COMPETITION AND THE COMPENSATORY REGULATION OF FRUIT AND SEED SET IN THE PERENNIAL HERB EPILOBIUM-DODONAEI (ONAGRACEAE)

I studied the effects of competition and soil fertilization on variati on of seed yield components of the outcrossing perennial Epilobium dod onaei Vill. using a randomized complete block design. Fertilization as a main effect was not significant. Competition, however, reduced the number of flower buds per shoot (-29%), the number of ovules per fruit (-12%), and the number of ripe fruits per shoot (-51%). In addition, competition caused an increase in abortion of flower buds. Consequentl y the fruit/flower bud ratio decreased from 0.71 to 0.47. Average seed mass was not reduced significantly by competition. Some of the negati ve effects of competition on fruit production were mitigated by fertil ization. However, competition considerably reduced the proportion of l ate-aborted seeds, which resulted in an increase of the seed/ovule rat io from 0.31 to 0.49 (+58%). As a consequence of this compensation, th e reduction in the number of seeds per shoot due to competition was no t significant. At the level of the genet, competition had a strong eff ect on seed yield due to decreases in the number of shoots produced. I discuss patterns of regulation at consecutive levels of reproduction. Shoots of plants suffering from competition initially invested less i n reproductive structures than the control and showed a higher abortio n rate of less costly structures early in reproductive development, bu t also had a lower abortion rate later in their development. The obser ved compensatory pattern in yield components illustrates the fine-tuni ng regulation capacity at different levels of reproductive development in plants.