Number of sites occupied by Castor canadensis, according to stream gradients, in the northern margin (striped bars), in the southern margin (white bars), and in the entire watershed (black bars), in the Lasifashaj river upper watershed, Tierra del Fuego.
The geomorphology of a Fuegian Andes watershed colonized by the introduced species Castor canadensis has been analyzed. The main objective was to distinguish the physical conditions of the occupied streams. Geomorphological analysis and mapping techniques were applied; also, colonization monitoring surveys in the entire watershed was made through t...
... Pastur et al. (2006) The analysis of the genetic attributes of invasive species suggests that their adaptive success involves genetic traits that are determinant enough to ensure rapid expansion in a new environment (Nei 1975;Roughgarden 1979;Sakai et al. 2001). Of particular interest is the concept that biological invasions allow species to alter their own genetic pattern (Wright 1955;Carson 1987) and exhibit an extremely wide range of evolutionary patterns (Brown and Marshall 1986). In addition, recent awareness of the loss of genetic variability due to inbreeding and founder effects in invaders (Sakai et al. 2001) and their significance for the preservation of these species warrants an extensive study of the Tierra del Fuego beaver population. ...
The North American beaver (Castor Canadensis) was introduced into Isla Grande de Tierra del Fuego, Argentina in 1946 as a potential source of wild fur. The species showed high growth potential, reaching close to 100,000 individuals from an original founding stock of 25 females and 25 males. Beavers adapted rapidly to their new environment and became invasive, providing an excellent model of successful adaptation of introduced populations to a new habitat. In this study, we used polymorphic mitochondrial (mt) DNA to evaluate genetic variation in the introduced beaver population from Tierra del Fuego. Nucleotide variation in partial sequences of Cytochrome b (500bp) and 12S rRNA (421bp) genes and the main non-coding D-loop region (521bp) were analyzed. Our study allowed to identify 10 different mtDNA lineages in the invasive population, none of them shared among the source populations. The pattern observed is a consequence of cessation of gene flow following expansion of the founding beaver population since the time of its introduction. This approach contributes to the understanding of effects of genetic changes on survival ability and reproductive success of invasive species. It also has important management implications to invasive species.
... The beaver introduced in Tierra del Fuego is considered as an invader because it modifies the local ecological interactions. Therefore, intensive studies have been carried out to understand the role of beavers on southern ecosystems and to compare this with boreal ecosystems (Lizarralde, 1993;Lizarralde and Escobar, 1999;Lizarralde et al., 1989Lizarralde et al., , 1996aLizarralde et al., , b, 2002Coronato et al., 2003). ...
... The different habitats were classified according to vegetation coverage and geomorphology. The physical characteristics of the streams colonized by beavers were also determined through geomorphological analysis and mapping techniques (Coronato et al., 2003). ...
... Low gradient (0-6º), first and second order streams were selected by beavers. Higherorder streams were seasonally occupied (Coronato et al., 2003). The rivers of the lateral hanging valleys were more densely occupied than those of the slope units. ...
Los castores (Castor canadensis) fueron introducidos en la Isla Grande de Tierra del Fuego, Argentina, en 1946. La ausencia de predadores y competidores naturales y la abundancia de alimento y sitios de refugio favorecieron su rápida expansión y crecimiento poblacional. Este artículo muestra el estado poblacional y las modificaciones al paisaje producidas por los castores en estos ecosistemas australes. Actualmente los castores son encontrados en todos los ríos de las áreas andinas y extra-andina y en casi la totalidad de hábitats acuáticos de la Isla Grande como también en otras islas chilenas del Archipiélago de Tierra del Fuego (70000 km
Resumen: En este artículo tenemos como objetivo analizar los vínculos, distancias y cercanías, entre ciertas propuestas de la ética utilitarista y la actual biología de la conservación, a la luz de otras éticas ambientales. Los autores que hemos elegido para tal análisis han sido Gifford Pinchot, un ingeniero agrónomo y político, que ha sido señalado al seno de la biología de la conservación como el "padre" de la llamada ética de conservación de recursos y Peter Singer, reconocido por su desempeño en el movimiento de liberación animal. Nuestros resultados indican que la mirada de "conservación de recursos" de Pinchot ha sido ampliamente integra-da en la biología de la conservación, principalmente a través de la noción de servicios ecosistémicos". Sin embargo, respecto de la ética "animalista" de Singer aparecen controversias con la biología de la conserva-ción, vinculadas principalmente a los diferentes niveles de la jerarquía biológica valorados. La perspectiva utilitarista se mantendría presente en las ciencias de la conservación actuales, no sin presentar ciertas contradicciones que deberían examinarse a través de una mirada que integre diferentes voces y saberes.
