UC Santa Cruz

Ecological complexity supports biodiversity, robust community structure, and resilient ecosystem functions. In agroecosystems, adding ecological complexity by diversifying crops and agricultural landscapes can help foster complex webs of relationships between pests and their natural enemies that leads to enhanced biological pest control. Urban community gardens provide a unique opportunity to investigate how differences in human management and urban landscapes affect the insect biodiversity, species interactions, and ecosystem services that support food production in urban settings. In my dissertation, I investigate various forms and scales of ecological complexity in community gardens of the California central coast to understand the social and ecological processes that give rise to this complexity as well as its implications for biological pest control in urban agriculture. First, I quantify ecological complexity at the local scale of individual gardener plots by measuring the density, diversity, and connectivity of plot vegetation and its impacts on garden herbivores and natural enemies (Chapter 1). Next, I use ecological networks of interactions between pests and parasitoid wasps to measure changes in pest–parasitoid interactions along gradients of local garden management and landscape composition (Chapter 2). Additionally, I examine the metacommunity structure of herbivores and natural enemies inhabiting urban gardens in the study region and identify garden habitat and landscape characteristics that influence arthropod metacommunity structure (Chapter 3). Finally, I examine how differences in gardener aesthetic norms and management priorities lead to variation in ecological complexity in community gardens (Chapter 4). In line with agroecological theory, this work finds that higher amounts of ecological complexity support greater natural enemy diversity and higher rates of pest parasitism. While common preferences for “tidiness” may limit ecological complexity in some garden plots, gardeners who prioritize “wildness” in their plots present viable alternatives for garden management that help to diversify the ecological habitat and resources provided by community gardens.