Rachel Abrams and Robert Gebeloff:

A quarter-century ago, there were 56 teenagers in the labor force for every “limited service” restaurant — that is, the kind where you order at the counter.

Today, there are fewer than half as many, which is a reflection both of teenagers’ decreasing work force participation and of the explosive growth in restaurants.

But in an industry where cheap labor is an essential component in providing inexpensive food, a shortage of workers is changing the equation upon which fast-food places have long relied. This can be seen in rising wages, in a growth of incentives, and in the sometimes odd situations that business owners find themselves in.

This is why Jeffrey Kaplow, for example, spends a lot of time working behind the counter in his Subway restaurant in Lower Manhattan. It’s not what he pictured himself doing, but he simply doesn’t have enough employees.

Mr. Kaplow has tried everything he can think of to find workers, placing Craigslist ads, asking other franchisees for referrals, seeking to hire people from Subways that have closed.