Ecological Dynamics on Yellowstone's Northern Range (2002) / Chapter Skim
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4 Present Conditions: Animals
4 Present Conditions: Animals
Pages 83-119
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From page 83... ...
The Army (and later NPS) managed and protected the resident ungulates and diligently controlled predators, which resultedin greatly reduced populations of coyotes, bears, and mountain lions, and the extirpation of wolves from Yellowstone National Park (YNP)
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From page 84... ...
19981. The conceptual basis of density-dependent population regulation is simple, and there are many examples of ungulate populations in which fecundity decTines or mortality increases as population density increases.
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From page 85... ...
19981. The northern range elk population, which had expanded to about 20,000 animals, responded to heavy snows in the winter of 1988-1989 by moving to a Tower-elevation winter range en masse.
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From page 86... ...
A significant proportion of the population has consistently migrated to the area of Dome Mountain in subsequentyears. From 1975 to 1988, an average of about 200 elk per year wintered north of Dome Mountain; the average increased to about 2,800 per year from 1989to2001 ~emkeetal.1998;Lemke 1999;T.Lemke,Montana Fish, Wildlife and Parks, personal communication, 20011.
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From page 87... ...
In response to the apparent need for a lower-elevation winter range, Montana Fish, Wildlife and Parks and the Rocky Mountain Elk Foundation collaboratively acquired 3,500 ha of key winter range on Dome Mountain (Lemke et al.
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From page 88... ...
The postulated effects of severe winter weather on elk have been corroboratedbysimulationmodeling. Landscape-scale simulations ofnorthew range elk identified winter severity as the primary cause of major mortality events (turner et al.
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From page 89... ...
Natural Variation in Elk Population Size Wildlife managers typically prescribe actions that reduce variation in population size or resources. Management of northern range elk has been no different, and observed population fluctuations would likely have been greater in the absence of annual herd reductions, acquisition of winter range, and provision of supplemental forage.
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From page 90... ...
~ 9891. Mortality during the 1988-1989 winter may have been increased by the previous summer's drought combined with the large elk population, although a similarly severe winter die-off was reported in 1919 (reviewed by Houston 1982)
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From page 91... ...
Most predators increase their consumption of prey as food becomes more available, thereby reducing the population growth rate of the prey and stabilizing population fluctuations. However, all predators exhibit satiation at some point, and if wolves become satiated when elk are highly abundant, then wolves are likely to have a destabilizing effect, exacerbating population fluctuations caused by severe winters or other factors.
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From page 92... ...
(YNP 1997~. With protection and intensive management, the bison population increased to more than 1,000 animals by the mid-1920s.
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From page 93... ...
, and the Madison/Firehole area in western YNP. Natural Regulation of YNP Bison Does the YNP bison population exhibit density dependence, and if so, how many bison is the park likely to support?
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From page 94... ...
Over this period, the average annual increment to the population was 145 individuals (NRC 1998) , which suggests a continuous decline in per capita reproduction throughout the range of population sizes.
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From page 95... ...
The corrected annual increment to the population is the difference in population size between years, with harvest added back (Nt+, - Nt + Ht)
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From page 96... ...
~ ~ ~ ..~-. · + · · + + , , , , 1 , , , , 1 , 1 1 1 1 , , , , 1 , , , , 1 0 1000 2000 3000 4000 5000 Population size FIGURE 4-6 Annual increment in the YNP bison population corrected for harvest (corrected increment)
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From page 97... ...
As population size and density increased, there was a large increase in the area used by bison during winter, from about 200 km2 in 1970 to more than 600 km2 in the 1990s. If intraspecific competition were an important factor regulating the size of the bison population, growth rate would be expected to decline as population size increased, after accounting for the effects of area.
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From page 98... ...
That density was approximated by the population of bison in ~ 984, when management actions began to remove significant numbers of bison at park borders. Bison used about 675 km2 of winter range at a population size of about 2,800, which may be the population size at which bison might remain inside YNP without management intervention.
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From page 99... ...
In severe and even during normal winters, elk are essentially confined to feedgrounds because of limited native winter range or because deep snows preclude them from leaving. Because animals standbodyto-body while eating, a birthing or abortion event of an infected elk could expose large numbers of animals to B
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From page 100... ...
