simulation experiments in which they varied the proportion of the 16
territories in core and peripheral ranges and observed the 50-year occupancy of that range by wolf packs. In the sensitivity analysis, they repeated
this set of experiments under different assumptions about pup and
dispersal mortality and immigration.
These sets of simulations supported a favorable outlook for the survival
of small, disjunct wolf populations like those in northern Wisconsin and
Michigan. The results showed that the level of occupancy increased as the
number of core sites and immigrants increased. With pup and dispersal
mortality rates that were consistent with disease-free and legally protected
populations, the model predicted that wolves would saturate a cluster of
16 territories with as few as two core, low-mortality sites, regardless of immigration rates. When pup and dispersal mortality rates were high, as few as
two immigrants per year helped maintain site occupancy in clusters with
four or more core sites.
These simulation results were consistent with observations of disjunct
wolf populations in the United States and Canada (Fritts and Carbyn 1995).
For example, during the past 60 years, a population of 40 to 120 wolves has
lived in and around Canada’s Riding Mountain National Park (3,000 km
2 ).
The park is surrounded by agricultural land, and the nearest wolf population is 45 km away. The population survived even though many of the packs
were vulnerable to human exploitation along the park boundary. Based on
empirical evidence and simulation results, Haight et al. (1998) concluded
that wolves can survive and thrive in networks of disjunct populations,
provided that they are linked by dispersal, human persecution is not excessive, and prey are abundant. Further, they concluded that, with continued
protection from deliberate killing, wolf range will expand in humandominated landscapes where prey are abundant. These predictions were
incorporated into wolf recovery and management plans written by state
agencies. The results also raised questions about the need for population
control, especially where wolf presence conflicts with other valued land
uses.
2.3.3 External Threats to Gray Wolves at Voyageurs
National Park
Voyageurs National Park is a small (882 km
2 ) reserve of boreal and mixeddeciduous forests and numerous lakes in the heart of wolf range on
Minnesota’s Canadian border. In the 1990s, park biologists were concerned
that high levels of human-caused mortality among wolves immediately
surrounding the park could combine with changing prey densities and
disease incidence to reduce or even threaten park wolves. Following interagency consultations to evaluate the impacts of proposed park recreation
development, park biologists commissioned use of a cumulative effect
model to address their concerns. Rather than build the comprehensive,
32
Jean Fitts Cochrane et al.
territories in core and peripheral ranges and observed the 50-year occupancy of that range by wolf packs. In the sensitivity analysis, they repeated
this set of experiments under different assumptions about pup and
dispersal mortality and immigration.
These sets of simulations supported a favorable outlook for the survival
of small, disjunct wolf populations like those in northern Wisconsin and
Michigan. The results showed that the level of occupancy increased as the
number of core sites and immigrants increased. With pup and dispersal
mortality rates that were consistent with disease-free and legally protected
populations, the model predicted that wolves would saturate a cluster of
16 territories with as few as two core, low-mortality sites, regardless of immigration rates. When pup and dispersal mortality rates were high, as few as
two immigrants per year helped maintain site occupancy in clusters with
four or more core sites.
These simulation results were consistent with observations of disjunct
wolf populations in the United States and Canada (Fritts and Carbyn 1995).
For example, during the past 60 years, a population of 40 to 120 wolves has
lived in and around Canada’s Riding Mountain National Park (3,000 km
2 ).
The park is surrounded by agricultural land, and the nearest wolf population is 45 km away. The population survived even though many of the packs
were vulnerable to human exploitation along the park boundary. Based on
empirical evidence and simulation results, Haight et al. (1998) concluded
that wolves can survive and thrive in networks of disjunct populations,
provided that they are linked by dispersal, human persecution is not excessive, and prey are abundant. Further, they concluded that, with continued
protection from deliberate killing, wolf range will expand in humandominated landscapes where prey are abundant. These predictions were
incorporated into wolf recovery and management plans written by state
agencies. The results also raised questions about the need for population
control, especially where wolf presence conflicts with other valued land
uses.
2.3.3 External Threats to Gray Wolves at Voyageurs
National Park
Voyageurs National Park is a small (882 km
2 ) reserve of boreal and mixeddeciduous forests and numerous lakes in the heart of wolf range on
Minnesota’s Canadian border. In the 1990s, park biologists were concerned
that high levels of human-caused mortality among wolves immediately
surrounding the park could combine with changing prey densities and
disease incidence to reduce or even threaten park wolves. Following interagency consultations to evaluate the impacts of proposed park recreation
development, park biologists commissioned use of a cumulative effect
model to address their concerns. Rather than build the comprehensive,
32
Jean Fitts Cochrane et al.