ALLOCATION OF REPRODUCTIVE RESOURCES WITHIN AND AMONG INFLORESCENCES OF LAVANDULA STOECHAS (LAMIACEAE)

Patterns of fruit set were studied in Lavandula stoechas, a Mediterranean shrub commonly occurring in southern Spain. The small, hermaphroditic flowers of this shrub are aggregated into dense, headlike inflorescences and exhibit extensive variations in fecundity. It was shown that as the number of developing fruits in the inflorescence increased, the probability of a flower setting fruit, the size of seeds, and their germinability decreased, most likely because of strong within-inflorescence resource limitation. An experiment was designed to ascertain whether increased fertility in late-opening flowers could be induced through reallocation of reproductive resources between different inflorescences. The experiment consisted of removing half of the inflorescence buds from a set of plants and comparing their fecundity with that of intact individuals. Thinning did not increase the proportion of flowers setting fruit which, in fact, was slightly lower than that of intact individuals (probably due to some reduction of floral display brought about by thinning). Although treated plants produced heavier seeds than controls, results suggest that inflorescences of L. stoechas behave as autonomous modules among which resources cannot be reallocated. Predispersal seed predation by insects accounted on average for a 31% reduction in fruit set. Predation was found to be nonrandomly distributed within inflorescences, with most damage concentrated on late fruits (i.e., those with smaller and less germinable seeds).