Click to enlarge. Note the shrinking black bar that represents first-time buyers.
FORTUNE — Bernstein’s Toni Sacconaghi produced the chart above for a report out Monday that raises what is, for Apple (AAPL), an existential question:
Are There Enough Wealthy People in the World to Sustain iPhone Unit Growth?
Note that the black bars in the chart that represent first-time buyers are shrinking.
Sacconaghi’s conclusion: Barring a signed contract with China Mobile (CHL) or an iPhone priced to sell to the developing world, there is, he writes, “a slim margin of error that Apple will attract sufficient first-time iPhone buyers going forward to meet consensus forecasts for FY14 and FY15.”