Transition probabilities from pollination to establishment in a rare dioecious shrub species (Rhamnus ludovici-salvatoris) in two habitats

1 We elucidated the critical life stages and processes in the recruitment of Rhamnus ludovici-salvatoris, a dioecious shrub endemic to the Balearic Islands (western Mediterranean), populations of which have been shrinking in recent decades. We evaluated transition probabilities between all stages involved in regeneration from pollination to seedling recruitment, in order to determine the overall probability of an ovule in a flower becoming an established individual in a population. 2 We compared populations in an oak (Quercus ilex) forest and in a more disturbed habitat (an abandoned field). We studied seed rain and probabilities of predation, germination and survival in the main microhabitats within each community. 3 High levels of seed predation after dispersal and unfavourable conditions (water deficit) during germination and recruitment periods were the most critical factors limiting population growth in both habitats. 4 The greater fecundity of shrubs in the abandoned field did not compensate for the lower probability of ovules recruiting new individuals in that habitat compared to the forest. 5 Spatial patterns of recruitment in this species cannot be predicted from seed dispersal patterns produced by frugivorous birds. In both habitats, but especially in the forest, there was strong spatial discordance between seed rain (most seeds were deposited under conspecifics) and seedling establishment. In the forest, most established Rhamnus are found under oaks, whereas in the abandoned field, saplings and juveniles are more equally distributed across different microhabitats. 6 This empirical study supports the idea that habitat disturbance, in general, may considerably alter the patterns of plant recruitment. For endemic species with restricted and rather small populations, the loss of natural habitat is likely to be detrimental for species' persistence, as recruitment in disturbed sites is greatly reduced.