Does narrow niche space in a 'cold-stenothermic' spring snail indicate high vulnerability to environmental change?

Niche breadth has fundamental ecological implications. Specialists with a narrow niche space are able to survive under specific conditions only, making them potentially sensitive to effects of environmental change. We here investigate (1) the factors restricting the specialized spring snail Bythinella dunkeri to its specific habitat, and (2) its capacity for plasticity to respond to changing environmental conditions, based on a combination of field work and laboratory experiments. By comparing occupied and unoccupied sites, we revealed that snail presence was most strongly affected by distance to the crop-out, water depth, pH value, and redox potential. In contrast, spring temperatures did not affect the occurrence of this 'stenothermic' snail, and laboratory experiments documented a high tolerance toward both high and fluctuating temperatures. However, B. dunkeri was found to be very sensitive to desiccation, such that changes in precipitation regimes may easily harm populations. The species investigated here may therefore indeed be sensitive to environmental change, but not because of limited thermal tolerance which initially seemed to be the most obvious reason. [ABSTRACT FROM AUTHOR]