Competition, predation and environmental factors as structuring forces in freshwater fish communities: Sumari (1971) revisited

A study by Sumari (O. Sumari. 1971. Ann. Zool. Fenn. 8: 406-421) of the fish communities in 32 Finnish lakes concluded that the main factors affecting perch (Perca fluviatilis) populations were biotic, of which the competitive interspecific effect of roach (Rutilus rutilus) was the main one analysed. A reanalysis of this data set suggests that abiotic factors such as conductivity and pH are also important in structuring fish communities. It is suggested that abiotic factors affect perch abundance mainly by their effects on other species' performance, particularly roach. The analyses of the whole data set and a subset of this data set consisting of nine lakes having perch only, or perch and piscivores only, also provided evidence that piscivores affect perch biomass. A positive relationship between piscivore biomass and roach biomass suggests that the piscivore-perch-roach interaction may have involved the presence of apparent competition between roach and perch.