RAMET BEHAVIOUR AND POPULATION GROWTH IN THE CLONAL HERB POTENTILLA ANSERINA

SUMMARY (1) Potentilla anserina is a stoloniferous plant in which the daughter ramets become independent during their first year of life. Ramets of P. anserina behave in four different ways. They may be inactive, flowering only, stolon-producing only, or both flowering and stolon-producing. The relationships between ramet size and type of behaviour, and transition probabilities between behavioural states during four successive years were derived from a field study of P. anserina on a Baltic seashore meadow. (2) Ramet behaviour and mortality were significantly size related. The results suggest that flowers and stolons are initiated when the physiological condition of ramets has reached some internal resource threshold. The size relationships form the basis for inferring phenotypically-expressed costs of different behaviour patterns from transition probabilities. (3) Several transition probabilities varied significantly between years, but some patterns of variation emerged. Inactive ramets which changed behaviour usually became 'flowering only' next year. There were no indications that reproduction per se incurred any costs for ramets. Flowering ramets had the greatest probability of flowering the following year. In contrast, stolon production had negative consequences both for survivorship and for future reproduction of ramets. (4) Simulations of a matrix model yielded different population growth rates (1 05, 0 91 and 0-68) during the study years. Simulated stable state distributions differed from the observed ones, which also varied significantly between years. Population growth rate was most sensitive to alterations in transitions from inactive to stoloniferous ramets, but these transitions are not common in the real population. Elasticity analysis revealed that growth rate instead depends mainly on survivorship of inactive ramets, and transitions from ramets which were flowering only. In addition, population growth rate depends much more on vegetative propagation than on seed reproduction. (5) The relevance of behavioural variation among ramets for genets and populations are further discussed. Behavioural variation among ramets appears to reflect both environmental variation, e.g. in resource availability, and cost relations for different behaviour patterns. The distribution of ramet behaviour patterns is an important aspect of the properties of genets, and thereby also of interpretations of life-history variation among clonal plants.