Table 1.

Ability of experimental, plant and natural enemy attributes to explain variance in diff.RR and predict non-independent interactions. L is the statistic for the log-likelihood ratio test. Justification for inclusion of these variables can be found in the electronic supplementary material.

variable and levels	significance in meta-analysis
	explanatory ability		enemies act independently at all levels?
	L	p-value
response measured (density/reproductive/vegetative/survival)	0.75	0.861	yes
method of enemy manipulation (added/removed)	1.22	0.270	yes
guild or species manipulated	1.13	0.288	yes
experimental location (greenhouse/common garden/field)	0.69	0.707	yes
unit of replication (plot/plant)	0.08	0.785	yes
length of experiment (no. days)	0.01	0.914	n.a.
plant life-history (annual/biennial/perennial)	4.69	0.096	biennials: antagonistic
economic status (model organism/crop/weed/native)	2.46	0.482	weeds: antagonistic
plant functional group (forb/grass/shrub/tree/vine)	0.49	0.975	yes
woody or non-woody	0.10	0.752	yes
plant family	18.77	0.547	Asteraceae: antagonistic Ranunculaceae: synergistic
enemy grouping (two arthropods versus an arthropod and a plant pathogen versus two plant pathogens)	0.23	0.893	yes
interaction type (direct/indirect)	3.25	0.072	direct: antagonistic
no. of generalists present (0, 1, 2)	0.98	0.612	yes
both enemies in the same order	0.03	0.862	yes
both enemies in the same family	0.02	0.882	yes
both enemies in the same feeding guild	0.006	0.936	yes
no. of chewers present (0, 1, 2)	1.64	0.441	yes
no. of sap-suckers present (0, 1, 2)	1.79	0.409	yes
no. of miners present (0, 1, 2)	0.26	0.879	yes
reproductive plant parts attacked	4.24	0.039	present: antagonistic
leaves attacked	0.85	0.356	yes
roots attacked	2.64	0.105	absent: antagonistic
stems attacked	0.0004	0.983	yes
Coleoptera present	0.009	0.926	yes
Lepidoptera present	0.84	0.358	yes
Diptera present	4.22	0.040	present: antagonistic
Hemiptera present	1.53	0.216	yes
fungi present	0.06	0.808	yes
virus present	0.35	0.554	yes