The Land Snails and Slugs of Tennessee, USA: Taxonomic Composition, Distribution, and an Evaluation of State-Wide Spatial and Taxonomic Survey Biases

Abstract

The increased availability of publicly available, digitally accessioned biodiversity data and scientific literature presents the opportunity to reassess geographical associations of understudied taxonomic groups. Using these resources, in addition to occurrence data managed by the National Park Service at the Great Smoky Mountains National Park and private collections, we have assembled an updated taxonomic checklist and robust geographic dataset of all records of terrestrial gastropods (land snails and slugs) within the state of Tennessee. Additionally, we quantified spatial and taxonomic biases in survey coverage and overall survey quality for terrestrial gastropods at two spatial resolutions: ecoregion and county. Our state checklist includes 301 species of terrestrial gastropods that have at least one occurrence record, which increases the number of species by 40 from previous assessments of terrestrial gastropod biodiversity in Tennessee. Spatial analyses revealed < 33% of ecoregions and < 18% of counties to be sufficiently sampled for any terrestrial gastropod group as inferred by accumulation curves and the ratio between number of records to number of genera within each spatial unit. Significant biases in survey coverage in the state were revealed at both spatial scales, and a disproportionate number of occurrence records were found in the eastern portion of the state near urban centers, universities, and the Great Smoky Mountains National Park. Taxonomic diversity estimates were similarly biased. Moreover, larger snails comprise the vast majority of occurrence records compared to snails less than 5 mm in shell diameter and slugs. From a conservation perspective, the addition of many newly reported species requires updating status assessments, and the spatial and taxonomic bias reported here should act as an incentive for future targeted gastropod survey effort, particularly in western Tennessee.