Exploring local borders of distribution in the shrub Daphne laureola: Individual and populations traits

Biogeographic models predict that marginal populations should be more geographically isolated and smaller than central populations, linked to more stressful conditions and likely also to a reduction in density of individuals, individual growth, survival and reproductive output. This variation in population features could have important consequences for different aspects of plant ecology such as individual reproductive success, population genetic structure or plant-animal interactions. In this study, we analyze if individuals of the evergreen shrub Daphne laureola at disjunt populations in a local border of its distribution area in southern Iberian Peninsula differ in individual size, shoot growth, reproductive output and the pollination environment from central continuous populations within the area. Plants of central continuous populations were larger and produced more flowers and fruits than plants of marginal disjunct populations suggesting more optimal conditions, although they had lower annual shoot growth. In contrast, fruit set was higher in plants at the local border, suggesting a more efficient pollinator service in these populations where the main pollinator in central continuous populations, the pollen beetle Meligethes elongatus, was not present. Our results do not support strong differences in the ecological stress between marginal disjunct and central continuous populations of D. laureola in the south of the Iberian Peninsula but indicate some changes in plant-pollinator interactions that could be relevant for the sexual polymorphism in this gynodioecious species.