A few years ago, Adalberto Martín began to see some troubling changes at work. As a veteran member of the room service staff at Marriott’s W Hotel in downtown San Francisco, he was an expert in delivering carefully assembled trays of food and drink to hungry guests. But the number of orders had sharply decreased. What was once 50 glasses of orange juice every morning had dwindled to 10, and Mr. Martín’s tip income fell accordingly. At lunchtime, he seemed to make more deliveries of plates and silverware than actual food.

Room service, as we imagine it in the movies, with white tablecloths and silver cloches, has long been in decline, even at the fanciest hotels. But Mr. Martín attributes his loss of earnings to the proliferation of food delivery apps such as Uber Eats, DoorDash and Postmates, successors of online ordering services like Seamless. Now he wonders if soon he’ll be out of a job altogether. “We’re always worrying and concerned when we see other hotels nearby closing room service,” Mr. Martín told me. “It’s just a matter of time.”

His co-workers at the W and staff members at other hotels report similar trends: The doormen and bellmen who once summoned cabs for guests, and were tipped in return, now watch lines of Ubers and Lyfts coil in front of the lobby doors, while concierges have had their work outsourced to iPad consoles. Some hotels offer tablets in every room preloaded with food-delivery apps, and give guests vouchers for Uber and Lyft rides. In the microcosm of the hotel, the app economy has expanded choices for some (the guests) and shrunk options for others (the workers).

These currents in hospitality represent a subtle, sneaky form of technological displacement, care of the gig economy. They’re not robots stepping in for humans on a factory floor, but rather smartphone-based independent contractors and supplemental “cobots” (a portmanteau of “co-worker” and “robot”) chipping away at the careers of full-time and in some cases unionized employees.