Table E-l. Model and description (continued) 
Spatially explicit, individual-based simulation. Higgins et al. (1996) use factorial design and simple linear 
regression-factors ([1] adult fecundity, [2] dispersal ability, [3] time to reproductive maturity, [4] temporal 
frequency of post-fire recruitment opportunities, and [5] fire survival by adults) to quantify interactions between 
factors on spread rate of Pinus species. All but fire survival can significantly affect Pinus spread rates. Efforts need 
to focus on obtaining empirical data for the four relevant factors. Authors conclude that it is important that factor 
determination and model development are correlated to ensure that the model is designed to fit with the biological 
processes it is modeling. __ 
Taxonomic model. Lockwood (1999) uses bionomial probabilities to predict establishment success of avian 
invaders. Specifically, the author creates a random estimation of the number of successful species per family using 
bionomical distribution. The results indicate (1) that some taxa are more likely to successfully establish themselves 
than others and (2) that human action (e.g., importing certain species) obscures trait-based taxonomic patterns in 
successful establishment. The author concludes that although the likelihood that transport can increase the amount 
of introduced species, this does not affect the amount of species that actually become established. 
Quantitative taxonomic model. Kolar and Lodge (2001) reviewed publications that use quantitative methods to 
assess characteristics of introductions and of species that invade to document taxa-specific trends. The authors 
review 16 publications that look at release event characteristics or species characteristics for plants (8) and animals 
(8). Using the literature, they evaluate characteristics of introductions associated with establishment and dispersal of 
nonnative species and describe characteristics similar to species that invade. The results indicate that propagule 
pressure is positively related to establishment success; and the region a species originated is significantly associated 
with establishment success. The authors recommend that predictive models be broadened to include earlier stages of 
invasion. 
Quantitative taxonomic models. Kolar and Lodge (2002) predict establishment, spread, and impact of invasive 
species in the Great Lakes, using quantitative, predictive risk assessment. Specifically, the authors employ 
discriminant analyses and categorical and regression tree analyses to identify traits of successful and failed invaders, 
considering stages of invasion separately. These two models also are used to assess the risk to the Great Lakes from 
species introduced by various vectors. Results show that quantitative models and taxon, ecosystem, and invasion 
stage specific data can be used for risk assessments and for guiding policy, education, and management efforts to 
prevent future invasions. The authors recommend that the approach they use to assess risk be applied to various 
aquatic and terrestrial plant and animal species. 
Probability. Huston (2004) uses a dynamic equilibrium model of species diversity to address (1) the probability of 
an invader’s successful establishment and (2) the probability the invader will become dominant in the invaded 
ecosystem. Productivity, disturbance, and environmental factors can be used to predict invasions. Areas with 
minimal productivity are easily invaded. Productive, undisturbed, and very unproductive areas are seldom invaded; 
the easiest areas to invade, establish, and impact are disturbed, productive areas. The author recommends 
understanding how the deviations in the landscape affect the probability and impact of invasions so that more 
efficient and effective monitoring and control programs can be developed. 
Demographic model. Bartell and Nair (2004) created a probabilistic risk assessment framework to evaluate the 
possibility of solid wood packing material (SWPM) pest establishment. The approach addresses (1) pest life history 
traits, (2) suitable host availability and environmental factors that affect establishment, (3) population dynamics, and 
(4) implications of uncertainty on estimates of risk and risk reduction. The results indicate that small increases in 
effectiveness of treatment of SWPM can have significant impact on reducing the risk of pest establishment. The 
authors conclude that the methodology is a sound, transparent, and repeatable approach, and it can be used for 
assessing the probability of establishment by invasive species. 
“Tens” rule. Williamson and Fitter (1996) use the “tens” rule and exceptions to the rule to answer the question 
“how might we explain [invaders]?” The “tens rule” states that 1 in 10 imported species appears in the wild, 1 in 10 
introduced species becomes established, and 1 in 10 established species becomes a pest. Three sets of factors are 
important for the tens rule and deviations of it: (1) propagule pressure, (2) factors allowing species to survive, and 
(3) factors determining local abundance. The authors conclude the “tens rule” does describe much of what is known 
and that a more exact algorithm could be developed. They recommend additional studies on early phases of 
establishment, causes of death and how density affects these causes, and the distribution of species during dispersal. 
E-6 
