ISSN: 2639-216X
Authors: Sullivan RM*
Church’s Sideband (Monadenia churchi) is a medium-sized endemic terrestrial snail with a broad geographic distribution. It provides an excellent opportunity to evaluate habitat variance across a diverse geologic, topographic, and ecologic landscape. Herein I document and model variance in macrohabitat characteristics of five riverine-segregated Eco-geographic Units (populations) within the range of the species (Mad and Sacramento rivers, and Northern, South-Central, and Western basins). The most common forest cover-types were Sierra Mixed Conifer (49.6%), Douglas Fir (14.1%), and Montane Hardwoodconifer (8.7%). Statistical comparisons showed significant differences in 93.3% of the cover-types among groups. Principal Components Analysis of macroscale biotic and abiotic ecological variables accounted for 51.7% of the combined variance along both vectors for the species. K-means clustering using Multidimensional Scaling showed good separation of point-samples for the Sacramento River and Western Basin, but there was considerable overlap in point-samples among the remaining groups. All Habitat Suitability Models showed suitable habitat widely distributed throughout the range of M. churchi, but most areas consisted of Low suitability interspersed with few areas of Moderate to High “quality” habitat. For all groups, Generalized Additive Model regression of grid-cell density against macroclimatic co-variates exhibited the best fit compared to models of Forest Structure and Exposure-Distance to Nearest Stream. Dot-plots of variable importance, produced by Random Forest Regression, showed that predictor categories with importance values > 10 were: 1) Macroscale Climate (64.0%, n = 78), followed by Exposure-Distance to Nearest Stream (20.0%), and Forest Stand Structure (16.0%).
Keywords: Generalized Additive Model; Grid-Cell Density; Klamath Bioregion; Predictors; Snail; Terrestrial Gastropods
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