RISKMAN: Risk Analysis for Harvested Populations of Age Structured, Birth-Pulse Species
Management recommendations, particularly harvest policies, are often based on life table
models of population dynamics. Estimates of population number, sex and age distribution,
survival, recruitment, and harvest (if any) may be used in age-structured, birth-pulse
simulation models to estimate population trend, status, or number at some future time, and
to explore the demographic consequences of a range of management options. Birth pulse models
include both standard life table models that mimic the reproductive biology of species that
reproduce annually (e.g. ungulates, wolves, and seals), and multi-annual models for species
that reproduce in 2 or 3 year intervals (e.g. bears, elephants, and walrus).
Models may allow both exponential growth and density-dependent feedback mechanisms. Harvest
can be modelled in a variety of ways ranging from detailed simulations that include the age
specific vulnerability and selectivity of the kill to simple apportionment of the kill
according to the relative abundance of the population sex and age types. RISKMAN (RISK
MANagement), a Windows© compatible program, was developed for the full range of options
Deterministic simulations are difficult to interpret because all results are based on
very uncertain estimates of input parameters, and cannot be objectively distinguished from
results based on relatively precise estimates of input parameters. Similarly, simulation
results from small populations are less certain than simulations for large populations.
RISKMAN provides a stochastic option that uses the variance of input parameters and the
structure identified by the simulation options that are selected. Monte Carlo techniques
are applied to generate a distribution of results, and that distribution is used to estimate
the variance of summary parameters (e.g. number at time, population growth rate, and
proportion of runs that result in a decline to a user set value). RISKMAN uses the correct
distributions of the population and rate variance estimates to provide accurate estimates
of the uncertainty of simulation results. Input parameters may co-vary or be independent;
RISKMAN allows the user to set the correlation to one or zero to bound the possibilities.
The following are publications where the authors used the RISKMAN software
for their population analysis:
Howe, E. J., M. E. Obbard, and J. A. Schaefer. 2007. Extirpation risk of an isolated carnivore population under different management scenarios. Journal of Wildlife Management 71: in press.
Clark, J. D., and R. Eastridge. 2006. Growth and sustainability of black bears at White River National Wildlife Refuge, Arkansas. Journal of Wildlife Management 70:1094-1101.
Taylor, M.K., J. Laake, P.D. McLoughlin, H.D. Cluff and F. Messier. 2006. Demographic parameters and harvest-explicit population viability analysis for polar bears in M'Clintock Channel, Nunavut, Canada. Journal of Wildlife Management 70: 1667-1673.
Dobey, S, D.B. Masters, B.K. Scheick, J.D. Clark, M.R. Pelton, and M.E. Sunquist. 2005. Ecology of Florida black bears in the Okefenokee-Osceola ecosystem. Wildlife Monograph No. 158.
Taylor, M.K., J. Laake, P.D. McLoughlin, E.W. Born, H.D. Cluff, S.H. Ferguson, A, Rosing-Asvid, R. Schweinsburg and F. Messier. 2005.
Demography and viability of a hunted population of polar bears.
Arctic 58: 203-214.
Abstract (Click, then scroll down)
Wear, B.J., R. Eastridge, and J.D. Clark. 2005. Factors affecting settling, survival, and viability of black bears reintroduced to Felsenthal National Wildlife ReFuge, Arkansas, Wildlife Society Bulletin 33: 1363-1374.
McLoughlin, P.D., M. Taylor, M. Kuc, M. Obbard, H. D. Cluff, and B. Pond. 2004.
RISKMAN: Risk analysis for harvested populations of age structured, birth-pulse species.
Poster presentation 15th International Conference on Bear Research and Management,
San Diego, CA, 8-13 February 2004.
Abstract (Click, then press END key)
McLoughlin, P.D., M.K. Taylor, H.D. Cluff, R.J. Gau, R. Mulders, R.L. Case, and F. Messier. 2003.
Population viability of barren-ground grizzly bears in Nunavut and the Northwest Territories.
Arctic 56: 185-190.
Abstract (Click, then scroll down)
McLoughlin, Philip D. 2003. Managing Risks Of Decline For Hunted Populations Of Grizzly Bears Given Uncertainty In Population Parameters. Final Report
to the British Columbia Independent Scientific Panel on Grizzly Bears.
Taylor, M. K., J. Laake, H.D. Cluff, M. Ramsay, and F. Messier. 2002.
Managing the risk from hunting for the Viscount Melville Sound polar bear population. Ursus
Howe, E. J. 2002. Population viability analysis for black bear (Ursus americanus)
on the Bruce Peninsula, Ontario, Canada. Unpubl. M. Sc. thesis, Trent University,
Peterborough, ON. 217p.
Eastridge, R. and J.D. Clark. 2001. Evaluation of 2 soft-release techniques to reintroduce
black bears. Wildlife Society Bulletin 29: 1163-1174.