The effect of biotic factors on overall model performance
The models improved significantly when the interacting species was
included, for all evaluation measurements: Area Under the Curve (AUC),
continuous Boyce index (CBI) and corrected Aikake information criteria
(AICc). The difference in these evaluation metrics is the change from
models with biotic interactions to models without biotic interactions.
The interacting species was included at a resolution of 1 km, which was
on average the optimal resolution for most models (fig. 2A). The models
of the cleptoparasitic, oligolectic and polylectic bees all showed a
statistically significant increase in evaluation AUC (fig. 3A),
evaluation CBI (fig. 3B) and a decrease in calibration and evaluation
AICc (fig. 3C; Appendix S5). There were not enough samples in the
evaluation data to calculate the AICc for a proportion of the bees
(34.02% of the species; 66 species) and only the cleptoparasitic bees
showed a significant improvement on the species and genus level (fig.
3D). The biotic interaction had a high contribution to the models of all
the functional bee groups relative to the climate, land use and soil
variables (fig. 4; Appendix S6). The biotic interaction had the highest
contribution to the models compared to the climate, land use and soil
variables for the cleptoparasitic bees.
The models of the cleptoparasitic bees showed a statistically
significant higher improvement in evaluation AUC, evaluation CBI and in
calibration and evaluation AICc compared to the oligolectic and
polylectic bees with the interacting species at both taxonomic levels
(Appendix S5). The difference in evaluation metrics between oligolectic
and polylectic bees was in no case significant.
We found that the relative performance of the interacting species
compared to any randomly chosen interaction was the highest for the
cleptoparasitic, oligolectic and polylectic bees respectively and the
polylectic bees showed a more general preference of biotic interactions
than the cleptoparasitic and oligolectic bees. The models with the
interacting species (added at species and genus taxonomic level) had an
evaluation AUC that scored within the highest 5% best performing models
of the nullmodels, i.e. the models with the random interactions, in
52.8% and 62.3% of cleptoparasitic bees, 36.4% and 43.2% of
oligolectic bees and 13.4% and 14.4% of polylectic bees (fig. 5;
Appendix S3). When the threshold was within the 25% best performing
models, these percentages increased up to 83% and 94% of the
cleptoparasitic bees, 56.8% and 63.6% of the oligolectic bees and
40.2% and 51.2% of the polylectic bees. The polylectic bees showed a
less skewed distribution, but more of a continuous distribution,
suggesting a less selective response to the interacting species and a
more general preference of biotic interactions (fig. 5A).