VARIATION IN FLOWERING PHENOLOGY AND ITS CONSEQUENCES FOR LUPINES COLONIZING MOUNT ST. HELENS

Species colonizing large-scale disturbances face heterogeneous environ mental conditions that may strongly affect the relationship between ph enotypic variation and reproduction. We investigated spatiotemporal va riation in individual plant flowering phenology, flower and fruit pred ation, plant size, and fruit production in populations of Lupinus lepi dus colonizing landscapes created by the 1980 eruption of Mount St. He lens. We quantified these variables in three populations in 1990, one that survived the 1980 eruption and two newly founded colonizing popul ations, and continued study of one newly founded population through 19 92. We used structural equation modeling (SEM) to analyze the direct a nd indirect effects of size, phenological variables, and predation on fecundity, and to compare path coefficients among years and population s. Flowering phenologies were constant among populations and years in colonizing populations, but plants in the surviving population flowere d earlier, more synchronously, and for a shorter duration. Flower and fruit predation by lepidopteran herbivores varied substantially among populations and years, and phenological variables strongly influenced herbivore damage. Although mean flowering date had a direct positive e ffect on fruit number in all three years in the large colonizing popul ation, the total effect of flowering date varied among years because l ater flowering resulted in greater fruit predation. In the surviving p opulation more asynchronous individuals had more fruits, but mean date had no effect. We conclude that substantial spatiotemporal variabilit y in optimal phenology may prevent fine-scale adaptation of flowering schedules, and that phenotypic variation and herbivory may affect the demography of colonization populations.