Studies of structured population dynamics often focus on asymptotic population growth rates, which assume that the population has reached the stable stage distribution. For many populations this assumption is not justified and the population is better described by short term or transient dynamics, which can be considerably different from asymptotic ones. Transient dynamics can be important for estimating invasion speed of non-indigenous species, population establishment after releasing biocontrol agents, or population management after a disturbance like fire. For ecothermal species like insects, temperature plays an important role in their developmental rate.  We developed two different models to explore the effect of temperature on the transient population growth rate, using pea aphids (Acyrthosiphon pisum) as a case study.  Both models are continuous in time: the first model uses the Lotka renewal equation to calculate population growth when survivorship and fecundity are continuous functions of age.  The second model is an individual based model with survivorship and first day of reproduction drawn from probability distributions, and fecundity is modeled as a continuous function of time from first day of reproduction. We estimated model parameters (survivorship and fecundity) at two different temperatures (20^oC and 24.4^oC), then scrutinized both model predictions by comparing observed and predicted transient population growth rates and the change in population size at 24.4^oC. Furthermore we explored the effect of modeling details on model prediction by comparing the predictions of the two models at both temperatures.

Results/Conclusions

Both models predict that an increasing temperature produces earlier, higher and sharper transient growth rates, but the predictions of the individual based model match observed transient dynamics much better than the Lotka renewal equation model