Life is out of whack

From Salon:

Story Current ecological data, much of it cited by Kricher in the tedious manner of an Ecology 101 lecture, scientifically supports the notion of balance in nature at least as strongly as it refutes the idea. For instance, consider research on the sea otter, which Kricher describes at great length, only rather obviously to conclude that “humans can unwittingly induce major alterations in ecosystem food webs.”

In fact, the research illustrates much more than that. Between 1990 and 1997, in the western Aleutian Islands, the otter population plummeted by 90 percent because orcas began feeding on them. Previously orcas subsisted on fish-eating harbor seals and sea lions, but human over-fishing in the region led to a drop in seal and sea lion populations, forcing orcas to broaden their diet. Since the otters preyed on sea urchins, fewer otters meant more urchins, a rapidly expanding population that decimated the undersea kelp forests on which they fed. The loss of kelp in turn further disturbed the fish in the area, which relied on kelp for shelter, exacerbating the seal and sea lion famine, impelling orcas to eat more otters. The effect was so dramatic because otters were a “keystone” species in the region, meaning that the stability of the food web depended disproportionately on their well-being. Which is to say that a steady otter population helped to maintain the balance of nature.

More here.