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Biological invasions are of special conservation concern in the Iberian Peninsula and other regions with high levels of endemism. Environmental variability, such as the seasonal fluctuations of Mediterranean streams, is a key factor that affects the spread of aquatic species in novel habitats. Fish parasites have a great potential to reflect such changes in the habitat features of freshwater ecosystems. The aim of this study consisted of seasonally analysing the health status and parasitological traits of non-native fish in Iberian waters. In particular, a strongly invasive population of Languedoc minnow Phoxinus septimaniae (leuciscid species native to south-east France) was assessed in Tordera Stream (north-eastern Iberian Peninsula, Mediterranean conditions). Fish were sampled in April, July, and October 2023 by electrofishing. Health status (external/internal organs) was significantly better in autumn (HAI = 28.8) than spring (HAI = 35.6). Life-cycle complexity was higher in spring (LCI = 1.98), whereas parasite abundance and Shannon diversity were significantly lower in autumn (TA = 19.6 and H’ = 2.15, respectively). In October (more ‘benign’ environmental conditions in Iberian streams), minnows could display elevated foraging activity, with fish increasing their health condition and level of parasite resistance/tolerance. Overall results showed a particular seasonal profile of health and parasite infra-communities that allow this minnow species to thrive under highly fluctuating habitat conditions. This information could help environmental managers to control non-native fish in Mediterranean streams.

A comprehensive review of the natural history of the Mummichog Fundulus heteroclitus in Spain.

BACKGROUND: In the Netherlands, Aedes albopictus has been found each year since 2010 during routine exotic mosquito species surveillance at companies that import used tires. We developed habitat suitability models to investigate the potential risk of establishment and spread of this invasive species at these locations. METHODS: We used two methodologies: first, a species distribution model based on the maximum entropy modelling approach (MaxEnt) taking into consideration updated occurrence data of the species in Europe, and secondly, a spatial logic conditional model based on the temperature requirements of the species and using land surface temperature data (LST model). RESULTS: Suitability assessment obtained with the MaxEnt model at European level accurately reflect the current distribution of the species and these results also depict moderately low values in parts of the Netherlands, Belgium, Denmark, the British islands and southern parts of Scandinavia. Winter temperature was the variable that contributed most to the performance of the model (47.3%). The results of the LST model showed that: (i) coastal areas are suitable for overwintering of eggs; (ii) large areas in the northern part of the country have a low suitability for adult survival; and (iii) the entire country is suitable for successful completion of the life-cycle if the species is introduced after the winter months. Results of the LST model revealed that temperatures in 2012 and 2014 did not limit the overwintering of eggs or survival of adults at the locations where the species was found. By contrast, for the years 2010, 2011 and 2013, overwintering of eggs at these locations is considered unlikely. CONCLUSIONS: Results using two modelling methodologies show differences in predicted habitat suitability values. Based on the results of both models, the climatic conditions could hamper the successful overwintering of eggs of Ae. albopictus and their survival as adults in many areas of the country. H

"This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Ecohydraulics on 24-01-2017, available online: https://www.tandfonline.com/doi/full/10.1080/24705357.2016.1276417", [EN] Competition with invasive species is recognized as having a major impact on biodiversity conservation. The upper part of the Cabriel River (Eastern Iberian Peninsula) harbours the most important population of the Júcar nase (Parachondrostoma arrigonis; Steindachner, 1866), a fish species in imminent danger of extinction. Currently, this species cohabits with several non-native species, such as the Iberian nase (Pseudochondrostoma polylepis; Steindachner, 1864) and the bermejuela (Achondrostoma arcasii; Steindachner, 1866). The potential habitat competition with these species was studied by analysing the spatial and temporal overlapping of suitable microhabitats. Generalized Additive Mixed Models (GAMMs) were developed to model microhabitat selection and these GAMMs were used to assess the habitat suitability (i.e. probability of presence) under several flows simulated with River2D. The Júcar nase will compete, spatially and temporally, for the few suitable microhabitats with bermejuela and, to a lesser extent, with small Iberian nase; conversely, large Iberian nase was of minor concern, due to increased differences in habitat preferences. This study represents an important assessment of potential competition and, therefore, these results might assist to better define future management practices in the upper part of the Cabriel River.

