Local and landscape responses of biodiversity in calcareous grasslands

Biodiversity and Conservation - Across Europe, calcareous grasslands become increasingly fragmented and their quality deteriorates through abandonment and land use intensification, both affecting...     

Linking biodiversity to ecosystem function: implications for conservation ecology

We evaluate the empirical and theoretical support for the hypothesis that a large proportion of native species richness is required to maximize ecosystem stability and sustain function. This assessment is important for conservation strategies because sustenance of ecosystem functions has been used as an argument for the conservation of species. If ecosystem functions are sustained at relatively low species richness, then arguing for the conservation of ecosystem function, no matter how important in its own right, does not strongly argue for the conservation of species. Additionally, for this to be a strong conservation argument the link between species diversity and ecosystem functions of value to the human community must be clear. We review the empirical literature to quantify the support for two hypotheses: (1) species richness is positively correlated with ecosystem function, and (2) ecosystem functions do not saturate at low species richness relative to the observed or experimental diversity. Few empirical studies demonstrate improved function at high levels of species richness. Second, we analyze recent theoretical models in order to estimate the level of species richness required to maintain ecosystem function. Again we find that, within a single trophic level, most mathematical models predict saturation of ecosystem function at a low proportion of local species richness. We also analyze a theoretical model linking species number to ecosystem stability. This model predicts that species richness beyond the first few species does not typically increase ecosystem stability. One reason that high species richness may not contribute significantly to function or stability is that most communities are characterized by strong dominance such that a few species provide the vast majority of the community biomass. Rapid turnover of species may rescue the concept that diversity leads to maximum function and stability. The role of turnover in ecosystem function and stability has not been investigated. Despite the recent rush to embrace the linkage between biodiversity and ecosystem function, we find little support for the hypothesis that there is a strong dependence of ecosystem function on the full complement of diversity within sites. Given this observation, the conservation community should take a cautious view of endorsing this linkage as a model to promote conservation goals. Received: 2 September 1999 / Accepted: 26 October 1999     

Soil seed-bank composition reveals the land-use history of calcareous grasslands

We compared soil seed banks and vegetation of recent (established on abandoned arable fields) and ancient (continuously managed as pastures at least since 1830) calcareous grasslands if there is any impact of former arable field use. The study was carried out in two regions of Southern Germany with well-preserved dry grassland vegetation: the western Jurassic mountains (Kaltes Feld) and the climatically drier eastern part of Southern Germany (Kallmünz).Total number of species in the seed bank was similar in both regions, but species composition partly differed, reflecting phytogeographical differences between the regions. The total number of emerged seedlings showed a large disparity (5457 compared to 2523 seedlings/m² in Kaltes Feld and Kallmünz, respectively).Though there were differences in seed bank composition and size, we found a uniform pattern of plant traits (affiliation to phytosociological groups, Raunkiaer plant life-forms and seed longevity), which depended on the age of the grassland.The main conclusion is that seed banks in contemporary calcareous grasslands still reflect the history of former land use – in this case arable cultivation, even though it occurred a long time ago (up to 150 years). Indicators of former arable fields are germinable seeds of weeds which have persisted in the soil to the present. By contrast, weedy species are completely absent from the seed banks of ancient grasslands. Soil seed banks of recent grasslands may be of substantial conservation importance because they may store seeds of rare and endangered weed species such as Kickxia spuria, Silene noctiflora and Stachys annua, the majority of which have already gone extinct from the current vegetation of the study sites.     

Linking community and disease ecology: the impact of biodiversity on pathogen transmission

The increasing number of zoonotic diseases spilling over from a range of wild animal species represents a particular concern for public health, especially in light of the current dramatic trend of biodiversity loss. To understand the ecology of these multi-host pathogens and their response to environmental degradation and species extinctions, it is necessary to develop a theoretical framework that takes into account realistic community assemblages. Here, we present a multi-host species epidemiological model that includes empirically determined patterns of diversity and composition derived from community ecology studies. We use this framework to study the interaction between wildlife diversity and directly transmitted pathogen dynamics. First, we demonstrate that variability in community composition does not affect significantly the intensity of pathogen transmission. We also show that the consequences of community diversity can differentially impact the prevalence of pathogens and the number of infectious individuals. Finally, we show that ecological interactions among host species have a weaker influence on pathogen circulation than inter-species transmission rates. We conclude that integration of a community perspective to study wildlife pathogens is crucial, especially in the context of understanding and predicting infectious disease emergence events.     

