Appendix B. Determination of net effects from minimal adequate models..
In the minimal adequate models, each response variable was significantly affected by several explanatory variables. To reveal a net effect of a particular explanatory variable, i.e., an effect attributable only to this variable and unbiased by other explanatory variables, all explanatory variables in the particular minimal adequate model, except that attributable to the particular net effect under consideration, were retained in the model, and the standardized residuals of the model were determined. To reveal the net effect, these residuals were then examined, using the residuals as the response variable, and the variable attributable to the particular net effect as the explanatory variable, assuming normal distribution of errors and identity link function (e.g., Lonsdale 1999; Pysek et al. 2002a,c; 2003b).
Lonsdale, M. 1999. Global patterns of plant invasions and the concept of invasibility. Ecology 80:1522–1536.
Pysek, P., V. Jarosík, and T. Kucera. 2002a. Patterns of invasion in temperate nature reserves. Biological Conservation 104:13–24.
Pysek, P., T. Kucera, and V. Jarosík. 2002c. Plant species richness of nature reserves: the interplay of area, climate and habitat in a central European landscape. Global Ecology and Biogeography 11:279–289.
Pysek, P., V. Jarosík, and T. Kucera. 2003b. Inclusion of native and alien species in temperate nature reserves: an historical study from Central Europe. Conservation Biology 17:1414–1424.