Mixed effects of urbanization on pollination services among four native plant species

Abstract The pollination services provided by insects maintain ecosystem functioning and services in urban green spaces. Most research investigates rural to urban gradients where it is found that pollination services are often greater in urban green spaces than in rural counterparts. However, as urbanization intensifies, the extent to which pollination services are maintained as urban green spaces are replaced and become increasingly fragmented requires further research. The purpose of this study was to examine pollination services across gradients of within‐city urbanization, urban green space fragmentation and local floral richness. We deployed four plant indicator (phytometer) species across 10 community gardens that varied in urban cover and urban green space edge density. We measured visitor rate and α‐diversity, and related these factors to plant reproductive outcomes for each phytometer species. While we predicted a negative effect of urbanization, we found limited evidence that pollination services decline across the sampled within‐city urbanization gradient. Contrary to our expectation, Lobelia siphilitica (Asterales: Campanulaceae) L. showed increased visitor α‐diversity and higher mass per seed in more urbanized gardens, suggesting positive urbanization effects. Fragmentation effects were mixed, with edge density positively correlated with one of the four phytometer species and negatively correlated with another species. Local garden richness did not influence pollination services, likely due to uniformly high floral richness across gardens. Our findings suggest that in some cases, highly urbanized community gardens can not only maintain pollination services but also outperform less urbanized gardens. However, both urbanization and fragmentation effects were highly species‐specific, highlighting the need for further research on how landscape heterogeneity and plant traits interact to influence urban pollination services.