Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect natural resources and commodities businesses to thrive, the SPDR S&P Global Natural Resources (NYSE: GNR) ETF could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in several dozen of them simultaneously. In one investment, you'll get oil, gold, copper, fertilizer, grains, steel, and more.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The natural resources ETF's expense ratio -- its annual fee -- is a fairly low 0.40%.

This ETF doesn't have much of a track record yet, as it's not even a year old. Year-to-date, it's underperforming the S&P 500, but such a short time frame is close to meaningless. As with most investments, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

What's in it?
Several of this ETF's component stocks have likely made strong contributions to its performance. PotashCorp (NYSE: POT), the world's largest fertilizer company, gained 61% and should profit in the long run as world demand for food rises along with population growth. Freeport McMoRan Copper & Gold (NYSE: FCX) gained 51%, and is still on fire, recently blowing away earnings estimates and declaring a supplemental cash dividend.

Other companies likely haven't added as much to the ETF's returns, but could have an effect in the years to come. Seed giant Monsanto (NYSE: MON) gained 13%, having struggled in recent years. It has its detractors (because of its genetically modified seeds, for example), but as our planet's growing population demands more food, it is likely to prosper. Brazil's Vale (NYSE: VALE), up 17%, is the world's second-largest mining company after BHP Billiton (NYSE: BHP), the largest of the ETF's holdings. As the global economic recovery gains steam, demand for building materials will consume a lot of iron ore from these companies.

The big picture
Demand for natural resources and commodities isn't going away anytime soon. A well-chosen ETF can grant you instant diversification across these companies -- and make investing in and profiting from the sectors that much easier.

ETFs can help you find the way to better investing results. To find some great ETF investing ideas, take a look at The Motley Fool's special free report " 3 ETFs Set to Soar During the Recovery ."