19981. Other Ungulates Populations of mule deer, white-tailed deer, pronghorn, bighorn sheep, mountain goats, and moose inhabit the northern range.
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From page 101... ...
The remaining 30% move to winter ranges within the park boundaries at Tower elevations (YNP ~ 9971. Some individuals migrate 80 km to their winter range (Walimo 19781.
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From page 102... ...
Pronghorn are intolerant of deep snow and their distribution in the northern range is restricted in winter to lower windswept areas where food is exposed throughout the winter, particularly sagebrush grassland (Barmore 19801. The area of pronghorn summer range is considerably greater than suitable winter range, but about 75% of northern range pronghorn are thought to reside in the same area throughout the year, and only about 25~o migrate seasonally to a higher-elevation summer range (Caslick 19981.
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From page 103... ...
Open circles are estimated population sizes and crosses are actual counts. Sources: YNP 1997, Lemke 1999.
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From page 104... ...
In Yellowstone, the diet of pronghorn on their winter range is similar to the diets of elk, bison, and deer, so these species may come into direct competition during winter (Wambolt 19961. Overlap is less in the other seasons (Schwartz et al.
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From page 105... ...
Bison management may also affect pronghorn because the Stephen's Creek bison facility, where bison are tested for brucellosis and then released or slaughtered, was built in key winter pronghorn range to hold bison that leave the park. Caslick and CasTick (annual reports ~ 995 to ~ 999)
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From page 106... ...
Fawn production depends on the ability of female pronghorn to maintain good condition, particularly during the winter, and this depends on the severity of the winter and the availability of food. An increasing elk population is reducing Me availability of sagebrush, a key winter forage for pronghorn.
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From page 107... ...
Many of the preferred foods of moose are early-successional plants; thus, disturbances such as fire and floods may be important for maintaining a suitable habitat. In general, moose are not migratory, although summer and winter ranges may differ in elevation.
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From page 108... ...
Small bighorn sheep populations may be highly susceptible to
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From page 109... ...
1997) , end ongoing studies of mountain lions may provide a better indication of the relative importance of factors that may control the bighorn sheep population.
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From page 110... ...
Bones of wolves, coyotes, end grizzly beers were foundin various strata during excavations at Lamar Cave, whose strata extend back about 3,000 years. Multiple Euro-American observers reported wolves, coyotes, grizzly and black bears, and mountain lions in the GYE before 1882 (Schullery and Whittlesey 19991.
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From page 111... ...
However, a complete moratorium on hunting grizzly bears anywhere in the GYE was not imposed until ~ 974. The GYE grizzly bear was listed as threatened under the Endangered Species Act in 1975 (Knight et al.
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From page 112... ...
Grizzlies are long-lived end females do not reproduce until they are about 6 years old. Grizzly bears are not easily observed as they are mostly solitary and travel over large home ranges in remote, mountainous, and largely forested country.
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From page 113... ...
as the focal wild population (Hedrick 1983~. Loss of genetic diversity reduces population fitness and the probability of longterm survival; thus YNP's grizzly bears probably need more protected habitat and dispersal corridors to preserve genetic diversity (Craighead et al.
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From page 114... ...
However, interactions between Yellowstone's black and grizzly bear populations have not been studied. Where both species coexist in Alaska, grizzly bears dominate black bears (Miller et al.
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From page 115... ...
19991. Presumably, these dispersal abilities enabled mountain lions to recolonize YNP after they were locally eradicated by predator control programs.
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From page 116... ...
Mountain lions are responsible for about 3% of the elk and 4% of the mule deer deaths in the northern GYE (Murphy 19981. Mountain lions kill about 12~o of the buck mule deer, No of the elk calves, and I% of the bull elk, but less than 5% of the other age-sex classes of elk and deer.
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From page 117... ...
Packs on the northern winter range killed an average of one ungulate every two to three days during March and one every three to four days during November and December. Wolves can adjust to changing prey abundance and vulnerability (Messier 1995)
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From page 118... ...
argued that these factors explain many of the differences between Yellowstone coyotes and those studied in other areas, including larger pack size, greater social stability, higher adult survivaIrates (91% per year) , higher mean age of adults, and lower dispersal rates of juveniles.
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From page 119... ...
. Some of the surviving coyote packs are smaller and are producing larger, healthier pups with higher survival rates.
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