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THE CASE FOR PREDATORS

by Dennis D. Austin

Before the Great Basin was settled by the Mormon pioneers in the mid-1800s, plant and animal communities had been developing for about two million years during the Pleistocene Epoch. During most of this Ice Age period, nature balanced evolving predator and prey species without human influence.

However, during the last 14,000 years, or since the end of the Ice Age, humans have been part of the formula. The advent of native American humans correlated with the extinction of over 50 percent of the mammals that were present at that time in North America. Species which vanished during this period included the mammoth, sloth, camel and a type of horse.

Natural regulation was altered again with European pioneer settlement in the mid-1850s. For the second time the human influence greatly changed the predator-prey relationships which had been evolving. Since the 1850s, humans have caused either extinction or virtual elimination of many predators as well as other plant and animal species within the Great Basin.

The major predators of the Great Basin in the 1850s included the gray wolf, grizzly bear, black bear, cougar, bobcat, coyote, gray fox, lynx, and wolverine. The minor predators were more numerous and included mink, badger, striped skunk, pine marten, ermine, long-tailed weasel, kit fox, black-footed ferret, and river otter. Non-native introduced predators include the red fox and raccoon.

The accompanying graph shows my interpretation of dominance for the major, minor and introduced predators of the Great Basin. Dominance suggests the lower predator may be displaced and/or preyed upon by the higher predator. Solid lines suggest a stronger relationship of dominance and influence, whereas dotted lines suggest a weaker relationship.

predators.gif (21588 bytes)The interrelationships between predators are not well defined and the accompanying figure is highly theoretical. Pioneers diligently and quickly eliminated predators as settlements were established, and studies having a full array of predators were not conducted. In addition only very limited observational data are available. However,

Aldo Leopold reported an intriguing insight in 1937 using his personal observations of wolves, coyotes and deer: "Have deer always fluctuated from scarcity to overabundance?....

"In Chihuahua, Mexico, one can glean by comparison a hint of what may be the matter with our (western United States) deer. White-tailed deer are abundant in the Sierras (Mexico) but not excessive. So are wild turkeys ... Deer irruptions are unknown.

"Mountain lions and wolves are still common. I doubt whether the lion-deer ratio is much different from that of Coronado's time. There are no coyotes in the mountains of Chihuahua, Mexico, whereas with us (western U.S.) there is universal complaint from Alaska to New Mexico that the coyote has invaded the high country to wreak havoc on both game and livestock.

"I submit for conservationists to ponder the question of whether the wolves have not kept the coyotes out? And whether the presence of a normal complement of predators is not at least in part accountable for the absence of deer irruption? If so, would not our rougher mountains be better off and might we not have more normalcy in our deer herds, if we let the wolves and lions come back in reasonable numbers?"

I agree with Leopold, the father of conservation in the United States, on his theory of predator interrelationships and the potential high values of maintaining a full complement of predators. Thus the presence of higher-order predators would likely depress the populations of lower order predators.

This effect would be most evident when prey species are reduced to low populations and predator competition for prey species is high. For example, coyotes may displace red and gray fox, and the current high populations of cougars may be controlling the current sparse population of bobcats.

Furthermore, as Leopold implied, decreased populations of coyote and cougar numbers could be caused by wolves. Thus the presence of wolves, potentially causing a decrease in total predator populations, may lead to increased growth and productivity of prey species such as mule deer. This would be especially significant when populations of mule deer are depressed.

Two additional benefits may potentially occur with a full complement of predators. First, a decrease in the total predator-caused livestock depredation losses seems likely because of a reduction in total predators. Second, as suggested by Leopold, because predator interactions would decrease as prey populations increased from decreased competition between predators, predators would tend to maintain deer populations below excessive numbers.

Unquestionably, the potential effects of a full complement of native predators are intriguing.

The ideas presented above are only theoretical. However, the reintroduction of the gray wolf to the Yellowstone ecosystem and the intense research being conducted will hopefully add significant information on predator interrelationships.

Will gray wolf populations expand into northern Utah? Probably. Within the next decade or sooner, Utah will likely have the opportunity to manage this unique predator within the state. A verified gray wolf was killed near Kemmerer, Wyoming, in 1 998, suggesting range expansion may be occurring much more rapidly than expected. Also, a few scattered, probably inaccurate, and unverified reports have been received from northern Utah in the last two years.

Visual observations of gray wolf, lynx, wolverine, pine marten, river otter or black bear are rare in northern Utah. Reports of observations of these predators are appreciated by the Utah Division of Wildlife Resources. Please call me at 435-245- 5261 or contact your local Utah Conservation Officer.

Ed. Note: Dennis Austin is the Cache District biologist with the Utah Division of Wildlife Resources.This article was reprinted from the Herald Journal, Logan, Utah, February 8, 2000 with his permission. his permission.


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