These changed environmental conditions exert unique selection pressures on their inhabitants, leading to physiological and behavioral adaptations in city-dwelling plant and animal species.
Shared aspects of cities worldwide give ample opportunity for scientists to study the specific evolutionary responses in these rapidly changed landscapes independently.
[6] Urbanization intensifies diverse stressors spatiotemporally such that they can act in concert to cause rapid evolutionary consequences such as extinction, maladaptation, or adaptation.
Specifically, pigeons in hotter areas showed elevated oxidative stress, suggesting that urban heat could compromise their health.
Human activities, including urbanization, have greatly increased selection pressures due to pollution of the environment, climate change, ocean acidification, and other stressors.
Over time, animals may adapt to these stressors through changes in their physiological systems, such as increased lung capacity or more efficient detoxification mechanisms to cope with pollutants.
The peppered moth (Biston betularia) is a classic example of industrial melanism, where moth populations adapted to increased soot and pollutants by evolving darker coloration, which allowed them to better blend into the soot-darkened trees during the industrial revolution[18][19] For plants, long-term exposure to pollutants like ozone can impair vital structures on their leaves, disrupting gas exchange and reducing growth.
These physiological changes to both flora and fauna influence urban ecosystems, determining which species can survive and reproduce in polluted environments.
[17] A study on Great tits (Parus major) also found that air pollutants, in combination with local tree composition and temperature, affect their nestling physiology.
Specifically, antioxidant capacity and fatty acid composition in these birds were influenced by the surrounding environmental conditions, including pollution levels.
Prolonged exposure to high noise levels can interfere with animals' communication, navigation, feeding behaviors, and stress response mechanisms.
These remnants of wild vegetation or artificially created habitats with often exotic plants and animals all support different kinds of species, which leads to pockets of diversity inside cities.
For instance, city-dwelling animals like birds may evolve shorter wings to better navigate between buildings, or insects might develop resistance to pesticides commonly used in urban settings.
example birds in cities often start singing earlier in the morning due to the prevalence of artificial lighting, which can affect their mating patterns.
Species in these fragmented areas often experience unique evolutionary pressures, leading to genetic drift and divergence from rural populations.
In one study, researchers examined how early life experiences, particularly adverse conditions, influence behavior in European starlings (Sturnus vulgaris).
The birds were found to be more efficient at locating food and gathering relevant information from their surroundings, suggesting that early adversity may encourage greater exploration and resource acquisition strategies as an adaptive response to uncertainty.
[25] Their findings imply that animals experiencing early adversity in fragmented environments may develop enhanced abilities to locate and exploit scattered resources.
Just as the starlings in the study displayed increased cognitive flexibility in their foraging and information-gathering behaviors, animals in urban ecosystems may also adopt similar strategies to cope with the effects of habitat fragmentation.
Cognitive flexibility enables animals to adapt to fluctuating conditions, such as changes in food availability or alterations to shelter and nesting sites, which are common in urbanized landscapes.
[27] Urbanization often leads to changes in the availability and distribution of food, water, and shelter, prompting behavioral, physiological, and morphological adaptations in species that can exploit new resource environments.
Resource availability also acts as a selective force in urban evolution, influencing the survival and reproductive success of species living in cities.
Urban areas offer a distinctive array of resources, including food sources like garbage, human waste, and crops, often differing in quantity and quality from those found in natural habitats.
[28] This can be seen in the New York City white-footed mice (Peromyscus leucopus) as its tooth rows adapt a structure that can chew on the foods and resources available.
A recent study reveals the urban raccoons ability to solve foraging challenges, demonstrating innovative problem-solving skills.
An example of nonadaptive change related to genetic drift and gene flow is the burrowing owl (Athene cunicularia) in urban Argentina.
Plants from different urban, suburban, and rural areas were raised under similar conditions and exposed to herbivory (locust grazing).
The new conditions associated with urban infrastructure, air and noise pollution, habitat fragmentation, differential food availability, humans and cars, and so on may be difficult for certain species to adapt to.