Trendy セミナー   2005-11-24 (木) 16:30   北大・大学院地球環境・A804 号室

Experimentally Reconstructed Nonlinear Dynamics of Alternate Bearing
-Modelling, Prediction and Control Methodology for a Very Short Ecological Time Series-

酒井憲司 (東京農工大学農学部 地域生態システム学科)

In order to develop ecology into a predictive and manipulative science, we need to have a method to reconstruct the nonlinear dynamics from a very limited dataset (data size-problem) and a method of controlling chaos (manipulation-problem).The discovery of nonlinear dynamics in natural ecological systems has attracted much attention after May’s historical work. Nonlinear time series analysis (NTSA) is used to investigate deterministic chaos. However, most ecological time series are too short to perform NTSA, which requires a time series whose size is in the thousands. We developed "ensemble reconstruction" of the dynamics from a very short ecological time series whose size is smaller than ten. Alternate bearing is a common phenomenon in tree crops such as citrus and nuts. Most tree crops such as citrus, nuts and acorn, show large fluctuations in annual yield, so-called alternate bearing and/or mast fruiting. In this presentation, I show a method of reconstructing the global and local dynamics from a very short ecological time series. For the global dynamics, we tested the feasibility of applying response surface methodology and for the local dynamics, I demonstrate the developed "ensemble reconstruction". We used an ensemble dataset consisting of the yields of 48 individual trees over 7 years to test our proposed method and successfully validated this method by one-year forward prediction three times in 2002, 2003 and 2004. Reconstructed models were also validated by one-year forecasting fitness and by controllability in numerical experiments based on the OGY method developed for controlling chaos.

Trendy Seminar
北海道大学大学院環境科学院 植物生態学