Understanding the urban ecosystem : interactions between plants, animals, and people

Sammanfattning: Cities are the pinnacle of human change to the environment, creating unique types of ecosystems which present many challenges to local organisms: habitat fragmentation, introduced species, and various pollutants. Being crucibles of anthropogenic effects, urban ecosystems offer opportunities to understand how humans impact nature. Moreover, since a majority of the world’s population resides in cities today, urban nature has become the most frequently encountered type of nature in everyday life. Studying urban ecology therefore has the potential to shed light on both sides of the interaction between people and nature. In this thesis, I used an interdisciplinary approach to explore the effects of urbanization on vegetation, arthropods, birds, and people. Studying several taxa, and using methods from Ecology, Physiology, Sociology, and Aerosol technology, I aimed to develop a holistic and multifaceted understanding of the urban ecosystem. Specifically, I investigated urban trophic interactions, how air pollution and nutrition may affect animal physiology, and how local wildlife influences children’s well- being and perception of nature. I outline three key findings from the six papers forming the basis of my thesis: (1) plant origin is a strong determinant for urban arthropod abundance and breeding success of birds. Namely, non-native trees show a negative effect, with a magnitude and consistency over years, which indicates that vegetation composition is a key driver limiting animal populations in cities. (2) urban birds are constrained by food quality (specific nutrients) during breeding, likely due to low abundances of certain arthropods in cities. Moreover, high quantities of low-quality food (e.g., from human sources) do not compensate for the urban birds’ dietary deficiency and may instead lead to reduced capacity to mount physiological responses to deal with air pollutants or infections. (3) children’s relation to nature (attitude and knowledge) is not impacted by urbanization but predicted instead by socioeconomic factors and the quality of nature close to their homes. These local differences call for more detailed approaches when studying cities since both social and environmental variation within urban areas can be more consequential than general divides. In this thesis, I demonstrate the importance of native vegetation in cities and food quality for urban animals. Local wildlife influences people and by better understanding the urban ecosystem, we are one step closer to building cities that will allow future generations to learn about species and enjoy nature near their homes.