Targeting season and age for optimizing control of invasive rabbits

The effectiveness of invasive species control can be influenced by seasonal fluctuations in reproduction in response to environmental conditions. However, it is difficult to determine how demography and environmental conditions affect the efficacy of different control efforts from field trials alone. We incorporated an ontogenetic growth model into a hierarchical Bayesian mark-recapture model to estimate age-structured seasonal survival rates for European rabbits (Oryctolagus cuniculus) in Australia, based on a >15-year data set. We integrated this demographic information into an individual-based simulation model, which reproduces seasonal birth-death processes, to test the effectiveness of pest-management schemes that differed in intensity, specificity to age groups, and seasonal timing. Control measures that were simulated to affect only juveniles had a negligible effect on population size, whereas targeting subadults and adults led to considerable population declines when applied after the breeding season. Management that affected rabbits of all age groups caused significant population reductions. However, even repeated control efforts that caused 95% mortality each year only resulted in predictions of local population extirpation after an average of 119 calendar weeks in the absence of immigration. Our simulation study supports the use of pest rabbit control methods that account for demographic dynamics explicitly, and target those individuals with high reproductive potential. More broadly, we show that local and temporal population extirpation, or recovery, depends largely on the trade-off between control intensity and frequency for species with recurrent population oscillations.