Reconstruction of the early invasion history of the quagga mussel (Dreissena rostriformis bugensis) in Western Europe

The recent introduction of the quagga mussel into Western European freshwaters marked the beginning of one of the most successful biological invasions during the past years in this region. However, the spatial and temporal origin of the first invasive population(s) in Western Europe as well as subsequent spreading routes still remain under discussion. In this study, we therefore aim at reconstructing the early invasion history of the quagga mussel in Western Europe based on an age-corrected temporally and spatially explicit spread model. Data were derived from time-series studies at selected sites as well as from a broad spatial survey in Western Europe. According to our spread model, the first successful introduction into Western Europe occurred in the Main-Danube Canal in early 2004, probably via inland navigation. Once populations were established, subsequent spread of the quagga mussel was characterized by a combination of jump dispersal and diffusive spread. This study gives insights into the very early invasion history of the quagga mussel and stresses the importance of the Main-Danube Canal for the introduction of non-native freshwater species into Western Europe

Deep drilling reveals massive shifts in evolutionary dynamics after formation of ancient ecosystem

The scarcity of high-resolution empirical data directly tracking diversity over time limits our understanding of speciation and extinction dynamics and the drivers of rate changes. Here, we analyze a continuous species-level fossil record of endemic diatoms from ancient Lake Ohrid, along with environmental and climate indicator time series since lake formation 1.36 million years (Ma) ago. We show that speciation and extinction rates nearly simultaneously decreased in the environmentally dynamic phase after ecosystem formation and stabilized after deep-water conditions established in Lake Ohrid. As the lake deepens, we also see a switch in the macroevolutionary trade-off, resulting in a transition from a volatile assemblage of short-lived endemic species to a stable community of long-lived species. Our results emphasize the importance of the interplay between environmental/climate change, ecosystem stability, and environmental limits to diversity for diversification processes. The study also provides a new understanding of evolutionary dynamics in long-lived ecosystems

Nematodes as Sentinels of Heavy Metals and Organic Toxicants in the Soil

Field and laboratory research has repeatedly shown that free-living soil nematodes differ in their sensitivity to soil pollution. In this paper, we analyze whether nematode genera proved sensitive or tolerant toward heavy metals and organic pollutants in six long-term field experiments. We discuss overlaps between nematode physiological responses to heavy metals and to organic pollutants, which may explain why nematodes can exhibit co-tolerance toward several contaminants. We propose a simple method for separating direct effects of soil contamination on nematode populations from indirect effects mediated through the food chain. Finally, we analyze the extent to which nematodes exhibited consistent responses across the experiments analyzed. Our results show that (a) indirect effects of pollution were generally strong; (b) fewer nematode genera were tolerant than sensitive; (c) many genera, including practically all Adenophorea, exhibited a common response pattern to contaminants; and (d) several genera of the Secernentea exhibited differential tolerance toward particular pollutants. We conclude that bioindication of soil contamination should preferentially be based on tolerant, and less on sensitive, nematodes. We provide a list of nematode genera that may potentially serve as differential bioindicators for specific soil contaminants

A GIS-based model of Serengeti grassland bird species

In this study we assess possible benefits of using satellite sensor data in large-scale landscape ecology. The study was conducted on the Serengeti Plains, Tanzania, combining (1) records from a bird survey, (2) local measurements of vegetation structure and precipitation, and (3) a habitat map derived from a Landsat satellite image classification. The question of whether ground-based or satellite data explained more of the species-environment relationships was explored by means of multivariate regression. On average across all 62 bird species recorded, the combination of satellite-based and groundbased data improved explained variance (R2 = 0.26), as compared to satellite sensor data, or ground-based data alone (R2 = 0.18 and 0.21, respectively). In spite of this low level of explained variance in the regressions, a classification of bird species according to utilised parameter space yielded reasonable results. Satellite image data seem to be suited to this kind of investigation. Ostrich 2007, 78(2): 259–26

Ring-based versus disc-based separation of spatial scales: a case study on the impact of arable land proportions on invertebrates in freshwater streams

