They shook up Wall Street, changing the way the financial industry trades stocks, bonds and derivatives. Now, high-speed traders are in retreat.

These upstart firms use sophisticated computer algorithms to move in and out of stocks, futures and other positions in fractions of a second. Known as high-frequency traders, or HFT, they thrived in the years following the financial crisis by exploiting the markets’ big price swings.

After big Wall Street banks lost business to these more nimble traders, they copied them and began to introduce HFT-style algos and technology on their own expansive trading floors.

But more recently, there have been fewer dramatic swings in stocks, commodities and other markets. The CBOE Volatility Index, a widely followed measure of expected U.S. stock-market volatility, has hovered near historic lows this year.

Now, one electronic trading firm’s deal to acquire a struggling rival shows how this persistently low volatility is upending the HFT world and forcing out weaker players.