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Do introduced North American beavers 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: 3.92). 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.
    Diversity and Distributions 11/2014; 20(2):214-211. DOI:10.1111/ddi.12147 · 5.47 Impact Factor
    • "Beaver impoundments have long-term effects on wetland soils, even after the pond has been drained (e.g., Johnston 2001 and references therein), due in part to increasing duration of soil saturation. Beaver activity results in increased total organic carbon and sediments (reflected in increased % TOC and % dry weight) in the pond soils and allow introduced plant species a greater opportunity for invasion in the wetland (reflected in lower VIBI scores) (Johnston 2001 and references therein; Anderson et al. 2009). In our study, % TOC was always higher in natural wetlands and % dry weight was generally higher in constructed wetlands. "
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    ABSTRACT: A persistent question among ecologists and environmental managers is whether constructed wetlands are structurally or functionally equivalent to naturally occurring wetlands. We examined 19 variables collected from 10 constructed and nine natural emergent wetlands in Ohio, USA. Our primary objective was to identify candidate indicators of wetland class (natural or constructed), based on measurements of soil properties and an index of vegetation integrity, that can be used to track the progress of constructed wetlands toward a natural state. The method of nearest shrunken centroids was used to find a subset of variables that would serve as the best classifiers of wetland class, and error rate was calculated using a five-fold cross-validation procedure. The shrunken differences of percent total organic carbon (% TOC) and percent dry weight of the soil exhibited the greatest distances from the overall centroid. Classification based on these two variables yielded a misclassification rate of 11 % based on cross-validation. Our results indicate that % TOC and percent dry weight can be used as candidate indicators of the status of emergent, constructed wetlands in Ohio and for assessing the performance of mitigation. The method of nearest shrunken centroids has excellent potential for further applications in ecology.
    Wetlands 12/2013; 33(6). DOI:10.1007/s13157-013-0464-3 · 1.44 Impact Factor
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    • "Therefore, differences in water bird consumption between both coasts of the BC (TDF and Navarino Islands) might reflect differential availability. Moreover, this finding highlights the idea that different ecosystems respond differently to the introduction based on intrinsic ecological factors of the site, rather than the invasive species per se (Anderson et al., 2009). "
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    ABSTRACT: The American mink (Neovison vison) is a semi-aquatic, generalist carnivore released onto Tierra del Fuego (TDF) Island in the 1940s, subsequently spreading to adjacent islands in the archipelago with potential effects on native prey populations. Knowledge of this new predator's trophic ecology is essential to identify threats, plan control strategies and conserve native fauna. We studied seasonal mink diet in TDF in different habitats. We identified undigested remains from 493 scats collected between May 2005 and March 2009 along marine coasts and freshwater shores (rivers and lakes). Small mammals and fish were the main mink prey in TDF (over 65% of diet items). Seasonal variations were not detected, but diet did vary significantly between marine and freshwater habitats, where more terrestrial items were consumed. Among mammals, mink consumed more small native rodents than exotic species. Native fish consumption was also important with greater representation of species from the families Nototheniidae and Galaxiidae in marine and freshwater habitats respectively. Birds were the third item in importance, but did not constitute a particularly large part of the mink's diet on TDF. Overall, differences found in mink diet between habitats reflected their generalist/opportunistic feeding behaviour and did not differ greatly from observations in its native range or in other areas where it has been introduced. Our results establish the interactions between this novel predator and its prey and also illustrate the need to continue research on native prey populations to quantify mink impact on them and understand the ecological context of this biotic assemblage.
    Mammalian Biology - Zeitschrift fur Saugetierkunde 02/2013; 78(2):104–110. DOI:10.1016/j.mambio.2012.11.007 · 1.48 Impact Factor
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