Potential effects of incorporating fertility control into typical culling regimes in wild pig populations

Abstract

Effective management of widespread invasive species such as wild pigs (Sus scrofa) is limited by resources available to devote to the effort. Better insight of the effectiveness of different management strategies on population dynamics is important for guiding decisions of resource allocation over space and time. Using a dynamic population model, we quantified effects of culling intensities and time between culling events on population dynamics of wild pigs in the USA using empirical culling patterns and data-based demographic parameters. In simulated populations closed to immigration, substantial population declines (50–100%) occurred within 4 years when 20–60% of the population was culled annually, but when immigration from surrounding areas occurred, there was a maximum of 50% reduction, even with the maximum culling intensity of 60%. Incorporating hypothetical levels of fertility control with realistic culling intensities was most effective in reducing populations when they were closed to immigration and when intrinsic population growth rate was too high (> = 1.78) to be controlled by culling alone. However, substantial benefits from fertility control used in conjunction with culling may only occur over a narrow range of net population growth rates (i.e., where net is the result of intrinsic growth rates and culling) that varies depending on intrinsic population growth rate. The management implications are that the decision to use fertility control in conjunction with culling should rely on concurrent consideration of achievable culling intensity, underlying demographic parameters, and costs of culling and fertility control. The addition of fertility control reduced abundance substantially more than culling alone, however the effects of fertility control were weaker than in populations without immigration. Because these populations were not being reduced substantially by culling alone, fertility control could be an especially helpful enhancement to culling for reducing abundance to target levels in areas where immigration can’t be prevented.

Ecological drivers of African swine fever virus persistence in wild boar populations: insight for control

“…Conception probability was density dependent such that conception did not occur in individuals in grid cells that were already at carrying capacity. The population-level host demographic dynamics were similar to a logistic model (Pepin et al 2017).…”

Ecological drivers of African swine fever virus persistence in wild boar populations: Insight for control

“…Conception probability was density dependent such that conception did not occur in individuals in grid cells that were already at carrying capacity. The population-level host demographic dynamics were similar to a logistic model (Pepin, Davis, Cunningham, VerCauteren, & Eckery, 2017).…”

Accounting for heterogeneous invasion rates reveals management impacts on the spatial expansion of an invasive species

“…) and fertility control (see Pepin et al. , b for theoretical evaluation). These are investments that have not yet been realized in terms of feral swine removals.…”

“…In addition, previous work has shown that prioritizing removals during non‐birthing periods can improve the efficiency of control (Pepin et al. , b), suggesting that further optimization of timing could be helpful. However, our results are national‐scale averages and previous work has indicated that forage availability can greatly impact feral swine population growth and establishment (Tabak et al.…”

“…Such research studies would also provide essential data for developing science-based approaches for optimizing management strategies adaptively in space and time. Also, some research funding from NFSP is going toward the development of new methods such as toxicants (e.g., Snow et al 2017b) and fertility control (see Pepin et al 2017a, b for theoretical evaluation). These are investments that have not yet been realized in terms of feral swine removals.…”