Changes in habitat use over the course of a biological invasion may influence the fraction of the landscape that is ultimately affected by the invader. However, this intermediate stage of invasion has been less studied than the initial or final stages. Here, we investigated the recent invasion by an ecosystem engineer, the American Beaver (Castor canadensis), in an area of the Patagonian steppe. We utilized repeated high resolution satellite images to identify beaver ponds, and used them to study changes in beaver abundance and habitat use over time. The number of beaver ponds increased 85 % between 2005 and 2014. During this period, beavers changed their habitat selection pattern, presumably as a response to increased density. Beavers established on small watercourses in canyons first, but as more canyons became occupied over time, beavers moved to less preferred watercourses in plains and U-shaped valleys. Potential new beaver colonies established close to existing beaver ponds, suggesting proximity to a beaver pond is an important determinant of beaver colonization. Identifying habitat preferred by beavers in the steppe, could help to increase early detection of the invader at the invasion front. Our work highlights the importance of the use of high resolution remote sensing technologies to better understand and control biological invasions.
Castor canadensis is considered an archetypical ecosystem engineer, which modifies the state of biotic and abiotic factors through non-trophic interactions. This species was introduced by the Argentinean government into Tierra del Fuego island in 1946, and subsequently colonized autonomously the neighboring islands of Navarino, Dawson and Hoste. Currently this invader occupies contrasting ecosystems such as the Magellan subpolar beech forest and Patagonian scrub and steppe. This ability to colonize contrasting habitats suggests that beaver expansion will be limited mainly by hydrological resources, threatening to colonize the complete extent of temperate beech forests on the mainland (from 35 to 55° S). The present review proposes three hypotheses regarding the underlying mechanisms to this successful invasion: natural enemy escape, resource opportunities, and self-facilitation through non-trophic interactions. Current knowledge regarding beaver colonization and foraging behavior (e.g., habitat selection independently of forest availability, irruptive population growth, and apparent selective exploitation of Nothofagus pumilio, dominant species in the Magellan forest) suggests that enemy escape and resource opportunity are the main mechanisms underlying this invasion. The observation of higher densities of active colonies, where the extent of beaver habitat modification is larger, suggests that self-facilitation may be relevant to the success of this invasion. Current information does not allow testing these hypotheses, but it provides a framework to develop future investigations regarding this invasion in Tierra del Fuego.
Question: Does understorey richness, cover and biomass change during succession in abandoned Castor canadensis impoundments of riparian Nothofagus forests? Location: Magellanic Nothofagus forests at Tierra del Fuego National Park (54°50′32.4″ S, 68°32′11.5″ W), Argentina. Methods: Five meadows of different time since abandonment (1, 5, 6, 9 and 20 years ago) and two controls (pure N. pumilio and mixed N. pumilio - N. betuloides forests) were sampled. Understorey variables (species richness, cover and biomass) in beaver meadows were measured at eight plots, as well as sapling and seedlings age and height. In control treatments, ten plots on each forest type characterized forest structure. Results: Beavers alter vegetation dynamics, modifying biomass and composition of the original forest communities. Richness, cover and biomass were significantly modified when compared to the original understorey. Ferns are the most affected group, while grasses became more abundant. Many species established in the impacted sectors, which did not grow in primary forests. Trees did not regenerate in impacted areas for long periods, and many understorey original species are missing. Nothofagus forests are not adapted to support a long-term beaver impact. Conclusions: Beavers modify the original ecosystem from closed forest to a grass- and sedge-dominated meadow, due to the lack of adaptive regeneration strategies in the Nothofagus forests. The maintenance of the present level of the beaver population is not sustainable over time, due to utilized and impacted tree biomass which could not be replaced by the natural dynamics of the forest ecosystem. Abbreviations: FA = Forest stand; GIS = Geographical information system; LF = Nothofagus pumilio forest; LGF = N. pumilio/N. betuloides mixed forest. Nomenclature: Correa (1969–1998); Moore (1983).
