Of niches and distributions: range size increases with niche breadth both globally and regionally but regional estimates poorly relate to global estimates

The relationship between species’ niche breadth (i.e. the range of environmental conditions under which a species can persist) and range size (i.e. the extent of its spatial distribution) has mostly been tested within geographically restricted areas but rarely at the global extent. Here, we not only tested the relationship between range size (derived from species’ distribution data) and niche breadth (derived from species’ distribution and co‐occurrence data) of 1255 plant species at the regional extent of the European Alps, but also at the global extent and across both spatial scales for a subset of 180 species. Using correlation analyses, linear models and variation partitioning, we found that species’ realized niche breadth estimated at the regional level is a weak predictor of species’ global niche breadth and range size. Against our expectations, distribution‐derived niche breadth was a better predictor for species’ range size than the co‐occurrence‐based estimate, which should, theoretically, account for more than the climatically determined niche dimensions. Our findings highlight that studies focusing on the niche breadth vs range size relationship must explicitly consider spatial mismatches that might have confounded and diminished previously reported relationships

EUNIS Habitat Classification: Expert system, characteristic species combinations and distribution maps of European habitats

Aim: The EUNIS Habitat Classification is a widely used reference framework for European habitat types (habitats), but it lacks formal definitions of individual habitats that would enable their unequivocal identification. Our goal was to develop a tool for assigning vegetation‐plot records to the habitats of the EUNIS system, use it to classify a European vegetation‐plot database, and compile statistically‐derived characteristic species combinations and distribution maps for these habitats. Location: Europe. Methods: We developed the classification expert system EUNIS‐ESy, which contains definitions of individual EUNIS habitats based on their species composition and geographic location. Each habitat was formally defined as a formula in a computer language combining algebraic and set‐theoretic concepts with formal logical operators. We applied this expert system to classify 1,261,373 vegetation plots from the European Vegetation Archive (EVA) and other databases. Then we determined diagnostic, constant and dominant species for each habitat by calculating species‐to‐habitat fidelity and constancy (occurrence frequency) in the classified data set. Finally, we mapped the plot locations for each habitat. Results: Formal definitions were developed for 199 habitats at Level 3 of the EUNIS hierarchy, including 25 coastal, 18 wetland, 55 grassland, 43 shrubland, 46 forest and 12 man‐made habitats. The expert system classified 1,125,121 vegetation plots to these habitat groups and 73,188 to other habitats, while 63,064 plots remained unclassified or were classified to more than one habitat. Data on each habitat were summarized in factsheets containing habitat description, distribution map, corresponding syntaxa and characteristic species combination. Conclusions: EUNIS habitats were characterized for the first time in terms of their species composition and distribution, based on a classification of a European database of vegetation plots using the newly developed electronic expert system EUNIS‐ESy. The data provided and the expert system have considerable potential for future use in European nature conservation planning, monitoring and assessment

Anthropogenic tritium in the Loire River estuary

International audienc

Forest plant community changes during 1989-2007 in response to climate warming in the Jura Mountains (France and Switzerland)

Question: How strong are climate warming-driven changes within mid-elevation forest communities? Observations of plant community change within temperate mountain forest ecosystems in response to recent warming are scarce in comparison to high-elevation alpine and nival ecosystems, perhaps reflecting the confounding influence of forest stand dynamics. *Location: Jura Mountains (France and Switzerland). *Methods: We assessed changes in plant community composition by surveying 154 Abies alba forest vegetation relevés (550-1,350 m a.s.l.) in 1989 and 2007. Over this period, temperatures increased while precipitation did not change. Correspondence analysis (CA) and ecological indicator values were used to measure changes in plant community composition. Relevés in even- and uneven-aged stands were analysed separately to determine the influence of forest stand dynamics. We also analysed changes in species distribution to detect shifts along the elevation gradient by focusing on the lowest, central and highest positions of lowland and mountain species altitudinal ranges. *Results: We found significant shifts along the first CA axis, which reflected a change in plant community composition towards a greater frequency of lowland species. Analyses of ecological indicator values indicated increases in temperature and light availability in A. alba stands, particularly in even-aged stands. However, no major changes in overall species distribution were found. *Conclusions: The community-level changes are consistent with effects of climate warming and local stand dynamics. Changes in species distribution were small in comparison to observed local temperature increases, perhaps reflecting dispersal limitation, phenotypic plasticity or microclimatic buffering by the tree canopy. Causality cannot rigorously be inferred from such a descriptive study; however, we suggest that recent warming is now driving plant community change in the climatically more moderate mid-elevation forest setting

Determination and speciation of anthropogenic tritium in the Loire River estuary (France).

International audienceThe aim of radioecology is to understand the transfer of radionuclides through the ecosystem. It relies strongly on field studies which can provide useful information on the presence of radionuclides in the environment, and their origins (natural and anthropogenic). In this study, the radioactive isotope of hydrogen, i.e. tritium (3H or T), is considered. Tritium is a beta emitter with a radioactive half life of 12.3 years. It is present in the environment in three principal forms: tritiated water (HTO or tissue free water), organically bound tritium (OBT) and tritiated gas (HT). Tritiated water is the most abundant chemical form of tritium in the aquatic and terrestrial environment. OBT can be subdivided in two fractions: the exchangeable OBT refers to tritium atoms that are easily exchanged (e.g. bound to nitrogen, oxygen or sulfur atoms), while the non-exchangeable OBT refers to the remaining OBT covalently bound to carbon atoms. The non exchangeable hydrogen pool is considered as the only hydrogen fraction that faithfully records the history of environmental tritium seen by living organisms. In this study, mud and water samples from the Loire estuary, the outlet of a watershed where several nuclear power plants are located, were analyzed. Mud samples were subjected to freeze-drying and combustion as pre treatment in order to recover free HTO and total OBT. HTO and total OBT activities ranged between 4 and 26 Bq.L-1 and between 10 and 25 Bq.L-1 of combustion water, respectively. To estimate the non exchangeable OBT activity in these samples, the exchangeable pool of hydrogen within the matrix has to be known. A dedicated experimental set up was thus developped in order to determine the fraction of exchangeable hydrogen (). It consists in a temperature and humidity controlled glove box where different environmental matrixes are exposed to specific atmospheres with fixed H/D (deuterium) or H/T pressure ratios. The calibration phase of the method was perfomed using cellulose matrix

Anthropogenic tritium in the Loire River estuary & hydrogen lability in matrices of interest

International audienc