Syntaxonomy and biogeography of dry grasslands on calcareous substrates in the central and southern Balkans

Questions

Which major syntaxa of dry grasslands supported by carbonate bedrock occur in the central and southern Balkans? What is their position along major ecological gradients and in the context of phytogeographic patterns of the region?

Location

Central and southern Balkans, including western Bulgaria, northern Greece, Kosovo, Macedonia (FYROM) and Serbia.

Methods

We compiled a matrix of 660 relevés of dry grasslands over lime‐rich bedrock, previously classified in the Festuco‐Brometea. We applied clustering techniques to classify separately synoptic and relevé data, and applied NMDS with passive projection of indicator values, climatic data and biogeographic geo‐elements onto ordination diagrams to assist interpretation of the syntaxonomic patterns. We constructed elevation distribution profiles for alliances and classes of grasslands of several grassland classes from a broader study area to elucidate the relationship of the elevational sorting of the syntaxa in relation to latitude.

Results

The analysis revealed six major vegetation types, classified into four orders: (1) Stipo pulcherrimae‐Festucetalia pallentis, incl. (sub)montane rocky steppic grasslands of the Saturejion montanae of central Balkans, and the Koelerio‐Festucion dalmaticae – submontane rocky grasslands of southern Serbia and Kosovo; (2) Astragalo onobrychidis‐Potentilletalia represented by the Saturejo‐Thymion (low‐elevation steppic grasslands of southern Balkans); (3) Festucetalia valesiacae represented by grasslands on deep soil and low elevation of northern Greece, and finally (4) high‐elevation rocky grasslands of southern Balkans, classified as a new alliance – Diantho haematocalycis‐Festucion hirtovaginatae, that might belong to a new, yet undescribed, syntaxonomic order. Ordination suggests that the major differentiation of the high‐rank syntaxa follows north–south geographic and low–high elevation gradients.

Conclusions

Because of the transitional biogeographic position of the studied region, as well as considerable large elevation span across latitudes, the diversity of vegetation types is high. The indication a putative new dry grassland order, the mid‐high altitudes of the southern Balkans points to a need to re‐assess the Balkan vegetation occupying the community niche between the low‐elevation dry grasslands (Festuco‐Brometea) and those typical of high elevations (Elyno‐Seslerietea and Daphno‐Festucetea), seeking parallels to patterns described from the western Alps, Pyrenees, and Apennines. This syntaxonomic unit is poised to expand the concept of the Festuco hystricis‐Ononidetea striatae to the Balkans.

     

A six-year experimental restoration of biodiversity by shrub-clearing and grazing in calcareous grasslands of the French Prealps

The conservation of dry calcareous grasslands in the French Prealps strongly depends on the maintenance of low-intensity farming systems supported by agri-environmental schemes. An experimental assessment of the effect of current agro-pastoral management on the biodiversity of plant communities was conducted during a six-year permanent plot survey in four sites with contrasting habitat conditions (mesic to xeric). Analyses of species changes showed: (i) a strong increase in species richness and open grassland species frequencies four years after shrub-clearing, and (ii) a noticeable recovery of rare annuals and perennial species of conservation interest establishing in gaps created by grazing. At the community level, the restoration effect was evaluated by a between-year Correspondence Analysis, explaining 10.9% of the total floristic variability versus 29.5% for the site effect (between-site CA). Species ordination by between-year CA showed similar trajectories of vegetation changes during restoration despite different habitat conditions and grazing regimes between sites. The successful restoration of prealpine calcareous grasslands was explained by the availability of seed sources during the study in adjacent grazed or mown grasslands. Thus, restoration assessment should focus on dispersal possibilities and functional roles of species rather than species richness only. Finally, the spatial (i.e. the area of patches that need to be restored) and temporal (i.e. the frequency of shrub-clearing) implications for the large-scale conservation of prealpine calcareous grasslands by current agro-pastoral management are discussed.     

