Species introductions threaten ecosystem function worldwide and interactions among introduced species may amplify their impacts. Effects of multiple invasions are still poorly studied and often the mechanisms underlying potential interactions among invaders are unknown. Despite being a remote and well–conserved area, the southern portion of South America has been greatly impacted by invasions of both the American Beaver (Castor canadensis) and Brown Trout (Salmo trutta fario). Here, we compared growth, condition, diet, and stable isotopes of sulfur δ34S, nitrogen δ15N, and carbon δ13C for stream-living Brown Trout from streams with (n = 6) and without (n = 6) beaver in Tierra del Fuego, Chile. We show that beaver may facilitate the success of trout by positively influencing fish growth. Beaver indirectly provide greater food subsidies (i.e., macroinvertebrate abundances) by modifying the local aquatic environment through active dam and lodge building suggesting a one–way positive interaction. Trout in beaver-influenced streams occupied a slightly higher trophic level with more depleted sulfur and carbon isotopic ratios suggesting that food web pathways rely on secondary production from autochthonous origin. Trout in beaver-influenced streams have a wider dietary breadth with diptera and amphipoda as the prey items providing most of the energy whereas in streams without beaver, trichoptera were the main source of energy for trout. Although these two invaders have never co-occurred naturally, their ecosystem function and the beneficial influences of coexisting life histories reported in their native ranges are similar to our findings from invaded systems.

Please see the associated manuscript that contains detailed methods.

The attached spreadsheet includes the data to conduct the analyses shown in the associated manuscript.