Ayres Abstracts

Tanhuanpää, M., Ruohomäki, K., Turchin, P., Ayres, M. P., Bylund, H., Kaitaniemi, P., Tammaru, T. and Haukioja, E. 2002. Population cycles of the autumnal moth in Fennoscandia. Pages 142-164 in A. A. Berryman (ed.), Population cycles: the case for trophic interactions. Oxford University Press, New York.
Northern populations of E. autumnata exhibit cyclic population dynamics, which are most easily understood as the result of delayed density-dependence. Two specific ecological processes known to produce delayed density-dependence in E. autumnata are delayed inducible resistance of the host plant (DIR) and parasitism by specialist wasps. We used empirically based population modeling to test whether parasitism is, by itself, able to produce population cycles of E. autumnata. The model was parameterized with empirical data. Simulations using the initial parameterization of a larval parasitism model failed to produce dynamics that matched empirical time series; endogenous dynamics were oscillations with a period that was somewhat too short and an amplitude that was much too low compared to natural cycles. However, it was possible to find statistically plausible parameters of the parasitism model that could produce realistic population dynamics. So it is possible that larval parasitism by itself can explain the endogenous population cycles of northern E. autumnata, but this conclusion must be qualified by noting that many different dynamics can be produced with statistically plausible parameters (and many of them do not match the data). Expansion of the time series data for this host-parasitoid system should allow refinement of the endogenous dynamics expected from larval parasitism alone. This will also facilitate tests of whether the multiple density-dependent feedbacks in this system interact to produce endogenous dynamics that cannot be easily predicted from the characteristics of any one ecological feedback system.