More than anything else, snails are sensitive to moisture levels in their immediate environment, since they can’t travel to water sources. The shaded area shows the species range for Mesodon thyroidus, a common large-bodied woodland species (the dots are individual county records). The isopleth map shows the species is restricted to areas with at least 32 inches of annual precipitation (the single outlier in the lower Rio Grande valley a restricted habitat of some sort). This plot uses geography to demonstrate moisture sensitivity, but we can also use this knowledge to trace changes over time instead of space.