The relative importance of sexual and clonal reproduction for population growth in the long‐lived alpine plant Geum reptans

Abstract

Summary Demographic studies in natural habitats are important for understanding the life history and mechanisms of population persistence of particular species. For plants living in high‐alpine habitats, it is of significant importance to what extent sexual or clonal reproduction contribute to population growth, but respective data are scarce. We studied the demography of Geum reptans, an alpine plant which reproduces by seeds and by vegetative rosettes formed at the ends of above‐ground stolons. In three consecutive years, growth, survival, and reproduction were measured in two populations with 579 and 301 individuals, respectively. The two resulting transition matrices per population were used to calculate population growth rates (λ) and elasticities, and to perform stochastic simulations to assess the relative importance of sexual vs. clonal reproduction for population growth. Population growth rates (λ) varied from 0.999 to 1.074 among years and populations. The frequency of seed and stolon production was relatively constant over the years. However, there was interannual variation in seed germination (0.7–2.4%) and in establishment of clonal offspring (53–74%). Elasticity analysis showed that changes in the survival of adults had the largest effect on λ, confirming the importance of longevity and persistence in the life history of G. reptans. Stochastic simulations showed that in G. reptans, independently of location and year, both sexual and clonal reproduction did not significantly differ in their contribution to the population growth rate λ. Establishment from seeds contributes to population growth particularly in favourable years, while the more regularly occurring reproduction by clonal offspring may ensure population growth in less favourable years. Sexual reproduction in clonal plants is frequently explained by the short‐ and long‐term benefits of genetic variation and the need for dispersal and colonization, for which seeds are better suited than vegetative organs. Our results, however, show the importance of sexual reproduction in a clonal plant for local dynamics as well, and prove the power of matrix models to evaluate the relative contributions of the two reproductive modes.