If you spend much time out in nature, you know how to recognize the subtle and unsubtle signs of an ecosystem in distress. It could be a forest that’s eerily silent where you should hear birds and insects. It could look like an invasive species run amok: leaping Asian carp in the lower Mississippi River, kudzu devouring the Southeast or blackberry brambles overtaking woods in Oregon. When I visit the North Shore of Lake Superior in Minnesota, a favorite childhood destination, what hits me are the ubiquitous stands of dead and dying birch trees where I remember lush summer greenery. (The story there is complicated: the birches themselves were a non-native arrival a century ago, supplanting pine forests that had been clear-cut.)

All of these things tell a story: Something is out of balance here. Something is not right with this picture.

I do a lot of thinking about the built environment of our cities and towns as a sort of ecosystem in its own right. Our human economy is a complex adaptive system. And like an ecosystem, the whole thing exhibits emergent order, even though individual cause-and-effect chains are dizzyingly complex. It's why we can observe phenomena such as supply and demand dynamics on a large scale, much as an ecologist might look at how predator and prey populations fluctuate. Build too much retail space, for example, and you'll watch rents fall and vacancies rise. Patterns observable in the world give us clues as to the health of the overall system as it tends toward some sort of stable equilibrium.

Here’s the question, though: do we know how to recognize the signs of disruption in our urban habitat, the way we can spot them in a natural one? Or are we so accustomed to living in deeply unnatural, disrupted environments that we take them for granted, the way you might have played as a child in a stream that in your grandparents' day was teeming with salmon, without ever becoming aware of the salmon's absence?

Take, for example, the surroundings we see around train stations in some of America's largest and wealthiest cities—and, by and large, don't blink an eye at.

A Twitter user who goes by @dataandpolitics shared a collection of photos taken at Caltrain commuter rail stations in the affluent southern suburbs of San Francisco. They made the striking observation that at station after station, the immediately adjacent land uses are remarkably low-value. Parking lots. Vacant lots. Strip malls, auto body shops, a range of boxy, mundane, single-story buildings. In some of America's wealthiest ZIP codes, there is a stunning lack of wealth, development, or much of, well, anything interesting at all, visible from most of the stations. Here are some of the photos (reproduced with permission; the original tweet thread has been auto-deleted with age):