Abstract
Cities around the world have converged on structural and environmental characteristics that exert similar eco-evolutionary pressures on local communities. However, evaluating how urban biodiversity responds to urban intensification remains poorly understood because of the challenges in capturing the diversity of a range of taxa within and across multiple cities from different types of urbanization. Here we utilize a growing resource—citizen science data. We analyzed 66,209 observations representing 5,209 species generated by the City Nature Challenge project on the iNaturalist platform, in conjunction with remote sensing (NLCD2011) environmental data, to test for urban biotic homogenization at increasing levels of urban intensity across 14 metropolitan cities in the United States. Based on community composition analyses, we found that while similarities occur to an extent, urban biodiversity is often much more a reflection of the taxa living locally in a region. At the same time, the communities found in high-intensity development were less explained by regional context than communities from other land cover types were. We also found that the most commonly observed species are often shared between cities and are non-endemic and/or have a distribution facilitated by humans. This study highlights the value of citizen science data in answering questions in urban ecology.
Highlights
Cities around the world exist in a range of environmental contexts, yet because of the requirements and preferences of their human inhabitants, they share commonalities such as landscape fragmentation, altered water and resource availability, and high densities of fabricated structures and impervious surfaces that alter climate (Rebele, 1994)
Our findings provide some support for biotic homogenization, no single species was recorded in the highest level of urbanization across all cities
While we find that community composition is significantly impacted by degree of urban intensification, the role of geographic and environmental region seems to have a larger role in determining communities
Summary
Cities around the world exist in a range of environmental contexts, yet because of the requirements and preferences of their human inhabitants, they share commonalities such as landscape fragmentation, altered water and resource availability, and high densities of fabricated structures and impervious surfaces that alter climate (Rebele, 1994). Plants have been found to bloom earlier in city centers due to the urban heat island effect (Mimet et al., 2009), bird migratory patterns have shifted to take advantage of resource availability (Tryjanowski et al, 2013), and invasive species can be more prominent because of increased rates of species introductions (Tsutsui et al, 2000) While such modifications are still relatively recent on an evolutionary time scale, phenotypic changes have been observed across taxa on a global scale as eco-evolutionary consequences of urbanization (Alberti, 2015). Understanding such changes can help us better plan for future ecological dynamics in cities, such as predicting population vulnerability to invasive species or minimizing human-wildlife conflicts, such as property damage or health hazards A review of 105 studies on species richness along urban to rural gradients demonstrated inconsistent patterns—while some studies found that species richness decreases with higher urban intensification, other studies found the opposite (McKinney, 2008)
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