Gerris Lacustris (Linaeus 1758) and Gerris Costae (Herrich-Schäffer 1850) Species - Habitat Relations on Mountainous Tributaries of Vişeu River (Maramureş, Romania)

Semi aquatic Heteroptera species from some mountainous tributaries of the Vişeu River were collected and their relations with habitat variables were investigated. Only two species, Gerris lacustris and Gerris costae were found, either one or both species, in almost half of the investigated sampling stations. Correlation analysis between samplings and habitat conditions showed that Gerris lacustris prefers small deep ponds or river banks with steep slopes and is easily adaptable to habitat changes, while Gerris costae is mostly found in large marshes with low, stagnant water and high amounts of vegetation. Both species are relatively tolerant to human impact in their habitat, Gerris lacustris more so. The two species are negatively correlated to each other, as an expression of competition between them. Principal Component Analysis resulted in two dominant factors explaining almost 60% of the habitat variation, and their graphic representation proved the observed correlations.