Read the following introductory paragraph: A slow, sad drama unfolding on a remote island is providing a grim challenge to the National Park Service's traditional policy
of letting nature take its course, Isle Royale in Lake Superior is home to the longest studied predator-prey relationship in the
world. For over sixty years biologists have been watching the island's moose and wolf populations, recording but not
interfering in their struggles. But now, the wolf population is doomed and the delicate island ecosystem is spinning out of
balance. It is time for NPS scientists to put down their notebooks and step in. It is time to save the wolves, and save the island.
What is the main function of the sentence "For over sixty years biologists have been watching the island's moose and wolf
populations, recording but not interfering in their struggles," in the paragraph?