ALBERT

Description: Questions Are species from different biogeographic groups (mediterranean, alpine and endemic) filtered in different ways by altitude and topography in alpine plant communities? What is the relative performance of these environmental factors at predicting the species diversity of the communities as a whole and of the geographic species groups? Location Picos de Europa, Cantabrian Range (Spain). Methods We sampled the presence and cover of vascular plants in 5-m radius plots on alpine grasslands between 1900 and 2500 m a.s.l. Five GIS-based terrain variables at 15 m × 15 m were used to model species richness and cover per plot using generalized and linear models, and the variation in species composition with redundancy analysis. The same analyses were repeated for the whole data set and for subsets of species from alpine, mediterranean and endemic distributions. Results The influence of altitude and topography on species richness, cover and composition differed for the whole data set and for the geographic species groups. Altitude was the main variable affecting floristic diversity in the communities as a whole, but the separate species groups were more influenced by slope, topographic wetness index and solar radiation. Richness and cover of mediterranean species showed the strongest relationships with topography. Alpine and endemic species showed relationships with topography for species cover and composition, but not for species richness. Conclusions In alpine landscapes, biogeographic deconstruction of the species pool can provide a better understanding of the influence of altitude and topography on local communities than analysis of the entire community alone. Furthermore, the strong influence of local topography on species groups improves our understanding of how alpine species will respond to climate change. We studied the influence of high-resolution altitudinal and topographic variables on species groups with different biogeographic history. Diversity estimates of the geographic groups showed remarkable differences in the relationships with temperature-related factors that were neglected when using data for the whole community. This procedure provides a better understanding of the influence of topography in species assemblages of alpine communities.

Description: Questions What changes have occurred in Mediterranean high-mountain communities during the last 50 yr? Do these changes reflect upward shifts and decline in dry grassland specialists due to climate warming? Location Upper belt (1900–2400 m a.s.l.) in Sierra de Guadarrama, Spain. Methods We re-surveyed dry grassland communities in 50 summits that were previously sampled between the 1960s and 1980s. New plots were placed in the same localities and the same conditions as the original surveys. Changes at the species level were evaluated by comparing, between the two survey periods, species frequencies and optimal altitude estimated by local distribution models done with Maxent. Changes at the community level were assessed by comparing species richness and composition of the two surveys in relation to altitude, plot size and time between surveys. We evaluated observed changes in the whole data set and species groups by structuring the species into dry grassland specialists, other alpine species and generalists occurring at wider altitudinal ranges. Results There was a general decline in the frequency of dry grassland specialists, an increase in frequency of generalists and no clear trends in the other species. Upward shifts were mainly detected in generalists, with significant increases in frequency. At the community level, we found a general increase in species richness that was mainly determined by the increase in generalists; coupled with a decline in number of dry grassland specialists. The structure of the communities evidenced changes between the historical surveys and the re-survey, which were mainly correlated with the number of years and the increasing dominance of generalists. Conclusions In contrast with trends observed in other Mediterranean high-mountain communities, our study reports a general increase in species richness, although this effect is concurrent with a decline in dry grassland specialists. The observed trends support on-going replacement of endemic species by low-altitude species, and associated changes in community assemblages. Despite the limitations of re-visitation studies for assessing climate-driven changes, our results highlight the necessity of developing more studies for assessing the effects of drought in Mediterranean high-mountain communities. Climate-driven changes in Mediterranean mountains have been rarely assessed. Through a re-visitation study on high-mountain sites sampled in the XX century, we detected temporal patterns of decline in specialists and increase in generalists and total species richness. Altogether. these patterns differ from changes observed in other Mediterranean or Temperate regions.