Conservation Targets Too Small To Stop Extinction

Study indicates 5000 mature individuals are needed for population viability

Conservation Targets Too Small To Stop Extinction

This determination could have profound implications for the protection of many species. Many biologists use a number of 2000 individuals in a population for maintenance of viable populations over the long term. In the Northern Rockies the USFWS believes that 1600 (and declining) wolves represent a viable population that can persist over the long term. The National Park Service presumes that maintaining only 2300 bison in Yellowstone will maintain the genetic diversity needed for long term viability. According the USFWS even fewer grizzlies are needed for recovery with 500-600 bears in the Yellowstone DPS.

According to the new study:

“populations of endangered species are unlikely to persist in the face of global climate change and habitat loss unless they number around 5000 mature individuals or more”

Grizzly Bear, Buffalo, Wolf © Ken Cole
Grizzly Bear, Buffalo, Wolf © Ken Cole


  1. Maska Avatar

    Thanks for the post, Ken. Future recovery planning (for example, for the Mexican gray wolf) needs to take this work into account in setting population goals.

  2. Virginia Avatar

    To me, this begs the question, “why are we basing current plans to avoid extinction on conditions that are no longer relevant?”

  3. Larry Thorngren Avatar

    I spent the day in the Lamar Valley here in Yellowstone. The Druid Pack chased an elk (cow or large calf) into the Lamar River where the elk eluded the pack as they swam after the elk for some time. The elk did a marvelous job of eluding the wolves. I ended up cheering for the elk. When I left just before dark, the elk was still in the river and the wolves were scattered in the grass 20-50 yards away.
    The wolves all had mange and almost no hair on their tails. I find it strange that the park allows darting of wolves to put radio collars on them but will not allow darting them to pour insecticide on their backs to eliminate the mange mites. Not natural.
    Ken- Bison genetic viablity in Yellowstone can be maintained by bringing in bison from other sources. I think the main objective with bison and elk in Yellowstone should be maintaining a heathly range for all range users. The actual numbers should be based on the measured carrying capacity. I saw a lot of bison today and the range looks great. Wolves can also be brought in to provide genetic variety. I think we should cocentrate on maintaining the wolves we have and not be concerned with trying to get the numbers up to 5000.

  4. Eric T. Avatar
    Eric T.

    aribitrary numbers
    arbitrary and capricious agruments
    yep, the math adds up all right.

  5. Ken Cole Avatar

    What other sources are there? All of the other sources, with the exception of the Henry’s Mountain herd in Utah, have documented cattle genes. They also only number around 700 so, combined, they number about 4000 until another big slaughter occurs and they have no connectivity to maintain genetic viability.

    Besides, there is no proposal to do what you suggest. In essence Yellowstone bison are genetically isolated and the slaughter does not select for a random sample of the population so genetic variability is not maintained.

    With this information it seems apparent that bison should not be confined to just the Park, they should be allowed to use public lands outside of the Park. Even when bison numbered 4900 the range looked good. That’s not the limiting factor. The limiting factor is winter range. The range can sustain much higher numbers if they are allowed to leave the Park during winter. During the winter the range inside the Park is covered with snow and is protected from overgrazing by bison. It’s not that there isn’t enough forage to sustain them in the Park during the winter it’s that they can’t physically get to it through the snow and ice.

  6. JimT Avatar

    Thanks for the link, Ken

  7. Ryan Avatar

    “In the Northern Rockies the USFWS believes that 1600 (and declining) wolves represent a viable population that can persist over the long term.”


    The wolves will be just fine due to the inflow of genetics from canada.

  8. gline Avatar

    not if they are being killed off

  9. Ken Cole Avatar

    The wolves just north of the Canadian border, to my understanding, are quite low in density. They have isolation issues just like those in the lower 48 so it’s hard to say that they can contribute much to US populations.


Ken Cole is a 5th generation Idahoan, an avid fly fisherman, wildlife enthusiast, and photographer. He is the interim Idaho Director for Western Watersheds Project.

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Ken Cole