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Figure 1 | BMC Ecology

Figure 1

From: Pervasive influence of large-scale climate in the dynamics of a terrestrial vertebrate community

Figure 1

The process-oriented ecological model of intra- and inter-trophic level dynamics in a simple, straight-chain community, based on empirical observations of interactions between wolves, moose, balsam fir, and climate on Isle Royale, USA. The effect of the herbivore on vegetation is specified as a current-year effect, but is likely to operate at a minimum lag of 3–6 months. In equations (2) of the Methods section, the climate term U is partitioned into the strictly direct influence of climate, U D , and the indirect influence that is reflected in prey vulnerability to predation, U P . In this scenario, climate may directly influence survival of wolves and/or moose, and hence changes in their numbers, from the beginning of winter to the end of winter. Similarly, climatic influences on the susceptibility of moose to predation may result in changes in the numbers of wolves and/or moose from the beginning to the end of winter. Partitioning of the climate term U into direct and indirect effects was achieved by setting U t = U Dt + U Pt , where U Dt is the NAO winter index in the current year, and U Pt is wolf pack size in the current winter. Note that this current year effect is actually a 3–4 month lagged effect, because it quantifies the influence of winter conditions from December–February on wolf predation and survival, and on moose survival, that may influence changes in estimates of wolf and moose density made at the end of winter.

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