A scientist is studying a species of gopher found in North America.  Population X lives in an area with hard packed soil, Population Y lives in an area with loose soil, and Population Z lives in an area with both hard and loose soil.   The gophers use their claws to dig through the soil and make burrows (homes).  There is variation in the claw structure of gophers, and claw structure is a heritable trait.  Based on this information, which of the following statement correctly pairs the likely effect of natural selection on the phenotype distribution in each population?