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Fearless birds and big city spiders: is urbanization pushing earth’s evolution to a tipping point?

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Pigeon. Birds in urban areas are growing tamer and bolder, outcompeting their country cousins.Credit: © Tatiana Katsai / Fotolia

Fearless birds and big city spiders: Is urbanization pushing earth’s evolution to a tipping point?

Posted: 18 Feb 2015 04:15 PM PST

That humans and our cities build affect the ecosystem and even drive some evolutionary change is already known. What’s new is that these evolutionary changes are happening more quickly than previously thought, and have potential impacts on ecosystem function on a contemporary scale. Not in the distant future, that is — but now. The signs are small but striking: Spiders in cities are getting bigger and salmon in rivers smaller; birds in urban areas are growing tamer and bolder, outcompeting their country cousins. …suggests that if human-driven evolutionary change affects the functioning of ecosystems — as evidence is showing — it “may have significant implications for ecological and human well-being.” Alberti, a professor of urban design and planning, said that until recently it was assumed that evolutionary change would take too long to affect ecological processes quite so immediately. Such thinking has prevented evidence from coming together “in a way that can only emerge through a cross-disciplinary lens,” she said, observing the interactions between humans and natural processes. “We now have evidence that there is rapid evolution. These changes may affect the state of the environment now. This is what’s called eco-evolutionary feedback. “Cities are not simply affecting biodiversity by reducing the number and variety of species that live in urban habitats,” Alberti said. Humans in cities are causing organisms to undergo accelerated evolutionary changes “that have effects on ecosystem functions such as biodiversity, nutrient cycling, seed dispersal, detoxification, food production and ultimately on human health and well-being.”… Humans in cities cause these changes through a variety of ways, Alberti said. Our urbanization alters and breaks up natural vegetation patterns, introduces toxic pollutants and novel disturbances such as noise and light and increases the temperature. Human presence also changes the availability of resources such as food and water, altering the life cycle of many species. Alberti said the emerging evidence prompts serious questions with implications for the focus and design of future studies:

• Can global rapid urbanization indeed affect the course of Earth’s evolution?

• Is urbanization moving the world closer to an environmental tipping point on the scale of the Great Oxidation Event that introduced oxygen into the atmosphere more than 2 billion years ago?

• Might different patterns of urbanization alter the effect of human action on eco-evolution?

Still, Alberti said hers is not a “catastrophic” perspective, but one that highlights both the challenges and the unique opportunity that humans have in shaping the evolution of planet Earth.

Ecosystems in urban environments are a sort of hybrid, she said: “It is their hybrid nature that makes them unstable, but also capable of innovating.” She explores the theme further in a book to be published in spring 2016, titled “Cities as Hybrid Ecosystems.” “We can drive urbanizing ecosystems to collapse — or we can consciously steer them toward a resilient and sustainable future,” Alberti said. “The question is whether we become aware of the role we are playing.”

 

Marina Alberti. Eco-evolutionary dynamics in an urbanizing planet. Trends in Ecology & Evolution, 2015; 30 (2): 114 DOI: 10.1016/j.tree.2014.11.007

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