Brucellosis in the Greater Yellowstone Area (1998) / Chapter Skim
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Part II: Transmission Among and Between Species
Part II: Transmission Among and Between Species
Pages 42-88
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From page 42... ...
The National Park Service's natural-regulation polity is discussed, as is the effect of B abortus on reproductive potential of bison.
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From page 43... ...
elk, in 1979-1980. Because the GTNP bison herd is isolated from the YNP bison here' by the continental divide, infection in GTNP bison is assumed to have derived from their contact with infected elk on the wintering grounds.
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From page 44... ...
abortus. Free-roaming elk herds, thought at the time of the first reports not to carry brucellosis, were found on further testing to have a relatively high proportion of seropositive inclivicluals.
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From page 45... ...
Tire facts were derived from field operations of the federal-state cooperative program to eliminate brucellosis from domestic cattle in the Uniter! States.
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From page 46... ...
abortus transmission are abortion or birth when infectious materials are in the environment. Because of long exposure of bison to B
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From page 47... ...
abortus is not self-sustaining in elk hercIs that are not concentratec! on winter feeding grounds.
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From page 48... ...
Abortion by B abortus-infected females is a more serious risk factor for disease transmission than is normal birth.
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From page 49... ...
Concentration of animals on winter feeding grouncis or, in bison, by the natural herd structure greatly increases the potential for contact with aborted fetuses and other afterbirth products. In addition, disruption of normal hormonal controls results in retention of placentae in bison ant!
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From page 50... ...
Current estimates of grizzly bear population size in the GYA are arounc! 300 (Eberhardt ant]
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From page 51... ...
abortus transmission within the wildlife community and between wilcllife anti clomestic stock. Predation and scavenging by carnivores likely biologically decontaminates the environment of infectious B
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From page 52... ...
abortus transmission by rec] foxes (Johnson 1992)
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From page 53... ...
commun., 1997) observed coyotes caching elk and bison (less commonly because bison mortalities are far fewer than those of elk)
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From page 54... ...
However, regurgitateci material is consumed by the pups immediately. To protect pups, den sites are usually I~iticien in rocky, rough, timbered areas where large herbivores are less likely to go.
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From page 55... ...
abortus must survive being transporter! to a cackle or den site; and it must persist at the new site long enough and in sufficient numbers to infect a susceptible bison, elk, or domestic cow that encounters the den site more or less through random movement.
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From page 56... ...
Weather and Bison The effect of winter weather on bison movements outside YNP boundaries is a topic that is amenable to modeling, but little effort has been given to it. The first issue is the frequency of hard winters in the GYA.
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From page 57... ...
The issue is acIciressed through regression analysis on data after the implementation of natural-regulation policies in 1967. The effects of incliviciual weather variables and indices anti estimated bison population size on bison moving out of YNP are examined by simple and stepwise multiple regression.
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From page 58... ...
Data on bison population are from Yellowstone National Park (1997: Appendix B) and bison removals from Dobson and Meagher 1996, Yellowstone Science 1997.
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From page 59... ...
Plot of bison removals on estimated bison population size for years under management by natural regulation (1963-1997~. 59 The final issue aciciresses relationships at populations above the 3,000 threshoicI.
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From page 60... ...
Plot of bison removals on snow water equivalent for bison populations greater than 3,000. Lines are least-squares fit ~ = -111.16 + 68.40(X)
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From page 61... ...
For the present, however, the importance ofthis analysis is the degree to which it reveals broad patterns. Bison population size appears to be the overwhelmingly significant variable controlling movement of bison out of YNP.
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From page 62... ...
That question can be addressed by examining the natural logarithm of bison population estimates over time ~ Figure 11-51. If the population growth rate is constant, then logarithmic plots on time shouic!
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From page 63... ...
fit ~_ .# ~ _ ~_ ~0 _ i ~_ ~O ·` as _ I ~1 1900 1920 19401960 1980 2000 Year ENSURE 11-5. Plot of loge of estimated bison population on year for YNP bison (filled circles)
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From page 64... ...
Thus, even in the most recent years with high bison numbers, there is little eviclence of natural diminution of bison population growth except that inciucec! by the severe winter in 1996-1997.
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From page 65... ...
ranges of total population size. We do not know what mechanism might be operating to stabilize the annual increment in YNP bison.
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From page 66... ...
These two possibilities are not mutually exclusive clominant females are likely to displace subordinates from the best habitat so both might be interacting to result in constant annual recruitment. YNP bison population behavior contrasts with the northern-range elk population behavior, in which the dynamic equilibrium is expressed by yearto-year changes.
