LONDON — Ample capacity from traditional and nontraditional sources plus changes in buying habits are resulting in a challenging environment for global reinsurers, Standard & Poor’s Corp. said Tuesday in a report.

But sound risk management and defensive moves such as mergers and acquisitions mean few changes are likely to reinsurers’ ratings in the coming year, said Dennis Sugrue, director and reinsurance sector specialist for the Europe, Middle East and Africa region at S&P in London.

Reinsurance buyers are looking to buy less reinsurance from fewer reinsurers, a trend that is spreading from larger cedents to midsize buyers, Mr. Sugrue said.

Reinsurance rates likely will continue to fall, though at a slower pace than 2014, Mr. Sugrue said Tuesday during a London briefing on the global reinsurance industry ahead of the Monte Carlo, Monaco, reinsurance Rendez-Vous de Septembre gathering next week where reinsurers, cedents and brokers meet to discuss the upcoming renewals.

Average rates for reinsurance business likely will fall up to 5% at the Jan. 1, 2016, renewals, with more pronounced rate declines for property catastrophe business, he said.

Reinsurers likely will be less able to rely on reserve releases to boost profits nor on investment returns with only modest interest rate increases expected, Mr. Sugrue said, though catastrophe losses have been benign.

Excluding catastrophe losses and reserve releases, most global reinsurers will post combined ratios between 95% and 100% for 2015, S&P said.

Most M&A activity in the sector is defensive, and there likely will be more before year-end, driven by a need for scale and diversification to meet the current challenges, Mr. Sugrue said.

Reinsurers can take advantage of reductions in catastrophe rates by buying more retrocessional coverage, he said. Several reinsurers also are increasing their proportional or primary underwriting; writing less excess-of-loss coverage; and diversifying away from property business into lines such as U.S. casualty, crop reinsurance and mortgage insurance business, he said.