Lake food webs: Species invasion progressively disrupts the trophic structure of native food webs

Species invasions can have substantial impacts on native species and
ecosystems, with important consequences for biodiversity. How these
disturbances drive changes in the trophic structure of native food webs
through time is poorly understood. Here, we quantify trophic disruption in
freshwater food webs to invasion by an apex fish predator, lake trout,
using an extensive stable isotope dataset across a natural gradient of
uninvaded and invaded lakes in the northern Rocky Mountains, USA. Lake
trout invasion increased fish diet variability (trophic dispersion),
displaced native fishes from their reference diets (trophic displacement),
and reorganized macroinvertebrate communities, indicating strong food web
disruption. Trophic dispersion was greatest 25-50 years after colonization
and dissipated as food webs stabilized in later stages of invasion
(>50 years). For the native apex predator, bull trout, trophic
dispersion preceded trophic displacement, leading to their functional loss
in late-invasion food webs. Our results demonstrate how invasive species
progressively disrupt native food webs via trophic dispersion and
displacement, ultimately yielding biological communities strongly
divergent from those in uninvaded ecosystems.