REPRODUCTIVE CHARACTERISTICS OF A STABLE-DUNE THEROPHYTE COMMUNITY IN DOÑANA (SOUTHERN SPAIN)

ABSTRACT

Aspects of the reproductive biology of 22 annual taxa inhabiting stabilized sand dunes at the Doñana National Park (southern Spain) were studied. In most instances, growth and reproduction of the plants took place during winter, with seedlings appearing mostly in January. The highest number of species in bloom was detected in March, while flowering and fruiting had ceased by June. Dependence on pollination vectors (insects or wind) for reproduction was ascertained by caging plants of the studied species with either mesh or acetate exclosures and comparing fruit set with that of uncaged individuals. Caging had little or no effect on the reproduction of most species. Facultative autogamy was widespread, and cleistogamy was detected in one species (Tuberaria inconspicua). Only two taxa (Andryala arenaria and Ononis broterana) showed zero fruit set when pollination vectors were excluded. Pollen-to-ovule (P:O) ratios were usually low (the median for the whole sample was 238), which is consistent with a high occurrence of self-pollination. A positive correlation was found between the P:O ratio and the date of flowering onset, indicating that the earlier the start of the blooming season, the more likely it is that the breeding system be dominated by autogamy. The reproductive characteristics of annuals contrast with those of co-occurring woody species previously studied at the same site.