Agonistic interactions between invasive aquatic species

Species invasions threaten the integrity of biotic communities, as invaders may outcompete and replace resident species. For many aquatic invaders, species replacements are driven by aggression. I explored this phenomenon through a quantitative synthesis and laboratory experiments. A quantitative synthesis of published studies on aggression in aquatic invaders found that body size and prior residency generally mediate the outcome of aggressive encounters, but there is no consistent tradeoff between intra- and interspecific aggression. As the majority of studies on agonistic interactions focus on phylogenetically related species, I investigated such interactions between two unrelated invasive species that occupy a similar niche: the round goby (Neogobius melanostomus) and the spinycheek crayfish (Orconectes limosus ), both benthic omnivores that compete for shelter. Laboratory experiments revealed that round gobies were more aggressive than crayfish, regardless of prior residency. Heightened aggression may be a selective advantage for an animal to invade a habitat occupied by another territorial species.