Is ecosystem size more important than locality in determining the environmental characteristics of temporary ponds

espanolEl tamano de los sistemas juega un papel clave en el funcionamiento de los mismos, afectando la estabilidad de las comunidades y su estructura, tanto a nivel funcional como taxonomico. Sin embargo poco se conoce de la relacion del tamano del sistema sobre las caracteristicas ambientales. Por ejemplo, ? tienen los ecosistemas de mayor tamano una mayor disponibilidad de nutrientes? Esta relacion es relevante para entender si el efecto del tamano es directo o indirecto. Efectos indirectos se dan si ecosistemas de mayor tamano presentan caracteristicas ambientales distintas a los de menor tamano. En ese caso, las diferencias observadas en el funcionamiento de las comunidades a lo largo del gradiente de tamanos podrian responder, por ejemplo, a distinta disponibilidad de nutrientes, y no unicamente a la diferencia de tamano de los sistemas. En este estudio se analiza si lagunas temporales de distinto tamano tienen distintas caracteristicas ambientales. Sin embargo, las lagunas temporales suelen encontrarse agrupadas, compartiendo unas mismas caracteristicas locales (p.e. la geologia, paisaje, la altitud, microclima, etc.), que pueden tambien afectar a sus caracteristicas ambientales. De ahi que sea necesario considerar el efecto localidad. Este estudio analiza el efecto del tamano y el de la localidad, sobre las caracteristicas ambientales de las lagunas temporales (nutrientes y clorofila-a, biomasa de macrofitos, temperatura del agua, conductividad, pH, oxigeno disuelto, y carbono organico e inorganico total). Para ello, se han considerado 5 sistemas de lagunas temporales. En cada sistema (i.e. localidad) se muestrearon entre 10 y 12 lagunas, seleccionadas para obtener el mayor rango de tamanos posible. Para identificar si las caracteristicas ambientales de las lagunas estudiadas eran representativas de lagunas temporales mediterraneas y si se podian discriminar de las observadas en lagunas temporales fuera de esta region, se ha realizado un meta-analisis (incluyendo 27 grupos de lagunas temporales). Nuestros resultados indican que la localidad es mas determinante que el tamano por lo que a caracteristicas ambientales se refiere. Solo la clorofila-a y la profundidad se relacionaron con el tamano de manera robusta (mostrando la misma relacion independientemente de la localidad). Ademas, algunas de las caracteristicas ambientales de las lagunas temporales se ven mas influenciadas por la tipologia de laguna (es decir, si se encuentran en zonas montanosas, de marisma, o en tierras bajas) que por el hecho de que la laguna se encuentre dentro de la region mediterranea. EnglishEcosystem size plays a key role in determining ecosystem functioning, affecting community stability and structure at both trophic and taxonomic levels. However, less is known about the influence of ecosystem size on environmental characteristics; for example, do larger ecosystems have higher nutrient availability? The nature of this relationship is important for gaining a better understanding of whether the effects of ecosystem size on community functioning are direct or indirect. Indirect effects may exist when the environmental characteristics of larger ecosystems are different from those of smaller ones, and thus the different functioning of communities observed along the ecosystem-size gradient may respond to, for instance, different levels of nutrient availability, and not uniquely to different ecosystem sizes. Here, we tested whether the environmental characteristics (i.e., the physical, chemical and biological characteristics) of temporary ponds of various sizes differed. We chose temporary ponds because they are abiotic controlled systems in which abiotic factors have a strong influence on aquatic communities. However, temporary ponds are usually spatially clustered; consequently, pond locality might also be important in determining the environmental characteristics of a pond (i.e., ponds close to one another may share similar features). We therefore examined whether pond locality is a more important factor than size in determining the environmental characteristics of a pond. To do so, we sampled environmental characteristics (chlorophyll-a, nutrient concentrations, macrophyte biomass, water temperature, conductivity, pH, dissolved oxygen, and total organic and inorganic carbon) of ponds in 5 different localities. A cluster of ponds (10 to 12) was sampled in each locality. Ponds encompassing a wide range of sizes were selected for sampling within each locality. We also performed a meta-analysis (including data from 27 temporary pond localities) to investigate whether the environmental characteristics of the ponds sampled in this study were representative of Mediterranean temporary ponds, and thus if such characteristics could be used to distinguish between Mediterranean temporary ponds from temporary ponds located outside of the Mediterranean region. Our results showed that locality had a strong effect on the environmental characteristics of temporary ponds, whereas size had only a weak influence; only chlorophyll-a and pond depth showed a robust relationship with size, as both increased with pond size independently of locality. Moreover, our results suggest that the typology of the temporary pond (i.e., if they were mountain temporary ponds, salt marsh ponds or lowland ponds) had a larger influence on several environmental characteristics than did regional location (i.e., Mediterranean).