Synurbization refers to the adaptation of wildlife to the unique conditions presented by urbanized environments, with a focus on how synurbic populations differ behaviorally, physiologically, and ecologically from populations of the same species living in their natural environments. Urbanization, in terms of ecology, is the process by which natural landscapes are transformed into built environments through human development and intervention, leading to altered environmental conditions and ecological dynamics within the area. Synurbization may occur as a response to the encroachment of cities into the existing habitats of wildlife, or through the colonization and expansion of wildlife into urban environments. These adaptations are necessary for the survival of the population, as individuals possessing advantageous variations in traits or greater behavioral flexibility ultimately have higher fitness in these urbanized settings. However, while some of the behavioral adaptations are favorable for the species and allow them to persist, some may have a negative impact on the species, and the broader consequences that stem from urbanization can negatively affect both wildlife and humans.
Changes in behavior When compared to members of their species that live in natural environments, urban-dwelling populations exhibit clear behavioral differences, collectively described as "urban wildlife syndrome" since the changes are not exclusive to one species, but rather are a pattern of behaviors that have been observed across multiple taxa due to the similar conditions and selective pressures that urban environments across the world present. Urbanization transforms ecological conditions where animals live due to habitat fragmentation, human proximity, and attraction to anthropogenic foods that change selective forces. For instance, with small mammals, striped field mice urban-inhabiting are bolder, more exploratory, and phenotypically plastic than their rural counterparts. They adapt to anthropogenic shelters, foods, and novel ecosystems from their tolerance of human-modified environments, the colonization of bolder mice, and urban-specific trait selection. White-footed mice adapted through behavioral and genetic changes also exist in fragmented, urban parks, and while they require more plasticity in response to urban predation patterns, adaptability promotes success within these fragmented patches. Birds like the noisy miner have been observed conducting innovative behaviors (i.e., opening sugar packets) that mirror those of small mammals and other birds in the same urban setting, yet taxonomic differences exist in the response to the challenges of novel habitats. Urbanized ecosystems act as a filter for which species can be innovative, adaptable, and risk-prone; urbanized small mammals and other species can flourish more than other species due to social learning and temporal-spatial adaptability, suggesting more of an ability to navigate the changes humans implement in their ecosystems.
Population density increase
Including the correlation between other variables, such as aggression and wariness, multiple studies show a population density increase. Population density is the population number in one unit of area at a given time. The increase in population density has been highly correlated with the reduction in species wariness, as well as their intra-species aggression. As population density increases, wariness of humans decreases- this is known as a negative correlation. As population density increases, intra-specific aggression increases- this is known as a positive correlation. Park spaces in urbanized spaces may contribute to this population density increase. These parks allow for species to mate, and access and be fed food by humans, with little to no predation.
Decreased wariness and increased boldness
Wariness is the observable fear or caution that animals exhibit when encountering humans, typically shown through a startled response or rapid retreat. Previous research hypothesized that population density is the main influence on this behavioral change. Through coexistence, animals grow accustomed to human presence, not only becoming less startled, but also more willing to approach and physically interact with humans. For urban squirrel populations in parks in particular, this behavioral change was in response to human willingness to feed them. This is a demonstration of boldness, which is characterized by the propensity of the animal to take risks, explore novel environments, or approach potentially threatening situations. When presented with the option of feeding in a farmland or a forested area, bolder individuals across a range of wildlife species consistently demonstrated a preference for the farmland despite the risk of encountering humans, whereas shy individuals selected the safer, forested area for foraging. Across various species, increasing levels of synurbization have been positively correlated with an increase in boldness. Species that colonized urban environment earlier consistently show increased boldness when compared to more recently synurbanized species, reflecting cumulative long-term processes rather than short-term plasticity alone.
Increased intra-specific aggression
Intra-specific aggression refers to antagonistic interactions toward members of the same species. The increase in intra-specific aggression may be the result of the increase in population density, as having more members of a species in a smaller unit area, all whilst still competing for the same resources, like food, shelter, and nesting sites, has been linked to competition and higher aggression levels. While these patterns favor the survival and reproductive success of bold or competitive individuals, they also introduce the risk for injuries and stress, and they negatively affect the fitness and survival of subordinate individuals.
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