Benthification, biotic homogenization behind the trophic downgrading in altered ecosystems

Abstract Several dozen fish species have been introduced into Neotropical waters, causing significant biotic changes that include deterministic predation interactions with ecosystem effects. In general, reservoirs are preferred over lakes as places for stocking policies, due to their artificial aspect, consequently promoting fish introductions. In a meta‐analytic approach, we compared the biomass of plankton‐feeding (and top predators) with bottom‐feeding fish species between reservoirs and lakes, considering the influence of invaders and trophic levels. Among the 26 ecosystems (12 reservoirs and 14 lakes), there is a dominance of non‐native bottom‐feeding species in artificial environments. We revealed a mechanism behind this dominance in a study case, a tendency for trophic downgrading and biotic homogenization based on interactions between an expatriate invasive centrarchid (sunfish family) predator from North America (the largemouth bass Micropterus salmoides ) and two omnivorous cichlids from Africa in novel environmental contexts in Brazil (the benthification process). Both juvenile and adult largemouth bass are keystone predators in aquatic food webs in both their native and introduced ranges. The omnivore–detritivore tilapiines Oreochromis spp. and the phytophagous–omnivorous Coptodon spp. are species that exhibits strong generalist tendencies. Such species feed on the omnivore and detritivore compartments, enhancing detritus cycling among a large variety of δ 13 C sources. Since their consumption is disproportionate, facilitation of other species occurs with multiplicative effects in the environment. Interactions between invasive species, that is, when an invasive predator (bird, fish, or invertebrate) eats an invasive prey (mainly fish and invertebrates), can serve to highlight biotic homogenization on fresh waters.