The evolution of generation time in metapopulations of monocarpic perennial plants: some theoretical considerations and the example of the rare thistle Carlina vulgaris

Life-history models for populations in a single patch, in which density dep endence occurs through competition between seedlings for safe-sites, sugges t that timing of flowering in monocarpic perennials is such that expected l ifetime reproductive success (R-0) is maximised. We discuss metapopulation models in which local populations go extinct either (1) because all rosette s die locally, or (2) because seedling recruitment is limited to restricted periods in time. In both cases there is selection for shorter optimal gene ration times than suggested by the single-patch model. The mechanism is tha t in young populations competition between seedlings for safe sites is rela xed for some years. This mostly benefits types with short generation times. Carlina vulgaris flowers earlier than the single-patch model suggests. The metapopulation effect is sufficiently strong to account for the difference s but other factors cannot be outruled. Data on other monocarpic perennials are discussed. Flowering in Cirsium vulgare is also earlier than suggested by the single-patch model, but for other species the picture is far from c lear.