PARENT SESSION
Poster Session #41: Plant Demography.
Thursday, August 9, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Little demographic effect of an extended flowering season for a Mediterranean perennial herb.

Pico, F. Xavier^1,3, de Kroon, Hans^2,3, Retana, Javier¹, ^{1 3 2}

ABSTRACT- Mediterranean plant species show concentrated flowering and fruiting seasons which last for 2-3 months. However, a few plant species can prolong their flowering and fruiting up to 10 months. This is the case of the short-lived polycarpic crucifer Lobularia maritima. We investigate the demographic implications of such unusual phenological pattern in a variable Meditarranean environment by using periodic matrix models. In particular, we test the hypothesis that extended flowering and fruiting may be a flexible mechanism to compensate for reproductive failure in different parts of the whole season. The population growth rate of the study population ranged from 0.25 to 4.81 over the 5 years of study. Periodic elasticity analyses revealed that only fecundity in the autumn periods made important contributions to the population growth rate (). Variance decomposition analyses showed that variance in fecundity in the autumn periods largely explained the observed variance in . Moreover, an important negative covariance in fecundity between the autumn periods contributed to a reduction in the observed variance in . Finally, stochastic simulations illustrated that extended flowering and fruiting do not significantly contribute to increase population persistence. Overall, results showed that only fecundity in autumn is important for the population, contributing to the population growth rate, buffering the variance in population growth rate, and determining population persistence. We discuss alternative ecological and evolutionary explanations for the unusually extended flowering and fruiting season of L. maritima in the Mediterranean environment.

KEY WORDS: periodic matrix models, elasticity analysis, variance decomposition analysis, stochastic simulations