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Rolf O. Peterson, a biologist at Michigan Technological University, and Brian McLaren have kept track of the wolf and moose populations on a 544-square-kilometer island in Lake Superior for the past 35 years. Recently, Brian McLaren added plants to this predator/prey relationship by studying the tree rings of the balsam fir. He found that the trees on that island go through periods of reduced growth, as indicated by a narrowing of the rings.
Interestingly, McLaren discovered a positive correlation between the number of wolves and the size of the tree rings. That is, as the number of wolves decreased so did the size of tree rings.
McLaren speculated that decreasing populations of wolves, due to disease, led to an increase in moose populations (a negative correlation). This then led to an increased grazing pressure on the balsam firs and thus their reduced growth.
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