11 Feb 2008, 12:35pm
Deer, Elk, Bison Population Dynamics Predators
by admin

The Need for the Management of Wolves

Bergerud, Arthur T. The Need for the Management of Wolves-An Open Letter. 2007. Rangifer, Special Issue No. 17, 2007: The Eleventh North American Caribou Workshop, Jasper, Alberta, Canada, 24-27 April, 2006.

Note: A.T. Bergerud is former chief biologist of Newfoundland. He has been a population ecologist involved in research on caribou populations in North America since 1955. Along with Stuart N. Luttich and Lodewijk Camps, Bergerud authored the just released The Return of Caribou to Ungava [here].

Full text [here]

Selected excerpts:

Abstract: The Southern Mountain and Boreal Woodland Caribou are facing extinction from increased predation, predominantly wolves (Canis lupus) and coyotes (Canis latrans). These predators are increasing as moose (Alces alces) and deer (Odocoileus spp.) expand their range north with climate change. Mitigation endeavors will not be sufficient; there are too many predators. The critical habitat for caribou is the low predation risk habitat they select at calving: it is not old growth forests and climax lichens. The southern boundary of caribou in North America is not based on the presence of lichens but on reduced mammalian diversity. Caribou are just as adaptable as other cervids in their use of broadleaf seed plant as forage. Without predator management these woodland caribou will go extinct in our life time.


A major ecological question that has been debated for 50 years is: are ecosystems structured from top-down (predator driven) or bottom-up (food limited) processes (Hairston et al., 1960; Hunter & Price, 1992)? Top-down systems can vary widely from sea mammals such as sea otters (Enhydra lutris) to ground nesting birds. The sea otter causes an elegantly documented trophic cascade through sea urchins (Strongylocentrotus spp.) down to kelp beds (Estes & Duggins, 1995). Ground nesting waterfowl and gallinaceous birds are not limited by food resources but are regulated by top-down nest predation caused by a suite of predators, mainly skunks (Mephitis mephitis), red foxes (Vulpes vulpes) and crows (Corvus brachyrhynchos) (Bergerud, 1988; 1990; Sargeant et al., 1993). Management decisions depend on understanding which structure is operational.

Discussions on top-down or bottom-up have been recently been rekindled with the introduction of wolves (Canis lupus) to Yellowstone National Park and Idaho in 1995 (Estes, 1995; Kay, 1995; 1998). The elk/wapiti (Cervus elaphus) population in Yellowstone prior to introduction were basically limited by a density-dependent shortage of food (Singer et al., 1997) but now is declining from wolf predation (Crête, 1999; White & Garrott, 2005). All three states, Wyoming, Idaho, and Montana, are litigating the federal government to get the wolf delisted so they can start wolf management to maintain their stocks of big-game.

We conducted a 30 year study (1974 to 2004) of two caribou (Rangifer tarandus) populations, one in Pukaskwa National Park (PNP) and the other on the Slate Islands in Ontario, relative to these two paradigms of top-down or bottom-up. (Bergerud et al., this conference). In Pukaskwa National Park, there was an intact predator-prey system including caribou, moose (Alces alces), wolves, bears (Ursus americanus), and lynx (Lynx canadensis). On the Slate Islands, our experimental area, there were no major predators of caribou. The PNP populated was regulated top-down by predation and existed at an extremely low density of 0.06 caribou per km2, whereas the population on the Slate Islands averaged 7-8 animals/km2 over the 30 years (100X greater than in PNP). In the absence of predators, these island caribou were regulated from the bottom-up by a shortage of summer foods and the flora was impacted, resulting in some floral extinctions. The extremely low density of only 0.06 caribou per km2 in PNP is normal for caribou populations coexisting with wolves (Bergerud, 1992a: Fig. 1, p. 1011). The top-down predator driven ecosystem of caribou in PNP also applies in Canada to moose, elk, and black-tailed deer (Odocoileus hemionus) that are in ecosystems with normal complements of wolves and bears (Bergerud, 1974; Bergerud et al., 1983; Bergerud et al., 1984; Messier & Crete, 1985; Farnell & McDonald, 1986; Seip, 1992; Messier 1994; Hatter & Janz 1994; Bergerud & Elliott, 1998; Hayes et al., 2003).

Of all the predator driven ecosystems of cervids, the threat of extinction is most eminent for the southern mountain and boreal woodland caribou ecotypes, both classified as threatened (COSEWIC 2002, Table 11). These herds are declining primarily from predation by wolves plus some mortality from bears. From west to east the equations for continued persistence are not encouraging — in British Columbia the total of the southern mountain ecotype is down from 2145 (1992-97) to 1540 caribou (2002-04) and four herds number only 3, 4, 6, and 14 individuals (Wittmer et al., 2005). In Alberta, the range has become fragmented and average recruitment recently was 17 calves/100 females, despite high pregnancy rates (McLoughlin et al., 2003). That low calf survival is less than the needed to maintain numbers - 12-15% calves or 22-25 calves per 100 females at 10-12 moths-of-age to replace the natural mortality of females (Bergerud, 1992a; Bergerud & Elliott 1998). In Saskatchewan, populations are going down, ?=0.95 (Rettie et al., 1998). The range is retreating in Ontario (Schaefer, 2003) as southern groups disappear; in Labrador the Red Wine herd is now less than 100 animals (Schmelzer et al., 2004); in southern Quebec, there may be only 3000 caribou left (Courtois et al., 2003), and in Newfoundland, herds are in rapid decline from coyotes (Canis latrans) and bear predation (G. Mercer and R. Otto, pers. comm.). In Gaspé, the problem for the endangered relic herd is also coyotes and bear predation (Crête & Desrosiers, 1995). In Gaspé, these predators have been reduced and there is a plan in place to continue adaptive management (Crête et al., 1994). Do we have to wait until the herds are listed as endangered to manage predators?

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