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 dependence occurs through competition between seedlings for safe-sites, suggest that timing of flowering in monocarpic perennials is such that expected lifetime reproductive success (R-0) is maximised. We discuss metapopulation models in which local populations go extinct either (1) because all rosettes die locally, or (2) because seedling recruitment is limited to restricted periods in time. In both cases there is selection for shorter optimal generation times than suggested by the single-patch model. The mechanism is that in young populations competition between seedlings for safe sites is relaxed 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 differences 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 clear.