Simulation of lethal control and fertility control in a demographic model for Brandt’s vole Microtus brandti

Abstract

Summary Brandt's voleMicrotus brandti is considered a pest in China and is actively managed through the use of toxic baits. A time-dependent density-dependent Leslie matrix model was developed to investigate the effectiveness of fertility control as an alternative. 2. Three annual cycles of Brandt's vole were observed between 1995 and 1998 at a site in the grasslands of Inner Mongolia, China. For each of these cycles, cohort-specific monthly survival rates were derived for the spring, summer and autumn months. Over the breeding season, monthly reproductive rates were obtained as numbers of young females per adult female. 3. Survival of voles over winter, a 5-6-month period, depended on age at the onset of winter and the density in autumn. 4. The model was parameterized with measured and continuously varying monthly data for vital rates. It was then used to predict the impact that fertility control, delivered with non-toxic baits, and lethal control would have had on the vole population if control had been imposed in the autumn of 1994 or spring of 1995. The timing and frequency of bait delivery were varied, and we considered the population response to bait that renders females sterile and bait that renders females only temporarily infertile. 5. The model suggested that the effectiveness of lethal control in spring could be matched by fertility control if it was applied twice in the spring of a year in which high densities were reached, or in the previous autumn. The latter requires that (i) infertility is long-lasting in treated animals and (ii) either high-density years be reliably forecast a year ahead or fertility control be applied every autumn. 6. Brandt's voles provide an exception to the general rule that fertility control is never more effective than lethal control applied at the same time with the same bait uptake. We found that when control was applied in autumn, fertility control was better than lethal control in reducing the numbers of voles over the following spring, summer and autumn. This is because normal density-dependent mortality over winter has a greater impact following fertility control than lethal control.

Regulating overabundant ungulate populations: An example for elk in Rocky Mountain National Park, Colorado

“…Density dependence occurs whenever the number of animals surviving to reproductive age per reproductive female decreases with increasing population size and has been modeled in numerous previous studies of contraceptive population control (i.e. Courchamp and Cornell, 2000;Shi et al, 2002;Hobbs et al, 2000;Zhang, 2000). In our model, density dependence decreases per capita recruitment as population size increases.…”

“…Once the effect of contraceptive agents on individual animals has been quantified, simulation models can provide insight into large-scale population-level response to treatment strategies, results that are not obtainable by traditional manipulative experiments or observational studies (Dell'omo and Palmery, 2002;Zhang, 2000). Models have been used to simulate the effect of contraceptive treatment on populations of horses (Gross, 2000), deer (Merrill et al, 2003), voles (Shi et al, 2002) feral cats (Courchamp and Cornell, 2000) and rodents (Chambers et al, 1997).…”

Anti‐fertility effect of levonorgestrel and quinestrol in Brandt's voles (Lasiopodomys brandtii)

“…During outbreak years, it is imperative that Brandt's voles be controlled. Poison baiting is widely used for vole control in the grasslands of Inner Mongolia, but this often brings serious pollution problems and poses a risk to non-target species (Zhong et al 1999;Shi et al 2002). Fertility control has been proposed as a potentially effective control method via simulation modeling (Zhang 2000a,b;Shi et al 2002), but no fertility control technique currently exists for this vole species.…”

Genetic structure of Brandt’s vole (Lasiopodomys brandtii) populations in Inner Mongolia, China, based on microsatellite analysis

“…Brandt's voles live in social groups with distinct boundaries among family holes (Zhang and Zhong 1981). A typical Brandt's vole family group consists of one or more overwintering voles, including adult males and females, as well as animals born in the current breeding season (Zhang and Zhong 1981;Shi et al 2002). Overwintering voles play a vital role in population reproduction before early July (those that survive winter are referred to as overwintering voles) (Liu and Sun 1993).…”