Raphaelle Juge

Does size matter? The relationship between pond area and biodiversity

Larger areas support more species. To test the application of this biogeographic principle to ponds, we consider the relationship between size and diversity for 80 ponds in Switzerland, using richness (number of species) and conservation value (score for all species present, according to their degree of rarity) of aquatic plants, molluscs (Gastropoda, Sphaeriidae), Coleoptera, Odonata (adults) and Amphibia. Pond size was found to be important only for Odonata and explained 31% of the variability of their species richness. Pond size showed only a feeble relationship with the species richness of all other groups, particularly the Coleoptera and Amphibia. The weakness of this relationship was also indicated by the low z-values obtained (< 0.13). The SLOSS analyses showed that a set of ponds of small size has more species and has a higher conservation value than a single large pond of the same total area. But we also show that large ponds harbour species missing in the smaller ponds. Finally, we conclude that in a global conservation policy (protection, restoration, management), all size ranges of ponds should be promoted.

Influence of water eutrophication on the macrophytic vegetation of Lake Lugano

The influence of water eutrophication on the macrophytic vegetation of Lake Lugano (Lago di Lugano) is demonstrated using two complementary procedures:A comparative study of the flora, floristic diversity and abundance of vegetation of the three main basins (Northern, Southern, and Ponte Tresa) differing in their geographical and limnological (trophic) characteristics. Our findings are briefly compared with the observations made on other Swiss lakes.A description of the qualitative and quantitative evolution of macrophytes based on the comparison of our results of 1980 and 1987 with those of Steiner in 1912. These three studies correspond to different trophic levels and provide trends to link the evolution of vegetation and flora to the phenomenon of eutrophication.

The prediction of macrophyte species occurrence in Swiss ponds

The study attempted to model the abundance of aquatic plant species recorded in a range of ponds in Switzerland. A stratified sample of 80 ponds, distributed all over the country, provided input data for model development. Of the 154 species recorded, 45 were selected for modelling. A total of 14 environmental parameters were preselected as candidate explanatory variables. Two types of statistical tools were used to explore the data and to develop the predictive models: linear regression (LR) and generalized additive models (GAMs). Six LR species models had a reasonable predictive ability (30–50% of variance explained by the selected predictors). There was a gradient in the quality of the 45 GAM models. Ten species models exhibited both a good fit and statistical robustness: Lemna minor, Phragmites australis, Lysimachia vulgaris, Galium palustre, Lysimachia nummularia, Iris pseudacorus, Lythrum salicaria, Lycopus europaeus, Phalaris arundinacea, Alisma plantago-aquatica, Schoenoplectus lacustris, Carex nigra. Altitude appeared to be a key explanatory variable in most of the species models. In some cases, the degree to which the shore was shaded, connectivity between water bodies, pond area, mineral nitrogen levels, pond age, pond depth, and the extent of agriculture or pasture in the catchment were selected as additional explanatory variables. The species models demonstrated that it is possible to predict species abundance of aquatic macrophytes and that each species responded individually to distinct environmental variables.

La végétation macrophytique d'un lac hautement eutrophe du Plateau suisse: Le Baldegger See

The study of the qualitative and quantitative distribution of the Baldeggersee macrophytic vegetation is undertaken in 1980 with the help of colour aerial photographies and verification on the field. The comparison with old data allows then a short survey of the macrophytic evolution in relation to the eutrophication.