Jean-Claude Moreteau

Stream community structure in relation to spatial variation: the influence of mesohabitat characteristics

Community structure of benthic macroinvertebrates was studied in six first- through fourth-order streams in northeast France, to elucidate changes in richness, abundance, diversity and evenness of mesohabitat assemblages as a function of environmental conditions. Patch samples were subjected to multivariate analyses to determine: (i) relationships among seven indices describing community structure (structure parameters); (ii) relationships among seven environmental variables; (iii) the relationship between community structure and environmental characteristics of patches. Faunal data showed that indices measuring the distribution of individuals among taxa (evenness, dominance) and richness are prominent in describing the structure of macroinvertebrate communities of mesohabitats. The analysis of environmental data demonstrated a major differentiating ability of current velocity and strong inter-relations among in-stream hydraulic-dependent parameters in structuring the mesohabitat environment. The co-structure (= relationship) between community organization and environmental variables indicated that substrate may be a primary determinant of community structure. Current velocity and water depth emerged as secondary factors. Trends in community structure were closely related to the spatial variability of mesohabitats. Species richness increased with habitat heterogeneity. Total abundance increased with trophic potentialities of patches. Equitability and diversity seemed to increase with patch stability.

The spatial heterogeneity of a river bottom: a key factor determining macroinvertebrate communities

We examined the relationships between mesohabitat heterogeneity and benthic macroinvertebrate assemblages in a fourth-order stream (Mortagne, North-Eastern France). The heterogeneity of the mesohabitat mosaic was described around each sampling point for eight different surfaces from 0.5 to 4 m radius. Environmental descriptors integrated both the composition and configuration heterogeneity of the substrate mosaic. Faunal data were analysed in terms of biocenotic indices and taxonomic composition. The maximum number of significant Spearman correlations was obtained for a mosaic with a diameter of 2 m around the sampling point and significant correlations were both the highest and the most numerous for this surface. Relationships were established between community structure and substrate heterogeneity. The faunal richness was higher in a heterogeneous environment composed of numerous substrates, an elevated patchiness and with high perimeters. Such a mosaic potentially offers a great number of niches for invertebrates. A reduced distance between two types of substrate favours exchange of species. At the opposite, a very homogeneous mosaic offers a low variety of niches and shelters fewer taxa. Furthermore, in a homogeneous environment we observed that one or two particular taxa dominated the community, probably because competition with taxa coming from neighbouring patches was reduced. The community composition mainly depended on the characteristics of the mesohabitat sampled. Our results showed that the neighbouring environment around such mesohabitats also had a significant influence. Further research must be conducted to specify the influence of the mosaic heterogeneity on biological and ecological traits of invertebrates.

GROWTH TEMPERATURE AND ADULT PIGMENTATION IN TWO DROSOPHILA SIBLING SPECIES: AN ADAPTIVE CONVERGENCE OF REACTION NORMS IN SYMPATRIC POPULATIONS?

Phenotypic plasticity of abdomen pigmentation was investigated in populations of the sibling species Drosophila melanogaster and D. simulans, living in sympatry in two French localities. Ten isofemale lines of each population and species were grown at different constant temperatures spanning their complete thermal range from 12 to 31°C. Genetic variability between isofemale lines was not affected by growth temperature, but was consistently less in D. simulans. For all traits, the dark pigmentation of the abdominal segments decreased according to growth temperature, in agreement with the thermal budget adaptive hypothesis. The shapes of the response curves were different between the abdominal segments, but for a given segment, quite similar in the two species. On average D. simulans was lighter than D. melanogaster, but the difference was mainly expressed at higher temperatures. An interesting result was the difference observed between the two localities: flies from the colder locality (Villeurbanne) were found to be darker than flies from the warmer locality (Bordeaux). Interestingly, this difference was expressed only at low temperatures, 21°C and below, that is, at temperatures encountered in natural conditions. This suggests an adaptive response resulting in a change of the shape of reaction norm and involving genotype‐environment interactions. When comparing the genetic structure of geographic populations for quantitative traits, several laboratory environments should be preferred to a single one.

