For species whose vital rates (i.e., survival and fecundity) are strongly dependent on environmental conditions, it is complicated to predict population dynamics when the environment fluctuates frequently. Several methods have been applied, but these methods often ignore the important transient dynamics (i.e., not asymptotic dynamics) that are likely to dominate in these systems. For example, as the environment shifts between ‘good’, ‘poor’, and ‘intermediate’ years, populations will not immediately behave with the asymptotic properties associated with these year qualities. Therefore, models of population dynamics for these species should avoid the assumption of asymptotic dynamics and incorporate transient effects. We developed a modeling framework that allows ecologists to predict the population dynamics of species whose vital rates are strongly dependent on environmental conditions when the environment shifts between different qualities. We applied our framework to wild pigs (Sus scrofa), an invasive species in many areas, whose vital rates depend on oak (Quercus spp.) and beech (Fagus spp.) mast. We used stochastic simulations to evaluate the probability of population establishment (> 50 individuals after 10 years) following introduction into new locations under different proportions of good and poor years and with different number of individuals introduced.
Results/Conclusions
We found that the probability of wild pig population establishment increased with the number of good (mast) years and with the number of individuals initially introduced. Since climate change models project an increased frequency of mast (i.e., more good years for wild pigs), we expect that introductions of wild pigs to new locations might be more likely to lead to establishment in the future. Their establishment following introduction is of concern because wild pigs spread disease to wildlife and livestock and cause billions of dollars (USD) of damage annually. This modeling framework can be used to estimate the probability of establishment following introduction for any invasive species for which vital rate data are available. This framework can also be used to project the future population dynamics of species whose vital rates depend on environmental conditions that fluctuate. Our methods also allow practitioners to simulate populations assuming either median or bounded (i.e., min and max) transient dynamics at each time step.