The impact of different land-use types on species is traditionally estimated by correlating landscape proportions recorded in buffer areas around focal points with species data observed at these sites. If a high proportion of a specific land-use type exists within a small radius, it will be accumulated in larger buffers and may confound the interpretation at larger scales. We sampled freshwater invertebrates in ten streams using cages with artificial substrate and compared the effects of arable land proportions calculated in disc-shaped buffers of increasing radius versus areas calculated from non-overlapping rings of increasing radius. We hypothesize that (1) the accumulative disc-based approach leads to confounding effects across increasing buffer size and that (2) the use of ring-based methods facilitates the identification of relevant scales for conservation measures. The abundance of crustaceans showed a positive relationship with arable land proportions, but Plecoptera abundance and the taxonomic richness of Ephemeroptera and Plecoptera decreased with increasing arable land proportions in the surrounding landscape. Our results further support the presence of confounding effects in disc-based analyses, as correlations between arable land proportions and Crustacea, or Plecoptera, respectively, were affected by the accumulation of small-scale area proportions. The distance at which arable land proportions significantly affected benthic fauna in freshwater streams was consistently shorter if calculated from rings rather than from discs. Although an a priori definition of ring width introduces new challenges, a combined use of disc- and ring-based techniques for the estimation of land-use effects may substantially improve the realization of conservation and protection measures in terrestrial and aquatic systems

Changes in nematode communities after manuring in millet fields in Senegal

Changes in the soil nematofauna community structure were followed in nine millet fields on seven farms in two villages in Senegal during one cropping cycle. Cultivation practices were done by field owners. One plot in each field was divided into two subplots; in one of these, manure (20 t ha-1 ) was added at sowing. Before the manure input, at mid-cycle and at millet harvest, the structure of the nematode fauna was studied. Soil physico-chemical characteristics, microbial carbon and plant production were measured at sowing and at millet harvest. In the sub-plots where manure was added, millet yield increased by 155%, the mineral nitrogen content of the soil increased by about 45%, while nitrogen flux increased by 150% and microbial biomass by 65%. The significant enrichment of soil by manure led to a 75% increase in total nematode population density at mid-cycle and to a 30% increase at harvest time. The density of opportunistic bacterial-feeding and fungal-feeding nematodes was significantly larger with than without manure. This result is similar to those of comparable studies in temperate areas; however the relative abundance of enrichment opportunists was extremely low with regard to that found under similar conditions in temperate ecosystems. Furthermore, the abundance of the c-p 2 bacterialfeeding nematodes, belonging mainly to the family Cephalobidae, was strongly correlated with soil microbial biomass. The other c-p feeding guilds showed no con-elation with nitrogen flux, or soil microbial biomass. (Résumé d'auteur

Resilience and alternative equilibria in a mire plant community after experimental disturbance by volcanic ash

Following disturbance events vegetation can either be resilient and return to its original state, or there can be shifts in vegetation composition and abundance patterns that may indicate alternative equilibiria. We conducted a long-term field experiment that simulated impact by aerially transported volcanic ejecta (tephra) in a Sphagnum-dominated plant community in order to test the effects of this type of large-scale disturbance. Sixty plots of 1.4 × 1.4 m were established at Sarobetsu mire in northern Hokkaido, Japan and subjected to seven treatments (including the control) with natural tephra or ground glass shards differing in grain size, layer thickness and season of application. Water chemistry and vegetation were surveyed before tephra application and during five and eight years after the perturbation, respectively. Leaching of ions from fine-grained glass shards caused a sustained increase of soil water pH and electric conductivity. Under coarser materials water quality differed little from the control, but a short-lived peak of potassium suggested that mechanisms like nutrient release from decomposing plant material may influence water chemistry after volcanic disturbance. The perturbation initially reduced the cover of the dominant functional group (Sphagnum mosses) in all treatments; vascular plants were less affected. All species were able to recover by growing through the tephra, and open tephra surfaces were colonized by ubiquitous cryptogams, but not by spermatophytes. In contrast to the overall resilient behaviour of the vegetation, in some plots that received natural tephra an alternative state with high cover of the dwarf shrub Myrica gale developed. The patterns indicated that physical and chemical properties of the tephra determined the initial effects on plants, but that stochastic processes contributed to subsequent succession. These are likely to have effects on ecosystem functioning, e.g. hydrological processes and carbon sequestration.