Inventariant els instruments científics de l'institut Jaume Vicens Vives de Girona

This paper presents the first results from the inventory of scientific instruments of Institut Jaume Vicens Vives of Girona. It consists of a sparse collection that has been subjected to several historical changes that affected both its integrity and state of conservatio

Llacunes de nova creació

Oasis d'optimisme enmig de la degradaci&oacute

Energy limitation or sensitive predators? Trophic and non-trophic impacts of wastewater pollution on stream food webs

Impacts of environmental stressors on food webs are often difficult to predict because trophic levels can respond in divergent ways, and biotic interactions may dampen or amplify responses. Here we studied food-web-level impacts of urban wastewater pollution, a widespread source of degradation that can alter stream food webs via top-down and bottom-up processes. Wastewater may (1) subsidize primary producers by decreasing nutrient limitation, inducing a wide-bottomed trophic pyramid. However, (2) wastewater may also reduce the quality and diversity of resources, which could decrease energy transfer efficiency by reducing consumer fitness, leading to predator starvation. Additionally, (3) if higher trophic levels are particularly sensitive to pollution, primary consumers could be released from predation pressure. We tested these hypotheses in 10 pairs of stream sites located upstream and downstream of urban wastewater effluents with different pollutant levels. We found that wastewater pollution reduced predator richness by ∼34%. Community size spectra (CSS) slopes were steeper downstream than upstream of wastewater effluents in all except one impact site where predators became locally extinct. Further, variation in downstream CSS slopes were correlated with pollution loads: the more polluted the stream, the steeper the CSS. We estimate that wastewater pollution decreased energy transfer efficiencies to primary consumers by ∼70%, limiting energy supply to predators. Additionally, traits increasing vulnerability to chemical pollution were overrepresented among predators, which presented compressed trophic niches (δ15 N-δ13 C) downstream of effluents. Our results show that wastewater pollution can impact stream food webs via a combination of energy limitation to consumers and extirpation of pollution-sensitive top predators. Understanding the indirect (biotically mediated) vs. direct (abiotic) mechanisms controlling responses to stress may help anticipating impacts of altered water quantity and quality, key signatures of global change

Dam regulation and riverine food-web sructure in a Mediterraenan river

Flow regimes are a major driver of community composition and structure in riverine ecosystems, and flow regulation by dams often induces artificially-stable flow regimes downstream. This represents a major source of hydrological alteration, particularly in regions where biota is adapted to strong seasonal and interannual flow variability. We hypothesized that dam-induced hydrological stability should increase the availability of autochthonous resources at the base of the food web. This, in turn, should favour herbivorous over detritivorous strategies, increasing the diversity of primary consumers, and the food-web width and length. We tested this hypothesis by studying the longitudinal variation in food-web structure in a highly-seasonal Mediterranean river affected by an irrigation dam. We compared an unregulated reach to several reaches downstream of the dam. Hydrological and sedimentological stability increased downstream of the dam, and altered the type and quantity of available resources downstream, prompting a change from a detritus-based to an algae-based food web. The fraction of links between top and intermediate species also increased, and the food web became longer and wider at the intermediate trophic levels. Food-web structure did not recover 14 km downstream of the dam, despite a partial restitution of the flow regime. Our results advance the notion that hydrologic alteration affects riverine food webs via additions/deletions of taxa and variation in the strength and distribution of food-web interactions. Thus, flow regulation by dams may not only impact individual facets of biodiversity, but also food-web level properties across river networks

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 comparació de les comunitats biològiques dels estanys i les basses temporànies de dues àrees de clima diferenciat, al massís de l’Albera (Alt Empordà) i als secans de Lleida (Segrià). L’objectiu del treball ha estat identificar les variables ambientals que determinen la composició d’aquestes comunitats, com la biodiversitat, la dinàmica temporal i la congruència taxonòmica en termes de riquesa d’espècies que es pugui donar entre els grups florístics i faunístics seleccionats. S’han observat diferències entre regions pel que fa a la dinàmica al llarg del cicle d’inundació, essent més marcada als estanys de l’Albera que no pas a les de Lleida, per a tots els grups d’organismes. Quant als patrons de congruència taxonòmica en termes de riquesa d’espècies, s’ha observat que la majoria de relacions no es mantenien entre regions. En conseqüència, suggerim que el clima pot trencar, a nivell regional, patrons de biodiversitat que es donen a nivell local.In this study we have compared the biological communities inhabiting seasonal pools in two different areas in Catalonia: the Albera mountain range and the Lleida steppes. We aimed at identifying the environmental variables that determine community composition in those habitats, as well as at describing the biodiversity attributes, the dynamics throughout the hydroperiod, and eventual relationships among taxonomic groups in terms of species richness. We observed interregional differences in community dynamics, with higher change between subsequent visits being observed in Albera rather than in Lleida seasonal pools, a pattern consistent across all the study groups. Regarding species richness patterns, we observed that most of the relationships across taxonomic groups did not hold when considering both regions. Therefore, we suggest climate may break, at a regional level, eventual biodiversity patterns existing at the local scale

Flow regulation increases food-chain length through omnivory mechanisms in a Mediterranean river network

[EN] Dams fragment river systems worldwide, and Mediterranean-climate rivers, characterised by highly seasonal hydrographs and adapted biotas, are particularly impacted by flow regulation. Whereas the effects of flow regulation on hydrology, sediment transport and biodiversity have long been examined, responses at the food-web level remain understudied. Environmental variation is a key control of food-web structure. Thus, we predicted that flow regulation would impact food-chain length (FCL) via changes in the flow variation regime, and we tested this prediction in a set of flow unregulated to completely regulated reaches in a Mediterranean river basin. In each reach, we characterised flow variation, together with two other putative controls of FCL (productivity and habitat size). We combined community data with carbon and nitrogen stable isotopes to estimate food-chain length, and Bayesian mixing models allowed estimates of dietary proportions of consumers. Flow variation was paramount in controlling FCL in the studied river network, and this same control largely explained the degree of omnivory among top predators. Thus, omnivory mechanisms were the main proximate structural mechanism allowing shifts in food-web structure and linking disturbance regimes to FCL. Our results suggest that flow regulation in Mediterranean rivers may impact food-web structure even when no significant changes in community composition are observed. If highly variable Mediterranean streams become increasingly affected by flow regulation, the resulting more stable conditions could enhance intraguild predation and thus lengthen riverine food chains.We thank Roberto Merciai, Jose Andres Lopez and Joan Font for their help in the field, Lina Ramirez-Solano and Emili Garcia-Berthou for their help with analyses and Marc Montenegro for the illustrations in Fig. 1. The Sabo Lab at Arizona State University and anonymous reviewers provided suggestions that improved the quality of the article. This study was funded by the Spanish Ministry of Economy and Competitiveness through the SCARCE project (CSD2009-00065). Authors acknowledge the support from the Catalan Government through the Consolidated Research Groups 'Fluvial Dynamics Research Group (2014 SGR 645)' and the 'Catalan Institute for Water Research (2014 SGR 291)'.Ruhí, A.; Muñoz, I.; Tornés, E.; Batalla, R.; Vericat, D.; Ponsati, L.; Acuña, V.... (2016). Flow regulation increases food-chain length through omnivory mechanisms in a Mediterranean river network. Freshwater Biology. 61(9):1536-1549. https://doi.org/10.1111/fwb.12794S1536154961