More invaders do not result in heavier impacts: the effects of nonnative bullfrogs on native anurans are mitigated by high densities of nonnative crayfish

1.With accelerating species introductions in an era of globalization, co-occurring alien species have become increasingly common. Understanding the combined ecological impacts of multiple invaders is not only crucial for wildlife managers attempting to ameliorate biodiversity loss but also provides key insights into invasion success and species coexistence mechanisms in natural ecosystems. Compared with much attentions given to single invader impacts, little is known about the impacts of multiple co-occurring invaders. 2.The American bullfrog (Lithobates catesbeianus = Rana catesbeiana) and the red swamp crayfish (Procambarus clarkii) are two aquatic invasive species in many different areas of the globe. They co-exist with native anurans in a variety of permanent lentic waters, which provide an ideal model system to explore the combined effects of multiple invaders from different trophic levels on native species. 3.Based on a global diet analysis covering 34 native and invasive bullfrog...