than real world plants. In isolation, 86% of allocation strategies were viable. In our framework, direct competition for water did not prevent coexistence for the majority of plant “species” that survived in isolation. The results are intriguing in the light of the competitive exclusion hypothesis. Next steps for examining our hypothesis more carefully include further development and calibration of the trait-based plant model and exploration of the climatic parameter space.