Search for: All records

Adelges tsugaeAnnand, the hemlock woolly adelgid, is an invasive insect pest ofTsuga canadensis(L.) Carriere, eastern hemlock, in the eastern United States. AnA. tsugaeinfestation often results in the death ofT. canadensiswithin years and has caused significant changes to hemlock forests. Cycles inT. canadensishealth andA. tsugaedensities seem to be an important feature inA. tsugaepopulation dynamics in the eastern United States. To investigate mechanisms leading to such cycles, we construct a model composed of systems of ordinary differential equations with time‐dependent parameters to represent seasonality. The model captures the coupled cycles inT. canadensishealth andA. tsugaedensity. We use field data from Virginia to develop the model and to perform parameter estimation. The mechanisms we represent in the model include anA. tsugaedensity‐dependentT. canadensisgrowth rate, aT. canadensishealth‐dependentA. tsugaemortality rate, and a density‐dependentA. tsugaemortality rate, which produce cycles inT. canadensishealth andA. tsugaedensity commonly seen with theA. tsugaesystem in the eastern United States. We test sets of initial conditions to determine the scenarios that will likely lead toT. canadensismortality and explore longer term dynamics of the system. In general, low and highT. canadensishealth initial condition values result in likelyT. canadensismortality whileT. canadensiswith medium health initial condition values are predicted to survive.

Metapopulation models include spatial population dynamics such as dispersion and migration between subpopulations. Integral projection models (IPMs) can include demographic rates as a function of size. Traditionally, metapopulation models do not included detailed populaiton models such as IPMs. In some situations, both local population dynamics (e.g. size‐based survival) and spatial dynamics are important.