The rate of urbanization is increasing greatly and with that, comes large human populations. Our population has increased from 6 billion people in 2000 to roughly 7.8 billion people in 2020 and in North America alone (~370 million people), over 80% of people reside in cities. These urban areas serve as an epicenter for human populations and are known to have many environmental consequences – creating heat islands, fragmenting populations, introducing pollution, and pushing some species towards extinction.
Broadly, urban ecology investigates how humans are affecting living organisms (i.e., animals, plants, microorganisms). However, since its inception, urban ecology has neglected to recognize the factors that influence the layout of a city and how humans interact with it. Urban ecology was originally developed as part of human ecology in the 1920s by a small group of sociologists at the University of Chicago. Even with sociologists at the core of urban ecology, the focus of the field was on topics such as competition, adaptation, dominance, and succession. Although these areas are crucial for understanding the systems within cities, these researchers still ignored factors such as redlining, segregation, and other racially influenced policies, that have shaped the way humans live.
When we fast forward to the 2010s, we see studies recognizing that factors such as socioeconomic status can influence the environment an animal encounters. Recently, Dr. Christopher Schell, an urban ecologist at the University of Washington (and contributor to this blog), and collaborators published a review paper in Science evaluating “The ecological and evolutionary consequences of systemic racism in urban environments”.
When investigating urban systems, it’s important to remember that this ecosystem is a complex, dynamic area with unique interactions. Urban areas are highly heterogeneous, encompassing a mix of structures ranging from tall buildings to small houses with changes in density. This heterogeneity creates unique spatial patterns that influence the movement patterns of animals, along with other behavior. To further understand these observations, we must recognize what has shaped this heterogeneity in cities. The unequal distribution of wealth has led to cities being split into different ecosystems an animal can experience. In richer areas (which are predominately white), we see greener spaces and overall, more flora which leads to more biodiversity (Figure 3). On the other side of this coin, we see poorer areas (predominantly composed of non-white individuals) have less tree coverage, less flora, which decreases biodiversity (Figure 3). This phenomenon has been termed the luxury effect. The luxury effect can vary between cities and along a socioeconomic gradient. With less biodiversity, more pollution and higher temperatures, animals in these areas can show phenotypic differences from their counterparts in rural or wealthier areas.
Although we see the effects of wealth on fauna/flora and their surroundings, Schell et al. points out that we must examine what has led to the disparity in wealth that has created these areas. At the heart of these issues is the systemic racism established with this country. Policies like redlining and segregation have indirectly affected the reduction in vegetation and biodiversity we observe in lower socioeconomic areas by enforcing the wealth gap (check out how cities across the nation were segregated with redlining practices). Studies have found that the spatial arrangement of vegetation can drive evolutionary change the way animals navigate the landscape and that impervious surfaces are linked with reduced movement in organisms. This is particularly important as individuals within these areas may experience lower gene flow leading to lower genetic diversity; tree cover has been shown to resolve this (ex. populations of white-footed mice in New York City).
Discriminatory policies like those discussed have led to populations of Black Americans disproportionally being housed near polluting industries and urban heat islands. Over time, these areas have created selected pressures, shaped mutation rates, and influenced disease dynamics for the flora and fauna there (Figure 1). These low-income communities often lack water sanitation, medical access, and intervention all while having high proximity to zoonotic disease.
Understanding the underlying mechanisms that have shaped these communities and the United State we see today is incredibly important for social and environmental justice. When we begin to investigate topics in ecology such as behavior or movement, we as scientists know to look at the history of the system and how mechanisms may have shaped what we are observing today.
Humans are the driving force for many systems and to understand this further, we must look at our own history to explain what we are observing. In order to move forward in urban ecology and evolutionary biology, we must have intersectionality within our work, on all levels; from the identities of authors to the departments involved. Dr. Schell and collaborators elaborate on future directions urban ecology, and science as a whole, must take in order to move forward in our field. As the authors stated, we cannot understand humans and urban ecosystems without dealing with systemic racism. Additionally, they highlight that conservation work in urban areas and social justice are intertwined and should not be considered two separate entities.
“We will not be able to successfully assess how racism and classism shape urban ecosystems – nor address their consequences – without a truly diverse and inclusive scientific community.” – Schell et al. (2020).
Read the full paper here and check out Dr. Christopher Schell’s lab here.
Featured Image: United States Federal Government, Holc redlining 1937, marked as public domain, more details on Wikimedia Commons
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