This DVD, (2019, distributed by PBS, available at vpl.ca) tells an exceptional story and is worth taking out of the library or purchasing. Prof. Bob Paine, a zoologist from the University of Washington in the Pacific Northwest, was the first scientist to discover an important pattern in nature. In 1964, he wanted to know what would happen if you removed the predators from the food chain and he was seeking a “natural community that he could easily manipulate.” He found it in the tip of the Olympic Peninsula in Washington State, in the tidal pools, which formed a complete ecosystem composed of filter feeders, plants, scavengers and hunters, such as the apex hunter, the starfish. With their arms, they could open mussel shells and then eat the bodies inside. Paine conducted an experiment in which he simply removed the starfish from one tidal pool and left them active in another. He watched the pools carefully. Within eight years, the tidal pool without the starfish was decimated, as the mussels took over and all the other species were gone. Removing one of the other species did nothing to alter the tidal pools. Paine learned that it was the predator that kept all species in balance and he named the starfish a keystone species.
In 1971, Prof. Jim Estes, a biologist, was sent by the Atomic Energy Commission to study sea otters in the chain of Aleutian Islands off Alaska. A chance meeting with Bob Paine changed his study question from, “what was the kelp forest doing for the otters, to what were the otters doing for the kelp forest?” The towering kelp forest under the frigid sea was a rich source of food and housed “dozens of species.” Estes observed all the islands where the sea otters were present, and went to the furthest tip of the Aleutians, to the small island called Shemya, where the otters had not established themselves. The results were dramatic. On the island where there were no sea otters, the kelp forest under the water was gone along with every other species, except for the sea urchins. They kept gorging on the kelp and with no sea others to eat them, their populations were not kept in check. Sea otters were the keystone species.
Forest ecologist John Terborgh, from Duke University, wanted to test the keystone species theory on land. He found his laboratory in Guri, Venezuela in 1990, where the tropical jungle had been flooded by the construction of a hydroelectric dam. The flooding had left pockets of wooded hilltops above the water from which the larger predators, such as jaguars, had fled because there was little food left. Terborgh discovered catastrophic results. The herbivores, unchecked by predators, had eaten every bit of the plant life and tree leaves, causing death to everything. Whether it was howler monkeys, or iguanas, or army ants, or leaf cutter ants, the foliage was devoured, and the trees eventually died. Terborgh remarked that the small islands looked like a hurricane had hit them. “It’s all predator driven, remove the predators” and it led to the deterioration of the whole system. Terborgh sounded the alarm when he spoke of forests around the world saying, because we have been systematically taking out our top predators, we have been taking nature apart, with a resulting loss in diversity. Terborgh warned us that because wolves are gone, “the deer have reached a plague abundance” and eaten down the forests to the browse line. ”The forests are collapsing.” He said that we couldn’t see it, but he could because the forests were less dense, and thinner as they showed the effects of overgrazing. “When the big trees are gone, there wouldn’t be a forest anymore,” he said.
In Yellowstone National Park, the keystone is the wolf. By 2016 Yellowstone was celebrating twenty years of the reintroduction of the wolf population (Yellowstone Science, Vol.24,Issue 1, June 2016), with healthy packs and a stabilization of wolf numbers. Elk herds had been reduced to healthy numbers below carrying capacity, and had become “leaner, meaner,” and less vulnerable because they were predator-tested. Before the wolves were reintroduced, the elk herds reproduced to carrying capacity, shared fewer resources and were in poorer condition. Now the ecosystem was in better balance. But an even greater benefit was achieved, according to Doug Smith, wildlife biologist in charge of the Yellowstone Wolf Project (article Brodie Farquhar, Jun 22, 2023). Smith explained that when the wolves were killed off in the 1930s in Yellowstone, the elk were still preyed upon by black and grizzly bears, cougars, and coyotes, but the wolves had been the major predator. Consequently, the elk population expanded and “browsed heavily on young willow, aspen and cottonwood plants.” The beaver relied on willows to live through the winter, but the willows were in poor shape. After reintroduction, the wolves kept the elk population on the move, which stopped over browsing, which in turn helped restore the willow and other plants. The beaver had a greater food supply and recolonized, constructed new dams and ponds, which provided shaded water for fish, and new habitat for songbirds who also returned. Introducing the wolf was bringing more biodiversity to Yellowstone, and the “ecosystem becomes whole again”.
The DVD reports several more interesting studies. Mary Power, a fresh water ecologist in Big Creek Oklahoma, in 1983 made an important discovery that the predator introduced a landscape of fear. And Tony Sinclair, a biologist at The Serengeti National Park, Tanzania, in the 1960s, revealed surprisingly that the keystone species wasn’t a predator but was the wildebeest. He also discussed the fascinating recovery from civil war devastation of Gorongosa National Park in Mozambique, after the war concluded in 1977, with the reintroduction of predators. In conclusion, the narrator stated that loss of diversity is a disturbing reality, but asked “is it earth’s destiny?” He closed on a hopeful message, “There are rules, we can harness them to heal our damaged earth…We are not alone. We now recognize a powerful ally, in nature itself.”
