Eglantine Chappuis

Environmental filtering determines community patterns in temporary wetlands: A multi-taxon approach

Climate characteristics appear to play a key role in filtering organisms based on their biological traits. If this trait filtering by climate indeed occurs, it should have effects on the composition, dynamics, taxonomic relatedness and co-occurrence patterns of local assemblages, regardless of the taxonomic group considered. This preliminary study aimed to assess the extent to which environmental variables might determine these patterns in local communities and to evaluate whether the ultimate cross-taxon congruence relationships are consistent across, or dependent on, the selected region. To this end, we studied the bryophyte, macrophyte, macroinvertebrate, and amphibian communities in two clusters of temporary wetlands on the NE Iberian Peninsula under mesothermal and semiarid climates. We observed effects of environmental filtering, with the communities differing between the climatic regions not only in their compositions but also in their dynamics and taxonomic relatedness patterns. Although the cross-taxon congruence in terms of species richness was high in the mesothermal climate, most of the congruent relationships were disrupted in the semiarid environment. Overall, because climate-dependent patterns appear to prevail over climate-consistent ones, we suggest that the use of surrogate taxa may be of limited value when aiming to assess wetland biodiversity across large areas.

Nitrogen Stable Isotopes in Primary Uptake Compartments Across Streams Differing in Nutrient Availability

High variability in the natural abundance of nitrogen stable isotopes (δ(15)N) has been reported for primary uptake compartments (PUCs; e.g., epilithon, filamentous algae, bryophytes, macrophytes) in human-impacted aquatic ecosystems, but the origin of this variability is not yet well understood. We examined how δ(15)N of different PUC types relate to δ(15)N of dissolved inorganic nitrogen (DIN) species (nitrate and ammonium) and to the stream nutrient concentrations in which they grow. We selected 25 reaches located across the fluvial network of La Tordera catchment (NE Spain, 868.5 km(2)), encompassing a gradient of human pressures from headwaters to the river valley. δ(15)N-PUC variability was mostly explained by location within the fluvial network and was strongly related to the δ(15)N of DIN species, especially of ammonium. Models were stronger for PUCs growing within the stream channel and thus using streamwater as their main source of nutrients. Regression models including nutrient concentrations improved the prediction power for δ(15)N-PUCs, suggesting that nutrient concentrations and stoichiometry cannot be ignored in explaining the natural abundance of nitrogen isotopes in PUCs. These results provide insights into what controls variability in δ(15)N of PUCs within a stream network, with implications for the application of stables isotopes as an ecological tool.

Deleterious interaction of light impairment and organic matter enrichment on Isoetes lacustris (Lycopodiophyta, Isoetales)

Light reduction and increased organic matter load often occur together in lakes undergoing eutrophication. We aimed at experimentally testing the relative importance of light availability, organic matter enrichment and their interactions in the collapse of healthy populations of Isoetes lacustris. We conducted an in situ shading (65 and 35% of incident light) and organic matter enrichment (10% enrichment) experiment in a Pyrenean pond (NE Spain). We followed plant performance using growth indicators, carbon balance indicators and individual survival. Severe light reduction (35%) resulted in a lengthening of the new leaves and no effects on mortality. Organic matter enrichment resulted in lower production and increased individual mortality. The combination of both stresses resulted in stronger negative effects and the highest mortality rate, which helps explaining I. lacustris die-offs observed after damming. Under severe light reduction (35%), plants used corm starch to keep growing. Consequently, starch percentage decreased and sucrose percentage increased as it was transported to the growing leaves. The most extreme changes were observed under severe light reduction and fertilization, which extremely increased the ratio between sucrose and total non-structural carbohydrates (TNC). Thus, I. lacustris sucrose:TNC ratio is a good indicator of light reduction and organic matter enrichment stresses.

The optimal sampling design for littoral habitats modelling: A case study from the north-western Mediterranean

Species distribution models (SDMs) have been used to predict potential distributions of habitats and to model the effects of environmental changes. Despite their usefulness, currently there is no standardized sampling strategy that provides suitable and sufficiently representative predictive models for littoral marine benthic habitats. Here we aim to establish the best performing and most cost-effective sample design to predict the distribution of littoral habitats in unexplored areas. We also study how environmental variability, sample size, and habitat prevalence may influence the accuracy and performance of spatial predictions. For first time, a large database of littoral habitats (16,098 points over 562,895 km of coastline) is used to build up, evaluate, and validate logistic predictive models according to a variety of sampling strategies. A regularly interspaced strategy with a sample of 20% of the coastline provided the best compromise between usefulness (in terms of sampling cost and effort) and accuracy. However, model performance was strongly depen upon habitat characteristics. The proposed sampling strategy may help to predict the presence or absence of target species or habitats thus improving extensive cartographies, detect high biodiversity areas, and, lastly, develop (the best) environmental management plans, especially in littoral environments.

Estanys de l’Albera i basses dels secans de Lleida: quines característiques ambientals determinen les seves comunitats i la seva biodiversitat?

En aquest estudi, hem realitzat una comparacio de les comunitats biologiques dels estanys i les basses temporanies de dues arees de clima diferenciat, al massis de l’Albera (Alt Emporda) i als secans de Lleida (Segria). L’objectiu del treball ha estat identificar les variables ambientals que determinen la composicio d’aquestes comunitats, com la biodiversitat, la dinamica temporal i la congruencia taxonomica en termes de riquesa d’especies que es pugui donar entre els grups floristics i faunistics seleccionats. S’han observat diferencies entre regions pel que fa a la dinamica al llarg del cicle d’inundacio, essent mes marcada als estanys de l’Albera que no pas a les de Lleida, per a tots els grups d’organismes. Quant als patrons de congruencia taxonomica en termes de riquesa d’especies, s’ha observat que la majoria de relacions no es mantenien entre regions. En consequencia, suggerim que el clima pot trencar, a nivell regional, patrons de biodiversitat que es donen a nivell local.