Invader species of Argentina: A review about beaver (Castor canadensis) population situation on Tierra del Fuego ecosystem

Abstract

Beavers (Castor canadensis) were introduced on Isla Grande of Tierra del Fuego, Argentina, in 1946. The suitable feeding and lodging sites coupled with the lack of natural predators or competitors favored rapid population growth and range expansion. This paper shows current population status and landscape modifications induced by beaver in these southern ecosystems. Beaver now occur in all streams in the Andean and extra-Andean areas and nearly all aquatic habitats on Isla Grande as well as other Chilean islands of Tierra del Fuego archipelago (70,000 km2). Low-gradient areas on small streams were more densely occupied than those of the slope valleys. Densities were similar to those in the Northern Hemisphere. Extensively colonized habitats showed 0.7 active beaver colonies per km2. Based on their different beaver occupancy patterns and frequency of colony sites, we developed four land capability classes-A, B, C and D-to use in planning and resource management. The highest densities were found in classes C and D -4.7 and 5.6 colony sites per km- indicating that both these areas had the greatest potential for beaver production. Beaver-altered sites had higher levels of organic and inorganic nitrogen suggesting that seasonal hydrological changes could be affecting nitrification and denitrification and also resulting in accumulated organic carbon and phosphorus in the stream channel. Beaver ponds may be considered sources of essential nutrients (P and N) and carbon. Chromosome analysis showed no differences with the North American karyotype. Genetic structure and variability of the beaver population are analyzed.