Latest news


There is new and enhanced SCTI website at !
For now, this site will remain active, but later it will be shut down and redirected to


Population Viability Analysis software


Vortex is an individual-based simulation of deterministic forces as well as demographic, environmental and genetic stochastic events on wildlife populations. It can model many of the extinction vortices that can threaten persistence of small populations. Vortex models population dynamics as discrete, sequential events that occur according to probabilities that are random variables following user-specified distributions. Vortex simulates a population by stepping through a series of events that describe an annual cycle of a typical sexually reproducing, diploid organism: mate selection, reproduction, mortality, increment of age by one year, dispersal among populations, removals, supplementation, and then truncation (if necessary) to the carrying capacity. The simulation of the population is iterated many times to generate the distribution of fates that the population might experience.


Click here to learn about an email discussion group (a "Listserv") for Vortex users.






Before downloading, please Register as a user to provide us with information about how Vortex is being used and how we can better serve species conservation.



Note: If the msi installation file does not work for you, try downloading the zip file, extracting the two files, and then running setup.exe.


Citation for software:

Lacy, R.C., and J.P. Pollak. 2014. Vortex: A stochastic simulation of the extinction process. Version 10.0. Chicago Zoological Society, Brookfield, Illinois, USA.


Creative Commons License
Vortex is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.



Vortex10 change Log

Go to Vortex FAQs


Go to Vortex Publications site built by Robert Lacy and JoAnna Kelly

Copyright 2019 Chicago Zoological Society / IUCN/SSC Conservation Planning Specialist Group