Expanding Capabilities of the Vortex Population Modeling Software
By Robert Lacey, PhD
Chicago Zoological Society

The Vortex simulation software for population viability analysis (PVA) is used globally to make projections of wildlife populations under various assumptions about species biology, habitats, and the impacts of human activities. These analyses can help to identify the most threatening processes, and the best options for management and conservation of the species. The large amount of data collected over the years on the dolphins of the Sarasota area provides the opportunity to use PVA models to make projections of the long-term trajectory of the population. The multiple and significant impacts of human activities on the dolphins provide strong reasons for us to assess the likely fate of the dolphin populations under various scenarios about changing human activities. However, the social system of dolphins and the spatial structuring of the dolphin populations add complexities to the population dynamics that would not be modeled well with any existing PVA model.

We are therefore working to extend the capabilities of the Vortex PVA software, to provide options to model more complex social systems (for example, making breeding success dependent on the social environment and on whether the female is a first-time mother), spatial structure of the populations (for example, allowing the overall population to be comprised of a number of social units that differentially use sections of the bays and coastal waters), and differences in habitat quality in various parts of the overall range of the population. To add these capabilities to the PVA model, we have allowed the program to assign and monitor variables that represent important characteristics of individual dolphins (such as past breeding history and subpopulation membership) and of the habitat (such as food resources, and local threats caused by human activities). We are now also making Vortex a component of a “meta-model”, in which the Vortex representation of the dolphin population can be linked to other computer models of habitat change, human activities, and wildlife disease. We will soon be testing this new meta-model with data on the Sarasota area dolphin populations, making projections under various scenarios of human activities, and comparing the results to those from other kinds of population models.

These efforts will provide us with the ability to integrate diverse kinds of data and knowledge into a more complete picture of the processes influencing the dolphin populations. In addition, by using the very extensive data on the dolphins to test and refine these new analysis tools, we (and the dolphins!) will be helping many more species that similarly are facing diverse threats from changing habitats and human activities. For example, people studying elephants in Burma, lion tamarins (a small monkey) in Brazil, elk in Canada, and cheetahs in Namibia are all eager to use our enhanced population models to explore the long-term prospects for their species. Funding for developing these conservation tools has been provided by NOAA Fisheries, the Chicago Zoological Society, and the Conservation Breeding Specialist Group of the World Conservation Union.