This stochasticity occurs even in a constant environment. In relatively small populations, demographic stochasticity can be an important factor influencing extinction probability. As population size increases, random demographic differences get averaged over larger and larger number of independent individuals. Large population sizes do less to buffer against extinction in this case, in contrast to demographic stochasticity. Natural catastrophes - extreme cases of environmental uncertainty, such as hurricanes and large fires.
Catastrophes are usually short in duration but widespread in their impact.
The model is based on the assumption of a stable but variable mean instantaneous rate of change. The model can be used to predict the likelihood of population persistence or conditional mean time to extinction. The program is based on the Dennis et al. It is a stochastic exponential model based on age-structured Leslie matrices. In other words, populations may be in trouble long before they go extinct.