Cannibalism Facilitates and Sustains the Invasion of Top‐predator Fish (cichlidae: Cichla) in Human‐modified Ecosystems

The strategies that allow invasive alien species to perpetuate themselves in the long term are still poorly understood in invasion science. Considering top predators, a key issue is how they overcome the prey decline which they have caused during the invasion process. We investigate factors related to the persistence, impacts and long-term success of the emerging peacock bass (Cichlidae: Cichla) invasion, a fish native to the Amazon biome that has been introduced globally. We analysed a robust temporal database that includes comparisons (1994-2002 vs. 2015-2017) on the diet of Cichla ocellaris, the abundance of this invader, its prey and competitors in a human-modified ecosystem. In addition, we compare the frequency of cannibalism (presence or absence) between native versus non-native populations, and between natural versus human-modified ecosystems in the American continent. Four hypotheses were tested: (i) prey and competitor populations decrease through time as a result of predation impacts; (ii) cannibalism is size- and density-dependent, and increases after native prey decline; (iii) cannibalism is more frequent in non-native populations; and (iv) the abundance of invader decreases over time because of reduced resources and increased cannibalism. Our results revealed that the impacts of introducing this predator into communities are temporally cumulative and continue to evolve even after 70 years since its introduction. These impacts have led to dramatic reductions in prey availability, resulting in widespread cannibalism. Adult individuals preying on juveniles in areas with higher abundances of peacock bass indicated that cannibalism is size- and density-dependent. Cannibalism was more frequent in non-native populations and in human-modified ecosystems. A complex feedback process (reproduce and cannibalise frequently) may be responsible for overcoming long-term resource scarcity, and the cannibalism may not be a regulatory force strong enough to surpass the reproductive success of the population. Our findings at the local and continental scale converge to confirm the cannibalism as an adaptive invasiveness strategy that facilitates the invasion process and makes populations self-sustainable in the long term, which may jeopardise the efficacy of management actions for these top predators introduced globally.