Volume 302, 24 April 2015, Pages 13–24
An individual-based model for southern Lake Superior wolves: A tool to explore the effect of human-caused mortality on a landscape of risk
Highlights
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- We developed an individual-based spatially explicit model for wolf recolonization.
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- We simulated 6 wolf harvest scenarios on a spatial mortality risk surface.
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- Simulated harvest reduced wolf breeding pair tenure.
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- Simulated harvest at 30% annually led to extinction in some populations.
Abstract
Gray wolves (Canis lupus)
have complex life-histories due, in part, to mating systems that depend
on intra-group dominance hierarchies set within an inter-group (pack)
social structure linked to philopatric territories. In addition to this
spatially oriented social structure, mortality risk associated with
interactions with humans varies spatially. We developed an
individual-based spatially explicit (IBSE) model for the southern Lake
Superior wolf population to better capture the life-history of wolves in
a harvest model. Simulated wolves underwent an annual cycle of
life-history stage-dependent mate-finding, dispersal, reproduction, and
aging on a simulated landscape reflecting spatially explicit state and
water boundaries, Indian reservation boundaries and ceded territories,
wolf harvest zones, livestock depredation areas, and a spatial mortality
risk surface. The latter 3 surfaces were linked to mortality events for
simulated wolves. We assessed our IBSE model and conducted a
sensitivity analysis of the most uncertain parameters with a categorical
calibration of patterns observed at the individual, pack, population,
and landscape level. We found that without recreational harvest, the
Wisconsin wolf population grew to an average carrying capacity of 1242
wolves after 50 years and breeding pairs persisted for a mean 1.8 years.
We simulated 6 recreational harvest scenarios with varying rates and
timings of harvest and assessed effects on population size, pack sizes,
age ratios, dispersal and immigration rates, and breeding pair tenures
of the Wisconsin wolf population. The simulated harvest with rates of
14% which corresponded to the 2012 harvest in Wisconsin reduced the
populations 4% in the first year of harvest and equilibrated to the
pre-harvest population size after 20 years of harvest, on average. A 30%
harvest rate across the simulation on average reduced the populations
by 65% after 20 years with some populations going extinct before 100
years. In general, harvest increased the proportion of pups in the
simulated populations and decreased breeding pair tenure. Targeted
lethal control was more effective than harvest for reducing the number
of wolves near known livestock depredation sites. Our model facilitates
prediction of important population patterns that is simultaneously
dependent on complexities associated with spatially structured life
history and mortality.
Abbreviations
- IBSE, individual-based spatially explicit;
- SLS, southern Lake Superior referring to Wisconsin and the Upper Peninsula of Michigan;
- WHZ, wolf harvest zone
Keywords
- Agent-based model;
- Canis lupus;
- Harvest;
- Management;
- Population dynamics;
- Recolonization
- Corresponding
author. Present address: Wisconsin Department of Natural Resources,
2801 Progress Road, Madison, WI 53716, USA. Tel.:
+1 608 221 6334.
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- Retired.
Copyright © 2015 Elsevier B.V. All rights reserved.
