Urban ecophysiology: beyond costs, stress and biomarkers

Abstract

Natural habitats are rapidly declining due to urbanisation, with a concomitant decline in biodiversity in highly urbanised areas. Yet thousands of different species have colonised urban environments. These organisms are exposed to novel urban conditions, which are sometimes beneficial, but most often challenging, such as increased ambient temperature, chemicals, noise and light pollution, dietary alterations and disturbance by humans. Given the fundamental role of physiological responses in coping with such conditions, certain physiological systems such as the redox system, metabolism and hormones are thought to specifically influence organisms’ ability to persist and cope with urbanisation. However, these physiological systems often show mixed responses to urbanisation. Does this mean that some individuals, populations or species are resilient to the urban environmental challenges? Or is something missing from our analyses, leading us to erroneous conclusions regarding the impact of urbanisation? To understand the impact of urbanisation, I argue that a more integrated mechanistic and ecological approach is needed, along with experiments, in order to fully understand the physiological responses; without knowledge of their ecological and evolutionary context, physiological measures alone can be misinterpreted. Furthermore, we need to further investigate the causes of and capacity for individual plasticity in order to understand not only the impact of urbanisation, but also species resilience. I argue that abiotic and biotic urban factors can interact (e.g. pollution with micro- and macronutrients) to either constrain or relax individual physiological responses – and, thereby, plasticity – on a temporal and/or spatial scale, which can lead to erroneous conclusions regarding the impact of urbanisation.

Anthropogenic food availability and body mass maintenance in urban Red-winged Starlings Onychognathus morio

“…Similar results were found in American Crows Corvus brachyrhynchos where nestlings in urban areas were also smaller and more nutritionally restricted than those in rural areas (Heiss et al 2009). A 'junk food' diet can be linked to reductions in dietary antioxidants and essential fatty acids with severe health implications (Isaksson et al 2017;Isaksson 2020). This can be exacerbated by the increased pro-inflammatory properties of some fatty acids found in urban diets (Andersson et al 2015).…”

Variation in Hematological Indices, Oxidative Stress, and Immune Function Among Male Song Sparrows From Rural and Low-Density Urban Habitats

“…However, even with increasing attention paid to interactions among wildlife and urban landscapes, it remains difficult to predict the costs and benefits of urbanization for wildlife due to a lack of consensus on how animals respond physiologically to urbanization. Recently, there has been growing recognition that site-specific differences in biotic and abiotic variables are major factors determining how animals respond to urbanization (Isaksson, 2020). For example, the anthropogenic landscape of high-density metropolitan habitats differs dramatically from low-density suburban habitats (Chace and Walsh, 2006;Aronson et al, 2014).…”

City comfort: weaker metabolic response to changes in ambient temperature in urban red squirrels

“…However, despite the central role of physiology, our understanding of its contribution to the adaptability of wildlife to urban conditions is still limited. Urban heat islands, characterized by higher T a , higher precipitation and altered wind velocity 22 – 24 are assumed to alter or negatively affect the metabolism of urban wildlife 11 , 12 , 25 , 26 . Access to human-derived foods in urban habitats offer a more stable year-round food availability compared to rural or undisturbed natural environments 8 .…”

“…Akin with findings from other urban species 28 , 43 , the diet composition of urban squirrels can differ from their rural counterparts and they may feed on nutrient poor food items 44 . Furthermore, urban populations can be exposed to higher levels of intra- and interspecific contact rates, parasite transfer, stress, and exposure to environmental pollutants that might impact metabolism 11 , 25 , 45 .…”