Inconsistent performance of Species Distribution Models (SDMs), which may depend on several factors such as the initial conditions or the applied modelling technique, is one of the greatest challenges in ecological modelling. To overcome this problem, ensemble modelling combines the forecasts of several individual models. A commonly applied ensemble modelling technique is the Multi Layer Perceptron (MLP) Ensemble, which was envisaged in the 1990s. However, despite its potential for ecological modelling, it has received little attention in the development of SDMs for freshwater fish. Although this approach originally included all the developed MLPs, Genetic Algorithms (GA) now allow selection of the optimal subset of MLPs and thus substantial improvement of model performance. In this study, MLP Ensembles were used to develop SDMs for the redfin barbel (Barbus haasi; Mertens, 1925) at two different spatial scales: the micro scale and the meso scale. Finally, the potential of the MLP Ensembles for environmental flow (e flow) assessment was tested by linking model results to hydraulic simulation. MLP Ensembles with a candidate selection based on GA outperformed the optimal single MLP or the ensemble of the whole set of MLPs. The micro scale model complemented previous studies, showing high suitability of relatively deep areas with coarse substrate and corroborating the need for cover and the rheophilic nature of the redfin barbel. The meso scale model highlighted the advantages of using cross scale variables, since elevation (a macro scale variable) was selected in the optimal model. Although the meso scale model also demonstrated that redfin barbel selects deep areas, it partially contradicted the micro scale model because velocity had a clearer positive effect on habitat suitability and redfin barbel showed a preference for fine substrate in the meso scale model. Although the meso scale model suggested an overall higher habitat suitability of the test site, this did n

"This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Ecohydraulics on 24-01-2017, available online: https://www.tandfonline.com/doi/full/10.1080/24705357.2016.1276417", [EN] Competition with invasive species is recognized as having a major impact on biodiversity conservation. The upper part of the Cabriel River (Eastern Iberian Peninsula) harbours the most important population of the Júcar nase (Parachondrostoma arrigonis; Steindachner, 1866), a fish species in imminent danger of extinction. Currently, this species cohabits with several non-native species, such as the Iberian nase (Pseudochondrostoma polylepis; Steindachner, 1864) and the bermejuela (Achondrostoma arcasii; Steindachner, 1866). The potential habitat competition with these species was studied by analysing the spatial and temporal overlapping of suitable microhabitats. Generalized Additive Mixed Models (GAMMs) were developed to model microhabitat selection and these GAMMs were used to assess the habitat suitability (i.e. probability of presence) under several flows simulated with River2D. The Júcar nase will compete, spatially and temporally, for the few suitable microhabitats with bermejuela and, to a lesser extent, with small Iberian nase; conversely, large Iberian nase was of minor concern, due to increased differences in habitat preferences. This study represents an important assessment of potential competition and, therefore, these results might assist to better define future management practices in the upper part of the Cabriel River.

Inconsistent performance of Species Distribution Models (SDMs), which may depend on several factors such as the initial conditions or the applied modelling technique, is one of the greatest challenges in ecological modelling. To overcome this problem, ensemble modelling combines the forecasts of several individual models. A commonly applied ensemble modelling technique is the Multi Layer Perceptron (MLP) Ensemble, which was envisaged in the 1990s. However, despite its potential for ecological modelling, it has received little attention in the development of SDMs for freshwater fish. Although this approach originally included all the developed MLPs, Genetic Algorithms (GA) now allow selection of the optimal subset of MLPs and thus substantial improvement of model performance. In this study, MLP Ensembles were used to develop SDMs for the redfin barbel (Barbus haasi; Mertens, 1925) at two different spatial scales: the micro scale and the meso scale. Finally, the potential of the MLP Ensembles for environmental flow (e flow) assessment was tested by linking model results to hydraulic simulation. MLP Ensembles with a candidate selection based on GA outperformed the optimal single MLP or the ensemble of the whole set of MLPs. The micro scale model complemented previous studies, showing high suitability of relatively deep areas with coarse substrate and corroborating the need for cover and the rheophilic nature of the redfin barbel. The meso scale model highlighted the advantages of using cross scale variables, since elevation (a macro scale variable) was selected in the optimal model. Although the meso scale model also demonstrated that redfin barbel selects deep areas, it partially contradicted the micro scale model because velocity had a clearer positive effect on habitat suitability and redfin barbel showed a preference for fine substrate in the meso scale model. Although the meso scale model suggested an overall higher habitat suitability of the test site, this did n

The impacts of invasive species are recognised as a major threat to global freshwater biodiversity. The risk of invasion (probability of presence) of two avowed invasive species, the northern pike (Esox Lucius, L.) and bleak (Alburnus alburnus, L.), was evaluated in the upper part of the Cabriel River (eastern Iberian Peninsula). Habitat suitability models for these invasive species were developed with Support Vector Machines (SVMs), which were trained with data collected downstream the Contreras dam (the last barrier impeding the invasion of the upper river segment). Although SVMs gained visibility in habitat suitability modelling, they cannot be considered widespread in ecology. Thus, with this technique, there is certain controversy about the necessity of performing variable selection procedures. In this study, the parameters tuning and the variable selection for the SVMs was simultaneously performed with a genetic algorithm and, contradicting previous studies in freshwater ecology, the variable selection proved necessary to achieve almost perfect accuracy. Further, the development of partial dependence plots allowed unveiling the relationship between the selected input variables and the probability of presence. Results revealed the preference of northern pike for large and wide mesohabitats with vegetated shores and abundant prey whereas bleak preferred deep and slightly fast flow mesohabitats with fine substrate. Both species proved able to colonize the upper part of the Cabriel River but the habitat suitability for bleak indicated a slightly higher risk of invasion. Altogether may threaten the endemic species that actually inhabit that stretch, especially the Jucar nase (Parachondrostoma arrigonis; Steindachner), which is one of the most critically endangered Iberian freshwater fish species. (C) 2016 Elsevier B.V. All rights reserved.

