The recent rally in the S&P 500 has been led by a small group of tech stocks propelled by enthusiasm about the profit-generating possibilities of artificial intelligence, especially for those at the heart of its development and the production of hardware needed to power it. Nvidia, the chip maker, has come to symbolize this newfound enthusiasm for A.I. because its semiconductors are used in the technology. The company has rallied almost 170 percent this year — gains that have brought its valuation close to $1 trillion.

The average individual stock in the S&P 500 has risen less than 3 percent this year, market data through Friday’s close shows, compared with a gain of over 11 percent for the index as a whole. Some 90 percent of the index’s rise is due to bumper gains for just seven of the biggest companies: Amazon, Apple, Meta, Microsoft, Nvidia, Tesla and Alphabet, the parent company of Google.

Apple rose 2.2 percent by early afternoon on Monday, briefly marking a new high for the company, before sliding to end 0.8 percent lower, weighing on the index.

The S&P 500 also tracks only the largest companies listed in the United States. Smaller companies are generally more exposed to fluctuations in the U.S. economy, because larger firms generate a sizable share of revenue overseas.

The Russell 2000 index, which tracks smaller public companies, has recently recorded more modest gains than its big-company counterpart. The index fell over 30 percent from its peak in November 2021 to its low last June. Since then, the index has risen about 9 percent. On Monday, the index fell 1.3 percent after weaker-than-expected economic data on the services sector.