On a secluded island in Lake Superior, captive wolf packs and moose populations depend on one another for survival: The moose are the wolves' chief nutritional source, and the wolves, in turn, help keep the moose population in check. But when the wolves eat too many moose, the resulting food shortage pares down the former's number, controlling their population, as well.
Teams of scientists from Michigan Technological University led by wildlife ecologist Rolf Peterson since 1975, and joined in 2000 by John Vucetich, assistant professor of forest resources and environmental science, have carefully monitored the waxing and waning of these animal populations. The link between hunter and hunted has revealed the species' interdependency, as well as their shared vulnerability to the isle's often-tough living conditions. The plant-eating moose must scrounge during the harsh winters to avoid starvation, living on pine needles and twigs. When food becomes too scarce and the moose populations decline, some of the wolves that rely on the moose also die out.
Scientists have found that there are currently four packs of wolves roaming the isle that continually battle for turf and food—and their rise and fall, as described by the researchers, can often stem from seemingly insignificant events.
For example, in January 2000 researchers watched as a lone female wolf entered the territory of one of the wolf bands they had dubbed the Middle Pack. She was attacked by the wolf pack and forced into the chilly water of Lake Superior. Though wounded, she swam back to shore and survived. A male split from the Middle Pack and came to her aid, staying with her and licking her wounds after she had been left for dead. The ostracized couple later mated, founding what became the Chippewa Harbor Pack, a group that has since conquered territory in the Middle Pack's dwindling empire.
Though the scientists don't know if such individual and pack behavior is a common occurrence, observations like these on Isle Royale provide insight into how animal societies function as well as the vicissitudes of the food chain cycle on Isle Royale, also helping to inform other models of the natural world.