Effect of Invasive Plant Removal on the Density of<i>Peromyscus sonoriensis</i>in Point Reyes National Seashore, California, USA

Non-native plants can affect communities through direct competition, and by providing refuge to seed predators, creating apparent competition with native plants. <i>Ammophila arenaria</i> (European beachgrass) has been introduced to coastal dune habitats throughout the western United States, where it forms dense monocultures, stabilizes dunes, and alters abiotic and biotic conditions. The dominance of European beachgrass is linked to declines of <i>Lupinus tidestromii</i> (Tidestrom’s lupine), an herb endemic to coastal dune communities in central and northern California. <i>Peromyscus sonoriensis</i> (western deer mice), a native seed predator, use beachgrass as refuge from predators. Tidestrom’s lupine near European beachgrass stands experience greater predation pressure from deer mice. At Point Reyes National Seashore, California, USA (PRNS), mechanical removal, manual pulling, and herbicide treatment have been used to reduce the density of European beachgrass near Tidestrom’s lupine populations. We trapped deer mice at five sites in PRNS that experienced different management regimes and used spatially-explicit capture-recapture models to estimate deer mouse density as a function of site and habitat treatment. We found that deer mouse density was lowest in areas where European beachgrass was mechanically removed and in herbicide-treated foredunes, and highest in areas highly invaded by European beachgrass and <i>Carpobrotus</i> spp. (iceplant). Deer mouse density increased from 2021 to 2022 at every site except one that underwent extensive mechanical removal of European beachgrass from 2010–2011. This study shows enduring effects of European beachgrass removal on the density of a native seed predator and highlights the importance of habitat management for conservation of Tidestrom’s lupine.