Coexistence by temporal partitioning of the available light in plants with different height and leaf investments

In natural vegetations, plants may show considerable variation in height. This suggests that plant types with different heights can persist over longer periods of time, despite the pressure of competition. We want to address the question whether plant types that differ in their investment in height can have a similar performance when competing for the available light and whether the frequency of competing types affects the outcome of competition.The question is addressed with a simulation of a de Wit replacement series, a much-used method to assess the competitive status of pairs of plant types. The basis for our calculations is a biologically realistic plant growth model that simulates interactions by mutual shading between annual plants.We found that plant types with different (low or high) investment in height growth partitioned the light that was available within a growing season and that plants of such types could perform more or less equally. The light that was available early in the season was intercepted mostly by plants with a low investment in height whereas the light that was available late in the season was intercepted mostly by plants with a high investment in height. Moreover, we found negative frequency dependence in the performance resulting from competition of plant types with such different (low or high) investment in height. With a higher frequency of con-specifics, plants remained smaller and they were more susceptible to the competitive pressure of the other type. Over the simulated growing seasons, this process directed the frequency of competing plant types to an equilibrium point at which the fitness of both types was equal. Negative frequency dependency was apparent in simulation runs with different densities and season lengths, implying a robust phenomenon.These findings reveal that, as a result of a difference in the temporal usage of light, plant types with different height-growth strategies can stably coexist by negative frequency dependent competition. This however holds only for pairs of types in which one has a high, the other a low investment in height growth.