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

Abstract

Summary 1We 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.

Seed germination at different temperatures and seedling emergence at different depths of Rhamnus spp

“…It is up to 2 m high, and its small leaves (the leaf area usually varies from 1 to 3 cm 2 ) are denticulate and elliptical to suborbicular. The species is mostly entomophilous and usually flowers during spring, with a peak at the end of April to mid-May [3]. As in R. alaternus, the flowers are pale yellow and grouped in racemes, and the fruit is a small drupe (diameter < 1 cm), usually bearing two seeds covered by an endocarp which opens when the fruit pulp is removed.…”

“…Several studies have suggested that seedling survival during the early stages is a critical phase in seedling recruitment success [1][2][3]. In Mediterranean ecosystems, many reports have identified summer drought as one of the main causes of seedling mortality during their first year, when plants still have an underdeveloped root system [2,[4][5][6].…”

“…R. alaternus is widely distributed in the Mediterranean basin, reaching Portugal and Crimea [8], whereas R. ludovici-salvatoris is an endemic species, only present in the Gymnesic Islands (Mallorca, Menorca and Cabrera) of the Balearic Archipelago, in the western Mediterranean basin [9]. Moreover, the distribution of R. ludovici-salvatoris has been declining over the last few decades, probably due to land use and to its poor seedling recruitment ability [3], which hinders species regeneration after ecosystem disturbance. In addition, when comparing both species, R. ludovici-salvatoris shows several traits which limit plant biomass production under Mediterranean conditions, such as a high ratio of respiration and photorespiration to photosynthesis and a low intrinsic water-use efficiency [10].…”

“…Both species have shown important differences in seedling emergence and survival in field studies [3,5], which may account for their different seedling recruitment abilities. Seedling emergence success depends on the seed's ability to germinate and on the capacity for seedling elongation to reach the soil surface.…”

Plant recruitment and range size: Transition probabilities from ovule to adult in two Ipomoea

“…Plant recruitment success depends on the success of individuals at different life-history stages (e.g., ovule, seed, seedling, adults) (Rey and Alcántara, 2000;Traveset et al, 2003). The need to studying those different lifehistory stages when looking for the demographic causes of narrow distributions has been recognized (Bevill et al, 1999) because it allows the identification of the stages where the mortality of potentially reproductive individuals is the highest, and thus of processes that might determine the colonization and persistence abilities of species.…”