The Arrival and Establishment of Non-indigenous Species: Mechanisms, Uncertainty, and Prediction

Non-indigenous species (NIS) have reduced native species abundances, increased native species extinction probabilities, and changed ecosystem functioning. In addition to the impact on the environment, economic losses are accrued to the public and industry. The inability to make successful predictions of which species will invade, where, and when, hinders invasive species management. My thesis objective was to develop a risk assessment framework for predicting the arrival and establishment of NIS. I used hierarchical probability models that capture the NIS arrival process, and I evaluated invasion risk using stochastic processes to produce invasion waiting times. This process was tested using experimentally manipulated propagule pressure of scentless chamomile (Matricaria perforata), which subsequently validated an invasion waiting time risk assessment approach. The approach was extended using relative measures of ballast water discharge of Chinese mitten crabs (Eriocheir sinensis) into North American ports, and the estimated transport of zebra mussels (Dreissena polymorpha) by recreational boaters in the United States. With these examples, I showed that relative measures require making mathematical and biological assumptions, which when violated, result in poor predictions. I considered the influence of the Allee effect on the invasion waiting time by formulating a hierarchical probability model of NIS establishment for semelparous, sexual species. The Allee effect is detected in the net geometric per capita growth rate, and I evaluated persistence with a stochastic process. With large fecundity, the influence of the Allee effect is negligible and invasion risk can be evaluated using the invasion waiting time based on the probability of one surviving, fertilized female persisting post arrival. This approach was applied to Chinese mitten crab and apple snail (Pomacea canaliculata).