Published: Urban socioeconomic inequality and biodiversity often converge, but not always

I remember when the idea of biodiversity inequality first took root in my brain. It all started with an entomology (study of insects) course at Boston University and our numerous field trips around the city looking for multi-legged critters. It is not surprising that insect diversity is unevenly distributed across a city, or any ecosystem for that matter, but the perniciously fascinating part of why is less obvious. Different insects require different habitat resources and will be more or less successful depending on the type of vegetation in an area, or the number of hungry birds, or how many places there are to hide, etc.

In cities throughout the world, researchers have sought to understand the relationship between animal and plant species diversity (“biodiversity”) and other measurable factors, such as how green a neighborhood might be, its housing density, or its median household income. One dominant trend is that wealthier areas often support greater biodiversity compared to poorer areas. There is even a name for this pattern, “The Luxury Effect,” which suggests that high socioeconomic status (“SES” – in the form of wealth or political power, for example) buys resources such as land, time, and labor, which can be used to increase local biodiversity.

From Fig. 4 in Kinzig et al. (2005), showing the relationship between species richness and median neighborhood income for birds in neighborhoods in Phoenix, Arizona.

During my Masters degree at UMass Amherst, I became involved in a project with my advisor Paige Warren and a working group of ecologists and sociologists. Our mission: systematically assess every published research paper about urban biodiversity and SES to see what lessons could be learned. Indeed, although the Luxury Effect seemed to be a common pattern, there were plenty of counter examples. What was going on?

As part of the UrBioNet Social-ecological Linkages working group, we found 84 case studies from 34 cities in which researchers assessed SES-biodiversity relationships. We used fuzzy-set Qualitative Comparative Analysis (fsQCA) to evaluate combinations of factors that might explain why these relationships varied city to city.

Fig. 3 from our paper: locations of the 34 case cities included in the meta-analysis.

While most cases showed the basic Luxury Effect pattern, we identified circumstances where other combinations of forces were at play, such as housing density gradients, human disturbance, and greenspace management practices.

Here’s what matters: the Luxury Effect is not a universal truth about how cities work. And that’s good news considering that for many other features of the urban environment, wealth is generally linked with the amenities (e.g., cleaner air, more trees, more parks) while poverty is linked with the hazards (e.g., hotter streets, polluted air, animal pests). While biodiversity often falls in line with this pattern, it doesn’t always, and by focusing on the exceptions, we can find paths forward to ensure that everyone in the city has access to biodiversity.

I’m happy to see our paper out in the world, published in the Journal of Landscape and Urban Planning. Download it here!

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