Amphipod crustaceans play a key role in macroinvertebrate communities and the diets of bentophagous fish in lakes. As part of global change, in many places, native amphipods are being displaced by the invasive ones from the Ponto-Caspian region (the lower basins of the Black and Caspian seas). In Lithuanian lakes, intentionally introduced alien amphipods have spread the most, but soon they will also have to face competition from the aggressive self-dispersed compatriot species. Temperature and dissolved oxygen should be investigated as the primary factors that determine the species’ competitiveness and the likely changes in the amphipod assemblages as the climate warms and lake productivity increases. In turn, amphipod species differ in their preferences to feed on plant detritus, filamentous algae, fine organics, or small animals. Shifts in their assemblages can thus lead to significant changes in lake functioning. This work aims to investigate the competitiveness, dietary preferences, and potential effects on lake functions of native and invasive amphipods that occur or are spreading across the lakes of our region under warming climate conditions. The topic foresees laboratory and field studies on the influence of temperature on oxygen consumption (1) and coexistence (2) of amphipod species, their feeding preferences (3), and the influence of amphipod assemblages on the functional structure of macroinvertebrate communities and the overall function of detritus shredding (4). The results will significantly contribute to the ecological knowledge of invasive species spreading across Europe and will help to predict shifts in amphipod assemblages as well as the associated ecosystem changes.