coverimage

Illustration by Sidra Dahhan

Urbanizing Ecosystems: What happens when we build cities where nature once was?

Urban environments affect us and other organisms in many unexpected ways. Here is a review of several studies and their intriguing findings.

Apr 2, 2023

From lizards to humans, studies conducted on mental wellbeing and physical adaptations have noted patterns of changes in response to the ways cities affect natural biological systems. Here are a few I found intriguing (and slightly concerning) to see in the rapid changes in organisms due to the modification of their surroundings.
Studying lizards as a source of adaptation in urban settings
The study and podcast under Proceedings of the National Academy of Sciences published by Kristen M. Winchell and her team explain how 96 species of the Puerto Rican lizard show similar adaptations to the change in the three landscapes even though they were genetically quite different from each other. The longer limbs and toe pads these lizards exhibit, when comparing the small anole lizards to their counterparts living in the forested areas surrounding the city, gave them an idea of the changes they had made in their bodies to help them cope with living in urban areas. DNA studies, especially of the sections that code for proteins, helped the researchers hypothesize these changes were for running faster in “open areas” or for holding on to smooth surfaces that do not exist in their natural environments.
This study can be used to maintain urban settings in a way that preserves species that live in them and understand how they function in man-made landscapes. It also looked at the similar evolution of animals in three distinct regions. This parallelism in the selection of characteristics is perhaps something we can appreciate in nature.
Relating cortisol levels with stress in deprived urban communities
Are green neighborhoods happy neighborhoods? Urban neighborhoods and the effects of the amount of greenery within them have been studied, specifically by comparing the levels of the stress hormone cortisol among people living there. Monitoring salivary cortisol levels of 96 men and women in an experiment in Dundee, UK, at regular intervals showed a clear correlation. Though cortisol levels have a strange curve (based on gender or conditions like depression), the results being adjusted for these still showed that healthier cortisol levels resulted from an abundance of greenery in their environments.
The Telomere Effect, by Elizabeth Blackburn and Ellisa Epel, also discussed this phenomenon in some depth, looking at studies where men in Hong Kong who lived in the city had shorter telomeres (caps that protect our DNA) and were prone to faster aging of cells. This makes illness inevitable as our cells stop dividing. Hence, other than the psychological help that greenery provides, as in increased happiness and benefits to mental health, they also protect us at the cellular level.
How Does Urbanization Affect Plants?
The picture of urbanization itself often has plants cut out of it, or rather, arranged in ways that ornament or pave pathways that keep the buildings in the spotlight. Changes like water and nutrient availability, pollution and traffic, also need to be taken into account. But apart from the obvious ways plants experience changes in an urban landscape, we also see that they no longer have one important obstacle: larger herbivores. The very thing that plants try to fight, with mechanisms like thorns or needles, dry leaves, or even spraying their own kinds of chemicals (like the white clover, that releases the wrath of hydrogen cyanide on its predators), is not a problem anymore. This causes the clover to not need the mechanism, and the ability to secrete is no longer a do-or-die factor (or a selection factor). Even the insects that live on or off them change behaviors due to the changes in the environment, such as arriving later in the season, or just being unable to survive. These factors may consequently impact the growth of these host plants.
Another effect discussed in an article by Lindsay S. Miles and her colleagues is the emergence of the power of the smaller herbivores, like insects. Some plants being under-watered or not being able to deal with temperature changes endure stress, and that seems to reduce their defense mechanisms against insects leading to their eventual demise. Another means is when they are able to adapt well to these changes and become larger or grow more, making them a better (and perhaps more inviting) potential meal for these critters.
The environment we live in is quite interconnected, and we depend quite heavily on each other unknowingly. Each of the examples may not lead to anything too harmful alone, but they happen simultaneously which needs to be examined closely. Urbanization is an issue of the present, with 56 percent of the global population living in cities with the population on a trend to double in 2050. While researchers work to make versions of eco-friendly cities, I believe it is important to raise awareness about how our landscapes are shaping our lives just as we shape them. I hope by highlighting some of their work, it may be easier to understand some of the complexities that arise with handling nature with care.
Iman Lalani is Columns Editor. Email them at feedback@thegazelle.org
gazelle logo