More than half of the world’s population lives in urban areas, and plenty of animals live among those billions of people.
A UCLA-led study examined how a city’s size relates to the number of animal species living in it by comparing 112 cities across the metropolitan areas surrounding Los Angeles, San Diego and San Jose, California. The paper found that although bigger cities in all three regions are home to more species on average than smaller ones, the natural bounty in larger cities is not distributed evenly.
The findings are significant in part because studies have shown that even small parcels of natural space in otherwise densely packed urban centers can contribute to overall environmental health and residents’ well-being. Recognizing where — and suggesting how — cities could incorporate more green spaces and retain more native animal species could be beneficial to those who live there.
The variability of natural areas in big cities provides ample habitat for wildlife, said Nurit Katz, a co-author of the paper and UCLA’s chief sustainability officer. Los Angeles, for example, is home to thousands of species, including more than 50 that are threatened or endangered, she added.
“But essentially, what we found is that although large cities may have more species, they don't necessarily do a great job of distributing them,” Katz said.
Some neighborhoods within big cities are home to few species or none at all, the study found. And wealthier neighborhoods with lots of open space and more trees, shrubs and grasses, are home to more species on average than denser, concrete-laden communities, according to the research.
“Neighborhood by neighborhood, you have winners and you have losers,” said Dan Cooper, the paper’s lead author and a former UCLA doctoral student. “In Los Angeles, for example, the winners are places like Brentwood and your losers are places like Exposition Park, where there’s almost no natural open space.”
To measure biodiversity, the researchers combined data on 17 representative species from iNaturalist and eBird, two social networks that collect experts’ and citizen-scientists’ observations of organisms and their tracks and nests, as well as other evidence. The researchers chose widespread, native terrestrial species that are easy to identify, such as the western fence lizard, western grey squirrel and California quail.
The study was conducted by a team that included collaborators from UCLA, the Los Angeles Department of City Planning, and Cal State Los Angeles, and published in Frontiers in Conservation Science.
The study also included an examination of the effects of Los Angeles County’s so-called general plans — long-term policy planning documents.
Municipalities whose plans included positive mentions of biodiversity and specific guidance for protecting it including Rancho Palos Verdes and Walnut. Hawthorne and San Fernando were among the cities that either failed to address biodiversity or included language that did so negatively.
“It was shocking to see how outdated many of the plans are,” said Anna Novoselov, a co-author of the paper and a UCLA sophomore majoring in environmental science. “Even if cities are currently unable to support much biodiversity, that doesn’t mean they can’t make improvements.”
With more people moving to cities year after year, scientists and documentarians increasingly are interested in understanding the dynamics of urban wildlife — and studies have shown that exposure to natural spaces and wildlife can improve humans’ physical and mental health. One 2020 paper by researchers at the U.K.’s University of Exeter, for example, found that people who spent two hours a week in parks or other natural environments were substantially more likely to report good health and psychological well-being.
But research on the topic has also raised concerns about lack of equity. In the UCLA-led study, the authors write that policymakers and the public often view heavily urban areas as ecologically irredeemable, and that planners “resist efforts to restore elements of nature” that would benefit people living in those areas, “many of whom are economically and socially marginalized.”