Perennial plant models to study species coexistence in a variable environment

Living organisms face a changing physical environment. One fundamental question is how environmental variation affects species coexistence. Modern understanding of environmental variation emphasized the hypothesis that possible adaptations to a fluctuating environment allow species to use different environments in different ways. Species can partition temporally their use of resources. Persistent stages in the life cycle such as prolonged longevity can buffer species through unfavorable environments. Differences in longevity will also lead to different nonlinear responses of population growth rate to fluctuating in resources. Questions arise: how do these possible adaptations to environmental fluctuations affect coexistence.;Being able to quantify coexistence mechanisms in the field is critical to understand different processes contributing to species coexistence in a community. In many respects, applications of those techniques for quantifying coexistence mechanisms have the potential for substantial improvements. In particular, very few studies directly quantify coexistence mechanisms for perennial plants. Coexistence of plant is often puzzling because they share similar resources. Environmental variation has been suggested as an important factor for niche partitioning but challenges for studying it in perennial plants are clear. The long generation time poses challenges to controlled experiments. Moreover, perennial plants have complex life histories. Vital rates change with size. In addition, tremendous temporal variation is observed in various life history processes. Furthermore, different processes in different stages of the life history can interact with environment and competition in different ways. Using perennial plants as an example, our study reveals a crucial role in theory development to summarize understanding of such a complex system. I start with the simple lottery model to study the relative importance of two coexistence mechanisms: the storage effect and the relative nonlinearity. Then I extend the model by showing that variation in individual growth can also lead to stable coexistence similar to the effect of variation in seedling recruitment. Species can benefit most from variable environments when the processes contributing most to capturing resources on average are also very sensitive to environmental fluctuations. New mechanisms arise through shifts in size structure, which depend on how vital rates change through ontogeny.