Do introduced North American beavers engineer differently in southern South America? An overview with implications for restoration.

C ANDERSON; G MARTÍNEZ PASTUR; MV LENCINAS; P WALLEN; MC MOORMAN

Mammal Review

Mammal Society

Año: 2009 vol. 39 p. 33 - 52

1365-2907

1. Twenty-five pairs of North American beavers (Castor canadensis Kuhl) were introduced to Tierra del Fuego Island in 1946. The population has since expanded across the archipelago, arriving atto the Chilean mainland by the mid-1990s. Densities range principally between 0.5 - 2.05 colonies km-1 of stream, impacting approximately 30-50% of stream length and occupying from 2-15% of landscape surface area with their engineered impoundments and meadows. 2. The pattern of colonization, colony densities and area impacted indicate that the habitat found in the austral archipelago is optimal for beaver invasion, due to low predator pressure and apt suitable food resources. Nothofagus pumilio forests are particularly appropriate habitat, but a more recent invasion is occurring in adjacent steppe ecosystems. Nonetheless, Nothofagus reproductive strategies are not well adapted to maintain high beaver population levels. 3. Our assessment shows that at the patch-scale for stream and riparian ecosystems, the direction and magnitude of exotic beaver impacts are predictable based on expectations from studies in North America, thus relating ecosystem engineering with underlying ecological mechanisms such as the relationships of habitat heterogeneity and productivity on species richness and ecosystem function. 4. Based on data from both its native and exotic range, our ability to predict the effects of beavers is based on: a) understanding the ecological relationships of its engineering effects on habitat, trophic dynamics and disturbance regimes, and b) having an adequate understanding of the landscape context and the natural history of the ecosystem in which it is engineering. 5. Potential eradication of beavers and subsequent ecosystem restoration efforts currently being considered in southern Chile and Argentina should focus on the ecology of native ecosystems rather than the biology of this invasive species per se. Furthermore, given the nature of the subantarctic landscape, streams will likely respond more quickly than riparian ecosystems to restoration efforts.