LAUSR

Spring ecosystems are exceptionally threatened and their conservation is often emphasized due to high levels of endemism among the groups inhabiting these ecosystems. This study includes gastropod assemblages of 36 springs situated in the northwestern part of Bosnia and Herzegovina. The aims of this paper were: to determine key factors for distribution of gastropod species on microspatial scale; to define the environmental preferences of gastropod species with respect to the physicochemical properties of water, the hydrological characteristics and the sediment structure; to determine species tolerance ranges and species optimums, with special emphasis on new and endemic species. Moreover the aim was to identify the species with highest extinction risk. The contribution of endangered and rare species to the total density was extremely high (64.6%). Species Response Curves were used to predict the distribution of gastropod species along the environmental gradient in the spring environments for the first time. The most important factors in structuring gastropod spring assemblages were oxygen and temperature. HOF (Huisman–Olff–Fresco) models may determine differences in range of environmental tolerance of species with similar ecological requirements. Our results have shown that two species: Ancylus fluviatilis and A. recurvus may be distinguished by their species response curves. Although there are no data on conservation status of A. recurvus , the extinction risk should be inferred as high, suggesting that IUCN status for this species should be updated to the category Vulnerable. Our study using HOF models revealed the potential gastropod species useful as indicators of karstic springs.