The luxury effect: why you’ll find more wildlife in wealthy areas – and what it means for your health | Biodiversity

FFor a long time, ecology has tended to ignore humans. He mainly focused on beautiful places far from large-scale human development: deep rainforests or pristine grasslands. Then, in the late 1990s, in the desert city of Phoenix, Arizona, scientists looked closer to home.

A team of ecologists traveled to their own neighborhood to map the distribution of urban plants in one of the first studies of its kind. Equipped with tape measures and clipboards, they documented the trees and shrubs, sometimes getting on all fours to crawl through the bushes as locals looked on curiously.

“We had a lot of fun. The little kids loved our measuring wheel,” says Professor Ann Kinzig of Arizona State University. “It made me look at cities differently.”

Existing ecological theories did not explain the distribution of plants in cities. In wild areas, plants are usually arranged based on factors such as geography and weather conditions: the rockiness of the soil, the level of precipitation, exposure to light and shade.

Scientists wondered whether a new theory was needed. “And the answer was: We did it,” Kinzig says.

The urban data told them the same thing: The most significant impact on plant distribution was not altitude, proximity to bodies of water, proximity to rural areas, or soil type. It was the wealth of the people living nearby. In 2003, his team published the first article on the “luxury effect”.

The phenomenon describes how wealthy areas of cities are home to more wildlife and greater wildlife diversity – a finding that may have profound implications for human health and well-being. In Phoenix, researchers wondered whether heat was to blame. It is a desert environment where water is scarce and temperatures can be punishing.

When the wealth of a Phoenix area increased, people typically planted more vegetation and kept it watered. A $10,000 (£7,500) increase in median household income at the Phoenix study site resulted in a 0.3°C (0.54°F) decrease in average surface temperature.

But since the first studies in Phoenix, researchers have observed the luxury effect in other cities with different species, and where heat was less crucial. In British Columbia, white-tailed deer frequented wealthier city neighborhoods with more gardens, golf courses and parks, according to a 2023 study.

The luxury effect has been noted in plants in North America, Burundi, China and Australia. It has also been documented in birds from North America, Europe and New Zealand. Birds depend on plant species, food and shelter. It is therefore possible that they follow the plants to luxurious neighborhoods. Even some bats gravitate toward the wealthier parts of the city. As far back as ancient Egypt, places where workers lived were home to different species of insects than wealthier areas.

“I was surprised – not that human action could shape biodiversity patterns in unexpected ways, but rather that the luxury effect occurs so well,” says Kinzig. “In other words, we would expect different types of people to create landscapes that support different types of other species, but we would not necessarily expect that the rich would almost always experience higher biodiversity. » (Fewer studies on the luxury effect have been done in tropical regions – one study from Burundi found a positive relationship between plant diversity and wealth, but another study in Puerto Rico found no correlation, perhaps because there is a smaller income gap between neighborhoods.)

In urban environments, “humans control everything,” says Jeff Ackley, a U.S. government regulatory biologist, who discovered the luxury effect on Phoenix’s “wealthy lizards,” finding that household income was one of the best indicators of nearby lizard diversity. “When people have the time and resources to do so, they can control the appearance of their backyard. And for the most part, people seem to like more diverse vegetation.”

But the luxury effect isn’t limited to gardens: it seems to happen indoors, too. Richer homes are home to more insects and spiders, according to a US study.

Researchers randomly sampled 50 homes in Raleigh, North Carolina, based on income range. The richest homes housed an average of 100 types of arthropods, twice as many as less wealthy homes, according to the study, which took into account the size of the house.

The results were counterintuitive, because people generally think that wealthier people have cleaner homes, highlighting “how much we still have to learn about indoor ecology,” the researchers wrote.

No studies have examined how the millions of species of microbes that live in cities might be influenced by the luxury effect, but research shows that poorer people generally suffer from more inflammatory and immune diseases, which could be linked to lack of exposure to microbial life. Contact with biodiverse environments, soil and animals has been associated with a multitude of positive health effects.

“Almost all diseases of the immune system are on the rise,” says Dr James Kinross, consultant surgeon at Imperial College London and author of Dark Matter: The New Science of the Microbiome. “There is something about the way we build and construct our urban systems that detaches us from nature, and therefore from these kinds of microscopic ecosystems that we need to maintain our health.”

Biodiversity loss is recognized as a pressing global problem, but it generally refers to extinctions and declines of species in the broader environment around us, rather than what is happening within the human body. A growing body of research, however, shows that they are closely related. Last year, an article coined the notion of “natural deficiency,” referring to how the loss of nature in the human body influences health.

To reverse these health inequities, scientists are looking to the outside world, where preserving and expanding biodiversity can make a difference. A study in Finland showed that adolescents living in biodiverse gardens, for example, had fewer allergy and autoimmunity problems.

“The luxury effect not only represents an interesting ecological model,” wrote a group of researchers examining the phenomenon. “[It is] it is also another layer of the social and structural injustices present in cities.

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