The impacts of invasive species are recognised as a major threat to global freshwater biodiversity. The risk of invasion (probability of presence) of two avowed invasive species, the northern pike (Esox Lucius, L.) and bleak (Alburnus alburnus, L.), was evaluated in the upper part of the Cabriel River (eastern Iberian Peninsula). Habitat suitability models for these invasive species were developed with Support Vector Machines (SVMs), which were trained with data collected downstream the Contreras dam (the last barrier impeding the invasion of the upper river segment). Although SVMs gained visibility in habitat suitability modelling, they cannot be considered widespread in ecology. Thus, with this technique, there is certain controversy about the necessity of performing variable selection procedures. In this study, the parameters tuning and the variable selection for the SVMs was simultaneously performed with a genetic algorithm and, contradicting previous studies in freshwater ecology, the variable selection proved necessary to achieve almost perfect accuracy. Further, the development of partial dependence plots allowed unveiling the relationship between the selected input variables and the probability of presence. Results revealed the preference of northern pike for large and wide mesohabitats with vegetated shores and abundant prey whereas bleak preferred deep and slightly fast flow mesohabitats with fine substrate. Both species proved able to colonize the upper part of the Cabriel River but the habitat suitability for bleak indicated a slightly higher risk of invasion. Altogether may threaten the endemic species that actually inhabit that stretch, especially the Jucar nase (Parachondrostoma arrigonis; Steindachner), which is one of the most critically endangered Iberian freshwater fish species. (C) 2016 Elsevier B.V. All rights reserved.

Habitat suitability models (HSM) are concerned with the abundance or distribution of species as a consequence of interactions with the physical environment. Generalized Additive Models (GAMs) were used to model brown trout (Salmo trutta L.) density as a function of environmental variables at the scale of river reach and hydromorphological units (HMU) in the Jucar River Basin (Eastern Spain). After 4years of observations (2003-2006) the data representing trout density were split into two categories, young (<2years) and adult (2years), for modelling independently. The environmental descriptors at reach-scale described the geographical position, hydrological conditions, proportions and diversity of habitats. At the scale of HMUs (pool, glide, riffle or rapid), habitat descriptors representing dimensions, substrate, cover and velocity were used. The best and parsimonious GAM for each category was selected after a comprehensive trial of all possible combinations of input variables. The models explained 61% (adult) and 75% (young) of the variability of the data (R(2)adj). The results demonstrated the relevance of mean width, mean depth, cover index, mean velocity and slope for adult brown trout. Young trout densities were mainly related to maximum depths, cover index, mean velocity, elevation, average distance between rapids and number of slow water HMUs. This article shows the relevance of considering geographical and habitat-related requirements at different scales to describe the patterns of trout density. Furthermore, the importance of considering non-linear relationships with habitat variables was demonstrated. The results are useful for environmental managers to design effective and science-based restoration measures, and result in a more efficient management of brown trout populations.

Habitat suitability models (HSM) are concerned with the abundance or distribution of species as a consequence of interactions with the physical environment. Generalized Additive Models (GAMs) were used to model brown trout (Salmo trutta L.) density as a function of environmental variables at the scale of river reach and hydromorphological units (HMU) in the Jucar River Basin (Eastern Spain). After 4years of observations (2003-2006) the data representing trout density were split into two categories, young (<2years) and adult (2years), for modelling independently. The environmental descriptors at reach-scale described the geographical position, hydrological conditions, proportions and diversity of habitats. At the scale of HMUs (pool, glide, riffle or rapid), habitat descriptors representing dimensions, substrate, cover and velocity were used. The best and parsimonious GAM for each category was selected after a comprehensive trial of all possible combinations of input variables. The models explained 61% (adult) and 75% (young) of the variability of the data (R(2)adj). The results demonstrated the relevance of mean width, mean depth, cover index, mean velocity and slope for adult brown trout. Young trout densities were mainly related to maximum depths, cover index, mean velocity, elevation, average distance between rapids and number of slow water HMUs. This article shows the relevance of considering geographical and habitat-related requirements at different scales to describe the patterns of trout density. Furthermore, the importance of considering non-linear relationships with habitat variables was demonstrated. The results are useful for environmental managers to design effective and science-based restoration measures, and result in a more efficient management of brown trout populations.

