We developed a species-by-species approach for selecting protected areas for conservation of native freshwater fishes in semiarid regions, with catchment as the fundamental landscape unit for conservation efforts. Input data were composed of occurrences of freshwater fishes and landscape variables, and general quantification of occurrence, abundance, and endemicity of each fish species, to derive an index of conservation value for each species. Probability of occurrence of each species was performed with logistic-regression analysis based on the landscape variables and extrapolated to the entire study area with a geographic information system. We estimated the conservation value of a stream reach by summing the predicted probability of occurrence of each species multiplied by its corresponding conservation value. To define and select reserves, we used a threshold that maximizes conservation value of the stream reaches but identifies the minimum number of reaches for protection. The approach was applied to native freshwater fishes in the Guadiana River basin (southern Iberian Peninsula), which are threatened by the construction of two major dams. We used the data from 1 sampling year (1999) to produce the models, which were validated based on data collected in 2000 and 2001. We used variables of climate (3), geomorphology (4), hydrology (7), and human influence (6) to build the predictive models, which revealed that native species occur over a wide range of riverine habitats, with stream order and location in the basin the most frequently selected variables. The conservation value of species varied considerably, with Anaecypris hispanica the highest-ranked species. The catchments selected for reserves were the mainstream of the Guadiana River (upstream and downstream of the Alqueva and Pedrogão reservoirs) and the Degebe, Ardila, and Enxoé catchments. Our approach is a pragmatic way to address the urgent need to protect Guadiana native fish species in light of the ongoing anthropogenic degradation of aquatic environments.Selección deÁreas Prioritarias para la Conservación de Peces en la cuenca del Río Guadiana, Península Ibérica Resumen: Desarrollamos un método especie-específico para seleccionaráreas protegidas para la conservación de peces nativos de agua dulce en regiones semiáridas, con la subcuenca como unidad paisajística fundamental para los esfuerzos de conservación. Los datos de entrada fueron las ocurrencias de peces de agua dulce y las variables de paisaje, una cuantificación general de la ocurrencia, abundancia y endemicidad de cada especie piscícola para obtener uníndice del valor de conservación para cada especie. La probabilidad de ocurrencia de cada especie se obtuvo con análisis de regresión logística basado en las variables del paisaje y extrapolado a toda elárea de estudio con un sistema de información geográfica. Estimamos el valor de conservación de un tramo sumando la probabilidad de ocurrencia de cada especie multiplicado por su valor de conservación correspondiente. Para definir y seleccio...

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Samples of the Squalius alburnoides complex, a hybridogenetic Iberian minnow composed of diploid, triploid and, less commonly, tetraploid forms, were collected from a tributary of the Ardila River (Guadiana River basin) between February 1999 and January 2001. Seasonal variation in diet was evident, and was probably linked to prey availability. Distinct foraging behaviours between ploidy forms were found towards several prey items, suggesting that diploid adult males fed mostly near the surface, whereas diploid adult females tended to feed near the bottom and submerged vegetation. Triploid females exhibited an intermediate foraging behaviour, although there was greater affinity towards diploid male feeding behaviour. Diploid males which, in contrast to diploid and triploid females, have non-hybrid genomes in the Guadiana drainage, exhibited a higher specialization for food. Despite considerable dietary overlap, there appeared to be spatial segregation of feeding niches between the three forms, especially during dry periods when prey availability was lower, which may be a strategy for diminishing competition for food. Therefore, considering asexual generalist and specialist hypotheses, it appears that the different ploidy levels are generalist, opportunistic feeders that partition the resources when limited. # 2005 The Fisheries Society of the British Isles