(Image source: petsmartcharities.org) Shares of PetSmart, Inc. (NASDAQ:PETM) are sinking this morning after the pet supplies retailer lowered its full year earnings outlook as result of disappointing first quarter sales. Same-store sales for the first quarter of 2014 fell 0.6 percent. The full-year earnings outlook was decreased to range of $4.29 to $4.39 a share, compared to the previous forecasted range of $4.42 to $4.54 a share. Management cited a competitive environment and changing consumer demand. The company also lowered its forecast for same-store sales growth. Year-to-day, PetSmart shares are down nearly 15 percent.