No abstract

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 to 50 y after colonization and dissipated as food webs stabilized in later stages of invasion (>50 y). 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.

Maximum daily consumption and spccific daily metabolic demand were determined for juvenile flathead catfish (Pylodictis olivaris) in the laboratory over a temperature range of 3-32 "C. Maximum daily consumption increased with increasing water temperature, was significantly higher at 19 "C than at colder temperatures, and remained elevated up to 32 "C. Fish rarely ate below 15 "C, most stopped feeding at I I "C, and no fish consumed anything at 7 "C or below. Specific daily metabolic demand showed a gradual increase with increasing temperature. The quantification of consumption and metabolic dcmand for juvenile flathead catfish was consistent with descriptions classifying the species as adapted to warmwater conditions.

Hybridization between native and invasive species, a major cause of biodiversity loss, can spread rapidly even when hybrids have reduced fitness. This paradox suggests that hybrids have greater dispersal rates than non-hybridized individuals, yet this mechanism has not been empirically tested in animal populations. Here, we test if non-native genetic introgression increases reproductive dispersal using a human-mediated hybrid zone between native cutthroat trout ( Oncorhynchus clarkii ) and invasive rainbow trout ( Oncorhynchus mykiss ) in a large and connected river system. We quantified the propensity for individuals to migrate from natal rearing habitats (migrate), reproduce in non-natal habitats (stray), and the joint probability of dispersal as a function of genetic ancestry. Hybrid trout with predominantly non-native rainbow trout ancestry were more likely to migrate as juveniles and to stray as adults. Overall, hybrids with greater than 50% rainbow trout ancestry were 5.7 times more likely to disperse than native or hybrid trout with small amounts of rainbow trout ancestry. Our results show a genetic basis for increased dispersal in hybrids that is likely contributing to the rapid expansion of invasive hybridization between these species. Management actions that decrease the probability of hybrid dispersal may mitigate the harmful effects of invasive hybridization on native biodiversity.