To resprout or not to resprout? Modeling population dynamics of a root-sprouting monocarpic plant under various disturbance regimes.
Monocarpic plants are favored in conditions of high mortality of reproductive individuals, whereas situations with low juvenile survival give an advantage to polycarpic perennials. However, certain plant species combine both strategies, showing high plasticity and life-history variation in recurrently disturbed habitats. Life-history variation caused by resprouting from roots after injury has been reported in many weedy and invasive species, but the long-term effects of resprouting on population dynamics are not known. In this study, we asked how different disturbance scenarios affect long-term fitness of plants with varied capacities for root-sprouting. We used projection matrix analysis to simulate growth of populations of the annual herb Rorippa palustris having factorial combinations of root-sprouting intensities, disturbance timings (intra-annual), and frequencies (inter-annual). The contributions of these factors to population growth variation were enumerated using variance decomposition. Population growth was affected by all examined parameters. Disturbance frequency negatively affected population growth rate, but its effect was modulated by disturbance timing. Summer disturbance decreased population growth rate dramatically, whereas winter disturbance had no effect. Resprouting from roots was important for plant overwintering. In pre-reproductive plants, disturbance frequency and root-sprouting intensity strongly interacted in the spring, such that the negative effect of frequent disturbance was overcome by resprouting. Our results imply that, in this species, conditions of unpredictable, severe disturbance, would select for high phenotypic plasticity in life histories, whereas only regular spring disturbance would favor resprouting.