When Amazon.com Inc. announced it was rolling out its popular Prime delivery subscription service in Brazil last month, shares of  local e-commerce competitors tanked. Investors also got jittery in 2017, when the world’s largest online retailer launched a marketplace to sell electronics. In both cases, the shares recovered quickly once investors reminded themselves of a durable truth about Brazilian e-commerce: Local firms have a firm grip on the market and are in little danger of succumbing to the American interloper.

When Amazon.com Inc. announced it was rolling out its popular Prime delivery subscription service in Brazil last month, shares of  local e-commerce competitors tanked. Investors also got jittery in 2017, when the world’s largest online retailer launched a marketplace to sell electronics. In both cases, the shares recovered quickly once investors reminded themselves of a durable truth about Brazilian e-commerce: Local firms have a firm grip on the market and are in little danger of succumbing to the American interloper.