The Population Viability Assessment Workshop: A Tool for Threatened Species Management

Tim W. Clark
Yale University School of Forestry and Environmental Studies, 301 Prospect Street, New Haven, CT 06511 and Northern Rockies Conservation Cooperative, Box 2705, Jackson, WY 83001
timothy.w.clark@yale.edu

Gary N. Backhouse
Department of Natural Resources and Environment, Victoria, Australia.

Robert C. Lacy
University of Chicago Division of Biological Sciences and Department of Conservation Biology, Chicago Zoological Park, Chicago, IL
rlacy@ix.netcom.com

Abstract
Population viability assessment (PVA) is a powerful tool in assessing the viability (i.e. likely persistence)
of small populations, and in setting target numbers and area requirements for species recovery.
By using computer models, four types of extinction processes can be simulated, and the effects
of both deterministic and stochastic forces can be explored. PVA's also explore the outcome of
management options. The utility of PVA was demonstrated at a workshop in Heidelberg, Victoria,
Australia. Using the computer program, VORTEX, to simulate genetic, demographic, environmental,
and random events, workshop participants: (1) examined the status of data on six threatened
species (mountain pygmy-possum, Burramys parvus; leadbeater's possum, Gymnobelideus
leadbeateri; eastern barred bandicoot, Perameles gunnii; long-footed potorroo, Potorous longipes;
orange-bellied parrot, Neophema chrysogaster, and helmeted honeyeater, Lichenostomus melanops
cassidix); (2) simulated their vulnerability to extinction; (3) examined outcomes of management
options to restore the species; (4) estimated population targets needed for recovery planning; and
(5) evaluated the potential of PVA as a teaching aid to illustrate extinction processes and management
options. Workshop results showed that the majority of the species were highly susceptible to
local extinction, though more field data would have been helpful. Simulation of management options
demonstrated that early action in conservation management could have significantly reduced
the current predicament of these species and that use of PVA's could greatly improve conservation
management for all six species. PVA's are therefore highly useful in the planning and carrying out
of species recovery programs.