Limnetica 35

Ecosystem 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).