Spatial Relations among Semi-Aquatic Mammals on the Riverside

Abstract

A total of 231 riverside cut-offs (0.5 km in length and approx. 10 m in width from the water edge) were investigated on the subject of the joint use by semi-aquatic mammals – the beaver (Castor fiber), otter (Lutra lutra), American mink (Mustela vison), and muskrat (Ondatra zibethicus) – in 10 rivers of south and southeast Lithuania. Relative abundance was expressed as the number of activity signs per a 0.5-km cut-off. The co-occurrence of two or more species on a single 0.5-km-long riverside cut-off and the correlation analysis of the relative abundance of semi-aquatic mammals were used to evaluate spatial relations in the community. High level of co-occurrence of semi-aquatic mammals was found. Of all the 0.5-km cut-offs investigated, 97.9% were used by two or more species. However, significant correlation in the relative abundance between two species of semi-aquatic mammals was found only in 6 of the 60 combinations possible. The average relative abundance of semi-aquatic mammals (except for the beaver) was remarkably higher in the rivers where at least one of the above correlations was established. The beaver showed the closest spatial relations with all the other species on the riverside. Despite the distinctly expressed co-occurrence on the same sections of limited length, strong spatial relations in the joint use of the riverside by semi-aquatic mammals seem to be uncommon phenomenon and appear under certain conditions only, e.g. high abundance of all coexisting species.