Macroecological patterns of species and genetic diversity in vascular plants of the Mediterranean basin

Aim We address the question of whether broad scale biogeographical structure of species diversity (SD) matches that of genetic diversity (GD) of vascular plants. Location The Mediterranean basin. Methods We normalized vascular plant species richness (SD) estimates per country using the Med‐Checklist taxonomic database. We used a linear regression analysis to correlate normalized country estimates with country longitudinal position. We also compiled published and geo‐referenced within‐population GD data for tree species, which had populations in the Mediterranean. We normalized GD estimates for each population across species. Again, we used a linear regression analysis to correlate GD with population longitudinal position. We then compared the populations’ geographical and bioclimatic trends for GD with Last Glacial Maximum (LGM) palaeo‐climate data and the species current ecological requirements. Results The eastern Mediterranean and the coast of former Yugoslavia had higher SD than other regions. There was no overall spatial structure of SD in the Mediterranean, whereas there was an east–west trend of decreasing GD. This trend for GD tended to covary with an east–west warm/wet–cold/dry trend detected during the LGM. Low elevation xerothermic pine species displayed significantly less GD than higher elevation mesothermic or mountain pine species. Main conclusions We suggest that LGM climate may have significantly shaped the current longitudinal and altitudinal patterns of GD we observed in woody taxa across the Mediterranean, although it did not affect comparable SD patterns. In particular, colder LGM summer temperatures in the western Mediterranean may have reduced population sizes significantly more than in the eastern Mediterranean. As plant species richness and GD did not covary, SD and GD may not be used as surrogates of one another in the Mediterranean basin. As they contain comparatively less GD, conservation priorities in the Mediterranean should focus on hot spots of endemism and Western Mediterranean populations and species.     

Community structure and diversity of bryophytes and vascular plants in abandoned fen meadows

We examined effects of abandonment on species diversity and species composition by comparing 21 calcareous fen meadows in the pre-alpine zone of central and northeastern Switzerland. Meadows were divided into three classes of successional stages (mown: annually mown in late summer, young fallow: 4–15 years, and old fallow: >15 years of abandonment). In each fen, we measured litter mass in four 20 cm×20 cm plots, as well as (aboveground) biomass and species density (number of species per unit area) of bryophytes and vascular plants. Bryophyte biomass was reduced in abandoned fens, whereas litter mass and aboveground biomass of vascular plants increased. Species density of both taxonomic groups was lower in abandoned than in mown fens. Young and old successional stages were not different except for bryophytes, for which old successional stages had higher species density than young stages. We used litter mass and aboveground biomass of vascular plants as covariables in analyses of variance to reveal their effects on species density of both taxonomic groups. For bryophytes, litter mass was more important than vascular plant biomass in explaining variance of species density. This indicates severe effects of burying by litter on bryophyte species density. For species density of vascular plants, both vascular plant biomass and litter mass were of similar importance in explaining the decreased species density. Canonical correspondence analyses showed that abandonment also had an effect on species composition of both bryophytes and vascular plants. However, young and old successional stages were not different indicating fast initial changes after abandonment, but slow secondary succession afterwards. Furthermore, indicator species analysis showed that there was no establishment of new species after abandonment that might dramatically alter fen communities. Re-introduction of mowing as a nature conservation strategy may thus be very promising – even for old fallows.     

Determinants of alpha and beta vascular plant diversity in Mediterranean island systems: the Ionian islands,Greece

The Ionian archipelago is the second largest Greek archipelago after the Aegean, but the factors driving plant species diversity in the Ionian islands are still barely known. We used stepwise multiple regressions to investigate the factors affecting plant species diversity in 17 Ionian islands. Generalized dissimilarity modelling was applied to examine variation in the magnitude and rate of species turnover along environmental gradients, as well as to assess the relative importance of geographical and climatic factors in explaining species turnover. The values of the residuals from the ISAR log₁₀‐transfomed models of native and endemic taxa were used as a measure of island floristic diversity. Area was confirmed to be the most powerful single explanatory predictor of all diversity metrics. Mean annual precipitation and temperature, as well as shortest distance to the nearest island are also significant predictors of vascular plant diversity. The island of Kalamos constitutes an important plant diversity hotspot in the Ionian archipelago. The recent formation of the islands, the close proximity to the mainland source and the relatively low dispersal filtering of the Ionian archipelago has resulted in islands with a flora principally comprising common species and a low proportion of endemics. Small islands keep a key role in conservation of plant priority sites.