When urban beekeeping gets too dense

Bees need a certain amount of nearby green space in order to find enough pollen to survive. Without that, bees can starve. They can also end up subsisting on a diet of syrup that's about as healthy for them as a diet of burgers and fries would be for you and I. London has had die-offs of bees in the past, when beekeeping got more popular than the city's limited green space could support. Some people are now worried that New York City could be headed toward that problem.