Removal of invasive shrubs reduces rodent consumption of invasive non-native animals and native understory seeds

Plant invasions can generate indirect effects on native plants and animals by modifying the behavior and abundance of their consumers. Native consumers can produce positive effects by attacking invasive species and negative effects by attacking native species. However, we lack studies that examine the indirect effects of invasive plants on seasonal patterns of consumer behavior and the consumption of native and invasive organisms. Therefore, we experimentally manipulated the presence of an invasive shrub, Rhamnus cathartica , to track seasonal differences in rodent and arthropod consumption of native understory plants ( Caulophyllum thalictroides, Geranium maculatum, and Aquilegia canadensis ) and a novel animal invasion, Amynthas spp.. We tested the seasonal effects of invasive shrub removal on rodent and arthropod predation of cocoons and seeds using two, 15-day experiments conducted over the summer and autumn seasons. Our results demonstrate that changes in rodent activity caused by invasive shrub presence can generate significant deleterious effects on both invasive animals and native plants during the summer and weakens during the autumn. Invasive shrub removal weakened biotic resistance against Amynthas spp. by reducing native rodent activity, but also reduced rodent seed predation on native herbaceous plant seeds. The extended leaf phenology of R. cathartica facilitated greater rodent activity during the autumn season; however, greater rodent activity did not translate into differences in consumer pressure and varied in strength by the species consumed. Our results suggest that species traits could predict optimal windows of restoration for native plants and the ability of invasive organisms to successfully invade new environments.