The potential of Multilayer Perceptron (MLP) Ensembles to explore the ecology of freshwater fish specieswas tested by applying the technique to redfin barbel (Barbus haasi Mertens, 1925), an endemic and mon-tane species that inhabits the North-East quadrant of the Iberian Peninsula. Two different MLP Ensembleswere developed. The physical habitat model considered only abiotic variables, whereas the biotic modelalso included the density of the accompanying fish species and several invertebrate predictors. The results showed that MLP Ensembles may outperform single MLPs. Moreover, active selection of MLP candidatesto create an optimal subset of MLPs can further improve model performance. The physical habitat modelconfirmed the redfin barbel preference for middle-to-upper river segments whereas the importance ofdepth confirms that redfin barbel prefers pool-type habitats. Although the biotic model showed higheruncertainty, it suggested that redfin barbel, European eel and the considered cyprinid species have similarhabitat requirements. Due to its high predictive performance and its ability to deal with model uncertainty, the MLP Ensemble is a promising tool for ecological modelling or habitat suitability prediction in environmental flow assessment.

En el presente proyecto nos centraremos en calcular qué factores pueden afectar a la abundancia y diversidad de los macroinvertebrados. para ello se han analizado una serie de muestras recogidas en los años 2004 y 2005, siempre en el mes de agosto, y procurando obtener muestras en los mismos puntos en ambos años. La finalidad del análisis ha sido ver que familias habitan en los puntos de muestreo, qué cantidad de ejemplares hay de cada familia por superficie y cual es su biomasa. Una vez finalizado el análisis, se calculó el índice de calidad del agua según la diversidad de especies existente. Con los datos obtenidos, se estudió cómo varían estos valores frente a condiciones hidráulicas en los tramos de estudio. De esta forma se ha intentado ver la influencia de la velocidad de la corriente y la profundidad sobre la densidad y biomasa de macroinvertebados.

The potential of Multilayer Perceptron (MLP) Ensembles to explore the ecology of freshwater fish specieswas tested by applying the technique to redfin barbel (Barbus haasi Mertens, 1925), an endemic and mon-tane species that inhabits the North-East quadrant of the Iberian Peninsula. Two different MLP Ensembleswere developed. The physical habitat model considered only abiotic variables, whereas the biotic modelalso included the density of the accompanying fish species and several invertebrate predictors. The results showed that MLP Ensembles may outperform single MLPs. Moreover, active selection of MLP candidatesto create an optimal subset of MLPs can further improve model performance. The physical habitat modelconfirmed the redfin barbel preference for middle-to-upper river segments whereas the importance ofdepth confirms that redfin barbel prefers pool-type habitats. Although the biotic model showed higheruncertainty, it suggested that redfin barbel, European eel and the considered cyprinid species have similarhabitat requirements. Due to its high predictive performance and its ability to deal with model uncertainty, the MLP Ensemble is a promising tool for ecological modelling or habitat suitability prediction in environmental flow assessment.

This study provides length-weight relationship (LWRs) information for two fish species (family Cyprinidae) in two headwater streams of the Júcar River Basin (Eastern Iberian Peninsula). Both species are endemic to the Iberian Peninsula and have no previous LWR estimates.

En el presente proyecto nos centraremos en calcular qué factores pueden afectar a la abundancia y diversidad de los macroinvertebrados. para ello se han analizado una serie de muestras recogidas en los años 2004 y 2005, siempre en el mes de agosto, y procurando obtener muestras en los mismos puntos en ambos años. La finalidad del análisis ha sido ver que familias habitan en los puntos de muestreo, qué cantidad de ejemplares hay de cada familia por superficie y cual es su biomasa. Una vez finalizado el análisis, se calculó el índice de calidad del agua según la diversidad de especies existente. Con los datos obtenidos, se estudió cómo varían estos valores frente a condiciones hidráulicas en los tramos de estudio. De esta forma se ha intentado ver la influencia de la velocidad de la corriente y la profundidad sobre la densidad y biomasa de macroinvertebados.

The potential of Multilayer Perceptron (MLP) Ensembles to explore the ecology of freshwater fish species was tested by applying the technique to redfin barbel (Barbus haasi Mertens, 1925), an endemic and montane species that inhabits the North-East quadrant of the Iberian Peninsula. Two different MLP Ensembles were developed. The physical habitat model considered only abiotic variables, whereas the biotic model also included the density of the accompanying fish species and several invertebrate predictors. The results showed that MLP Ensembles may outperform single MLPs. Moreover, active selection of MLP candidates to create an optimal subset of MLPs can further improve model performance. The physical habitat model confirmed the redfin barbel preference for middle-to-upper river segments whereas the importance of depth confirms that redfin barbel prefers pool-type habitats. Although the biotic model showed higher uncertainty, it suggested that redfin barbel, European eel and the considered cyprinid species have similar habitat requirements. Due to its high predictive performance and its ability to deal with model uncertainty, the MLP Ensemble is a promising tool for ecological modelling or habitat suitability prediction in environmental flow assessment.

