Reproductive rates of invasive Castor canadensis respond to management in Tierra del Fuego, Argentina

Abstract

The effects of population management on reproductive traits of invasive mammals are poorly known (specifically concerning trapping aimed to reduce population density). The beaver (Castor canadensis) is an invasive species on Isla Grande de Tierra del Fuego (“Isla Grande”), Argentina, with significant ecological impacts. At seven pilot areas of Isla Grande subject to an experimental eradication program between 2016 and 2018, we assessed the effect of several population management histories (removal intensities of individuals) on age-specific fecundity and fertility rates and reproductive values of beaver females. We also proposed a reproductive schedule for Isla Grande. Reproductive rates were found to increase with population management intensity, by contrasting: (1) areas with historic management (historical trapping) showed high production of kits at earlier ages; (2) areas with focused management diminished the reproductive value; (3) an area reinvaded after an eradication presented higher reproductive values, delays in breeding onset, and late senescence; and (4) areas without or with very low management (without trapping) produced less kits, with later breeding onset and senescence at the middle of the life cycle. Gestation and parturition periods in the pilot areas were longer than previously reported in Tierra del Fuego. When beavers reinvade an area, they express their maximum reproductive potential. Also, the removal of animals at areas without previous management would relax density-dependence of reproductive rates. The value of beaver control by landowners needs to be reevaluated. Focusing trapping effort on the estrus period would reduce beaver fertility while also reducing the impact of capturing lactating females on offspring welfare. Continuity in the active surveillance to remove re-invaders represents the main challenge to restore the Fuegian environment affected by beavers.