Emmanuel Castella

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.

Macroinvertebrates as describers of morphological and hydrological types of aquatic ecosystems abandoned by the Rhône River

Samples of aquatic macroinvertebrates were taken from abandoned beds of the river Rhône in the Brégnier-Cordon area. This sector of the French Upper Rhône is particularly rich in old beds or ‘lônes’ which vary in age and morphological type and have more or less direct connections with the river.Samples were collected using a hand net in eight different ‘lônes’. The results concerned five groups of fauna: Mollusca, Crustacea, Ephemeroptera, Coleoptera, Trichoptera. The study revealed a wide range of fauna, and the fact that group of taxa can be used to describe types of ‘lônes’ defined by morphological and hydrological characteristics. This kind of research adds to our understanding of how such aquatic ecosystems evolve, and may be applied in a more general way to other important river systems.

The effects of water abstractions on invertebrate communities in U.K. streams

There are increasing concerns about the ecological effects of water abstraction and in the UK, these concerns have been hightened by the 1976, 1984 and 1988-92 droughts. This paper assesses macroinvertebrate and environmental changes induced by surface and groundwater abstractions on 22 streams throughout the UK.The approach involved comparative research to assess differences between reference and impacted sites.Using a database comprising 204 sets of biological and environmental data (89 taxa and 16 environmental variables) a preliminary ordination using principle components analysis clearly differentiated three types of sites: upland, lowland and an intermediate type. At this scale, any effects of abstractions on invertebrate communities are shown to be insignificant relative to regional controls. A simultaneous ordination of the environmental and faunal differences between pairs of sites was undertaken separately for each of the three regional groups. Differences are considered as vectors having both direction and amplitude and the analysis elucidates common patterns in the faunal and environmental data. Important changes were observed in two situations: upland streams affected by major diversions as part of hydro-power schemes in Scotland and lowland rivers impacted by groundwater abstractions.No strong patterns of change (either in amplitude or orientation) were demonstrated within any of the taxonomic groups. However, within the upland type some rheophilous taxa were shown typically to be reduced in abundance at impacted sites. Within the lowland type, a consistent pattern in the dataset is demonstrated by a group of taxa that are reduced in abundance at the impacted sites.

Relationship between biomass and surface area of six submerged aquatic plant species

Mathematical relationships relating the biomass to the surface area of Elodea canadensis Michx., Myriophyllum spicatum L., Nitellopsis obtusa (Desv.) J.Gr., Potamogeton lucens L., Potamogeton pectinatus L. and Potamogeton perfoliatus L. were developed. The methods leading to these relations are presented for plants from Lake Geneva (Switzerland). Results include three sets of data for each species: leaves, stems and whole plant. Differences were evidenced according to plant species; for a same biomass E. canadensis and M. spicatum offered the highest surface area, P. pectinatus and N. obtusa the lowest. For 1.0 g dry weight of whole plant, the surface area was 1255 cm2 for E. canadensis, 1205 cm2 for M. spicatum, 560 cm2 for N. obtusa, 653 cm2 for P. lucens, 500 cm2 for P. pectinatus, and 762 cm2 for P. perfoliatus. Plants with dissected morphology did not necessarily offer the largest surface area per unit biomass.

Biodiversity in the floodplain of Saône: a global approach

Biodiversity of European floodplains is seriously threatened mainly due to (1) modifications of river courses such as channelisation or embankments, and (2) changes in traditional agricultural practices (i.e. usually pastures), into intensive production using drainage and fertilisation. A upstream-downstream survey of the Saône floodplain (France) has been done to identify the contribution of habitats to the floodplain biodiversity. Selected taxa were aquatic and terrestrial vegetation, Odonata, Coleoptera, Amphibians, and birds. The taxa were sampled in different habitat types that were: forests, grasslands and aquatic habitats. Tributary confluences with the river and cut-off channels contributed greatly to the floodplain diversity according to their invertebrates and aquatic vegetation communities. The abundance of rare species (benefitting of a national or regional protection status) was the highest in hygrophilous grasslands. Moreover, we demonstrated that diversity of breeding bird communities was correlated with the size of these habitats. We demonstrated also that alluvial forests contributed to maintain some particular species as Middle-spotted Woodpecker (Dendrocopus medius), while new plantations were colonized by openland bird communities sensible to the edge effect. Grassland fragmentation for agriculture appeared to be a major cause in biodiversity loss. Any alteration of the floodplain dynamics must be avoided to preserve the present diversity of riverine wetlands.

Aquatic macroinvertebrate response along a gradient of lateral connectivity in river floodplain channels

