Next up in the urban wildlife series is the ways in which certain species are adapting to the urban environment.
Pre-adaptation and plasticity
Plants and animals are able to adapt to unfamiliar or challenging conditions of the city in a few different ways, and it’s not necessarily a slow, time-intensive process to get them up to speed.
One method of adaptation is, as Menno Schilthuizen describes in Darwin Comes to Town, “pre-adaptation” or “predisposition.” This is the coincidental existence of a quality that helps a species thrive in the urban environment, some gene that happens to be well suited to urban living, that can then be honed as they continue living in the city. This is called ‘soft selection’
[The house sparrow]…has become an urban species because it was already adapted to a lifestyle that, purely by accident, prepared it for the niches that we have created in cities. The urban environment offers conditions that happen to resemble one or more aspects of a species’ way of living in pre-urban times. And it is those species that are pre-adapted to the novel niches in the city. – Menno Schilthuizen
Another way species are making themselves at home in seemingly uninhabitable cities is “behavioral plasticity. Gavin Van Horn in The Way of Coyote uses this to explain why coyotes are so numerous and comfortable in Chicago. As it sounds, “behavioral plasticity” is a species’ ability to adapt their behaviors to the context of their surroundings. This has nothing to do with evolving genes and only to do with changing a pattern of behavior. For the coyote example, Van Horn explains that they vocalize less than their non-urban counterparts, adjust their omnivorous diet to what’s available in the city, and group together or travers alone, among other adaptations.
Another plasticity comes from the many combinations DNA can make, for instance hair, eye, and skin color in humans. Schilthuizen calls standing genetic variation a species’ “evolutionary capital” because it allows a species to “immediately come up with any combination of genes that a changed environment requires.” This is why Schilthuizen cautions against assuming the coloring of a species is necessarily evolution, it may just be a species’ use of its “evolutionary capital.”
Adaptations for the urban jungle
For those that can adapt, there are numerous examples of how species are evolving or altering their behaviors. And it’s a good thing since there’s a lot to adapt to in a city, like noise pollution. Nathanael Johnson (Unseen City) describes gray squirrels alerting each other to danger using tail flicks rather than squeaks to avoid being drowned out by the urban cacophony. Schilthuizen explains how birds make their morning calls earlier than their country companions to get ahead of the day’s noises, or some bird species sing at higher frequencies to be heard over the noise. Van Horn notes that coyotes in Chicago have reduced their “chatter,” though in this case it’s likely less about being heard over noise and more about remaining undetected.
Species are adapting to manage physical pollutants emitted in our urban environment. Regions that experience harsh, snowy winters (like Chicago) use road salt to keep roads and sidewalks safe, but this practice introduces excess chlorides into soils when it’s launched from roads by speeding cars and runs off into waterways when the snow melts. Some fish and other species are evolving processes for counteracting the disruption to their bodies that salt causes. Schilthuizen also notes how studies indicate pigeon feathers are growing darker because darker feathers are believed to have detox properties. While we work to clean up and subject our environments to less pollution, it’s nearly impossible to eliminate it all, so these adaptations are important to these and other species’ survival. As will be explored in the next post, while pollutants can drive out native species, it is often non-native species that can then move into a polluted water body or terrestrial area, cleaning it up enough for natives to return.
Regardless of the ways species are adapting, there will certainly be many left behind who do not happen to have genes lying around, perfectly suited to an urban ecosystem, or those who might get there eventually but the change of pace is too rapid. But the hopeful message is that species do not have to go extinct in our cities; there are many that can adapt to the challenges (and opportunities) of the urban environment through evolving genes predisposed to some element of city living, or they can adapt behaviors tailored to it. Cities are therefore not uninhabitable deserts lacking diversity.
As all three authors point out, our cities are actually wildly diverse and offer up a great deal of habitat to a variety of species. For one thing, as discussed in a previous post, as ecosystem engineers our behaviors create food, shelter, etc. for wildlife to live off. Also, the agricultural land often found immediately outside of cities is practically barren in its manicured and managed state, compared to the messiness of cities and the diversity that can be found from the mixing of people and goods from all over. Not to mention the variety of places in a city, from backyard gardens, to vacant lots, to parks and green roofs.
Studies have found there is very low diversity in bird species at the concrete core of a city when there are no nearby parks. The biodiversity of remote woodlands is higher than that. But the greatest number of unique bird species can be found in cities that have big parks. – Johnson
For these reasons, wildlife is making its way and adapting to cities. With such a globalized world, it’s often nonnative species that are able to adapt to the city they find themselves in. These species are usually labeled invasive. Until I read a few of these books about urban wildlife, I knew of invasives as the bane of environmentalists, governments, and others’ existence for numerous reasons. I’ve discovered another side though, one that claims invasives may actually be our salvation. This contentious debate between native and nonnative species is the topic of the next post.