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From page 67... ...
Effects on habitat are a natural consequence of building populations, and no Elimination of absolute population growth is apparent. Whether diminution of population growth will occur in the future can be determined only with time.
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From page 68... ...
, increased population growthwould be expected. That proposition can be examined by looking at bison population growth before and after bison use of groomed trails began in the winter of 1980-1981.
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From page 69... ...
Certainly, periodic starvation of some bison in YNP during hard winters has occurred over many years (Meagher 1973~. But many YNP bison in recent years have moved in search of better conditions elsewhere rather than attempt to survive winter in their traditional locale within park boundaries.
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From page 70... ...
Second, measurement error applies to weather variables as well, although these errors are more likely insignificant for the purposes of the analysis. BISON IN GRAND TETON NATIONAL PARK AND THE NATIONAL ELK REFUGE Bison summer in GTNP ant]
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From page 71... ...
ELK IN THE GREATER YELLOWSTONE AREA As did bison, elk have consistently increased from low numbers since the beginning of the both century (see Figure 21. However, elk population size is substantially greater than that of bison.
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From page 72... ...
Northern Elk Herd Movements Out of Yellowstone National Park In contrast with bison, there is substantial evidence that elk of the YNP northern range show density-clepenclent demography and are fluctuating about a dynamic equilibrium in response to resource carrying capacity, as well as being influenced by density-inclependent winter stress conditions (Houston 1982; Merrill and Boyce 1991; Coughenour ant] Singer 1996~.
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From page 73... ...
Because the kills did not contribute to the prediction of tile next year's elk population, either elk kills were swamped by density-ciependent population changes, the kill was compensatory with natural mortality, or a combination of the two. Although the dynamic equilibrium shown in Figure 11-8 is characterized by high variance, the population size where difference = zero gives an estimate of mean carrying capacity.
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From page 74... ...
common., 1997~. Natural regulation of elk population size occurs in the northern range of YNP (albeit with considerable amplitude in the dynamic equilibrium)
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From page 75... ...
As for Figure 11-8 except using corrected elk population size. The least-squares regression equation was Y = 9333.435 - 0.524(X)
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From page 76... ...
Other Elk Herds in the GYA Because of the controversy over the National Park Services's natural-regulation policy, the most attention paid to elk is paid to the northern-range herd in YNP, but that herd constitutes less than 20% of the elk in the GYA. One herd, the Maclison-Firehole herd, is mainly (75%)
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From page 77... ...
e elk couIci have come from southern herds to winter with the northern herd, it does not Simon that they did. Yet, interpretation of the presence of seropositive elk in the northern range depends entirely on whether these are the same animals that came from herd areas with high seropositive rates, rather than animals that came into contact with B
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From page 78... ...
bison populations (females only) under brucellosis-free and brucellosis-infectec!
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From page 79... ...
In YNP, artificial removal has been important in bolting bison population growth to near zero at times, particularly from 1935 to 1965, widen the here! was manager!
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From page 80... ...
19901. YNP bison herds have had little or no contact with outside bison since the early 1900s.
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From page 81... ...
Elk densities in YNP reach those of the winter feeding grounds (p. 76, "Other Elk Herds in the GYA")
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From page 82... ...
the occurrence of a case of undulant fever in an elk hunter in the northern range (where seropositive rates of elk are low) , whereas no cases in hunters in the southern range (where seropositive rates are high)
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From page 83... ...
, and this casts doubt on that source of infection. If movement of southern-range elk to the northern range is not responsible for tl~e seropositive rate in northern elk and if northern-range elk are not in close contact with southern-range elk, then the rate wouic!
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From page 84... ...
in the winterkilled sample leaving YNP had a 57% culture-positive rate compared with 24% for cows; for GTNP, bulls had an 84% seropositive rate compared with 69% for cows. Furthermore, the difference is already present in subadult males (Meyer and Meagher 19971.
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From page 85... ...
Although possible, this explanation seems at odcis with the typical higher male calf mortality that results in a prevalence of females among adult bison. Higher seropositive rates in bison males are unlikely to be due to differential mortality by sex in calves.
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From page 86... ...
any infection in them wouic! be inconsequential for tire control of brucellosis in bison and elk populations.
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From page 87... ...
Cure is not ensured, especially in chronic clisease, which can be lifelong. OTHER SPECIES OF BRUCELD4 AND BRUCELLOSIS IN WILDLIFE Species of BrucelIa other than B
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From page 88... ...
In one study, four of eight cattle penned with 14 naturally infected reindeer became infected with B suds ant!
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