CHAPTER 1: AFFEC TKD KNVIKONMENT 



recolonization of northwestern Montana by relatively few wolves from Canada and the reintroduction of 

 wolves into YNP and central Idaho. In northwestern Montana, the founding population was small enough 

 that inbreeding among closely related individuals was possible. Fortunately, the genetic variation among 

 the first colonizers was high (Forbes and Boyd 1996). The combination of high genetic variation among 

 colonizers and ongoing natural dispersal to and from Canadian populations was adequate to assure long- 

 term population viability, provided that genetic exchange continued. 



Similar inbreeding concerns existed for the relatively small founding population reintroduced to YNP and 

 central Idaho. But wolves were trapped from two distinct source populations in Canada. The genetic 

 variation among reintroduced wolves (and the source populations from which they came) was also high 

 (Forbes and Boyd 1997). Overall, genetic diversity was similar among samples of natural recolonizers, 

 reintroduced individuals, and the Canadian source populations. Field studies of wolf dispersal and 

 migration distances supported the genetic results (Ream et al. 1991, Boyd et al. 1995, Boyd and Pletscher 

 1999). Wolf populations in the northern Rockies should not suffer from inbreeding depression. 



An underlying tenant of the federal wolf recovery and restoration program is that each state's wolf 

 population is functionally connected so that genetic material can be exchanged among the wolves in the 

 three recovery areas and Canadian wolves. In isolation, none of the three populations could maintain its 

 genetic viability (USFWS 1994a, Fritts and Carbyn 1995). 



Population Growth. Wolf populations increase or decrease through the combination and interaction of 

 wolf densities and prey densities (Keith 1983, Fuller 1989). Actual rates of change depend on whether 

 the wolf population is pioneering vacant habitat (as in YNP and central Idaho), whether the population is 

 well established (as in northwestern Montana), and food availability. The degree and type of legal 

 protection, agency control actions, and regulated harvest also influence population trends. Once 

 established, wolf populations apparently can withstand human-caused mortality rates up to about 30% of 

 the fall population (Keith 1983, Fuller 1989). 



If protected, low density wolf populations can increase rapidly if prey is abundant. Keith (1983) 

 speculated that a 30% annual increase could be the maximum rate of increase for any wild wolf 

 population. Once densities were high enough, social interactions probably intensify. Conflict and 

 increased competition for food eventually cause a wolf population to level off or decline (Keith 1983, 

 Fuller 1989). 



Wolf populations in the GNP area (northwestern Montana and southeastern Alberta) increased an average 

 of 23% annually from 1986-1993 (Fritts et al. 1995). After 1993, the population leveled off (Pletscher et 

 al.l997). Those packs produced dispersers that eventually colonized vacant habitats in western Montana 

 (USFWS unpubl. data). Some packs which formed in the Northwestern Montana Recovery Area since 

 the early 1990s persisted, but others did not. Packs have been lost due to illegal killing by humans, 

 agency control actions where livestock depredation was chronic, and for other unknown reasons. 



The average annual rate of increase from 1992 to 2000 in northwestern Montana was 4.7% (USFWS et al. 

 2001 ). In 1992, the minimum mid-winter count (including pups) was 41 wolves. Sixty-two wolves were 

 counted in 2000. The highest count was 70 wolves, at the end of 1996. The population grew in some 

 years, but declined in others. Some of the variation probably reflects true changes in wolf numbers, but 

 some variation may be due to decreased monitoring. 



Prey populations innuenced recent wolf population dynamics in northwestern Montana. White-tailed 

 deer populations expanded from the late 1970s through the mid 1990s, in part precipitating and sustaining 

 increases in wolf numbers and distribution. However, the winter of 1996/97 was exceptionally severe, 

 and white-tailed deer populations declined significantly (Sime, unpubl. data). Other prey populations also 



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