A citizen science approach to evaluating US cities for biotic homogenization

Area of Science:

• Urban Ecology
• Conservation Biology
• Biodiversity Science

Background:

• Cities worldwide share structural and environmental traits, creating similar eco-evolutionary pressures.
• Understanding urban biodiversity responses to intensification is challenging due to data limitations across diverse urban settings.
• Citizen science offers a valuable, large-scale data resource for ecological studies.

Purpose of the Study:

• To investigate urban biotic homogenization across varying levels of urban intensity in 14 U.S. metropolitan areas.
• To assess the influence of regional context versus local factors on urban biodiversity composition.
• To evaluate the utility of citizen science data for urban ecology research.

Main Methods:

• Analyzed 66,209 citizen science observations (5,209 species) from the City Nature Challenge (iNaturalist).
• Integrated remote sensing data (NLCD2011) to quantify urban intensity.
• Employed community composition analyses to compare biodiversity patterns across land cover types and urban intensities.

Main Results:

• Urban biodiversity composition is largely driven by local taxa, with limited evidence of widespread biotic homogenization.
• Communities in high-intensity urban development were less explained by regional context compared to other land cover types.
• Frequently observed species across cities were often non-endemic and/or human-facilitated, suggesting facilitated dispersal.

Conclusions:

• Citizen science data is a powerful tool for understanding urban biodiversity dynamics.
• Urbanization does not necessarily lead to homogenization; local factors remain dominant drivers of biodiversity.
• Highly urbanized areas may exhibit unique biodiversity patterns less influenced by broader regional species pools.