Changes in functional biodiversity in an invaded freshwater ecosystem: the Moselle River

The spread of non-indigenous species and the decline of autochthonous ones are leading to a homogenization of freshwater fauna in terms of systematic units, but the functional consequences are poorly documented. We studied the peculiar case of the lower, French section of the Moselle River where 20 invertebrate species have been introduced since 1854, with a rate increasing exponentially with time. Dredge sampling performed in 1994, 1996, 2000 and 2001 at four sampling stations allowed for an evaluation of faunal changes in terms of composition, structure and function. During this period, no structural changes were recorded in spite of multiple, new and successful introductions. The evaluation of functional modifications was based on a typology of taxa exhibiting homogeneous biological/ecological traits. Functional diversity, measured as the diversity of taxa distribution among functional groupings, revealed a significant increase between 1994/1996 and 2000/2001 because those species that were over-represented during the former period reached more equilibrated densities during the latter. The major, indirect implications of these functional changes are discussed.

Light body pigmentation in indianDrosophila melanogaster: A likely adaptation to a hot and arid climate

We analysed reaction norms of pigmentation (thorax and abdomen) according to growth temperature for 20 isofemale lines collected near Delhi (India) and compared them to results obtained for two French populations. The climatic conditions of the two locations were strongly different, with monthly average temperature ranging between 4.2°C and 20.5°C in France and between 14.3°C and 34.3°C in India. For each segment, a decrease of the pigmentation was observed with increasing temperature and the shapes of the reaction norms were more or less parallel. On average Indian flies were lighter than French ones, in agreement with the thermal budget hypothesis. We further investigated the shapes of reaction norms by polynomial adjustment and observed significant differences. In several cases, a maximum divergence was observed at high temperature, implying a change in the shape of the norm. Characteristic values related to the thermal reactivity were also significantly different between populations but no general tendency was found. Genetic variability, estimated by the coefficient of intraclass correlation, was significantly lower in India (0.27 ±0.026) than in France (0.39 ±0.028), and we discuss the significance of this difference.

Temperate freshwater fouling on floating net cages: method of evaluation, model and composition

Abstract Biofouling is a major problem in floating net cage culture during summer months especially at marine sites. The experiments were conducted in two freshwater sites (Eastern France) in order to determine appropriate variables to describe freshwater fouling and to provide a description of its spatial variation. Different mesh size nylon nets were submerged below the surface of the water, from 12 August 1991 to 9 September 1991 in Mirgenbach reservoir (28 days), and from 22 August 1991 to 29 October 1991 in Lindre pond (69 days). Nets (mesh 2–20 mm) were weighed (wet and dry) before and after different submersion times. The rate of dry weight gain of the nets (DG) in Mirgenbach reservoir reached 350% after one month of submersion and was less than 50% during 2 months of submersion in Lindre pond. Biomass of wet fouling did not exceed 110 g m −2 (69 days of submersion) at Lindre (3–5 mm mesh). In Mirgenbach, only 21 days were necessary to obtain 400–1400 g m −2 (2 to 20 mm mesh) and the estimated wet weight of a net bag 5 × 5 × 3 m ranged from 24.4 to 48 kg. Biomass of dry fouling per unit of net surface (Dn) ranged from 100 to 250 g m −2 . The value per unit of settlable thread surface (Ds) ranged from 62 to 340 g m −2 after 21 or 28 days of submersion at Mirgenbach; Ds was less than 25 g m −2 at Lindre (69 days submersion). The Mirgenbach Ds results suggested that fouling biomass increased as a bivariable logistic function of submersion time and net surface. This was the first step of colonization. Fouling was mostly composed of Bryozoan Plumatella repens and Cyanobacteria Oscillatoria sp. at Mirgenbach and Cyanobacteria Aphanizomenon sp. at Lindre. Biofouling development depends on depth, maximum values were observed at 0.4 and 1 m depth. After 4 weeks of submersion in Mirgenbach reservoir, net meshes were obstructed by fouling, while this was not observed after 69 days of submersion in Lindre pond. Differences in fouling rates could be related to reservoir characteristics (temperature, current velocities). An increase in diameter and in distance between threads facilitated algae and animal settlement on nets. Settlable thread surface was a determining factor for biofouling settlement. Constraints generated by fouling should be evaluated prior to selection of culture facilities. Also, two complementary indexes are suggested: percentage cover and dry biomass fouling per unit of settlable thread surface.