The potential of Multilayer Perceptron (MLP) Ensembles to explore the ecology of freshwater fish species was tested by applying the technique to redfin barbel (Barbus haasi Mertens, 1925), an endemic and montane species that inhabits the North-East quadrant of the Iberian Peninsula. Two different MLP Ensembles were developed. The physical habitat model considered only abiotic variables, whereas the biotic model also included the density of the accompanying fish species and several invertebrate predictors. The results showed that MLP Ensembles may outperform single MLPs. Moreover, active selection of MLP candidates to create an optimal subset of MLPs can further improve model performance. The physical habitat model confirmed the redfin barbel preference for middle-to-upper river segments whereas the importance of depth confirms that redfin barbel prefers pool-type habitats. Although the biotic model showed higher uncertainty, it suggested that redfin barbel, European eel and the considered cyprinid species have similar habitat requirements. Due to its high predictive performance and its ability to deal with model uncertainty, the MLP Ensemble is a promising tool for ecological modelling or habitat suitability prediction in environmental flow assessment.

En el presente proyecto nos centraremos en calcular qué factores pueden afectar a la abundancia y diversidad de los macroinvertebrados. para ello se han analizado una serie de muestras recogidas en los años 2004 y 2005, siempre en el mes de agosto, y procurando obtener muestras en los mismos puntos en ambos años. La finalidad del análisis ha sido ver que familias habitan en los puntos de muestreo, qué cantidad de ejemplares hay de cada familia por superficie y cual es su biomasa. Una vez finalizado el análisis, se calculó el índice de calidad del agua según la diversidad de especies existente. Con los datos obtenidos, se estudió cómo varían estos valores frente a condiciones hidráulicas en los tramos de estudio. De esta forma se ha intentado ver la influencia de la velocidad de la corriente y la profundidad sobre la densidad y biomasa de macroinvertebados.

The richness of native fish is considered to be an indicator of aquatic ecosystem health, and improving richness is a key goal in the management of river ecosystems. An artificial neural network (ANN) model based on field data from 90 sample sites distributed throughout the Júcar River Basin District was developed to predict the native fish species richness (NFSR). The Levenberg-Marquardt learning algorithm was used for model training. When constructing the model, we tried different numbers of neurons (hidden layers), compared different transfer functions, and tried different k values (from 3 to 10) in the k-fold cross-validation method. This process and the final selection of key variables with relevant ecological meaning support the reliability and robustness of the final ANN model. The partial derivatives method was applied to determine the relative importance of input environmental variables. The final ANN model combined variables describing riparian quality, water quality, and physical habitat and helped identify the primary drivers of the NFSR patterns in Mediterranean rivers. In the second part of the study, the model was used to evaluate the effectiveness of two restoration actions in the Júcar River: the removal of two abandoned weirs and the progressive increase in the proportion of riffles. The model indicated that the combination of these actions produced a rise in NFSR, which ultimately reached the maximum values observed in the reference site of that river ecotype (sensu the European Water Framework Directive). The results demonstrate the importance of longitudinal connectivity and riffle proportion for improving NFSR and the power of ANNs to help decisions in the management and ecological restoration of Mediterranean rivers. Furthermore, this model at the basin scale is the first step for further research on the effects of water scarcity and global change on Mediterranean fish communities.

Habitat degradation has reduced the complexity of the Mediterranean streams in Spain and contributed to decreasing the historical range of the endangered Júcar nase, Parachondrostoma arrigonis. This species is endemic to the Júcar River Basin (Spain), and most of its populations live in the Cabriel River, which is divided into two segments by the large Contreras Dam. The main objective of this study was to develop a multivariate habitat suitability model (HSM) for this species that can be used to evaluate environmental flows and water management scenarios for the Cabriel River. We first assessed the fish densities (from 2006 to 2008) and compared the habitat characteristics and variability among eight study sites based on the physical characteristics of hydromorphological units (HMUs) or mesohabitats. The abundance of the Júcar nase then was related to the HMU type, and generalized additive models of fish abundance were developed for the sites for both small and large fish. Both models showed acceptable or good performance (adjusted R 2 of 69.4 for small fish and 72.4 for large fish), and fish abundance was used as an indicator of potential habitat quality ['potential nase habitat' (PNH)] for the Júcar nase. The final step was to apply the HSM to evaluate environmentally friendly flow regimens. Hydraulic simulations were used to estimate the PNH under two flow regimen scenarios and in the actual flow regimen for the regulated study site located below the large dam. This article supports the need for new management actions in the Cabriel River, such as implementation of an environmental flow regimen, and illustrates a procedure for the practical application of habitat selection models at the mesohabitat scale.

