Stochastic processes are especially important for small populations.
Demographic variation is the normal variation in the population's birth and death rates and sex ratio caused by random differences among individuals. For example, in extremely small populations, it is possible through random chance for all offspring born during one generation to be of one sex. In addition, rare catastrophic events, such as disease epidemics, fires, or floods, can greatly affect small populations. Lastly, small populations can be affected by the loss of genetic variation through genetic drift and inbreeding. Computer simulation modelling provides a tool for exploring the viability of populations subjected to many complex, interacting deterministic and stochastic processes.