New York City: A true urban jungle

We have all heard the expression “It’s a jungle out there” when referring to the world’s teeming metropolises. When evolutionary scientists say it, however, they really mean it. An increasing number of enlightened academics have been studying the changes that occur to the animals, birds and insects that live in New York City, and their findings are nothing short of amazing.

While most evolutionary scientists head off on gruelling expeditions to the jungles of the Amazon or deepest Africa, 28-year-old Jason Munshi-South prefers to stay close to home. “New York City provides me with all I need for my research into the behaviour and evolution of the white-footed mouse,” he says as he leans up against a tree in Central Park surrounded by one of the world’s most densely populated cities. “I don’t just work in Central Park; there are four other New York parks which are larger and provide amazing opportunities for research.”

Munshi-South’s work doesn’t have to be confined to the green spaces in the city and can include waterways, median strips between freeways and even the rooftops of skyscrapers.

For his latest field trip he, and two graduate students who are assisting him, took New York’s famous A train. Alighting from the subway at the 168th Street Station in Washington Heights — an area which overlooks the Harlem River about 5 kilometres north of Central Park — Munshi-South and his two assistants made their way up into the bright sunlight loaded with backpacks and boxes full of scientific equipment.

‘One huge laboratory’

Although still surrounded by street traffic and apartment blocks it doesn’t take long for the group to enter into another world via Highbridge Park. “This area is perfect for our work because it’s at the edge of ‘civilisation’ and offers some nice ravines where the vegetation is virtually untouched,” Munshi-South explains. As they walk deeper into the heavy undergrowth beneath tall trees and finally reach the field site for their research, the sun all but disappears.

Munshi-South, an assistant professor at Raruch College, has made his mark in evolution within an urban environment. “Even in the most urbanised areas there are animals, insects and birds that have made their home there,” the bespectacled academic says. “When I look out across the skyscrapers of Manhattan, what I see is one huge laboratory.” Most animals that live in this thriving metropolis have had to adapt over time to survive in what is a constantly changing environment. New York never sleeps, but it doesn’t stay the same for long either.

White-footed mice living in isolated urban “islands” adapt to cope with stress, fish in the Hudson have to deal with contaminated water and insects make homes in small patches of grass or in rooftop gardens. Over time these creatures evolve or mutate. On the famous Broadway native American ants find refuge from the traffic and a place to make their home on the central median strip. Just about any creature living in the city has to make sure it can move with the times to survive.

“While all animals have had to adapt to changes in the environment over billions of years, in the city it’s the same but time speeds up,” Munshi-South says. Here in Highbridge Park white-footed mice — Peromyscus, a native species only superficially related to the common house mouse, with white legs and paws that make them agile and good jumpers — are the focus of his attention. “I’ve been working on this project since 2008 and what I’ve discovered is fascinating,” he says. “These resilient little creatures can make their homes in what can sometimes be a pretty inhospitable environment.”

Getting to work in Highbridge Park, his assistants spread out a large blue tarp on the forest floor while Munshi-South goes over to an orange flag planted on the ground. Near it is a metal box and inside a small white-footed mouse. Very gently Munshi-South pops the tiny rodent into a bag so it can be weighed and then measured by his team before being released back into the forest. The data collected is entered into a log and will be used to make comparisons over time and at different locations.

“What we’ve found is that the DNA of mice taken from various parks across the city is not the same,” the scientist says. “They are genetically different and that’s very interesting. We have found as much variation in the DNA in New York mice as you would expect to see in the animals collected across the whole of the United States.”

There is no escaping evolution. “It’s all around us and is one of the constants,” he says. “Species change or sometimes become extinct and many things, including urban development, can steer the evolutionary path in new directions.” New cities, such as New York, which have evolved over just hundreds of years, opposed to thousands, make particularly good research locations. The first Europeans to arrive in the area cut down most of the native forest to build roads and divide the land into housing blocks. Everything also gets affected as chemicals and pollution enters the air, soil and water systems.

Another example of how animals must adapt to new conditions in New York is the plight of the fish in the Hudson River. They were exposed to PCB — a by-product of oil — used by General Electric for more than three decades until 1977. The toxic waste has been shown to cause deformities in fish larvae. However some fish, namely the tomcod which lives and feeds on the bottom of the river, were not affected due to their gene AHR2. They survived while others didn’t.

While evolution can work to an animal’s advantage, scientists have discovered that when the environmental changes are fast so are the changes in an animal’s DNA to cope with this. Munshi-South has identified more than 1,000 genes in New York’s mice which show changes. Mice living in relatively undisturbed conditions outside the city limits don’t show the DNA change. The alterations present in the city mice highlight how they help with coping with stress, exposure to chemicals and harmful bacteria as well as boosting the tiny mammals’ reproductive systems. “What is even more fascinating,” Munshi-South says, “is that these DNA changes are slightly different depending on which neighbourhood of New York you study.”

A real New Yorker agility

White-footed mice are native to a large part of North America and can be found from Canada to New Mexico. They made the New York region their home after the Ice Age some 12,000 years ago. Since the 18th century, when their forest home became a city, they have managed to survive by migrating to the various parks and wooded areas. “My research shows that the white-footed mouse has adapted quite well,” Munshi-South says. Some of the mice when trapped for research show a real New Yorker agility and courage and make a bolt for it as soon as the trap’s door opens.

Working in the thick of New York’s traffic are two other dedicated evolutionary scientists. James Danoff-Burg and Robb Dunn spend time down on all fours on the grassy median strip of Broadway on the Upper East Side between the two lanes of traffic. They are looking for ants and particularly for Crematogaster lineolata which has never been sighted previously in this hostile New York habitat.

“Both James and I are fascinated with how biodiversity is affected along the median strip of Broadway,” says Dunn as he takes a moment to rest on the grass. “It’s a completely artificial, green environment which was created after the subways were built.”

What the two academics have discovered is a mix of ant species living together. Some have been around since before Europeans arrived and others are relative newcomers. “They arrive on ships, in cars, on people’s clothes,” Dunn explains. One of the most common is what is known as the pavement ant — Tetramorium caespitum, which came from Europe and has adapted very well to its new home.

Scientists find a variety of native and non-native creatures across New York. There are mice in the parks, birds in the marshy areas in Brooklyn and insects and bacteria just about everywhere. It is a process of constant change as species evolve, become extinct and learn to live with other invading species.

What Danoff-Burg and Dunn are particularly interested in is how the balance is maintained. “Not all environments work the same for ants,” Dunn remarks. “In the artificial median strips there is less biodiversity. We have evidence to show that this is because only the strongest can survive in this harsh habitat.” Their research has also shown how the native ants have become stronger to live in coexistence with new species.

There is no shortage of animals — of all sizes — for scientists to study out there between the skyscrapers, neon lights and bitumen. “New York really is a jungle and it’s evolving as we speak,” Dunn says.

Scott Adams is a journalist based in Madrid.