That doesn’t mean that cities are a great substitute for the natural habitats they replace. Generally, only a small number of species (one in 12 birds; one in four plants) survive urbanization in place. This has conservationists worried. The pace of urban growth worldwide is the equivalent of building a city the size of Vancouver each and every week. Between now and 2030, we will urbanize a portion of the globe the size of Mongolia. And because the most successful human settlements tend to occupy fertile and fragile lands — river deltas, estuaries and boundary ecosystems of all kinds — the ecological impact of a city is disproportionate to its size. But then, too, the absence of nature in cities is to be expected. Creating an environment free from the twisting vines, buzzing insects and predatory beasts of the wild is kind of the point.
“Yes, there’s bad news: We’ve lost species,” says Madhu Katti, a professor of ecology at California State University, Fresno, and one of the study’s co-authors. “And yet, these are not national parks we’re talking about; these are concrete cities. And there are still plenty of species.” Singapore — hardly a rugged and untamed metropolis — alone harbors 12 threatened species of birds and 41 threatened species of plants inside the city. On the whole, that’s good news, even if it also places greater pressure on cities to consider their role in the ecosystem.
Not only are cities not ecological steamrollers, they show surprising internal variety. “As the world becomes more global and more homogenous, we’re creating very similar environments worldwide,” notes Frank La Sorte, an ornithologist at Cornell and co-author. “There’s potential to go more and more in that direction as cities become bigger, as population grows. As goods and services are transported around the globe, you’re going to be transporting invasive species as well. [But] right now that doesn’t appear to be the case. It’s certainly less homogenous than we had expected.”