McEVERS: In the 1960s, Midwestern farmers began focusing on single commodities, like pigs.

NPR: Family Farms Lose Out on Upswing of Pork Exports

The firm described a picture in which there were outflows from the broadly diversified ETPs but inflows into ETPs that track certain single commodities, such as gold, silver, oil and natural gas.

FORBES: ETF Securities: Precious-Metals ETPs Attract Money Inflows In 2Q; Overall Commodity ETP Market Declines