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We analyzed demographic data of a long‐lived high mountain Mediterranean plant, Silene ciliata Poirret, over a 4‐yr period. Selected populations were located at contrasting altitudes at the southernmost margin of the species (Sierra de Guadarrama, central Spain), representing a local altitudinal range at the rear edge of its overall distribution. Previous studies have suggested that differences in the reproduction and performance of individuals at upper and lower populations may have implications for population dynamics. We used matrix analysis to assess their demographic behaviour. Life Table Response Experiments were used to identify the life history stages most relevant to observed differences in population growth rates between populations. Transition matrices revealed great spatio‐temporal variability in demographic traits. Seedling recruitment was very low each year in all populations. Maximum longevity of S. ciliata individuals in the lower peripheral population was much lower compared to the central population, probably due to higher adult mortality. Population growth rate (λ) showed a declining trend at the lowest altitude and a relatively stable trend at the central population. Long‐term simulations also indicated a great risk of quasi‐extinction at the lowest population. Our results suggest that rear edge populations of S. ciliata at Sierra de Guadarrama are suffering demographic processes that may be leading to the latitudinal displacement of the species' range.

In 1996, we investigated the female reproductive success of the narrow endemic Erodium paularense in a population with a mixture of rock and lithosol microhabitats. The main purposes of this study were to determine the main factors that affected reproductive success and whether these factors were influenced by differences in the two contrasting microhabitats. In both microhabitats, fruit set was low, and seed abortion rates were very high. Lithosol plants were larger and had higher flower, fruit, and seed production than rock plants. We used structural equation modeling (SEM) to analyze the effects of plant size, phenological variables, competition, and flowering synchrony on fecundity and to compare path coefficients among microhabitats. In both microhabitats reproductive success was strongly predicted by plant size and to a lesser extent by flowering synchrony. Flowering moment and intensity did not have a significant effect on fruit set, suggesting that pollinator availability is not a limiting factor in total seed production. This was further corroborated by hand-pollination experiments. Resource limitations, inbreeding depression, and environmental restrictions may be responsible for the high rates of seed abortion. Multisample comparison of path coefficients for the two microhabitats rejected the possibility that reproductive patterns could be described by one single model. The main divergences in both microhabitat models were related to competition. Reproductive data from 1995, a year with below-average rainfall, showed remarkably lower seed production at the lithosol microhabitat and similar values at the rock microhabitat as compared to 1996. The variation of the reproductive parameters between the two years was evaluated by multisample analyses in which 1995 data were fed into the 1996 models. At the lithosol microhabitat, two constrained paths involving seed production produced a significant decrease in fit, whereas at the rock microhabitat, significant differences were found in three paths involving only phenological variables. Thus, the lithosol microhabitat may contribute to greater seed production in favorable years while the rock microhabitat may provide more stable conditions over time.

The species seemed to be considerably well adapted to the environmental unpredictability characteristic of Mediterranean systems, considering its ability to maintain reproduction across contrasting environments and contrasting climatic conditions. These findings make us face the question of what must be considered stressful conditions in the case of a stress-tolerant specialist.

Several studies have evaluated the effect of population size on plant reproductive output, but there are few studies concerning the effect of other population structure variables on plant reproduction. In this study, we went beyond population size effect and we tested the effect of some population spatial variables such as plant density, plant aggregation, population structure, and population identity on plant reproductive success and fitness in large populations (>1000 individuals) of Centaurea hyssopifolia Vahl., an endemic species of central Spain. We analysed the reproductive output (capitula, flowers, and seeds) and another two components of plant fitness (seed mass and germinability) in 350 individuals from seven populations in 2002 and 2003. All populations were similar in size but differed in other population spatial characteristics (density, plant aggregation pattern, population plant size structure). We used Morisita's aggregation index to characterize the level of plant aggregation within populations. Population plant size structure variable determined the proportion of different sized plants in a population. We used generalized linear mixed models to model the contribution of these population spatial variables to several reproductive parameters. Our results showed that whereas the aggregation index exerted a positive control on plant seed set, plant density had a negative effect, and plant population size structure did not significantly influence any response variable. Density only exerted a negative effect on seed set. On the contrary, plant aggregation had a positive effect. Seed mass was also larger in more aggregated populations, although no differences in seed germinability were observed. We detected the effect of population attributes on reproduction in terms of seed set, but we did not detect any effect on other overall reproductive variables measured at plant level. To sum up, our results showed that if population fragments were large enough, spatial population attributes became crucial factors for plant reproductive output and fitness. These easily measurable population variables may improve the conservation management of rare plant species.Résumé : Plusieurs études ont évalué l'effet de la dimension des populations sur le rendement reproductif des plantes, mais peu d'études concernent l'effet des autres variables de la structure des populations sur la reproduction des plantes. Dans cette étude, les auteurs vont au-delà de l'effet de la dimension des populations. Ils évaluent les effets de certaines variables spatiales des populations, telles que la densité des plantes, l'agrégation des plantes, la structure de la population et l'identité de la population sur le succès reproductif des plantes et l'adaptation, dans de grandes populations (>1000 individus) du Centaurea hyssopifolia Vahl., une espèce endémique du centre de l'Espagne. Ils ont analysé le rendement reproductif (capitules, fleurs et graines) et deux autres composantes de l'adaptation (dimension des graines et pouvoir germinatif), ch...

Background: Under the current warming process, with its implications of higher temperatures, less rainfall, snowfall and snow cover, low-edge populations of high-mountain plants are expected to decline. Demographic studies are useful to foresee the future dynamics of species ranges. Adaptation, phenotypic plasticity, and demographic compensation have been proposed as mechanisms to cope with climate change. Aim: We studied the population dynamics of the high-mountain narrow endemic Armeria caespitosa at the extremes of its altitude distribution (low versus high edge), the high edge representing colonised summits that provide optimal growing conditions. The focus of the study was to establish if the species is retracting at its lower distribution range. Methods: We used 4 years of population censuses and soil seed bank data. Population matrix models allowed us to study the stochastic population growth rates, the species long-term viability under higher frequency of extreme years, and the life cycle transitions responsible for the differences in population dynamics between elevation range edges. Results: The low edge of the A. caespitosa elevation range appeared stable, with positive population growth rates under current environmental conditions, and a null quasi-extinction probability in the long-term under scenarios of high frequency of extremely dry years. Conclusions: The species will likely withstand the current climate-warming scenario along its elevation range. Results supported the role of so-called demographic compensation at a small spatial scale, which we argue might be common in the Mediterranean mountains.

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