Self-inhibition and optimal ramet mortality in clonal plants

Abstract

We used a spatially explicit dynamic model for studying the relationship between stochastic ramet and genet mortality in clonal plants. Since genets consist of ramets, a naive hypothesis would suggest that genet mortality increases monotonically with ramet mortality. Our simulations show that the relationship is non-monotonous. There is an optimum in ramet mortality at which the genet's mortality is minimal. The reason is that clonal growth is directional, and thus the existing ramets may block some growth directions. This blockage can lead to the formation of rings and other characteristic growth patterns. Ramet death can remove the blockage. Our results suggest that terminal vs. internal ramets along the branches have different effects. The genet's survival probability is strongly influenced by the terminal ramets but is almost unaffected by the internal ones in a broad parameter range. However, in a narrow range in which both mortality rates are low, and thus the frontline of spreading is densely populated, internal ramets become decisive. They strongly influence the genet's survival and almost exclusively determine its size (i.e., the number of ramets) in the steady state. We discuss the implications of within-genet regulation of death for the occupation of space and species coexistence in plant communities.