Habitat selection patterns of a species at the edge \u2013 case study of the native racer goby population in Central Europe

Abstract

Invasive alien species are regarded a nuisance. This extends into a lack of conservation efforts in their native range. As a consequence, conservation of e.g. range-edge populations is neglected. Gobiidae have many representatives of alien species in European freshwaters, and therefore they have a bad reputation. Objectives of this study were to: define the habitat selection patterns of a species at the edge, and examine the ontogenetic variation in its distributions, i.e. spatial distribution of different size classes. A racer goby Babka gymnotrachelus (syn. Neogobius gymnotrachelus) population was selected for the model. In numerous European river basins, Ponto-Caspian racer goby has been an invasive alien species of interest to researchers for many years. Recently, however, native populations of the species have been described in the Polish tributary of the upper Dniester River (Black Sea basin). We used habitat data and densities of racer goby to disentangle the habitat selection patterns of the species at a river reach at the edge of its native range. Evident preferences towards habitats with large submerged objects serving as hiding places were characteristic of the largest gobies. Adult, largest gobies were very likely to choose the ‘boulders’ site, while forcing smaller individuals to occupy places with faster water current, i.e. less suitable in terms of saving energy. At a larger geographic scale, a significant portion of the submountain river was unsuitable for racer gobies. At the edge of the racer goby range, patches providing habitats suitable for the species were scarce and scattered. With regard to invasive populations, the presence of stony bottoms, quite certainly cannot be considered as a factor excluding potential colonisation by racer goby, and in submountain rivers it might be the preferred kind of bottom.