Featured Image Caption: Cities are ecosystems riddled with change. Animals must adapt to the rapid changes brought about by humans to survive city-life (Source: via Wikimedia Commons).
Reference: Alberti, M., Palkovacs, E. P., Des Roches, S., De Meester, L., Brans, K. I., Govaert, L., Grimm, N. B., Harris, N. C., Hendry, A. P., Schnell, C. J., Szulkin, M., Munshi-South, J., Urban, M. C., & Verrelli, B. C. (2020). The complexity of urban eco-evolutionary dynamics. BioScience, 10 (9), 772-793. https://doi.org/10.1093/biosci/biaa079
What’s the Deal with Cities?
Our planet is urbanizing rapidly. This means that more and more people are living in cities. Cities are unique habitats with multistory buildings, endless pavement and concrete, and tons of people. In addition to being habitats for humans, cities are homes for many plants and animals that must adjust to the environmental changes we cause.
Cities have existed for thousands of years. So, why should we be concerned about the impact of city-life on plants and animals? Advancements in technology have allowed us to live more densely than ever before. Cities accommodate growing populations by expanding into natural habitats. Humans pose threats to plant and animal life, especially in cities. But, why are cities such a challenging habitat for many organisms? Marina Alberti, and many other experts in the field of urban ecology and evolution, reviewed how humans in cities alter the environment and cause rapid evolution of the organisms that live there. Many other factors exist in addition to those summarized below.
i. Altering and Disturbing Habitats
One of the most obvious ways that humans influence the environment is by disturbing habitats. When we alter natural habitats to build cities, plants and animals either die or adapt to the changes. Extinction is likely if organisms cannot keep up with their change. If only a few individuals survive, low gene diversity could threaten persistence. Diverse genes among individuals allow a population to adapt to changing environments. Increased variation may ensure that at least some individuals can survive disturbances. Consider having a toolbox in your home that contains diverse tools. You would be ready for many problems that arise in your home. However, fixing these issues could become harder if you lack the appropriate tools.
Pollution from emissions and pesticides also creates challenging conditions. Pollutants are excreted into the water supply because pavement and concrete deplete the ability of soil to retain water. This is why cities are called concrete jungles. These surfaces also trap heat from the sun and increase the average temperature in cities.
ii. Creating Diverse Patches that Lack Connection
Humans fragment the natural green spaces in cities and the resulting patches are not well-connected. It can be a treacherous task for animals to get from one suitable patch to another. Take for example a fox that depends on wooded areas for shelter. When he decides to look for a mate, the closest wooded area is across the other side of the city. As a result, the fox is isolated to the few female foxes in his patch that may be closely related. Mating individuals that share genes cause further declines in gene diversity.
Further, patches are quite different from one to the next. A patch in the center of the city will have limited green space, bright lights through the night, and high levels of air pollution. A nearby patch in a city park will have thicker tree cover and more diverse animal life. In a dry climate, one house may use sprinklers to keep their grass lawn watered, while their neighbor grows native plants adapted to the dry conditions. People living in residential patches often provide seed for birds, whereas garbage and litter are the available food source in city centers. The variation in patch quality could pose challenges for animal movement and food availability.
iii. Changing Species Interactions
Humans affect interactions between species. Advancements in transportation technology – such as the introduction of ships, airplanes, and cars – increased our mobility. As a result, we transport and introduce organisms to new habitats either purposely or accidentally. When organisms are introduced to new habitats, they could compete with native species for food and other resources. These interactions can affect the function and structure of an ecosystem. We also change the way that organisms interact with us. Some city animals show less fear of humans due to constant contact with people. You may have encountered fearless squirrels that will walk right up to you and beg for food!
Cities as Diverse, Complex, and Shared Habitats
Cities are complex habitats, and no two cities are alike. Cities differ in age since foundation, socioeconomic factors, population density, and demographics. Each of these factors will impact what plants and animals can survive. Public policy also dictates how we design cities. The impact of cities on plant and animal life reaches beyond city boundaries. For example, pollution contributes to climate change, which affects organisms in every habitat. To further complicate things, it takes time to see the effects of our actions.
The environmental changes humans cause, in turn, affect humans. Altered ecosystems affect food quality, aquatic health, disease transmission, and the cultural values of organisms and natural spaces. Researchers in urban ecology and evolution are learning more and more about city habitats. They study plant and animal responses to city conditions across cities and over time. One way you can help reduce the effects of urbanization is to vote for and join initiatives that increase public transportation, add green spaces to cities, and combat poverty by creating job opportunities.