Habitat degradation has reduced the complexity of the Mediterranean streams in Spain and contributed to decreasing the historical range of the endangered Júcar nase, Parachondrostoma arrigonis. This species is endemic to the Júcar River Basin (Spain), and most of its populations live in the Cabriel River, which is divided into two segments by the large Contreras Dam. The main objective of this study was to develop a multivariate habitat suitability model (HSM) for this species that can be used to evaluate environmental flows and water management scenarios for the Cabriel River. We first assessed the fish densities (from 2006 to 2008) and compared the habitat characteristics and variability among eight study sites based on the physical characteristics of hydromorphological units (HMUs) or mesohabitats. The abundance of the Júcar nase then was related to the HMU type, and generalized additive models of fish abundance were developed for the sites for both small and large fish. Both models showed acceptable or good performance (adjusted R 2 of 69.4 for small fish and 72.4 for large fish), and fish abundance was used as an indicator of potential habitat quality ['potential nase habitat' (PNH)] for the Júcar nase. The final step was to apply the HSM to evaluate environmentally friendly flow regimens. Hydraulic simulations were used to estimate the PNH under two flow regimen scenarios and in the actual flow regimen for the regulated study site located below the large dam. This article supports the need for new management actions in the Cabriel River, such as implementation of an environmental flow regimen, and illustrates a procedure for the practical application of habitat selection models at the mesohabitat scale.

The richness of native fish is considered to be an indicator of aquatic ecosystem health, and improving richness is a key goal in the management of river ecosystems. An artificial neural network (ANN) model based on field data from 90 sample sites distributed throughout the Júcar River Basin District was developed to predict the native fish species richness (NFSR). The Levenberg-Marquardt learning algorithm was used for model training. When constructing the model, we tried different numbers of neurons (hidden layers), compared different transfer functions, and tried different k values (from 3 to 10) in the k-fold cross-validation method. This process and the final selection of key variables with relevant ecological meaning support the reliability and robustness of the final ANN model. The partial derivatives method was applied to determine the relative importance of input environmental variables. The final ANN model combined variables describing riparian quality, water quality, and physical habitat and helped identify the primary drivers of the NFSR patterns in Mediterranean rivers. In the second part of the study, the model was used to evaluate the effectiveness of two restoration actions in the Júcar River: the removal of two abandoned weirs and the progressive increase in the proportion of riffles. The model indicated that the combination of these actions produced a rise in NFSR, which ultimately reached the maximum values observed in the reference site of that river ecotype (sensu the European Water Framework Directive). The results demonstrate the importance of longitudinal connectivity and riffle proportion for improving NFSR and the power of ANNs to help decisions in the management and ecological restoration of Mediterranean rivers. Furthermore, this model at the basin scale is the first step for further research on the effects of water scarcity and global change on Mediterranean fish communities.

Los estudios acerca de la ecología de los peces tienen como una de sus principales bases la evaluación de las poblaciones, encaminados a definir el conjunto de los individuos de una misma especie que vive en un espacio común. Por lo tanto, el análisis del hábitat es clave para la estructura de las poblaciones. Desde el punto de vista de la teoría jerárquica ecológica, los patrones biológicos que gobiernan a las poblaciones de peces de los ríos son controlados y ajustados por los patrones físicos del hábitat. Así pues, una descripción exacta de los ríos es un primer paso en la descripción de los requerimientos ecológicos de los organismos durante su vida así como en los procesos que influyen en su abundancia y distribución. En este sentido, esta tesis aporta un mayor conocimiento de las poblaciones de trucha común (Salmo trutta) y de sus hábitats en ríos mediterráneos. El estudio se llevó a cabo en cuatro ríos de la Comunidad Valenciana (España) donde hoy en día la especie habita de forma natural; Ebrón y Vallanca (en la provincia de Valencia), Villahermosa y Palancia (en la provincia de Castellón). Los muestreos se realizaron entre los meses de Junio y Agosto entre los años 2003 y 2006. El primer año se establecieron dos estaciones de muestreo en cada río. En los restantes años se amplió a cuatro estaciones de muestreo en cada río. Se destaca el hecho de que en los dos últimos años de estudio (2005 y 2006) hubo una fuerte sequía que hizo que los tramos más altos de los ríos Vallanca y Villahermosa se secaran, perdiéndose tres de las dieciséis estaciones establecidas. En total se muestrearon 50 tramos en los cuatro años de muestreo. Para la caracterización del hábitat se adaptó el protocolo de muestreo "Basinwide Visual Estimation Technique - BVET". Esta técnica consiste en estratificar visualmente el cauce según sus diferentes biotopos (unidades hidromorfológicas o mesohábitats), registrándose en ellos las distintas características hidromorfológicas.

