Citation: Sandvik, H., and B.-E. Sæther (2012) Testing og modifisering av modeller for å estimere spredning og etablering av fremmede arter. [Tests and modifications of models to estimate spread and establishment of alien species (in Norwegian with English abstract)]. Utredning for Direktoratet for naturforvaltning, 10(7), 1–51.

Key words: Alien species, ecological risk assessment, invasion biology, modelling of spread, quantitative set of criteria, spread velocity.

A simulated range expansion of an alien speciesAbstract: Risk assessments of alien species in Norway is currently based on a novel quantitative classification system that takes the species’s invasion potential and their ecological effects into account. The estimation of invasion potential is grounded in a modelling of the species’s rates of establishment and spread. This report summarises the methodological improvements that are suggested to the classification system. We present an improvement of existing models, development of novel models and a test of these models by means of 14 real and 200 simulated datasets on biological invasions.
    Based on our findings we recommend to (1) maintain the classification system’s three criteria to assess invasion potential, viz. establishment success, spread velocity and area of landscapes colonised; (2) modify the definition of establishment success to expected population lifetime; (3) maintain the definition of spread of alien species as any form of translocation, irrespective of the mechanisms, vectors and pathways involved.
    In terms of methodology, we (4) identify population growth rate and environmental variance to be the most influential determinants of establishment success; (5) improve models of spread; (6) identify the models and parameterisations that result in the best fit to the real and simulated data.
    However, a clear caveat emerged from the results, too, viz. that there is no single model fitting all invasion processes and data qualities. In choosing a method, one has to take into account sampling design and the number of separate introductions.

Full text: © 2012 The Norwegian Directorate for Nature Management. If you accept (i) that further reproduction, and all further use other than for personal research, is subject to permission from the publisher (The Norwegian Directorate for Nature Management), and (ii) that printouts have to be made on recycled paper, you may download the report here (in Norwegian; pdf, 5.0 MB).