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Do introduced North American beaver Castor canadensis engineer differently in southern South America? An overview with implications for restoration

Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, USA,
Mammal Review (Impact Factor: 4.26). 10/2008; 39(1):33 - 52. DOI: 10.1111/j.1365-2907.2008.00136.x

ABSTRACT

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.

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    • "The study was conducted between 2003 and 2006 in both the Argentine and Chilean portions of the TDF Archipelago, which encompasses the islands south of the Strait of Magellan . Since their initial introduction in 1946, beavers have colonized most of the archipelago, and as of the 1990s were also established on the mainland (Anderson et al., 2009). As a result of its relatively recent glaciation and fragmented geography, the archipelago's native vertebrate community is relatively species poor, especially potential predators of beavers (Anderson et al., 2006; Valenzuela et al., 2014). "
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    ABSTRACT: AimEcological theory predicts that invasive ecosystem engineers like the American beaver (Castor canadensis) in Tierra del Fuego (TDF) affect landscape-level biodiversity and ecosystem function (BEF) when engineered habitats are novel or extensive. We tested these hypotheses on freshwater BEF, sampling benthic habitat and macroinvertebrates in natural lotic (forest and grassland streams) and natural lentic habitats (bogs, lakes) and beaver-modified lentic ecosystems (active and abandoned ponds). LocationTierra del Fuego Archipelago (Chile and Argentina). Methods To determine effects on patch-scale BEF, we assessed two drivers: substrate diversity (H) and benthic organic matter standing crop (BOM, gm(-2)). Extent of impact was estimated as relative stream length (%) for each patch type in four 1000ha images. ResultsThe freshwater landscape was 56% free-flowing streams (natural lotic), 13% bogs and lakes (natural lentic) and 31% active and abandoned beaver ponds (beaver lentic). While engineering significantly modified lotic habitats (converting them to ponds), the beaver ponds were largely similar to natural lentic systems, but engineered lentic patches retained more BOM. While benthic biodiversity in beaver ponds was less than streams, the assemblage contained no habitat-specific taxa and was a subset of the natural lentic community. Main conclusionsInvasive beavers engineer habitats whose biodiversity is similar to the landscape's natural lentic habitats, but by increasing the surface area and unit area retention of BOM via its impoundments, this invasion augments carbon standing stock approximately 72% in watersheds. While this invasion is considered the largest alteration to TDF's forested biome in the Holocene, here we discover that its impact is to ecosystem function, rather than biodiversity in the aquatic landscape.
    Full-text · Article · Nov 2014 · Diversity and Distributions
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    • "On the one hand, context dependence significantly hinders the generalization of the results. " However, while the impacts of beavers are recognized as large, widespread and visually dramatic, until recently it was not possible to produce a synthesis of their effects across various taxa and ecosystems… " (Anderson et al., 2009, p. 35). On the other hand, the acknowll edgement of this correlation allows one to understand why the engineers can have a limited influence or no influence at all; how many transformations the envii ronment may permit an engineer to perform or where lie the borders of possibilities of engineers; and how BIOLOGY BULLETIN REVIEWS Vol. 4 No. 2 2014 ZAVYALOV fast the habitats created by an engineer deteriorate. "
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    ABSTRACT: A review of the literature on the influence of beavers on the environment has been presented with regard to following aspects: (1) specific features of the ecology of beavers crucial for understanding their effects on the environment: (2) changes in the physical characteristics of habitats due to the activity of beavers (beavers as engineers); (3) the role of the beaver as a phytophage; (4) long-term changes of vegetation in beavers’ habitats and the possible consequences of these changes for beavers.
    Full-text · Article · Mar 2014
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    • "Earlier publications mostly were in regional journals and technical/governmental reports, while later we see more international, indexed research papers (Fig. 2). Historically, the political border between Argentina and Chile clearly limited archipelago-wide research, and bi-national efforts in exotic species research are very recent (Anderson et al., 2009). "
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    ABSTRACT: Understanding processes and impacts of biological invasions is fundamental for ecology and management. Recent reviews summarized the mechanisms by which invasive species alter entire ecosystems,but quantitative assessments of these mechanisms are lacking for actual assemblages to determine their relative importance, frequency and patterns. We updated information on introduced vertebrates in theTierra del Fuego Archipelago (TDF) via an exhaustive literature review and new data to evaluate eco-system impact mechanisms and provide management recommendations. To date, 24 exotic vertebrateshave naturalized in TDF, outnumbering natives nearly 2:1, with the North American beaver (Castor canadensis) and muskrat (Ondatra zibethica) being the most widely distributed species and alsoimpacting the ecosystem through the greatest number of mechanisms. Introduced vertebrates occupiedmost parts of the archipelago with human-inhabited islands having greater taxa richness. All exoticspotentially altered ecosystems by one or more mechanisms: 100% food webs, 92% invasional meltdown,42% habitat modification, 38% disease or parasite transmission, 21% soil property and disturbance regimechanges. Impact to habitat structure was the main clustering criterion for this assemblage. Within thespecies that physically alter habitats, we found two sub-groups: 1) large herbivores and 2) “others” including beavers and muskrats. Species that did not alter habitat were divided further into those withpredatory trophic effects (carnivorous mammals and trout, sub-group 4) and the rest with assortedimpacts (sub-group 3). By establishing high quality information on archipelago-wide assemblage, dis-tribution, impacts and mechanisms for exotic vertebrates, we recommend, based on ecological criteria,prioritizing the management of sub-group 2. A secondary priority might be given to the carnivores insub-group 4, while species in sub-groups 1 and 3 are less urgent. As the first systematic survey of introduced fauna on an archipelago-scale, we identified knowledge gaps, such as population abundanceand dynamics for specific species, which are needed to orient future work, but the notable progress madeto date is highlighted.
    Full-text · Article · Jan 2014 · Acta Oecologica
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