Warmer Temperatures and Smaller Body Size May Favor Biological Competition of Invasive Neogobius fluviatilis with Native Gobio gobio in Central European Bioregion

We conducted experiments to assess the importance of the effects of interactions between individuals of co-occurring species, the Common Gudgeon Gobio gobio, native to Europe, and the invasive Monkey Goby Neogobius fluviatilis. We examined the influence of the size of the competitor and the temperature of the water on competition for food between these two species. To investigate whether this food competition is dependent on the size of invasive competitors, we used three size classes of the invasive N. fluviatilis and a single size class of the native G. gobio in a tank-based experiment. To reflect the possible impact of temperature, we used two different water temperatures: 16 °C preferred by the G. gobio and 22 °C preferred by the N. fluviatilis. Based on the number of prey consumed, time to start feeding, and the total time spent hunting prey, we provided direct confirmation that the invasive N. fluviatilis in Europe is the superior competitor for food at both tested temperatures, eating twice as much prey, feeding 2–4 times faster, and spending up to three times more time on hunting. Food competition was size-dependent: the greater threat for native species is invasive fish, which are smaller or similar to them in size. Warmer temperatures (22 °C) gave more than twice as much advantage to the invaders under all tested feeding parameters. Therefore, we concluded that populations of invasive N. fluviatilis present a serious threat to native European benthic fish species (i.e., G. gobio). Increasing temperatures, better tolerated by invasive species, compound this problem.