Species diversity and life history traits in calcareous grasslands vary along an urbanization gradient

Calcareous grasslands are among the most species-rich plant communities in Europe with a particularly high nature conservation value. During the past centuries their distribution has markedly decreased, at least partly due to urbanization. Thus we investigated the effects of urbanization on species diversity along a spatio-temporal urbanization gradient from traditionally managed grassland to areas affected by urban developments, which was situated in the plains northwest of Munich, Germany. Both a RLQ analysis linking species and environmental traits, and a redundancy analysis of the plant community features showed that soil disturbance, soil sealing and mean temperature explained most of the environmental variation along the gradient. The species in urban habitats showed increased insect pollination, earlier flowering and prolonged seed longevity. While urbanization favored short-lived species with dysochorous dispersal, the reference grasslands harbored more wind-pollinated perennials with effective vegetative spread and relatively large, short-lived seeds. Compared to the urban sites, traditionally used grasslands had a higher species diversity, more threatened species and a lower proportion of non-natives. We conclude that even under conservation management, urban habitats are not capable of maintaining the original biodiversity. However, we also found threatened species occurring exclusively in urban sites. Hence, urbanization decreased the area and diversity of traditional calcareous grasslands, but it also established niches for endangered species which are not adapted to the living conditions in calcareous grasslands.     

Fragmentation in calcareous grasslands: species specialization matters

Habitat fragmentation resulting from anthropogenic land-use change may negatively affect both biodiversity and ecosystem structure and function. However, susceptibility to fragmentation varies between species and may be influenced by for instance specialization, functional traits and trophic level. We examined how total and specialist species richness, species composition and functional trait composition at two trophic levels (vascular plants and sap-feeding hoppers) vary with habitat fragmentation (patch size and connectivity) in dry calcareous grasslands in southeast Norway. We found that fragmentation affected plant and hopper species composition both totally and of habitat specialists, but with a net species loss only for the specialists, indicating greater susceptibility of specialized species. Reductions in patch size and increasing isolation negatively affected plant specialists with different sets of traits, effectively reducing the number of species with trait combinations suitable to persist in small and isolated patches. Fragmentation influenced trait composition of the total hopper community, but not of habitat specialists. A lesser degree of habitat association could explain why hoppers, despite belonging to a higher tropic level, seemed to be less susceptible to fragmentation than plants. Nonetheless, our study shows that habitat fragmentation affects both species richness, species composition and trait composition of plants and hoppers, indicating that fragmentation leads not only to a loss of species, but also alters dominance hierarchies and the functionality of grassland communities.     

Dark diversity in dry calcareous grasslands is determined by dispersal ability and stress‐tolerance

Temperate calcareous grasslands are characterized by high levels of species richness at small spatial scales. Nevertheless, many species from a habitat‐specific regional species pool may be absent from local communities and represent the ‘dark diversity’ of these sites. Here we investigate dry calcareous grasslands in northern Europe to determine what proportion of the habitat‐specific species pool is realized at small scales (i.e. how the community completeness varies) and which mechanisms may be contributing to the relative sizes of the observed and dark diversity. We test whether the absence of particular species in potentially suitable grassland sites is a consequence of dispersal limitation and/or a low ability to tolerate stress (e.g. drought and grazing). We analysed a total of 1223 vegetation plots (1 × 1 m) from dry calcareous grasslands in Sweden, Estonia and western Russia. The species co‐occurrence approach was used to estimate the dark diversity for each plot. We calculated the maximum dispersal distance for each of the 291 species in our dataset by using simple plant traits (dispersal syndrome, growth form and seed characteristics). Large seed size was used as proxy for small seed number; tall plant height and low S‐strategy type scores were used to characterise low stress‐tolerance. Levels of small‐scale community completeness were relatively low (more species were absent than present) and varied between the grasslands in different geographic areas. Species in the dark diversity were generally characterized by shorter dispersal distances and greater seed weight (fewer seeds) than species in the observed diversity. Species within the dark diversity were generally taller and had a lower tolerance of stressful conditions. We conclude that, even if temperate grasslands have high levels of small‐scale plant diversity, the majority of potentially suitable species in the regional species pool may be absent as a result of dispersal limitation and low stress‐tolerance.     