Abstract Large river floodplains potentially include the full range of freshwater ecosystems from permanently flowing channels to temporary pools and springs. Attempts to restore such complex systems require tools adapted to assess restoration success. In an analysis of invertebrate assemblages in the Rhône River floodplain (France), taxonomic-based indices (rarefied richness and assemblage composition) were compared with functional metrics using trait-based ratios as surrogates of ecosystem processes. Their ability to respond to a gradient of hydrological connectivity was assessed in 7 cut-off channels. The sampling design included 2 sites/channel (upstream and downstream), 4 randomly chosen sampling points (0.5 × 0.5-m quadrats)/site, and 2 sampling seasons (spring and summer). Water physicochemical and habitat variables were recorded when invertebrates were sampled. Environmental variables, including water conductance, [NH3-N], submerged vegetation cover, diversity of sediment grain size, and organic matter content of the sediment, were used to construct a synthetic variable describing the hydrological connectivity of each site with the main river channel. A quadratic regression of rarefied taxonomic richness and the connectivity gradient was not quite significant, but assemblage composition was strongly related to the gradient. Four of 8 trait-based metrics were correlated with the connectivity gradient. Values of metrics that are surrogates for top-down control of assemblage structure and habitat stability (based on functional feeding groups) declined along the gradient from disconnected sites to more connected sites. Values of metrics that are surrogates for voltinism and food supply for water-column-feeding fish increased with connectivity. Top-down control and voltinism surrogates suggested a decline in predator–prey relationships and lower habitat stability, respectively, in the more connected sites. Assemblage composition and some of the trait-based metrics were sensitive to a flood that occurred before one of the sampling dates. Some of the trait-based metrics showed potential for explaining floodplain invertebrate assemblages and for monitoring postrestoration conditions in floodplain water bodies. However, the metrics were developed initially for studies of lotic systems and their use in heterogeneous floodplain water bodies will require further investigation, e.g., delineation of reference conditions for trait-based metrics.

Parallel changes in genetic diversity and species diversity following a natural disturbance

We examined the spatial and temporal variation of species diversity and genetic diversity in a metacommunity comprising 16 species of freshwater gastropods. We monitored species abundance at five localities of the Ain river floodplain in southeastern France, over a period of four years. Using 190 AFLP loci, we monitored the genetic diversity of Radix balthica, one of the most abundant gastropod species of the metacommunity, twice during that period. An exceptionally intense drought occurred during the last two years and differentially affected the study sites. This allowed us to test the effect of natural disturbances on changes in both genetic and species diversity. Overall, local (alpha) diversity declined as reflected by lower values of gene diversity HS and evenness. In parallel, the among‐sites (beta) diversity increased at both the genetic (FST) and species (FSTC) levels. These results suggest that disturbances can lead to similar changes in genetic and community structure through the combined effects of selective and neutral processes.

An approach to interpretation of lists of insects using digitised biological information about the species

Predicted species lists are generated from regional species pools, coupled to codified habitat, microhabitat and biological trait data for the species. At site level, habitat association data are used to tailor the predicted list to site conditions and comparison between predicted and observed species lists is used to explore elements of site quality and site management options involving microhabitat and trait data for the species in the process. It is pointed out that this approach makes possible the interpretation of insect species lists by non-specialist site managers. At larger geographic scales, attributes of regional lists are identified. Throughout, the approach is considered in the context of its potential to contribute to resolution of issues relating to maintenance of biodiversity in Europe and the taxonomic group employed is the Syrphidae (Diptera).

Occurrence of Characeae in Switzerland over the last two centuries (1800–2000)

Some 3100 specimens of Characeae from herbarium collections and recent sampling programmes in Switzerland were redetermined and their provenance analysed, in order to investigate historical changes in frequency, distribution and current status of the species. Altitudinal and geographic distribution patterns of 27 taxa are described in 125 km2 grid squares covering Switzerland, and an analysis was made of species richness of Characeae in different grid squares. Data were available for approximately half (117 out of 262) of the grid squares covering Switzerland, showing that the recording effort had not been uniform. The lowland was better investigated than either the hills or the mountains. And 17 taxa were categorised as rare, on the basis that they were each known from <100 records. Ten taxa were classified as not uncommon, among which Chara vulgaris and C.globularis are the most frequent and widespread species. The distribution of some species shows a significant relationship with altitude, but analysis of the species distributions shows only a weak relationship with altitude of the grid square and biogeographical region, revealing that these two variables are not the main factors explaining the distribution of the species. Over the last 200 years, regression has occurred in the species that were formerly the rarest and expansion has occurred in a few species that were previously the most common. Further investigations are needed to precise the distribution of the declining species, particularly in the under-prospected parts of the country and in poorly known habitats.

Morphological traits and spatial heterogeneity of aquatic plants along sediment and depth gradients, Lake Geneva, Switzerland

Abstract The morphological response and distribution of Potamogeton pectinatus L., P. lucens L. and P. perfoliatus L. were investigated in relation to sediment and depth gradients within the littoral zone of Lake Geneva. Biomass, maximum shoot length, shoot biomass and biomass density were the plant traits analyzed, together with sediment characteristics: texture, water content, organic nitrogen and carbon, and exchangeable phosphorus and potassium. The relationships between (i) depth and sediment characteristics vs. species distribution and (ii) depth and sediment characteristics vs. plant traits were first studied. Regression models for the biomass and the shoot length of each species are proposed. These models are applied in a related article (Lehmann et al., 1997) in order to study the relationship between plant traits vs. species distribution through a Geographic Information System modeling. Besides the fact that P. pectinatus was more often found in sediments with higher organic content, no direct relationships were found between sediment characteristics and species distribution. Neither could the presence of patches of bare substrate be explained by differences in sediment characteristics. The effect of the sediment characteristics on plant growth showed in general a negative influence of organic matter content (except for P. pectinatus), and a positive influence of the fine texture and phosphorus. P. pectinatus grew better in shallower water, P. lucens appeared to have the best competitive abilities and P. perfoliatus performed best at deeper sites.