Predation Management and Spatial Structure Moderate Extirpation Risk and Harvest of Northern Bobwhite

Density dependence, immigration, and emigration can considerably influence wildlife population demographics. Population models used to evaluate common actions like predator management and harvest in the absence of these processes may lead to poor management decisions. We built a novel population simulation model for the northern bobwhite (Colinus virginianus; bobwhite) that included implicit spatial structure (ingress and egress of individuals), density dependence, and harvest. We used 42 years of data (1970-2012) from a relatively stable population to create and validate the simulation model. We then used this simulation model to predict the effect of meso-mammal trap and removal, a management action that increases bobwhite fecundity, on population abundance, cumulative harvest through 50 years, and extirpation risk. We conducted a population sensitivity analysis to understand the implications of meso-mammal trap and removal to populations with varying vital rates. Incorporating ingress and egress of individuals and density dependence improved the understanding of bobwhite population dynamics and reduced the uncertainty about the efficacy of predator management across a range of environmental conditions. Increased number of immigration sources decreased extirpation risk and increased bobwhite abundance. A key outcome of our modeling process was that density-dependent processes did not fully compensate for harvest. Cumulative harvest through 50 years increased with increasing harvest rate but started to decline when harvest rate was >0.35 for populations with meso-mammal removal and 0.25-0.30 for populations without meso-mammal removal. Meso-mammal removal increased the harvest capacity of populations and produced greater harvest opportunity over time. Meso-mammal removal also buffered populations from extirpation risk resulting from too few immigration sources. Practitioners often ignore the contribution of immigration and emigration to local demographics or assume density-independent vital rates; however, recent literature reviews and our study indicate that these processes are important to the understanding of animal ecology and management. In the interest of the conservation of species that are hunted and at risk of extirpation in some geographies, predator management may increase hunter success and be a tool to reduce extirpation risk, although the degree of effectiveness likely varies geographically. This manuscript could serve as a framework for predicting the effects of management on bobwhite at the population level. (c) 2020 The Wildlife Society.

Automated summary

Density dependence, immigration, and emigration have significant impacts on wildlife population demographics. A population simulation model can help predict the effects of management actions on population abundance, cumulative harvest, and extirpation risk. Incorporating these factors into models improves understanding of population dynamics and management effectiveness.