The interplay of stress and mowing disturbance for the intensity and importance of plant interactions in dry calcareous grasslands

Background and Aims There is still debate regarding the direction and strength of plant interactions under intermediate to high levels of stress. Furthermore, little is known on how disturbance may interact with physical stress in unproductive environments, although recent theory and models have shown that this interplay may induce a collapse of plant interactions and diversity. The few studies assessing such questions have considered the intensity of biotic interactions but not their importance, although this latter concept has been shown to be very useful for understanding the role of interactions in plant communities. The objective of this study was to assess the interplay between stress and disturbance for plant interactions in dry calcareous grasslands. Methods A field experiment was set up in the Dordogne, southern France, where the importance and intensity of biotic interactions undergone by four species were measured along a water stress gradient, and with and without mowing disturbance. Key Results The importance and intensity of interactions varied in a very similar way along treatments. Under undisturbed conditions, plant interactions switched from competition to neutral with increasing water stress for three of the four species, whereas the fourth species was not subject to any significant biotic interaction along the gradient. Responses to disturbance were more species-specific; for two species, competition disappeared with mowing in the wettest conditions, whereas for the two other species, competition switched to facilitation with mowing. Finally, there were no significant interactions for any species in the disturbed and driest conditions. Conclusions At very high levels of stress, plant performances become too weak to allow either competition or facilitation and disturbance may accelerate the collapse of interactions in dry conditions. The results suggest that the importance and direction of interactions are more likely to be positively related in stressful environments.     

Typology and ecology of Californian serpentine annual grasslands

Abstract. A first classification for serpentine annual grasslands distributed throughout northern and central California is proposed. This study has followed the Braun‐Blanquet phyto‐sociological system based on floristical, biogeographical and bioclimatic features of the sampled areas. Numerical analyses of classification and ordination were applied to the floristic relevés. Minimum Variance Clustering grouped relevés into basic classification units that allowed us to define low‐hierarchical syntaxonomical units (associations) and ‘communities’. A Principal Coordinate Analysis was used to extract those ecological parameters related to the axes that separate those classification units from the previous dendrogram. The results showed that differences in species composition was mainly due to a continentality gradient and the shady effect of an overstory vegetation. On the basis of both analyses we propose a first syntaxonomic scheme on ultramafic (mainly serpentine) annual plant communities of the biogeographical Californian Region that comprises four associations, two subassociations and some provisional communities.     

Integrative freshwater ecology and biodiversity conservation

Freshwater ecosystems provide goods and services of critical importance to human societies, yet they are among the most heavily altered ecosystems with an overproportional loss of biodiversity. Major threats to freshwater biodiversity include overexploitation, water pollution, fragmentation, destruction or degradation of habitat, and invasions by non-native species. Alterations of natural flow regimes by man-made dams, land-use changes, river impoundments, and water abstraction often have profound impacts on lotic communities. An understanding of the functional interactions and processes in freshwater ecosystems presents a major challenge for scientists, but is crucial for effective and sustainable restoration. Most conservation approaches to date have considered single species or single level strategies. In contrast, the concept of ‘Integrative Freshwater Ecology and Biodiversity Conservation’ (IFEBC) proposed herein addresses the interactions between abiotic and biotic factors on different levels of organization qualitatively and quantitatively. It consequently results in a more holistic understanding of biodiversity functioning and management. Core questions include modeling of the processes in aquatic key habitats and their functionality based on the identification and quantification of factors which control the spatial and temporal distribution of biodiversity and productivity in aquatic ecosystems. The context and importance of research into IFEBC is illustrated using case studies from three major areas of research: (i) aquatic habitat quality and restoration ecology, (ii) the genetic and evolutionary potential of aquatic species, and (iii) the detection of stress and toxic effects in aquatic ecosystems using biomarkers. In conclusion, our understanding of the functioning of aquatic ecosystems and conservation management can greatly benefit from the methodological combination of molecular and ecological tools.     

分子生态学研究与动物多样性保护

分子生态学的发展揭开了生物多样性保护研究的新篇章。分子技术的应用克服了传统生态学方法中的一些难题,如野外调查周期长、分辨率有限、实验条件不易控制等。应用各种分子标记（如：RFLP 、VNTR、 RAPD、 DNA测序等）可以分析种群地理格局和异质种群动态、确定种群间的基因流、研究瓶颈效应对种群的影响以及确定个体间的亲缘关系等等。所有这些研究都是指导物种保护和濒危种群的恢复所必需的。种或品系特异性的分子标记技术能够解决形态分类中的模糊现象,确定基于遗传物质的谱系关系,还可以用来分析近缘种间杂交问题。这些问题的解决有助于确定物种优先保护顺序,选择保护地区。近年来引起重视的主要组织相容性复合体（MHC）DNA变异分析可能会在研究种群对疾病的易感性等一系列种群特异性问题方面非常有用。随着分子技术的不断发展,会有更多的保护生物学问题得到解决,尤其是结合野外调查统计数据应用多个分子标记对目标种群进行研究,所得到的结果会更精确,更有说服力。