Demographic plasticity in an invasive species: The effects of time since invasion and population management history on beavers in Tierra del Fuego, Argentina

Abstract

The North American beaver (Castor canadensis) has been an invasive species in the Tierra del Fuego archipelago since its intentional introduction in 1946. Its activities have led to such severe impacts on various environments that eradication has been tested as a management strategy. We assessed how vital rates (i.e., survivorship and reproduction) of the beavers were affected by time since invasion and population management history (such as lethal control). We constructed vertical life tables and compared survivorship, age-specific survivorship, generation time, and life expectancy for different landscapes and management histories. As part of an eradication pilot program conducted between 2016–2018, 922 beavers were removed in seven pilot areas of the Isla Grande de Tierra del Fuego, Argentina. Areas in which beavers have resided longest since invasion, areas without hunting pressure, and areas previously cleared of beavers had higher survivorship and longer generation time and life expectancy. Areas where beaver management was historical (trapping performed by the provincial government) or focused (trapping by landowners) had shorter life expectancy and generation time and advanced age at first reproduction. Beavers showed demographic plasticity in relation to time since invasion (increasing survivorship, generation time, life expectancy, and cohort life expectancy consistent with populations close to carrying capacity in areas with low or null management). They also exhibited plasticity in response to management histories (advanced breeding onset, reduced survivorship, and life expectancy in managed areas—similar to managed populations in their native range). We present management implications from demographic perspective for a future eradication or control program of beavers. We also highlight the importance of landowners in shaping beaver demography for the future management of the species. Beaver demography reacts dynamically and rapidly to local removal, creating challenges for management based on the removal of beavers.