COS 233-4 - Landscape-scale interaction networks reveal geographic variation in the identity of keystone native host and nectar plants for Lepidoptera in California

Abstract: While Lepidoptera conservation in the US has focused mainly on planting milkweeds for monarchs, hundreds of other butterfly and moth species are declining. Like the monarch, each species requires specific native host and nectar plants, which are disappearing due to climate change, habitat destruction, and other stressors. As resources for conservation are limited, it is important to prioritize conservation actions to maximize benefits to biodiversity. For example, prioritizing certain keystone plant species for habitat restoration projects may help support entire insect communities. However, there has been little work to identify these keystone plant species, especially across large geographic regions where community composition and ecological interactions can shift significantly. Integrating conservation science with network theory provides a robust, quantitative approach to prioritizing species based on their functional importance in communities. Here, we leverage scientific databases and community science data sets to construct interaction networks comprising thousands of Lepidoptera species and their native host and nectar plants in California. Using a spatially explicit approach that considers species distributional overlap, we analyze species roles in network modules to identify keystone plant species that support community stability at both local and landscape scales. We find that the composition of these keystone species varies significantly between California ecoregions and habitat types, highlighting the importance of considering spatial variation. We also find that across communities, the composition of Lepidoptera host plants differs significantly from nectar plants, indicating the need to plant both to support entire Lepidoptera life cycles. This research contributes valuable information to advance Lepidoptera conservation in California, and demonstrates a landscape-scale and community-level approach to conservation prioritization that can be extended to other geographic areas and taxonomic groups. In order to help the general public participate in Lepidoptera conservation, we have partnered with The California Native Plant Society to incorporate our findings into free online tools designed to help people select local keystone host and nectar plant species to use in landscaping projects.