Island biogeography in the city: How urban park characteristics shape Lepidoptera communities in metropolitan landscapes

Global Lepidoptera populations are declining due to increasing habitat loss, pesticide use, and urbanization. Yet urban green spaces may serve as important conservation refuges. However, the role of these green spaces in supporting Lepidoptera population dynamics remains poorly understood, particularly across diverse metropolitan regions. We investigated how urban park characteristics influence Lepidoptera populations across two major US metropolitan areas: 475 parks in Los Angeles and 1,353 parks in New York City. We analyzed 32,619 iNaturalist research-grade observations from 2020-2024, examining 1,167 species using dynamic occupancy models. Our analysis examined how park characteristics (size, connectivity, flowering plant diversity, and land cover composition) and species traits including wingspan (affecting dispersal capacity) and flight phenology (onset and duration of flight periods) affected occupancy, colonization, persistence, and detection probabilities. We hypothesized that larger, well-connected parks with diverse vegetation would support higher occupancy, colonization, and persistence probabilities, and that species traits would influence detection probability. Consistent with island biogeography theory, larger parks increased occupancy probability in both metropolitan areas. Species with greater wingspan showed higher colonization probability, while higher flowering plant richness promoted population persistence. Species with earlier and longer flight periods had higher detection probability. These findings suggest that urban park design should prioritize larger park size and higher flowering plant diversity to maximize conservation benefits for Lepidoptera. We plan to expand this framework to additional metropolitan areas to develop comprehensive urban pollinator conservation guidelines across the United States.