Guest commentary: Numbers don't dd up for grizzly delisting

By Mike Gilpin

What are the numbers for the grizzly bear in Yellowstone National Park? Do such numbers merit the delisting of this or any other species?

In considering these questions, please take note of the flagship status of the grizzly bear. Together with the bald eagle, it is one of the reasons we got the Endangered Species Acts of 1968 and 1973. What we decide for the Yellowstone grizzly could very likely become precedent setting for other listed species. That is, before acting locally, we should think globally.

Here is a minimal set of numbers for the Yellowstone grizzly: 600, +3 percent, 0, 75 percent, 0.125, -1 percent, 50/50 and 90 percent.

Six hundred is the estimated population of grizzly bears in the Greater Yellowstone Ecosystem, one of five grizzly bear recovery zones; and 3 percent is its average population growth for the last three decades. These are good numbers. They are numbers in which the members of the grizzly bear recovery team should take pride. They are the ones to which politicians, real estate developers and, now, editorial writers like to point. They are the numbers currently emphasized by government scientists, so their use by nonscientists is somewhat justified.

While basic population size is important, it takes more than one or two numbers to describe the conservation status of a population. Below is a brief explanation for the other important numbers for the Yellowstone Grizzlies:

Zero is the migration rate of bears into the Greater Yellowstone Ecosystem. Migrants bolster population growth rates, can prevent or correct local population extinction, and continuously add new genetic material to the local population. As best we can tell, the grizzly bears in the GYC are totally isolated (completely insularized). Migration provides none of these benefits.

Seventy-five percent is an estimate of the retained genetic heterozygosity of today's Yellowstone grizzly bear population compared with what the species would have had a century ago. If Yellowstone were a zoo for grizzly bears it would be considered a failure by this criteria alone.

The 0.125 is the inbreeding coefficient of grizzly bears in the Yellowstone population. It is what one would get from a marriage of first cousins. Well before a science of genetics existed, Charles Darwin, no biological fool, married his first cousin. The deleterious effects of the resulting inbreeding on his children caused him anguish in the last 20 years of his life.

The -1% is the inexorable, per-generation loss of genetic heterozygosity in the Yellowstone grizzly bears. Inbreeding builds at the same rate.

The 50/50 is the rough breakdown of the ratio between source habitat (positive population growth rate) and sink habitat (negative population growth rate). Such spatial features of the habitat makes very questionable the use of a single number for population growth.

Ninety percent is the rough probability for a near-term catastrophic change in the populations ecology of the Yellowstone grizzly. This seems certain to come from the loss of the white bark pine, whose pine nuts supply the bears with a rich source of fat and protein in the month before hibernation.

Taken together, these are not a set of good or encouraging numbers. It is unconscionable that government conservation scientists do not present all the relevant numbers. It is grievously erroneous that the public base policy decisions on incomplete science.

Dr. Michael Gilpin is Professor of Conservation Biology (Emeritus) at the University of California, San Diego. He is an Affiliated Professor at Montana State University. He has been involved with grizzly bear conservation issues since 1985. He has served on two U.S. Fish and Wildlife Service recovery teams and has consulted with state and federal agencies on 20 other endangered species.

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