CBSG's PHVA workshop process builds extensively upon the familiar analytical assessment tool known as population viability analysis, or PVA. Traditionally, PVA combines the specification and quantification of threats to wildlife populations with detailed mathematical models of population dynamics in order to evaluate the risk of population extinction under a variety of alternative future scenarios. However, these traditional approaches to extinction risk assessment are almost always conducted with a very narrow focus on the analysis of species biology data available from the primary literature.
The analytical process is often completed by a relatively small team of experts in species biology and management, with little or no involvement from the large number of other stakeholder domains that are closely linked to the focal species and its future. This isolated professional approach results in a significantly reduced sense of stakeholder ownership of the analytical product and whatever recommendations stem from it. In turn, absence of broad product ownership frequently leads to a marked reduction in the prospects of political and social changes required for effective collaboration in the management and conservation of habitat fragments and their species components.
In contrast to this traditional approach, the PHVA process uses PVA methodologies as only a single component of a much larger interactive, participatory workshop environment explicitly designed to broaden stakeholder involvement and enhance information sharing across disparate scientific and social domains (Seal 1993; Lacy 1993/1994; Westley and Miller 2002). Through this methodology, the conservation decision-making process is improved with considerably greater local ownership of the recommendation that are developed and presented by the participants themselves.
The workshop process generates extinction risk assessments based upon in-depth analysis of information on the life history, population dynamics, ecology, and history of the populations. Information on demography, genetics, and environmental factors pertinent to assessing population status and risk of extinction under current management scenarios and perceived threats are assembled in preparation for and during the workshops. Modeling and simulations provide a neutral externalization focus for assembly of information, identifying assumptions, projecting possible outcomes (risks), and examining for internal consistency.
A stochastic population simulation model is a kind of model that attempts to incorporate the uncertainty, randomness or unpredictability of life history and environmental events into the modeling process. Events whose occurrence is uncertain, unpredictable, and random are called stochastic. Most events in an animal's life have some level of uncertainty. Similarly, environmental factors, and their effect on the population process, are stochastic - they are not completely random, but their effects are predictable within certain limits. Simulation solutions are usually needed for complex models including several stochastic parameters.
A Vortex model in progress
There are a host of reasons why simulation modeling is valuable for the workshop process and development of management tools. The primary advantage, of course, is to simulate scenarios and the impact of numerous variables on the population dynamics and potential for population extinction. Interestingly, not all advantages are related to generating useful management recommendations. The side-benefits are substantial.
- Population modeling supports consensus and instills ownership and pride during the workshop process. As groups begin to appreciate the complexity of the problems, they have a tendency to take more ownership of the process and the ultimate recommendations to achieve workable solutions.
- Population modeling forces discussion on biological and physical aspects and specification of assumptions, data, and goals. The lack of sufficient data of useable quality rapidly becomes apparent and identifies critical factors for further study (driving research and decision making), management, and monitoring. This not only influences assumptions, but also the group's goals.
- Population modeling explicitly incorporates what we know about dynamics by allowing the simultaneous examination of multiple factors and interactions - more than can be considered in analytical models. The ability to alter these parameters in a systematic fashion allows testing a multitude of scenarios that can guide adaptive management strategies.
- Population modeling results can be of political value for people in governmental agencies by providing support for perceived population trends and the need for action. It helps managers to justify resource allocation for a program to their superiors and budgetary agencies as well as identify areas for intensifying program efforts.
At the present time, our preferred population dynamics model is called Vortex. This model, developed by Bob Lacy (Chicago Zoological Society), is designed specifically for use in the stochastic simulation of the extinction process in small wildlife populations. It has been developed in collaboration and cooperation with the CBSG PHVA process. The model simulates deterministic forces as well as demographic, environmental, and genetic events in relation to their probabilities. It includes modules for catastrophes, density dependence, metapopulation dynamics, and inbreeding effects. The Vortex model analyzes a population in a stochastic and probabilistic fashion. It also makes predictions that are testable in a scientific manner, lending more credibility to the process of using population-modeling tools.
Using our familiar topic-based working group approach, the PHVA participants develop detailed management and research recommendations and write the draft report during the workshop itself. Because of this emphasis on report generation during the workshop, full reports can be distributed, reviewed and finalized in as few as 2-3 months. This rapid product turnaround greatly enhances the utility of the workshop as a whole and helps to stimulate positive conservation action.
References
Lacy, R.C. 1993/1994. What is Population (and Habitat) Viability Analysis? Primate Conservation 14/15:27-33.
Seal, U.S. 1993. Population and Habitat Viability Assessment Reference Manual. Apple Valley, MN: IUCN/SSC Conservation Breeding Specialist Group.
Westley, F.W., and P.S. Miller (eds.). 2003. Experiments in Consilience: Integrating Social and Scientific Responses to Save Endangered Species.
Island Press, Washington DC.
