Stable isotope ecology, (delta O-18, delta C-13, delta N-15) of modern land snails along an altitudinal gradient in southern Appalachian Mountains, USA

The first isotopic baseline is established for the snail Neohelix from the Big Santeetlah Creek watershed (Appalachian Mountains). Shell delta O-18 (-3.6 to + 0.4 parts per thousand) declined with altitude 0.06 parts per thousand per 100 m and correlated with measured rain delta O-18. A flux balance model suggests that relative humidity increased from similar to 0.89 at 710 m to similar to 0.91 at 1620 m, in agreement with higher precipitation at higher altitudes. Coherent relationships between shell, precipitation and humidity suggest that this taxon should be a valid paleoprecipitation archive in North America. The respective delta C-13 and delta N-15 values of body (-28.3 to -23.2 parts per thousand; + 0.4 to + 4.9 parts per thousand) and shell organics (-28.2 to -24.0 parts per thousand; + 0.0 to + 3.4 parts per thousand) did not exhibit a trend with altitude and were uncorrelated with potential food resources. A stable isotope-mixing model suggests that Neohelix primarily consume fungi (similar to 48%) and lichen (similar to 17%), with minimal ingestion of C-3 plants. The relative contributions of different food items, however, varied in an unpredictable fashion along the altitudinal gradient. This study illustrates that even though snail foraging ecology from woodlands is complex and more variable than anticipated, combining several isotope systems permits dietary inferences more easily than field observations alone.