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Nicolas Loeuille1 and Michael Ghil2
1Laboratoire d’Ecologie, UMR 7625, Ecole Normale Supérieure, 46 rue d’Ulm, F-75230 Paris cedex 05, France
2Département Terre-Atmosphère-Océan, Ecole Normale Supérieure, 24 rue Lhomond, F-75231, Paris cedex 05, France, and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, USA
Extensive work has been done to identify and explain multi-year cycles in animal populations. Several attempts have been made to relate these to climatic cycles. We use advanced time series analysis methods to attribute cyclicities in several North-American mammal species to abiotic vs. biotic factors.
We study eleven century-long time series of fur-counts and three climatic records – the North Atlantic Oscillation (NAO), the El-Niño-Southern Oscillation (ENSO), and Northern Hemisphere (NH) temperatures – that extend over the same time interval. Several complementary methods of spectral analysis are applied to these 14 times series, singly or jointly. These spectral analyses were applied to the leading principal components (PCs) of the data sets. The use of both PC analysis and spectral analysis helps distinguish external from intrinsic factors that influence the dynamics of the mammal populations.
Our results show that all three climatic indices influence the animal-population dynamics: they explain a substantial part of the variance in the fur-counts and share characteristic periods with the fur-count data set. In addition to the climate-related periods, the fur-count time series also contain a significant 3-year period that is, in all likelihood, caused by biological interactions.
Keywords: population dynamics, climatic effects, principal component analysis, spectral analysis, multi-annual periodicities.
◊An open access article from BMC Ecology 2004, 4:6, viewed from biologyonline.com.