Humans are becoming ever more urban in their habits, yet it is only recently that scientists have attempted to quantify the impact of urbanization on levels of biodiversity around the world. One striking recent global analysis of bird and plant diversity showed just how dramatically the built environment hits birds. For every species spotted in a given urban environment, there are typically more than 10 in an equivalent area of non-urban habitat.
This might sound like a dismal statistic, but it is also an opportunity — a valuable benchmark against which improvements can be planned.
“There are many reasons why urban biodiversity matters,” said Mark Goddard, a biologist at the University of Leeds and one of the authors of the recent paper.
Illustration: Tania Chou
For a start, many of the world’s major cities are located in prime locations that are naturally rich in species and still support a significant number. Singapore is the standout example, a city in which it is possible to spot 347 native birds, of which 12 are on the International Union for Conversation of Nature Red List of Threatened Species.
In India, thanks to the reverence that Hinduism places on cows, elephants and monkeys, there is room for all these animals in even the busiest of cities. Indeed, when conditions in the countryside get really hostile, the urban environment may be the best place for animals to be.
This was probably the case for Hanuman langur monkeys during a severe drought in Rajasthan in 2000 that caused around half of the non-urban population to die off. In Jodhpur, where the animals had access to plenty of food and water, there was almost no change in the population size.
Among primates, it is baboons that do best in a human-altered world. One of the best-studied urban populations is in Cape Town, South Africa, where the Chacma baboon has been living cheek-by-jowl with humans since at least the 15th century. In spite of the increasing pressures on the wild spaces around the city, the local baboon population is estimated to have risen from 365 in 1998 to 475 in 2011.
Part of the baboons’ success is their strong social network, their unfussy diet and behavioral adaptability. In urban settings like Cape Town, baboons appear to have honed their raiding skills, zipping into densely populated areas to steal high-value human foodstuffs.
Similarly, the Barbary macaques of Gibraltar, emboldened by their friendly contact with tourists, have been carrying out forays further into human territory, raiding dustbins and running amok. Black bears in Nevada also make grub out of garbage, with urban bears far less active yet far heavier than their wild counterparts.
Even carnivores, it seems, can survive the big city, though they are probably benefiting from the abundance of rats and other rodents (which make up almost half their diet) rather than human food. In Chicago, researchers conducting the largest urban study of coyotes in the world have found these animals are more active at night, which brings them into less frequent contact with humans and traffic.
Other species have come up with different solutions to city life. There is good evidence, for instance, that urban great tits deliver their songs faster and at a higher pitch so they can be heard above the hectic soundscape. In Belo Horizonte in Brazil, black-tufted marmosets have altered their sleeping habits, carefully selecting trees that domestic cats cannot easily climb.
In short, there are still plenty of city-dwelling species to protect, but how can we make our cities more inviting places for these and other creatures — and, to put it bluntly, why should we bother?
Goddard is unequivocal.
“If cities are to support a burgeoning human population, the maintenance of functioning urban ecosystems and the plethora of services they provide will be imperative for human health and well-being,” he said.
It is widely acknowledged that cities with some kind of functioning ecosystem make for better places for humans to live. Certainly, less green and more gray can often result in an increase in pollution and flooding. However, more plants and animals in cities also make for happier, healthier people.
A study conducted on green spaces in Sheffield, England, for instance, revealed that the greater the biodiversity, the greater the psychological well-being of the city’s residents. In Paris, researchers found that getting city dwellers to take part in day-long activities involving urban wildlife opened their eyes to the natural world (for a time, at least).
Few cities have been tangling with urban ecology for as long as Berlin. Slow economic recovery after World War II meant that reconstruction took a long time. This provided local ecologists with the ideal conditions to develop an ambitious ecological research program in the bombed-out wastelands of West Berlin, said Jens Lachmund, a sociologist at the University of Maastricht in the Netherlands and the author of Greening Berlin: The Co-production of Science, Politics and Urban Nature.
The pioneering work in Berlin had several consequences, notably the formation of significant natural spaces within the city, such as the Sudgelande Nature Park.
“Berlin has indeed benefited a lot from being a case study in urban ecology,” Lachmund said.
The proximity of a city to a national park or other protected area is also likely to make it more species-rich. With the Nairobi National Park just a few kilometers from the city center, Kenya’s capital boasts over 300 species of bird. Likewise, there is Table Mountain National Park in and around Cape Town, the Sanjay Gandhi National Park in the center of Mumbai, the Saguaro National Park just outside Tuscon, Arizona, and the National City Park in Stockholm.
The recent research conducted by Goddard and his colleagues confirms the importance of natural spaces within an urban setting. Essentially, the greener the city, the greater the proportion of native biodiversity that is retained.
“The key message from this work is very simple,” Goddard said. “The protection of existing green spaces and the creation of new habitats is essential for supporting wildlife in cities. How we actually do this is more challenging, and will require collaboration between scientists, urban planners and habitat managers.”
Over the last decade, there have been some significant milestones on the way to figuring out the answers. In 2006, a number of pioneering city governments, from Curitiba, Brazil, to Joondalup, Australia, got behind Local Action for Biodiversity, a program “aimed at improving and enhancing ecosystem management at the local level.”
In 2008, the parties to the Convention on Biological Diversity (CBD) began developing the City Biodiversity Index, a protocol for evaluating urban wildlife. Then, in 2012, the CBD launched Cities and Biodiversity Outlook, an effort to provide “a global assessment of the links between urbanization, biodiversity and ecosystem services.”
Cities take up just 3 percent of the terrestrial surface area, yet according to the most recent estimate from the UN, some 3.6 billion people (just over 50 percent of the global population) now live in urban areas. By 2050, this figure is projected to have risen to 6.3 billion.
Without animals and birds to keep us company, it is a bleak prospect.
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