Cities as Novel Ecosystems: Adaptions to Urban Conditions
A guest post from PLOS Ecology Reporting Fellow, Liz Kimbrough, on research from the Ecological Society of America Scientific Meeting in Ft. Lauderdale, Florida, August 7-11, 2016.
Are cities unnatural? Are urban landscapes disturbed or damaged? “There is no right answer. We can think of cities in many ways,” says Dr. Paige S. Warren of the University of Massachusetts. “Cities are sources of novelty, hotpots of resource inputs, and drivers of evolutionary change.”
Warren spoke as part of this year’s ESA session “Novel Ecosystems in Cities: Adaptation to Urban Conditions.” The theme of the 2016 ESA conference was, “Novel Ecosystems in the Anthropocene.” Cities, according to the researchers in the session, are among the most understudied of novel ecosystems and new research needs to focus more on adaptation and evolution of life in the city.
Extreme environments drive adaptation. With the habitat fragmentation, light and noise pollution, soil impaction, new food sources (like trash), and the myriad other changes that come cities bring, the urban landscape is ripe territory for adaptation.
“Phenotypic plasticity is covered,” says Dr. Michael McKinney of the University of Tennessee, “we need more research focused on micro-evolutionary change. We need to ask about the pace of evolution.”
Though some urban areas are rapidly developing, others are shrinking. After massive population declines in the past decades, the human population of Cleveland, Ohio is today roughly what it was in 1900. Now, over 20,000 vacant lots (3,600 acres of land) are sprinkled throughout the city. Vacant lots are typically ignored in conservation planning in the US, however, as we start to follow the lead of the UK and Europe, vacant lots are being re-imagined as spaces for gardening, parks, and “pocket ecosystems.”
Dr. Mary M. Gardiner of Ohio State University noticed that lots in Cleveland are diverse weedy habitats that host many early successional and rare species. Gardiner studies sheet web weaver spiders and, among other things, how urban crop assemblages effect their populations. She found that while vacant lots had more consistent spider communities, there was more variation in community gardens. She also determined that bare ground is not so good for spiders, and mulch can reduce natural pest management in community gardens. Keeping some naturally occurring grass habitat in these lots, she determined, is beneficial for spiders and gardens.
In Baltimore, another shrinking city, Dr. Charles Nilon of the University of Missouri studies the way that birds use vacant lots. Baltimore has 42,000 acres of vacant lots spread throughout the city (7% of the total city area). Nilon noticed a pattern in these lots; some are more vegetated and contain large trees, while others have less vegetation and more paved or bare ground. These two categories of lots also followed a socioeconomic pattern, with the lush lots occurring in middle class and wealthier areas of town and the barren lots in lower income communities.
Noticing this, Nilon and his then graduate student, Dr. Christine Brodsky of Pittsburg State University, asked the questions: How are birds using these novel habitats? Is one “better” for birds than the other? The answer was, not really. He found that the two lot types host a different composition of bird species. Lots clustered near forests with lots of trees had higher species richness, and shrub density related to nesting success in vacant lots.
The story of urban birds adapting to cities is one most ecologists are familiar with. There are examples of birds changing their calls in response to background noise, singing at much higher frequencies in cities than their country cousins, and even putting cigarette butts in their nests to reduce parasites. But fewer people have considered what is going on below the surface in cities.
Solitary digger bees change their nesting behavior in compacted urban soil, making shallower, horizontal tunnels. Vibration alters turning behavior in isopods. One species of earthworm, Dichogaster bolaui, has expanded its range in Africa all they way to European sinks and bathtubs, moving through sewers. In a survey of Central Park, Ramirez 2014 found that microbes are highly adapted to urban environments. And insects such as the silverfish (Lepisma saccharina) can live entirely without soil.
The adaptations of soil organisms to urban environments are what interest Dr. Katalin Szlavecz of Johns Hopkins University. Which macro invertebrates are successful in urban environments and why? Is this phenotypic plasticity or adaptation? Along with the Global Urban Soil Ecological Education Network (GLUSEEN), she is working to answer these and many other questions about the life under your feet.
And what about the plants? With access to floras from 112 cities including both natural and spontaneous vegetation since 1975, Dr. Myla Aronson of Rutgers University along with the Urban Biodiversity Research Coordination Network (UrBioNet) is asking questions about the ways in which cities influence global, regional, and local patterns in plant diversity.
So far, they are seeing that plants in cities are over 70% native in terms of species richness. At least 8% of cities contain threatened species (a conservative estimate as Australasian species are not included on the IUCN red list of threatened species). Indo-Malaysian cities harbor the greatest number of invasive plant species, and the species present in cities are more similar within biogeographic realm.
Invasive plants do provide function, but how do we balance costs and benefits for the suite of traits we want for cities and our conservation goals. In some places natives can’t provide what we need, so cities need to be kept in check and wilderness needs to be maintained.
During the presentations, many researchers gave calls to action for future research or engagement. McKinney and others on the panel urge ecologists to collaborate with designers, architects and planners with the hope that we can design urban habitats with evolution in mind.
Currently, urban spaces are designed with aesthetics, functionality, recreation, and ease of maintenance in mind. Including the ideas of ecological function, biodiversity, education, and conservation in design is not beyond us. McKinney highlighted the urban wilderness movement, in particular the Knoxville Urban Wilderness, which boasts one thousand forested acres along the city’s waterfront. This project has been hugely successful economically, educationally, and ecologically.
McKinney also urged ecologists to “focus on positive things” and embrace opportunities such as vacant lots, the urban wilderness movement, the green infrastructure movement (storm water management, green landscaping), and the green roof movement. These are all avenues for change.
Finally, Nilon urges us recognize and remember that cities are places where people live. It is important respect the knowledge of city dwellers just as you would respect the traditional knowledge of any other local people. Wilderness conservation often fails when locals are not deeply involved and invested in the project and this holds true in the city.
“The take home message of the symposium,” said the session’s organizer, Dr. Rebecca W. Dolan of Butler University, “is that there are great opportunities for ecologists and evolutionary biologists to make significant contributions to the emerging field of urban ecology. Cities are giant, landscape-scale experiments in novel ecosystems.”
And cities are not going anywhere. With more than half of the world’s human population living in urban areas, their importance to the global ecological equation cannot be dismissed, especially by ecologists. After all, ecologists are people too.
Liz Kimbrough is a Ph.D. student in the Van Bael lab at Tulane University. You can find her in New Orleans studying the microbial communities of bald cypress trees, writing about science, and playing her washboard. Though she hails from Alabama, Liz earned her Bachelor’s in botany amongst the redwood trees at Humboldt State University. Liz discovered a passion for bringing science and environmental news to the public when she began writing for mongabay.org in 2012. Liz is currently a NSF Graduate Research Fellow and is excited to continue communicating science to the public and working in coastal and tropical ecosystems. (Follow Liz on Twitter @lizkimbrough_ )