Understanding the effects of physiological and ecological conditions on the fitness consequences of different life history strategies is critical for explaining the diversity of life histories and for predicting the ecological and evolutionary responses of populations to changing environmental conditions. In herbaceous plants, life history strategies vary tremendously within and among taxa, but whether (and how) these qualitatively and quantitatively distinct strategies arise from ecological and physiological differences remains poorly understood. To provide a theoretical basis for understanding life history evolution in herbaceous plants, we combined a mechanistic model of ontogenetic growth, which we modified to apply to the yearly re-growth of photosynthetic tissues and stored reserves in herbaceous plants, with a stochastic dynamic programming model to predict schedules of reproduction and prolonged dormancy that maximize lifetime seed production.
Results/Conclusions
The predictions of our model capture several facets of allocation strategies observed in herbaceous plants. If the probability of surviving the winter is low or if plants on average accumulate little reserves, an annual strategy maximizes lifetime seed production. Under favorable conditions for survival and reserve accumulation, plants maximize seed production through a perennial strategy, but whether this strategy is monocarpic (semelparous) or polycarpic (iteroparous) depends on the relationship between reserves allocated to reproduction and the number of seeds produced. For polycarpic perennials, the amount of storage retained between growing seasons increases with reserve production but decrease with overwinter survival, suggesting that the net effect of environmental changes on life history strategies may depend on relative influence of the change within versus between growing seasons. Our model also suggests that reserve accumulation and increased survival during prolonged dormancy may favor the evolution of dormancy in the absence of environmental stochasticity, particularly if sprouted plants accumulate few reserves and winters are harsh.