Abstract
Quantifying the presence and environmental impact of invasive species is the starting point for research on management and nature conservation. North American beavers (Castor canadensis) were introduced to Argentina from Canada in 1946, and the species has been identified as a major agent of environmental change in the Tierra del Fuego archipelago in the Anthropocene. We studied the invasion status (distribution and density) of beavers through analyses of the dam densities in the Tierra del Fuego landscapes. We identified beaver dams with a GIS using visual interpretation of high-resolution aerial imagery from Microsoft Bing, Google Earth and HERE and related them to natural environmental gradients. These factors comprised geographic (vegetation zones and distance to streams), climatic (temperature, precipitation, evapotranspiration and net primary productivity) and topographic (elevation and slope) data. The datasets (dams and factors) were combined, and the data from the different zonation classes were subsequently compared using ANOVAs and Tukey’s mean comparison tests. Deviations from the mean density (x mean density—x total mean density) were calculated to visualize the deviations for the studied factors. The datasets were also evaluated using principal component analyses (PCA). Our results showed a total of 206,203 beaver dams (100,951 in Argentina and 105,252 in Chile) in the study area (73,000 km2). The main island of Tierra del Fuego presented a greater degree of invasion (73.6% of the total study area) than the rest of the archipelago, especially in areas covered by mixed-evergreen and deciduous forests. The studied geographic, climatic and topographic factors showed positive trends (higher beaver preference) with beaver spread, which were all significant (p <0.05) when compared across the landscape. Although beavers are flexible in their habitat use, our empirical records showed that they had marked preferences and were positively influenced by the most productive forests. Here, we describe a scientific panorama that identified the drivers of species invasion based on satellite data and the available ecological datasets. The identification of such drivers could be useful for developing new tools for management and/or control strategies of the beavers in the Tierra del Fuego archipelago.
Highlights
North American beavers (Castor canadensis) have been recognized as ecosystem engineers [1]
The mixed-evergreen forests (103,947 dams) and deciduous forests (55,843 dams) were the most extensively invaded among the defined vegetation zones (50.4% and 27.1% of the total beaver dams, respectively), whereas the ecotone (19,379 dams) was the least affected (9.4%)
We presented a density map of beaver dams for the entire Tierra del Fuego archipelago that explained the changes across the landscape in relation to different environmental factors
Summary
North American beavers (Castor canadensis) have been recognized as ecosystem engineers [1]. They build dams in riparian forests or where suitable aquatic environments prevail [2], mainly using the branches and trunks of trees [3], which change the stream hydrology, plant assembly and soil biogeochemistry, both at the local and landscape levels [4, 5]. Beavers were introduced from Canada to Argentina on the main island of Tierra del Fuego in 1946 to develop a potential fur industry, which was later became unsuccessful [8] Since they have spread throughout the Tierra del Fuego archipelago [9], nearly reaching the Cape Horn islands [10] and reaching the mainland near the city of Punta Arenas [7]. The availability of water and wood resources and the capacity of the beavers to change habitat structure, the high reproductive rate, and the lack of natural predators have contributed to the growth of the beaver populations [11, 12]
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