Geology constrains biomineralization expression and functional trait distribution in the Mountainsnails (Oreohelix)

Aim: Geographic variation in metabolic resources necessary for functional trait expression can set limits on species distributions. For species that need to produce and maintain biomineralized traits for survival, spatial variation in mineral macronutrients may constrain species’ distributions by limiting the expression of biomineralized traits. Here, we examine whether threatened, heavily biomineralized Oreohelix land snails are restricted to CaCO3 rock regions, if they incorporate greater amounts of CaCO3 rock carbon in their shell than less biomineralized smooth forms, and if ornamentation increases shell strength.
Location: Western United States
Methods: We used random forest (RF) classification models at multiple spatial resolutions to evaluate the contribution of topographic, vegetation, climate, and geologic variables in predicting the presence of heavily biomineralized shell ornaments. We then measured and compared shell biometric variables, 14C/12C ratios, and peak force for fr..., RF predictors:
Predictor Dataset Creation
The predictors used in this study came from a variety of sources (Supplementary Table A1). In this section, we will detail how they were made to facilitate replication of our results. All predictors were reprojected in ArcGIS Pro v.2.6.0 to WGS1984 and clipped to the same raster resolution. Predictor names used in the R code are shown in parentheses. See Supplemental Table A1 for references.

Elevation (elevation): This layer was sourced from the publicly available ASTER Global Digital Elevation data reprojected to 90m resolution using the Project tool and clipped to the desired extent using the Clip Raster tool.

Slope (slope): This layer was created using the Slope tool in ArcGIS on the 90m elevation data using a z-factor of 0.00001171 appropriate for 40 degrees latitude (https://pro.arcgis.com/en/pro-app/latest/tool-reference/3d-analyst/applying-a-z-factor.htm) which is close to the mean latitude of our study area.

Compound topographic inde..., ArcGIS Pro/QGIS to modify layers
R for scripts