a maximum of 15 territories, 3 inside the park and 12 surrounding the park.
The demographic parameters represented current regional conditions for
prey biomass, human-caused mortality, wolf disease, and immigration.
Cochrane (2000) defined 125 disturbance scenarios based on type of
disturbance event and frequency of occurrence within the park. The five
types of disturbance events were loss of one, two, and three wolves; loss of
an entire litter; and displacement of an entire pack from its territory. The
25 frequency classes had average intervals between events from 1 to 100
years. Each disturbance scenario was simulated 1000 times, and the
response variables were the average size of the wolf population in the
park after 30 years and the likelihood of falling below population-size
thresholds, as in the previous study.
The disturbance events had little effect on population size when the
number of years between events averaged 6 years or more (Figure 2.4).
When disturbances occurred with an average return interval of less than
6 years, scenarios involving losses of litters resulted in the smallest wolf
populations. The results in Figure 2.4 can be used to inform the development of management guidelines for controlling disturbance events. For
example, to obtain a population of at least 24 wolves after 30 years, a litter
of pups cannot be lost more often than once every 6 years. The results in
Figure 2.4 are projections of average responses to simulated disturbance
events under current conditions, and we explained to park managers that
they should not expect to see such a specific or precise impact, given the
diverse factors affecting park wolves at any time.
2. Modeling for Endangered-Species Recovery
35
Average Event Frequency (no. years between events)
17
18
19
20
21
22
23
24
25
26
27
20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Avg. No. Wolves
Event
1 wolf
2 wolves
3 wolves
Pack
Litter
X
Figure 2.4. Predicted relationships between the average number of wolves in
Voyageurs Park after 30 years and the frequency of disturbance events. The five
types of disturbance events were loss of one, two, and three wolves; loss of an entire
litter; and displacement of an entire pack from its territory.
The demographic parameters represented current regional conditions for
prey biomass, human-caused mortality, wolf disease, and immigration.
Cochrane (2000) defined 125 disturbance scenarios based on type of
disturbance event and frequency of occurrence within the park. The five
types of disturbance events were loss of one, two, and three wolves; loss of
an entire litter; and displacement of an entire pack from its territory. The
25 frequency classes had average intervals between events from 1 to 100
years. Each disturbance scenario was simulated 1000 times, and the
response variables were the average size of the wolf population in the
park after 30 years and the likelihood of falling below population-size
thresholds, as in the previous study.
The disturbance events had little effect on population size when the
number of years between events averaged 6 years or more (Figure 2.4).
When disturbances occurred with an average return interval of less than
6 years, scenarios involving losses of litters resulted in the smallest wolf
populations. The results in Figure 2.4 can be used to inform the development of management guidelines for controlling disturbance events. For
example, to obtain a population of at least 24 wolves after 30 years, a litter
of pups cannot be lost more often than once every 6 years. The results in
Figure 2.4 are projections of average responses to simulated disturbance
events under current conditions, and we explained to park managers that
they should not expect to see such a specific or precise impact, given the
diverse factors affecting park wolves at any time.
2. Modeling for Endangered-Species Recovery
35
Average Event Frequency (no. years between events)
17
18
19
20
21
22
23
24
25
26
27
20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Avg. No. Wolves
Event
1 wolf
2 wolves
3 wolves
Pack
Litter
X
Figure 2.4. Predicted relationships between the average number of wolves in
Voyageurs Park after 30 years and the frequency of disturbance events. The five
types of disturbance events were loss of one, two, and three wolves; loss of an entire
litter; and displacement of an entire pack from its territory.