Los estudios acerca de la ecología de los peces tienen como una de sus principales bases la evaluación de las poblaciones, encaminados a definir el conjunto de los individuos de una misma especie que vive en un espacio común. Por lo tanto, el análisis del hábitat es clave para la estructura de las poblaciones. Desde el punto de vista de la teoría jerárquica ecológica, los patrones biológicos que gobiernan a las poblaciones de peces de los ríos son controlados y ajustados por los patrones físicos del hábitat. Así pues, una descripción exacta de los ríos es un primer paso en la descripción de los requerimientos ecológicos de los organismos durante su vida así como en los procesos que influyen en su abundancia y distribución. En este sentido, esta tesis aporta un mayor conocimiento de las poblaciones de trucha común (Salmo trutta) y de sus hábitats en ríos mediterráneos. El estudio se llevó a cabo en cuatro ríos de la Comunidad Valenciana (España) donde hoy en día la especie habita de forma natural; Ebrón y Vallanca (en la provincia de Valencia), Villahermosa y Palancia (en la provincia de Castellón). Los muestreos se realizaron entre los meses de Junio y Agosto entre los años 2003 y 2006. El primer año se establecieron dos estaciones de muestreo en cada río. En los restantes años se amplió a cuatro estaciones de muestreo en cada río. Se destaca el hecho de que en los dos últimos años de estudio (2005 y 2006) hubo una fuerte sequía que hizo que los tramos más altos de los ríos Vallanca y Villahermosa se secaran, perdiéndose tres de las dieciséis estaciones establecidas. En total se muestrearon 50 tramos en los cuatro años de muestreo. Para la caracterización del hábitat se adaptó el protocolo de muestreo "Basinwide Visual Estimation Technique - BVET". Esta técnica consiste en estratificar visualmente el cauce según sus diferentes biotopos (unidades hidromorfológicas o mesohábitats), registrándose en ellos las distintas características hidromorfológicas.

[EN] The hydromorphological units or mesohabitats of the headwaters of four Mediterranean streams were studied by classifying them according to their length, width, average and maximum depth, percentage of substrate and water volume. These characteristics of the streams were assessed over four consecutive years (2003-2006). The main objective of the study was to analyse the spatial and temporal pattern of the physical attributes of the mesohabitats. Classification strength and dendrograms were examined for each stream, mesohabitat type, and combination of stream and mesohabitat type and for stream mesohabitat type and year, whereas Nonmetric Multidimensional Scaling ordination (NMDS) was used to analyse classification patterns. The Villahermosa and Ebr ón streams were more homogeneous than the Palancia and Vallanca streams, whereas riffles and glides were more homogeneous than pools and rapids. The NMDS indicated that the slow water-velocity (pools, glides) and fast (riffles, rapids) mesohabitats tended to group together. Temporally, the Ebr ón stream pools were homogeneous and very stable over the four years, whereas the Vallanca and Villahermosa pools showed a certain degree of variability. The Palancia pools were the most variable and heterogeneous during the study period. These results underscored the importance of separating different types of deep, slow-velocity habitats in mesohabitat inventories and the importance of evaluating habitat classifications in eco-hydromorphological and hydrobiological studies, especially in Mediterranean streams and rivers., [ES] Las unidades hidromorfologicas o mesoh ´ abitats de cuatro r ´ ´ıos mediterraneos de cabecera fueron estudiadas en funci ´ on de su ´ longitud, anchura, profundidad media y maxima, porcentaje de sustrato y volumen de cada mesoh ´ abitat durante cuatro a ´ nos ˜ consecutivos (2003-2006). El objetivo principal fue analizar la variacion espacio-temporal de los diferentes mesoh ´ abitat ´ segun sus atributos f ´ ´ısicos. La fortaleza de la clasificacion y su dendrograma se examin ´ o seg ´ un cada r ´ ´ıo, cada tipo de mesohabitat, una combinaci ´ on de cada r ´ ´ıo y tipos de mesohabitats y seg ´ un cada r ´ ´ıo y tipos de mesohabitats de los cuatro a ´ nos ˜ de muestreo. El Escalado Multidimensional No Metrico (NMDS) se us ´ o para analizar los patrones de las clasificaciones. El ´ NMDS indico que tanto los mesoh ´ abitats lentos (pozas y tablas) como los mesoh ´ abitats r ´ apidos (corrientes y r ´ apidos) tienden ´ a agruparse juntos. Desde la una perspectiva temporal, las pozas del r´ıo Ebron fueron homog ´ eneas y muy estables durante ´ los cuatro anos de muestreo, mientras que las pozas de los r ˜ ´ıos Vallanca y Villahermosa mostraron un cierto grado de variabilidad y las del r´ıo Palancia fueron las mas variables y heterog ´ eneas durante el periodo de estudio. Los resultados ´ destacan la importancia de diferenciar distintos tipos de habitats lentos en los inventarios de mesoh ´ abitat, y la importancia ´ de evaluar las clasificaciones de los mesohabitats en estudios de eco-hidromorfolog ´ ´ıa e hidrobiolog´ıa, especialmente los desarrollados en r´ıos mediterraneos.

