Stochastic modeling of non-indigenous species establishment.
Jerde, Christopher *,1, Lewis, Mark1, 1 Dept. of Biological Sciences, Edmonton, Alberta, Canada
ABSTRACT- Propagule pressure and survival are two significant components to the establishment of Non-Indigenous Species (NIS). Propagule pressure can be described as the number of individuals entering a system (N). Survival can be described as the probability that an individual survives to establish (P). We use these parameters to formulate a stochastic binomial process to describe NIS establishment. As a result of the stochastic process, the time to establishment is a geometric distribution with mean N*P. From this result it is possible to order a NIS pool from most to least threatening based on the distributions of the time to establishment. The role biological control plays in reordering the threat of establishment is evaluated using hypothesis testing in a likelihood framework. This technique has the ability to identify those NIS most likely to establish which is important for the prevention of new establishments. Also, by using a hypothesis testing framework, the influence of biological control can be evaluated for effectiveness in the prevention of establishment. Lastly, the threat of NIS establishment for a pool of invaders can be compared before and after a bio-control application. This is critical as bio-control applications may detrimentally target one or more species from the NIS pool while increasing the establishment potential of other NIS. Recent literature has highlighted the importance of considering Allee effects in the establishment of NIS. This model does not consider Allee effects and inference should be limited to the immigration of NIS propagules. However this stochastic process coupled with a population growth model may provide an even more powerful tool in evaluation of the threat NIS pose to establishment in new environments.
Key words: propagule pressure, stochastic processes, invasive species, establishment
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