By calculating the amount of food lost because of dropping sea levels, and combining this with estimates of the food needed to keep a whale alive, the two researchers calculated the impact of global cooling on gray whale populations and the populations that would have had to exist in order for the whales to survive.
They concluded that populations would have had to have alternative feeding modes sufficient to support a population of around 70,000 during warm periods so that population drops during glacial periods wouldn't be below 5,000-10,000 whales. Much lower numbers would have produced a genetic bottleneck obvious in the DNA of the whales, and such a signature has not yet been seen.
"We don't yet have the ability to look deep enough into the whale genome to see this type of bottleneck," Pyenson added, though genetic analysis that has been done shows no evidence of a bottleneck much shallower in time, just before humans targeted the mammals for whaling.
The carrying capacity of the North Pacific could have been as high as 170,000, "assuming modern day values for benthic productivity, food density, and gray whale energetics," the authors concluded. If gray whales also exploited non-benthic organisms, such as krill, the populations could have been even higher.
If gray whales do respond well to the rising temperatures and sea levels predicted for the future, that may not be true for the birds and other marine mammals that feed in the Bering Sea, one of the most productive marine ecosystems during the summer.
"If this environment disappears in glacial maxima, we really need to rethink what we know about the ecological history of all the other organisms that make a living in the Bering Sea," Pyenson said. He and Lindberg urge other scientists to focus on the historical ecology of species to fully understand their co
|Contact: Robert Sanders|
University of California - Berkeley