Analysis 1: Relationship between species distribution and environmental variables
To test for species habitat-association through plant development, we first used the variance inflation factor (VIF) to check whether our seven environmental variables were multicollinear (VIF > 10, Zuur et al. , 2007). None of them showed multicollinearity and thus all were included in our models.
Without habitat association, the intensity function λ is spatially constant and given by the mean number of points (i.e. individuals) per unit area of the study plot. However, under habitat association, the intensity differs at different positions x, y in the study plot, thus λh (x, y ). To determine the relationship between species distribution and environmental variables, we modelled the intensity functionλh (x, y ) at the location (x ,y ) as a function of the sum of the variables on a log scale. The corresponding log-linear regression model yields:
log(λh (x , y )) =β 0 + β 1v 1(x , y ) + … +β 7 v 7(x , y ),