Resumo

LIZARRALDE, Marta; ESCOBAR, Julio  e  DEFERRARI, Guillermo. Invader species in Argentina: A review about the beaver (Castor canadensis) population situation on tierra del fuego ecosystem. INCI [online]. 2004, vol.29, n.7, pp.352-356. ISSN 0378-1844.

Beavers (Castor canadensis) were introduced at Isla Grande, Tierra del Fuego, Argentina, in 1946. Suitable feeding and lodging sites, coupled with lack of natural predators or competitors favored rapid population growth and range expansion. This paper shows the current population status and landscape modifications induced by beavers in these southern ecosystems. Beavers are now found in all streams in the Andean and extra-Andean areas, and in nearly all aquatic habitats on Isla Grande as well as other Chilean islands of the Tierra del Fuego archipelago (70000km²). Areas with low gradient in small streams are more densely occupied than those in slope valleys. Densities are 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, four land capability classes (A, B, C and D) were established 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 km²) indicating that both these areas had the greatest potential for beaver production. Beaver-altered sites had higher levels of organic and inorganic N, suggesting that seasonal hydrological changes could be affecting nitrification and denitrification, also resulting in accumulated organic C and P in the stream channel. Beaver ponds may be considered sources of essential nutrients (P and N) and C. Chromosome analysis showed no differences with the North American karyotype. Genetic structure and variability of the beaver population are analyzed.

Palavras-chave : Beaver; Castor canadensis; Colonization; Ecosystem; Invader; Tierra del Fuego.