Stable isotope ecology (δ18O, δ13C, δ15N) of modern land snails along an altitudinal gradient in southern Appalachian Mountains, USA

Abstract

The first isotopic baseline is established for the snail Neohelix from the Big Santeetlah Creek watershed (Appalachian Mountains). Shell δ18O (−3.6 to +0.4‰) declined with altitude 0.06‰ per 100m and correlated with measured rain δ18O. A flux balance model suggests that relative humidity increased from ~0.89 at 710m to ~0.91 at 1620m, 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 δ13C and δ15N values of body (−28.3 to −23.2‰; +0.4 to +4.9‰) and shell organics (−28.2 to −24.0‰; +0.0 to +3.4‰) 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 (~48%) and lichen (~17%), with minimal ingestion of C3 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.