Why invasive Patagonian beavers thrive in unlikely habitats: a demographic perspective

Abstract

Understanding the demography of an invasive species is crucial to better guide managers seeking to slow the spread of the invader. Habitat differences can affect demographic rates, which may in turn impact the speed of the invasion, but this has been rarely addressed. We studied the demography of invasive North American beavers (Castor canadensis) in 2 contrasting habitat types of the island, forest and steppe, on Tierra del Fuego in southern Patagonia. We used repeated observations, mark-resight methods, telemetry, and camera traps to estimate colony size and demographic rates of beavers in the 2 habitats. Colony size and the number of offspring (?kits?) produced per colony per year were higher in the steppe, contrary to the belief that forest is better habitat. This may be the result of the longer time since invasion in the forests of Tierra del Fuego and that the forest subpopulation is showing density-dependent regulation. Survival of beavers was high in all age classes and was higher than survival rates recorded in North America. Our work shows that plasticity of habitat use and predator release have likely facilitated beaver invasion in Patagonia. The higher productivity and detectability of beavers in the steppe call for active management in a habitat previously assumed to be subprime.