Philonotis species are frequent and often dominant components of many wetland habitats. We modeled ecological optima of the four commonest Philonotis species in three regions of Europe, using measurements of pH, water conductivity, altitude and vegetation gradients. We did not observe obvious differences in ecological optima among three climatically and geographically different regions. Philonotis calcarea was well separated from other species along the water pH and conductivity gradient and occupied the most mineral-rich and alkaline springs in all cases. Philonotis seriata was at the other end of the mineral-richness gradient. The morphologically similar species, P. fontana and P. caespitosa, had very little differentiated niches with respect to water pH and conductivity, which differed slightly among regions. Whereas P. fontana occupied more alkaline and mineral-rich habitats than the rarely occurring P. caespitosa in the West Carpathians, the opposite situation was recorded in Mid-West Europe. In Bulgaria, these two species exhibited practically the same niches with respect to mineral richness. The ecological niche of P. fontana was wider in all regions when compared to P. caespitosa. Altitude represents a discriminating factor only for P. seriata, whereas other species exhibit very wide intervals of response to altitude. We concluded that species with clearly differentiated niches like P. seriata, P. fontana and P. calcarea are accurate indicators of the chemical parameters of spring waters. Alternatively, known water pH and conductivity can support or call into question the reliability of Philonotis determinations. The total species composition of vegetation can also have a certain predictive value for species occurrence.
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Vol. 110 • No. 4