Relative influence of environmental variables in boosted regression tree models.

Relative influence of each environmental variable from three categories (physical, land use and chemical) on the boosted regression tree models predicting taxonomic richness and the main axis of regional faunal composition (Metacom 1) in 168 low-mountain streams and rivers in central Germany categorised into all sites (N = 168), headwaters (N = 48), mid-sized (N = 69) and large rivers (N = 51). The top plot shows the relative influence of each individual variable and the bottom the combined influence of each category of variables. Note catchment size was removed from all size-based models (i.e. headwaters, mid-sized and large rivers). See Table 1 for a description of variables and Table 3 for the results of BRT analyses.