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Un article de Lukas Denzler sur nos recherches concernant le cynips du châtaignier et son antagoniste, le Torymus sinensis, paru dans le NZZ, aujourd’hui.
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1. Studies on biodiversity and ecosystem functioning (BEF) have elicited debate over the interpretation of the positive relationship between species richness and plant productivity. Manipulating richness cannot be achieved without affecting composition; it is thus essential to consider the latter in statistical models.
2. We firstly review existing approaches that use species richness as an explanatory variable and propose modifications to improve their performance. We use an original dataset to illustrate the analyses. The classical method where composition is coded as a factor with a level for each different species mixture can be improved by defining the levels using clustering. Methods based on ordinations reduce the dimensionality of plant composition and use the new coordinates as fixed effects; they provide a much better fit to our observations.
3. Secondly, we develop a new method where composition is included as a similarity matrix affecting the residual variance-covariance. Similarity in composition between plots is treated in the same way as shared evolutionary history between species in phylogenetic regression. We find that it outperforms the other models.
4. We discuss the different approaches and suggest that our method is particularly suited for observational studies or for manipulative studies where plant diversity is not kept constant by weeding. By treating species composition in an intuitive and sensible way, it offers a valuable and powerful complement to existing models.
Sandau S, Rohr RP, Naisbit RE, Fabian Y, Bruggisser OT, Kehrli P, Aebi A and Bersier LF (in press) Including community composition in biodiversity-productivity models. Methods in Ecology and Evolution
«La gestion de la biodiversité autour d’une Faculté des Sciences se doit d’être exemplaire!» Ce cri du coeur d’un professeur de biologie a été le point de départ d’un projet interdisciplinaire, entre la biologie et l’ethnologie, ayant pour but de remettre la biodiversité au goût de tous à (et autour de) l’Université de Neuchâtel. Lire l’article PDF
Une brochure née d’un projet pédagogique en biologie ethnologie, durant lequel nous nous sommes penchés sur les châtaigniers et Dryocosmus kuriphilus, le cynips du châtaignier. Ce document est le résultat d’une démarche participative impliquant des biologistes, des ethnologues, des producteurs de châtaignes et des représentants des services cantonaux et fédéraux concernés. L’objectif de cette brochure est de redessiner le contour d’un problème “simple” à première vue. PDF / Dessin: Clotide Rigaud
Declining plant species richness in agro-ecosystems and thus reduced habitat quality can have cascading effects on ecosystem functioning, leading to reduced pollination and biological control. Here we test if plant diversity can affect arthropod diversity and abundance on a very small scale, manipulating plant species richness (2, 6, 12 and 20 sown species) in small adjacent subplots (63 9 m) in 10 wildflower strips in an agricultural landscape. We simultaneously analyzed the effect of plant species richness, vegetation structure, and plant composition on the species richness and abundance of cavity-nesting wild bees, wasps, their prey and natural enemies, and on the structure of their food webs. By separating the trap-nesting species into functional groups according to their prey, we aimed to understand the underlying patterns for the effects of plant diversity. Increasing plant species richness had a significant effect only on spider-predating wasps, the group of wasps trophically most distant from plants. In contrast, bees and food-web structure were unaffected by plant diversity. Spider-predating wasp abundance negatively correlated with the abundance of spiders, suggesting top-down control. Interestingly, the abundance of spiders was the only variable that was strongly affected by plant composition. The hypothesis that the effect of plant diversity decreases with increasing trophic level is not supported by our study, and the mobility of species appears to play a greater role at this small spatial scale.
Fabian, Y., N. Sandau, O. T. Bruggisser, A. Aebi, P. Kehrli, R. P. Rohr, R. E. Naisbit, and L.-F. Bersier. 2014. Plant diversity in a nutshell: testing for small-scale effects on trap nesting wild bees and wasps. Ecosphere 5(2):18. http://dx. doi.org/10.1890/ES13-00375.1 PDF
Aim To quantify the relative importance of propagule pressure, climatematching and host availability for the invasion of agricultural pest arthropods in Europe and to forecast newly emerging pest species and European areas with the highest risk of arthropod invasion under current climate and a future climate scenario (A1F1).
Methods We quantified propagule pressure, climate-matching and host availability by aggregating large global databases for trade, European arthropod interceptions, Koeppen–Geiger world climate classification (including the A1F1 climate change scenario until 2100) and host plant distributions for 118 quarantine arthropod species.
Results As expected, all the three factors, propagule pressure, climate suitability and host availability, significantly explained quarantine arthropod invasions in Europe, but the propagule pressure only had a positive effect on invasion success when considered together with climate suitability and host availability. Climate change according to the A1F1 scenario generally increased the climate suitability of north-eastern European countries and reduced the climate suitability of central European countries for pest arthropod invasions.
Main conclusions To our knowledge, this is the first demonstration that propagule pressure interacts with other factors to drive invasions and is not alone sufficient to explain arthropod establishment patterns. European countries with more suitable climate and large agricultural areas of suitable host plants for pest arthropods should thus be more vigilant about introduction pathways. Moreover, efforts to reduce the propagule pressure, such as preventing pests from entering pathways and strengthening border controls, will become more important in north-eastern Europe in the future as the climate becomes more favourable to arthropod invasions.
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