"Handle With Care": Consequences of Different Removal Pressures on Population Growth of the Invasive Beaver in Tierra del Fuego, Argentina.

Abstract

The population regulation of animals depends on fertility and survivorship. Hunting can affect population growth through changes in reproduction and survivorship. Understanding these changes in vital rates is crucial for the control of invasive mammals. With the objective to assess the influence of different population removal pressures on the finite population growth rate (𝝀) of an invasive mammal, this research used demographic data estimated from 922 invasive beavers (Castor canadensis) eradicated from seven areas from Isla Grande de Tierra del Fuego, Argentina. Areas were classified into four removal pressures: higher, high-intermediate, low-intermediate, and lower removal pressure. The hypothesis states that the higher removal pressure produces higher population growth and resilience. Leslie matrix models were used to estimate 𝝀, generation time, damping ratio, stable age distribution, reproductive value, and the sensitivity-elasticity of survivorship and fertility of the females for each removal pressure. The 𝝀 and damping ratio increased with the removal pressure, as expected; the inverse occurred with the generation time. The survivorship of the younger age classes was the most sensitive and elastic vital rate regardless of removal pressure, followed by the breeding onset. The fertility was less relevant on 𝝀. The beaver population would depend more on the survival of kits, 1-year-olds, and subadults, than the number of offspring produced. A management strategy is proposed focusing on affecting the survivorship of younger age classes, eliminating first the adult animals and then the younger beavers.