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Across the boreal forest of Canada, lynx populations undergo regular density cycles. Analysis of 21 time series from 1821 onward demonstrated structural similarity in these cycles within large regions of Canada. The observed population dynamics are consistent with a regional structure caused by climatic features, resulting in a grouping of lynx population dynamics into three types (corresponding to three climatic-based geographic regions): Pacific-maritime, Continental, and Atlantic-maritime. A possible link with the North Atlantic Oscillation is suggested.
Periodic population fluctuations of the Canada lynx (Lynx canadensis) have greatly influenced both ecological theory and statistical time series modeling [(1, 2); see (3) for a summary]. Recent analyses have focused on the extent of synchrony in population fluctuations, assessing the importance of external abiotic factors (such as weather) and internal biotic factors (such as dispersal among populations) in causing spatial patterns (4). Such empirical and theoretical approaches have, however, assumed that the populations were structurally similar [that is, the density-dependent relationships are identical among populations (5)]. This assumption has never been thoroughly evaluated. To do so requires determining whether the lynx populations display the same phase- and density-dependent structure (3) and then searching for similar underlying causes of the observed dynamics. Using new statistical methods developed for this purpose (6), we ask to what extent the time series on the Canada lynx (Fig. 1) compiled by the Hudson Bay Company for the period 1821 to 1939 (7) and the corresponding more modern time series compiled by Statistics Canada for the period 1921 to present (8), taken together, are structurally similar. Specifically, we ask whether the phase- and density-dependent structure of changes in lynx abundance cluster into groups defined according to ecological-based features (9) or according to climatic-based features (10, 11).
The available time series (Fig. 1A) cover two ecosystems (referred to below as ecological regions): the northern, open boreal forest (Fig. 1B) and the southern, closed boreal forest. In western Canada, the mountainous topography adds complexity. Additionally, the series cover three climatic regions defined by the spatial influences of the North Atlantic Oscillation (NAO) [Fig. 1C; see (12)], which may contribute to spatial differences in trophic interactions (13).
Previously, we fitted a piecewise linear autoregressive model (14) to each of the series (3). A general hare-lynx model...