How Long Does a Short-Lived Perennial Live? A Modeling Approach

We have composed a “scale of ontogenesis,” i.e., the sequence of ontogenetic stages, and the life cycle graph (LCG) for Androsace albana, a monocarpic plant species that is considered a short-lived perennial, according to annual observations on permanent sample plots in an alpine lichen heath during the 2009–2016 period. There is only one reproduction event in the LCG, which eliminates any reproductive uncertainty from the data of “identified individuals” type so typical for the former projects with polycarpic species, while the monocarpic cycle excludes any returns from the generative stage to a non-flowering status. The LCG describes the ontogeny through five successive stages: seedlings, juvenile, immature, adult virginal, and generative plants, the generative plants perishing after they have flowered and produced seeds. We have constructed a matrix model of the stage-structured population that corresponds to the LCG; its calibration has reduced to calculating the vital rates directly from the data of one time step, i.e., from the censuses at two successive years of observation. Therefore, the nonautonomous model represents a set of 7 annual matrices, each giving a quantitative measure of how the local population is adapted to its environment as the dominant eigenvalue of the model matrix. Its variations have turned out quite significant from year to year, signifying either a growth or decline of the local population and, in general, its vulnerability to stress factors of the environment. Averaging the annual matrices geometrically over the whole observation period has revealed the tendency to decline and enabled us to extract certain age-specific traits (in years) from the stage-structured model using the technique of virtual absorbing Markov chains and their fundamental matrices. The mean life expectancy at various stages of the A. albana ontogeny has turned out maximal in the adult virginal plants, while the mean age at flowering equal to 13 years has exceeded the horizon of the observation time series, thus proving the technique to be efficient. The model indicates that A. albana plants spend most of their life spans as virginal adults, which characterizes the space holder strategy by Körner (2003), or the delayed-development strategy by Zhukova (1995). The model outcome gives another evidence that the A. albana population is endangered.