Cities: Evolutionary hot-spots for wildlife

When it comes to field visits, animal biologist and professor at Fordham University Jason Munshi-South doesn’t travel too far. In fact, his research sometimes takes him just as far as his backyard. ‘Our field sites are literally right outside our homes and universities,’ he explains, ‘I can squeeze in some trapping or other sampling in a city park before teaching in a classroom.’

Munshi lives in New York and is studying rodents in the Big Apple. Currently along with his team he is focussing on obtaining specimens of rats from all postal ZIP codes in Manhattan and will ultimately branch out to the other boroughs.

When one thinks of studying animal biology and evolution, grimy city streets and busy subways wouldn’t seem like the ideal spots. Though they appear sterile and lifeless, cities are in fact a hotbed for studying evolution of various species ranging from insects to mammals to birds. The fickle and erratic nature of cities—their constant commotion and dizzyingly fast changes pose various challenges to urban wildlife. Unlike their rural counterparts, animals in cities must learn to solve new problems every day—this means, like the city, they must change. Some scientists now believe that cities could actually be causing evolutionary changes in wildlife much faster than previously believed possible.

‘Cities contain unique communities of organisms that have never occurred together before,’ explains Munshi-South. ‘These communities are composed of native organisms that have survived urbanisation, and species that have been moved around the world (intentionally or unintentionally) by humans. Many native species are extirpated from cities, but the ones that survive have often found ways to deal with very extreme conditions.’

Researcher Emilie Snell-Rood from University of Minnesota found that one of the ways in which animals could be adapting is through bigger brain sizes. She studied 10 species of small mammal skulls including mice, gophers, voles and bats. Comparing 500 specimens spanning across the 20th century from the Bell Museum of Natural History, she found that some urban mammals had evolved bigger brains as compared to their rural counterparts. ‘Cranial capacity is just one way in which animals adapt to cities. Some species could be reproducing more or there can be genetic variations as a result of urbanisation,’ she explains.

She says urban environments are different than what species have ever seen in their evolutionary history before. ‘Some flexible and plastic species are actually able to adapt and do better in cities. Maybe they are evolutionarily tracking the city,’ she adds.

From bacteria to birds, cities are influencing different species. There are ample examples of species adapting to changes brought on by urbanisation. An old and well known instance is that of peppered moths in Manchester, England during the industrial revolution. The moths evolved from having light coloured wings to dark coloured wings to camouflage better due to pollution.

In New York’s Hudson River, scientists have found tomcod fish that have swiftly evolved to become resistant to Polychlorinated biphenyls (PCB), a now banned chemical released in the water. There are examples from around world of mammals such as raccoons and coyotes that have grown all too comfortable with the ways of the big city and know where and when to forage for food. In India, leopards in the city of Mumbai are known to visit the city to prey on stray dogs, which have become an important part of the big cat’s diet.

In cities, urban species are exposed to various transient factors. ‘The types of food that are present, how they would go about finding that food, newer predators, traffic, pollution, habitat destruction. It’s a very different environment,’ says Snell-Rood.

Survival in human dominated areas means many species must evolve to cope with competition, new surfaces, disturbed environments and issues of connectivity among other factors. Some species go extinct, others animals learn to change behaviourally and some biologically.

Birds in cities

Photo by eFesenko / Shutterstock
Photo by eFesenko / Shutterstock

A 2006 study that included 10 European cities found that great tits had evolved to sing faster and in higher pitches than in close-by forests. A more recent study in five European airports (Berlin, Barcelona, Madrid, Valencia and Malaga) by Dr Diego Gil noted that birds near the airports have evolved to have earlier dawn choruses due to the noise and artificial light in the night.

Evolutionary ecologist Madhusudan Katti studies biodiversity in social-ecological systems such as cities and is particularly interested in city birds. Among the vertebrates, he says birds are definitely ‘up there’ when it comes to species capable of adapting to cities. Scientists are studying changes in bird morphology, social behaviour and foraging patterns in birds in human dominated areas. ‘Cities tend to be warmer and provide seasonality, there are more and more examples of migratory patterns of birds changing because of cities. Canadian Geese for example have become residents in many areas throughout North America,’ he says.

Katti, along with other researchers, compiled a list of birds in 54 cities spanning all continents except Antarctica. The study found that native species of birds such as house sparrows, European starlings, mynas, etc. did much better in cities than exotic species.  

Why study how animals adapt

The last century has seen an unprecedented growth of cities. Today, more than 54% of the world’s population lives in urban centres and this number will only swell further. Even as relentless urbanisation is changing the face of the planet, understanding how animals cope with these changes will perhaps give us a better chance at protecting various species.

Munshi-South’s current study for example aims to understand how rats use urban spaces, particularly how they disperse through city infrastructure. ‘We are comparing fine-scale relatedness of rats across Manhattan to models of rat movement based on our hypotheses of what infrastructure types are most important. For example, do they use subway tunnels or sewers preferentially to move north-south in Manhattan? We are also exploring whether the socioeconomics of neighbourhoods influences rat genetic patterns and movement on a fine scale,’ he says.

Photo by Iakov Kalinin / Shutterstock
Photo by Iakov Kalinin / Shutterstock

The long term aim is to use these studies to build cities better. Munshi asks, ‘Can we design parks, other green infrastructure, and the built environment to allow animals and plants to disperse through the city? Can these designs maintain connectivity across the city, and connectivity with the surrounding area? Can they be designed to limit conflict with humans?

Katti believes that studying how species relate to urban changes gives clues on how to conserve biodiversity. ‘We can design our cities in a way that they can accommodate many more species than they do now. Even in rooftop gardens, decorative plants can provide habitats for species of insects,’ he says.

This knowledge can perhaps help us reconcile human development with what is good for us and other species as well.

[geoip-content not_country=”CA”]

See the future of city life as it plays out in Linz, one of Europe’s most modern and ecologically friendly cities in City of Steel, City of Life, now streaming on our app. From amphibians in man-made swamps to the foxes and racoons that call the city home, witness a place industry and culture and nature become one. WATCH NOW.