Plants that differ in height investment can coexist if they are distributing non-uniformly within an area

In nature, there is a large variability in the intrinsic height of plants living within an area. The question arises whether these height differences affect the plants' ability to coexist and thus is an adaptive trait. Using a biologically mechanistic model, we explored the possibilities for coexistence of plant types that differ in their pattern of allocation between stem (i.e. height growth) and other organs. We simulated the competition for light between growing individual plants. The study was game theoretical in the sense that each individual plant at any time affected the light availability for all plants in a locality, making conditions variable throughout the growing season and between seasons when the composition of competing plants changed. It was found that plant types that differed in their allocation to height growth could coexist over the course of years when these plants distributed their seeds non-uniformly in space, creating local differences in plant density. At each different density, one type with a specific investment in height performed better (i.e. achieved a greater seed production) than the rest of the types, thus preventing the exclusion of that type over the years. The resulting model community was self-assembling; local densities and competitive pressures originated as traits from the model plants themselves and were not the result of imposed external factors acting upon the model community. This mechanistic modelling approach shows that a condition as simple as a non-uniform distribution of seeds can generate the conditions for plants of various height growth strategies to live together over multiple generations. This study suggests that differences in plant height can be an emerging property of dispersing populations. (C) 2007 Elsevier B.V. All rights reserved.