[EN] In recent years, fuzzy models have been acknowledged as a suitable approach for species distribution modelling due to their transparency and their ability to incorporate the ecological gradient theory. Specifically, the overlapping class boundaries of a fuzzy model are similar to the transitions between different environmental conditions. However, the need for ecological expert knowledge is an important constraint when applying fuzzy species distribution models. Moreover, the consistency of the ecological preferences of some fish species across different rivers has been widely contested. Recent research has shown that data-driven fuzzy models may solve this `knowledge acquisition bottleneck¿ and this paper is a further contribution. The aim was to analyse the brown trout (Salmo trutta fario L.) habitat preferences based on a data-driven fuzzy modelling technique and to compare the resulting fuzzy models with a commonly applied modelling technique, Random Forests. A heuristic nearest ascent hill-climbing algorithm for fuzzy rule optimisation and Random Forests were applied to analyse the ecological preferences of brown trout in 93 mesohabitats. No significant differences in model performance were observed between the optimal fuzzy model and the Random Forests model and both approaches selected river width, the cover index and flow velocity as the most important variables describing brown trout habitat suitability. Further, the fuzzy model combined ecological relevance with reasonable interpretability, whereas the transparency of the Random Forests model was limited. This paper shows that fuzzy models may be a valid approach for species distribution modelling and that their performance is comparable to that of state-of-the-art modelling techniques like Random Forests. Fuzzy models could therefore be a valuable decision support tool for river managers and enhance communication between stakeholders.

[EN] In recent years, fuzzy models have been acknowledged as a suitable approach for species distribution modelling due to their transparency and their ability to incorporate the ecological gradient theory. Specifically, the overlapping class boundaries of a fuzzy model are similar to the transitions between different environmental conditions. However, the need for ecological expert knowledge is an important constraint when applying fuzzy species distribution models. Moreover, the consistency of the ecological preferences of some fish species across different rivers has been widely contested. Recent research has shown that data-driven fuzzy models may solve this `knowledge acquisition bottleneck¿ and this paper is a further contribution. The aim was to analyse the brown trout (Salmo trutta fario L.) habitat preferences based on a data-driven fuzzy modelling technique and to compare the resulting fuzzy models with a commonly applied modelling technique, Random Forests. A heuristic nearest ascent hill-climbing algorithm for fuzzy rule optimisation and Random Forests were applied to analyse the ecological preferences of brown trout in 93 mesohabitats. No significant differences in model performance were observed between the optimal fuzzy model and the Random Forests model and both approaches selected river width, the cover index and flow velocity as the most important variables describing brown trout habitat suitability. Further, the fuzzy model combined ecological relevance with reasonable interpretability, whereas the transparency of the Random Forests model was limited. This paper shows that fuzzy models may be a valid approach for species distribution modelling and that their performance is comparable to that of state-of-the-art modelling techniques like Random Forests. Fuzzy models could therefore be a valuable decision support tool for river managers and enhance communication between stakeholders.

[EN] In the year 2003, populations of Salmo trutta fario were studied in the Valencian rivers. Habitat conditions were also studied along the successive hydro-morphological units in 300 m long reaches, along with geographic and water-quality variables. With the objective of relating density and biomass with the habitat, all the independent variables were used in a stepwise multiple regression analysis (for common trout density and relative biomass). Through a step-wise analysis, the most significant variables were chosen for each of the two multivariate models, showing all a low correlation coefficient, but with good significance (p < 0.10). The most relevant variables in both models were stream width (negative correlation) and percentage of cobbles (64-256 mm) in each mesohabitat. The water surface area, and mean and maximum depth did not appear in the final model, but their correlation with stream width was demonstrated. All these variables were included within the mesohabitat characteristics, having being discarded the rest that were not significant at the scale of the study., [ES] En el año 2003 se estudiaron las poblaciones autóctonas de Salmo trutta fario en los ríos valencianos. Por otro lado se midieron las condiciones del hábitat según las sucesivas unidades hidro-morfológicas en tramos de 300 m de longitud, junto con variables geográficas y de calidad del agua. Con el objeto de relacionar densidades y biomasas con el hábitat, todas las variables independientes fueron introducidas en modelos de regresión múltiple (para la densidad y la biomasa relativa de trucha común). Mediante análisis paso a paso eliminatorio quedaron seleccionadas las más significativas para cada uno de los dos modelos multivariantes, obteniéndose en todos un bajo coeficiente de correlación pero con una significación adecuada ( p < 0.10). Las variables establecidas en los dos modelos fueron la anchura del cauce (con signo negativo) y el porcentaje de cantos rodados (64-256 mm) en cada mesohábitat. La superficie, así como la profundidad media y máxima no aparecieron en el modelo final, pero se demostró su correlación con la anchura del cauce. Todas estas variables estaban englobadas dentro del grupo de características del mesohábitat, habiéndose descartado las demás que no fueron significativas a la escala del estudio.