A simple formula for calculating the lower limit of Shannon's diversity index

Abstract The purpose of this note is to demonstrate that the exact value of the lower limit of Shannons diversity index (called Hmin′) can be calculated with a very simple formula when data are in the form of counts: Hmin′ = ln(Q) − ((Q - S + 1)ln(Q - S + 1))/Q where S = species richness. Q = total number of individuals. S and Q are integers and Q ≥ S. Hmin′ is generally neglected in ecological studies although it can be very different from zero. Hmin′ is more and more important when the ratio S/Q approaches unity and, then, the interpretation of Shannons diversity or of an eveness index should take it into account. For this reason, we recommend the use of Hurlberts index as an eveness measure rather than Pielous index when Hmin′ > 0. Calculations realized on three examples show that results can be appreciably different. Depending on the cases, eveness differences between two communities can be increased or decreased if we use Hurlberts instead of Pielous index. Moreover, one example allowed us to show that an eveness calculated with Pielous index, even if it is large ( = 0.67), can be in fact the minimal diversity which is mathematically possible. In all of these cases, the ecological interpretation of data can be highly simplified when using Hurlberts index, owing to the fact that Hmin′ is integrated into the calculation of this index.

Assessing Changes in Community Structure by Dominance Indices: A Comparative Analysis

ABSTRACT We compared the sensitivity of four dominance indices to variations in freshwater macroinverterbrate community structure. Three types of simulations generated variations in communities mat could be expected to be found in fieldwork, on rare, median and dominant taxa. Camargo index was the most sensitive to change in rare taxa and the least sensitive to change in dominant taxa. Berger-Parker and Simpson measures were strongly influenced by sample size. McIntosh and Simpson indices were strongly correlated but did not have the same sensitivity. We think that the McIntosh index is the best compromise between a strong sensitivity to dominant taxa and a lesser sensitivity to variations in the other taxa.

Salinization consequences in running waters: use of a sentinel substrate as a bioassessment method

Abstract Salinization has been disturbing increasing numbers of inland waterways, and new analytical tools are needed to survey water quality and to assess the impact of salinization. Researchers have developed new protocols that reduce the number and type of samples required to reduce the cost of existing assessment methods. Our study contributes to this effort with the primary objective of identifying a single, unique river-bottom substrate that could be sampled to detect the impact of rising salinity on macroinvertebrate assemblages. We hoped to define a new concept of sentinel substrate, a substrate with an invertebrate assemblage that would signal an environmental impact (in this case increasing salinity) and that could be used at the site scale to assess that impact. We worked on the Meurthe River, which presents a significant salinity gradient (from 0.2 to 2.6 g/L) over a 19-km section of river in which all other physicochemical variables remain stable. We sampled substrates present at each of 4 sites along the salinity gradient in 2002 and described the effects of rising salinity on the structure (richness, diversity, and dominance) of the macroinvertebrate assemblage in each substrate type. Only the assemblage in pebbles adequately reflected site-level responses. Moreover, only assemblages in pebbles satisfied important criteria such as widespread availability, low variability among seasons, and high invertebrate diversity.

Temporal distribution of perch (Perca fluviatilis L.) in a lake-reservoir (Moselle, France): analysis of catches with vertical gill nets

Four fishing periods within a yearly cycle between 1990 and 1991 were carried out in the lake-reservoir of Mirgenbach, lake of the nuclear power station in Cattenom (Moselle, France). The catches of perch (Perca fluviatilis L.) were analyzed.