Research

Kaiser, A., & Resasco, J. (2024). The impact of impervious surface and neighborhood wealth on arthropod biodiversity and ecosystem services in community gardens. Urban Ecosystems, 27(5), 1863-1875. https://doi.org/10.1007/s11252-024-01560-y 

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Abstract: As the number of humans living in cities has grown, interest in the value of community gardens to provide agricultural products has increased. However, neighborhoods with different land cover patterns and socioeconomic characteristics often differ in their ecological attributes, leading to potential differences in biodiversity-mediated ecosystem services (e.g., pollination and pest control). Here we ask, how do impervious surface and socioeconomic features of the urban matrix around community gardens impact arthropod biodiversity and pollination and pest control. services? We collected arthropods (insects, arachnids, myriapods, and isopods) across community gardens in Boulder Co., CO, and used experimental jalapeño pepper plants as a sentinel crop to measure herbivory damage and pollination services. We categorized arthropods into functional guilds to see how impervious surface and neighborhood wealth in the urban matrix surrounding a site impacts the abundance of three focal groups – pollinators, herbivorous pests, and predators. We also looked at how bee Hill-Simpson diversity responded to these variables. Through structural equation modeling, we found that fruit size increased as bee biodiversity increased, and bee biodiversity and overall pollinator abundance were negatively related to neighborhood wealth. Additionally, pollinator abundance was lower in gardens surrounded by higher amounts of impervious surfaces. Neighborhood wealth and impervious surfaces were positively correlated with herbivore and predator abundances, but these abundances had no relationship with herbivory damage in our plants. This research shows that reducing the amounts of impervious surface in the urban matrix can help increase bee biodiversity and abundance and improve pollination services in urban community gardens.

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Kaiser, A., Resasco, J. & Dee, L.E. Synthetic control methods enable stronger causal inference using participatory science data in cities. Nature Ecology & Evolution (2026). https://doi.org/10.1038/s41559-026-03084-4  

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Abstract: Urban environments pose unique challenges for understanding drivers of biodiversity change, as fragmented land ownership makes traditional biodiversity monitoring and randomized experiments logistically difficult. While participatory science platforms such as iNaturalist offer a promising data source by providing extensive biodiversity data from urban areas, inferring causality remains challenging because of confounding factors in observational data. To leverage these data advances, we offer a framework that combines records from iNaturalist with synthetic-control methods, a quasi-experimental approach. We demonstrate this approach in a case study assessing the impact of Hurricane Ida (2021) on the number of research-grade iNaturalist bee observations, used as a proxy for bee abundance, in Philadelphia, USA. The synthetic control estimated a 15.5–20.9% decline in bee observations in the 2 years post-event. By contrast, three conventional ecological analyses—an interrupted time-series regression, before–after comparison and a before–after control impact design—failed to detect this decline. Synthetic-control methods offer a powerful tool for estimating city-wide biodiversity responses to climate events and policy interventions, enhancing the utility of participatory science data for urban ecology.

Keywords: citizen science, community science, GBIF, causal analysis, urban biodiversity, driver attribution

Kaiser A, Mayer N, Aronson Cajas PR, Resasco J. (2026) Urbanization and wealth alter arthropod biodiversity and pollination services in community gardens. Preprint: https://doi.org/10.64898/2026.09.18.752681 

1. As city populations expand globally, understanding how urbanization shapes ecosystem services is increasingly important. Urban agriculture plays a key role in food access, particularly in low-income areas with limited access to fresh produce. Arthropods play important roles in these systems through pollination, herbivory, pest control, and nutrient cycling. Urban development of natural areas often reduces biodiversity, including that of arthropods. Additionally, urban biodiversity frequently correlates positively with socioeconomic conditions, a pattern known as the luxury effect.

2. In this study, we examined how gradients in urbanization and socioeconomic context relate to local and landscape habitat quality, arthropod abundance, and pollination services across 21 community gardens in the Denver, CO Metro Area. To quantify ecosystem services, we employed a sentinel plant, Cucumis sativus (cucumber), and collected arthropods (insects, myriapods, arachnids, isopods), assigning them to functional groups based on their known feeding behavior. We evaluated direct and indirect pathways linking urban matrix characteristics to arthropod-mediated ecosystem services.

3. The abundance of all arthropod groups (including pollinators, herbivores, and natural enemies) declined steeply with increasing impervious surface. Neighborhood wealth was associated only with bee species richness and Shannon diversity and displayed a hump-shaped pattern that peaked at wealth levels 35-46% above the national average, then declined. Multivariate GLMs revealed that Western honeybees (Apis mellifera) were the only species driving differences in bee community composition, with their abundance positively related to neighborhood wealth.

4. We also observed pollen limitation in our cucumber plants, and as bee Shannon diversity increased, cucumber production increased. Environmental covariates alone showed no direct relationship with cucumber production, indicating that insect pollination mediated this effect. This work identifies the biophysical and social-ecological drivers of urban arthropod biodiversity and ecosystem services, revealing where crop production may be most vulnerable to decline in cities.

Keywords: urban biodiversity, socioecological, pollinators, insects, urban agriculture, cucumbers