This chapter focuses on the physical geography of Late Cenozoic of Patagonia and Tierra del Fuego. This chapter discusses a junction of natural elements in the southern end of South America. Bedrock substratum and structure, climate, distribution of the superficial runoff, soils, and vegetation, all act together in a systematic, cause–effect relationship and form a group of homogeneous geographical spaces that are joined under first-order geological and atmospheric elements, such as tectonic plates and the general atmospheric circulation. The interaction of the wetter Pacific winds and the Andean Cordillera is the basic natural condition that determines the geographical aspects of the natural, physical environment of the southernmost end of South America. The pluvial and snow régime of the streams, the allochtonous character of the tableland streams, the development of contrasting biomes, such as jungle-like forests and rainshadow deserts, with a modest thermal régime are a consequence of the orographic barrier interaction with the air masses of the Southern Pacific anticyclonic centers and the polar front.
Twenty-five pairs of North American beavers Castor canadensis Kuhl were introduced to Tierra del Fuego Island in 1946. The population has expanded across the archipelago, arriving at the Chilean mainland by the mid-1990s. Densities range principally between 0.5-2.05 colonies/km. They have an impact on between 30-50% of stream length and occupy 2-15% of landscape area with impoundments and meadows. Beaver impacts constitute the largest landscape-level alteration in subantarctic forests since the last ice age. 2. The colonization pattern, colony densities and impacted area indicate that habitat in the austral archipelago is optimal for beaver invasion, due to low predator pressure and suitable food resources. Nothofagus pumilio forests are particularly appropriate habitat, but a more recent invasion is occurring in adjacent steppe ecosystems. Nonetheless, Nothofagus repro- ductive strategies are not well adapted to sustain high beaver population levels. 3. Our assessment shows that at the patch-scale in stream and riparian ecosystems, the direction and magnitude of exotic beaver impacts are predictable from expectations derived from North American studies, 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 the species' native and exotic range, our ability to predict the effects of beavers is based on: (i) understanding the ecological relationships of its engineering effects on habitat, trophic dynamics and disturbance regimes, and (ii) having an adequate compre- hension of the landscape context and natural history of the ecosystem being engineered. 5. We conclude that beaver eradication strategies 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. Further- more, given the nature of the subantarctic landscape, streams will probably respond to restoration efforts more quickly than riparian ecosystems.
This study analyses large wood (LW) storage and the associated effects on channel morphology and flow hydraulics in three third-order mountain basins (drainage area 9–12 km2) covered in old-growth Nothofagus forests, ranging from the temperate warm Chilean Andean Cordillera to the sub-Antarctic Tierra del Fuego (Argentina). Amount, characteristics and dimensions of large wood (>10 cm diameter, >1 m long) were recorded, as well as their effects on stream morphology, hydraulics and sediment storage. Results show that major differences in LW abundance exist even between adjacent basins, as a result of different disturbance histories and basin dissection. Massive LW volumes (i.e. >1000 m3 ha−1) can be reached in basins disturbed by fires followed by mass movements and debris flows. Potential energy dissipation resulting from wood dams is about a quarter of the total elevation drop in two streams, with a gross sediment volume stored behind wood dams of around 1000 m3 km−1, which appears to be of the same order as the annual sediment yield. Finally, the presence of wood dams may increase flow resistance by up to one order of magnitude. Copyright © 2007 John Wiley & Sons, Ltd.