A comparative study of the population dynamics of five species of Veronica in natural habitats

The population dynamics of three annual species of Veronica (V. arvensis, V. hederifolia and V. persica) and two perennial species (V. serpyllifolia and V. chamaedrys) were compared in six sites in which one or more of the species grew naturally. A survey of the populations of buried viable seeds in the sites showed that in some sites where growing plants were absent seeds of three or four of the species were present. The perennials generally contributed less to the buried seed population than the annuals, although some seeds of V. serpyllifolia were present in the soil of all the sites. The species differed in times and rates of germination. The seeds of the two winter annuals V. hederifolia and V. arvensis germinated in the autumn and early spring. The time of germination of V. persica was much less specific and occurred at several periods during the autumn, spring and summer. Seedlings of the perennials V. chamaedrys and V. serpyllifolia were observed in the summer. Many seeds of V. hederifolia, V. serpyllifolia and V. chamaedrys were lost from the populations between the time of seed dispersal and the subsequent winter. This contrasts with the behaviour of V. arvensis and V. persica in which significant mortality did not start until after seedling emergence. Seedlings of V. arvensis, V. serpyllifolia and V. persica were killed during winter but those of V. hederifolia were undamaged. Flowering in V. arvensis and V. hederifolia started early in spring when some plants bore only one or two pairs of leaves, and seeds were produced shortly after flowering. In contrast, in V. persica seeds were produced more than one month after the first flowers opened. All plants of the annuals died after flowering--they produced no persistent vegetative shoots. V. serpyllifolia was able to flower in its first year of growth in open habitats, although many plants remained vegetative until the second year; the population produced more seeds in its first year than were present in the sites at the beginning. Even in plants that flowered, however, a number of shoots remained vegetative. In grassland a much higher proportion of the plants remained vegetative. This species, which has a much more compact growth habit than V. chamaedrys, seems to maintain itself through production of numerous seeds and its perennial habit. V. chamaedrys requires long vernalization before flowering and is unable to flower in its first year. It is the only obligate outbreeding species among the five and the only one to have conspicuously low seed set capsule(-1) and a low proportion of flowers producing mature capsules. It has a much more diffuse pattern of clonal growth than V. serpyllifolia and its persistence in grasslands may depend on this clonal growth habit more than on repeated establishment from seed. The species can be placed in order with respect to their increasing length of life, ability to form adventitious roots, reduced degree of self-pollination and openness of their habitats: V. hederifolia < V. arvensis < V. persica < V. serpyllifolia < V. chamaedrys. There are some slight deviations from this order among the annuals with respect to the timing of the mortality risk and persistence of seeds in the soil. The major deviation from this ordering occurs with V. hederifolia, which produces only c. two seeds capsule(-1), and these have a mean seed weight seventy-two times larger than that of V. serpyllifolia. This is associated with a much lower risk of post-emergence mortality than that observed in the other annuals.