Mice in New York City are evolving to thrive on fatty diets thanks to the abundance of fast food trash. In Japan, street-smart crows hang out near a driving school and crack walnuts by placing them in front of the car wheels. Philadelphia’s house sparrows have traded their seed diet for pizza crust and bread crumbs. City sparrows sacrificed song virtuosity for volume to be heard above traffic noise. Wildlife evolution in urban areas is occurring faster than anything recorded by Charles Darwin and other early evolutionary biologists who studied life in relatively pristine undeveloped habitats. For those animals who cycle through generations quickly, such as the NYC mice who reproduce annually, the pressures of urban life drive rapid evolutionary change.
These animals are wild biohackers who have no other choice but to evolve or die. They aren’t just making behavioral changes, clever adaptations to a new environment. They are evolving, claims Dutch evolutionary biologist Menno Schilthuizen in his book Darwin Comes to Town: How the Urban Jungle Drives Evolution.
Urban ecology is a relatively new field of study, arising in the 1970s. In the U.S., until recently, it centered on human social systems, while in Europe urban ecology has looked more at the biota, although both consider human activities as the driver. In 1859 when Charles Darwin published On the Origin of Species, he viewed natural selection as a slow process. But urban environments are pressure cookers for evolution. Survival in the city causes species to evolve rapidly. Schilthuizen claims, “This process is happening all the time.”
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Schilthuizen tells compelling life histories in Darwin Comes to Town. One story relates how European blackbirds (Turdus merula) have changed after adopting an urban life. Until the end of the 19th century, the reclusive birds occupied forests and were rarely seen in towns. Then, for whatever reason, they began appearing in urban parks and gardens (he says this began in the 1920’s in London). Collection specimens allowed scientists to compare pre-urban dwelling blackbirds with contemporary city birds and proved their beaks are stubbier. Recorded data showed their songs now are higher pitched, and sung earlier in the day. The birds are less reclusive, and nest earlier in spring. These changes are reflected in genetic differences between contemporary individuals and those from a century ago, claims Schilthuizen.
“We are affecting the evolution of species,” he said. “Evolution will continue all the time, and it will speed up. It will result in the formation of new species.”
However, the planet can’t rely on urban wildlife to replace all those species that are losing their habitat as a result of human impact such as climate change, he warned.
“We are going to lose a lot of species — those that need untouched habitats will suffer,” Schilthuizen said. The biodiversity of urban habitat is much lower than that of the wild, he explained. In the pristine rainforests, “there are species being discovered that we hadn’t even seen yet. Some species may be gone without us knowing they existed.”
We are replacing natural habitats with human developed landscapes. Our gardens, parks, green roofs, and even golf courses form a mosaic of different habitat types amidst freeways and human occupation. Many of the plants in these habitat patches come from garden centers and are not native to the region. Thus, we have new habitat types and species assemblages as human activities modify the landscape. How urban design affects wildlife is still being documented, such as the two genetically distinct groups of Los Angeles bobcats whose gene flow is divided by the 101 and I-405 freeways.
“Become an urban naturalist,” urges Schilthuizen. He encourages people to participate in citizen science social platforms. These “digital snapshots in time” are important data similar to natural history collections gathered over the last couple centuries by historic and more modern naturalists. Now, we have citizen science collections like eBird, iNaturalist, and others with millions of records gathered in just over a decade.
As urban areas change the landscape, the alterations change the plants and animals living in cities. By documenting nature in urban areas, we create baselines that form a useful record for comparisons as changes continue. This information is also valuable to city planners designing the future. We can incorporate wildlife corridors to unite populations, establish vacant lots that naturally are colonized by “neo-indigenous” urban life, and recommend suitable plants for parks to offer healthier options for pizza-eating sparrows.
Anyone who’s marvelled at weeds emerging from cracks in an expansive paved parking lot, has seen the resiliency of nature. Schilthuizen believes that urban planners can benefit from the findings of evolutionary biologists and citizen scientists. Through informed urban design, nature also will benefit.
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