Carsten Hobohm

SPECIES RICHNESS OF VASCULAR PLANTS, BRYOPHYTES AND LICHENS IN DRY GRASSLANDS: THE EFFECTS OF ENVIRONMENT, LANDSCAPE STRUCTURE AND COMPETITION

We studied the relative importance of local habitat conditions and landscape structure for species richness of vascular plants, bryophytes and lichens in dry grasslands on the Baltic island of Öland (Sweden). In addition, we tested whether relationships between species richness and vegetation cover indicate that competition within and between the studied taxonomic groups is important. We recorded species numbers of vascular plants, bryophytes and lichens in 4 m2 plots (n=452), distributed over dry grassland patches differing in size and degree of isolation. Structural and environmental data were collected for each plot. We tested effects of local environmental conditions, landscape structure and vegetation cover on species richness using generalized linear mixed models. Different environmental variables explained species richness of vascular plants, bryophytes and lichens. Environmental effects, particularly soil pH, were more important than landscape structure. Interaction effects of soil pH with other environmental variables were significant in vascular plants. Plot heterogeneity enhanced species richness. Size and degree of isolation of dry grassland patches significantly affected bryophyte and lichen species richness, but not that of vascular plants. We observed negative relationships between bryophyte and lichen species richness and the cover of vascular plants. To conclude, effects of single environmental variables on species richness depend both on the taxonomic group and on the combination of environmental factors on a whole. Dispersal limitation in bryophytes and lichens confined to dry grasslands may be more common than is often assumed. Our study further suggests that competition between vascular plants and cryptogams is rather asymmetric.

Plant species diversity and endemism on islands and archipelagos, with special reference to the Macaronesian Islands

Summary Values for vascular plant species density as a principal feature of diversity are calculated for 57 islands and archipelagos worldwide and for 30 Macaronesian Islands. Correlation analysis confirms the significance of certain ecological and biogeographical factors for the number and composition of the species. It can also be shown that neither the distance from the mainland nor the proportion of endemics – both of which have been used in the past as indicators of the degree of isolation – are significantly correlated with the α-index which indicates the extent of the species diversity. Various hypotheses which are based on the richness or paucity of endemic species are discussed.

Endemism in Mainland Regions – Case Studies

Vascular plant endemism of different mainland regions in relation to ecological conditions and habitats is analysed in detail. The regions belong to different biogeographical zones, climates and are of different sizes. Because of their species richness, level of endemism, and a long history of human occupation affecting the biota, some of the regions are partly or completely located in Biodiversity Hotspots.

Factors That Create and Increase Endemism

Since the term endemism was defined by De Candolle in 1820, many hypotheses have been published to explain regional endemism over time.

The Increasing Importance of Endemism: Responsibility, the Media and Education

Endemism was first defined in the 1800s, a term borrowed from medicine to describe taxa restricted to small geographical areas. We discuss how our knowledge of the causes of regions of high endemism and our recognition of the importance of endemism for conservation purposes has grown but remains incomplete. Recording areas with high endemism is increasingly recognized as important for conservation activities. As a result of concepts such as biodiversity hotspots and documents such as the Convention on Biological Diversity, endemism is now a common concept in scientific, political, and conservation circles. However, we conclude that there is much work to be done in increasing awareness of the role of endemics in conservation efforts through education.

How to Quantify Endemism

While the definition of endemism is clear, there are multiple ways of measuring endemism, and each has its own inherent biases. We discuss the most frequently used and recently developed measures. Ultimately all these measures are relative (i to iii), and care must be taken when making comparisons. Further, issues such as the species concept (i), the dependency on regional species-richness or the distribution of range sizes in the whole species pool (ii), and special problems in statistics, e.g. spatial autocorrelation (cf. Bruchmann. Plant endemism in Europe: spatial distribution and habitat affinities of endemic vascular plants. Dissertation, University of Flensburg, Flensburg. URL: www.zhb-flensburg.de/dissert/bruchmann, 2011; Kuhn, Divers Distrib 13:66–69, 2007), need to be accounted for, since they can introduce bias.

Factors That Threaten and Reduce Endemism

The factors that threaten and reduce the biota on earth are varied. Here we describe and discuss mass extinctions in the past, different natural and anthropogenic circumstances and processes that promote the loss of species and increase extinction risk.

Biogeography of Endemic Vascular Plants – Overview

Endemics are not incidentally or uniformly distributed around the world. We describe and analyse general distribution patterns of endemic vascular plants in different climate zones, ecoregions, and altitudes. We distinguish endemism of vascular plants related to mainland, continental and oceanic islands and different physiognomic habitat types.

Identifying long-term stable refugia for relict plant species in East Asia

Today East Asia harbors many “relict” plant species whose ranges were much larger during the Paleogene-Neogene and earlier. The ecological and climatic conditions suitable for these relict species have not been identified. Here, we map the abundance and distribution patterns of relict species, showing high abundance in the humid subtropical/warm-temperate forest regions. We further use Ecological Niche Modeling to show that these patterns align with maps of climate refugia, and we predict species’ chances of persistence given the future climatic changes expected for East Asia. By 2070, potentially suitable areas with high richness of relict species will decrease, although the areas as a whole will probably expand. We identify areas in southwestern China and northern Vietnam as long-term climatically stable refugia likely to preserve ancient lineages, highlighting areas that could be prioritized for conservation of such species.East Asia contains “relict” plant species that persist under narrow climatic conditions after once having wider distributions. Here, using distribution records coupled with ecological niche models, the authors identify long-term stable refugia possessing past, current and future climatic suitability favoring ancient plant lineages.

Endemism on Islands – Case Studies

Vascular plant endemism in the diverse vegetation zones and physiognomic habitat types of some islands or archipelagos is described and analysed in detail. The Juan Fernandez Islands, Madeira Archipelago, Corsica and Madagascar, located in different regions and oceans of the world, present their own unique evolutionary histories and composition of habitats and endemics.