Supporting information
Table S1 Results of a linear mixed effects model using larval relative growth rate as dependent variable. Due to missing data we had to remove 8 of 17 species. We had complete data for the mycorrhizal fungal treatment only.
Fixed factors
Induced (I)
Status (S)
Herbivore (H)
Mycorrhiza (M)
I × S
I × H
S × H
I × M
S × M
H × M
I × S × H
I × S × M
I × H × M
S × H × M
I × S × H × M
Random factors
Block
Genus
Species (Genus)
Genus × H both AMF treatments
Chi
2 df P-value
5.572
1 0.018
0.476
1 0.490
0.405
1 0.524
0.268
1 0.605
0.406
1 0.524
0.386
1 0.534
0.095
1 0.759
0.080
1 0.777
0.004
1 0.950
0.057
1 0.811
0.760
1 0.383
0.020
1 0.887
0.752
1 0.386
0.412
1 0.521
0.444
1 0.505
AMF treatment only
Chi
2 df P-value
3.894
1 0.048
0.036
1 0.851
3.907
1 0.048
-
0.685
1 0.408
1.298
1 0.255
3.174
1 0.062
-
-
-
-
-
-
-
0.405
1 0.525
-
-
-
-
-
-
-
-
0.527
1 0.468
90.065
1 <0.0001
37.685
1 <0.0001
13.312
1 0.004
0.979
1 0.322
83.503
1 <0.0001
35.169
1 <0.0001
-
1

Text S1 Effects on herbivore growth rate, separately for each plant species
Because the effects of induction and mycorrhizal fungi, and their interacting effects on herbivore performance appeared to vary among species (Fig. 4), we analysed the effect of mycorrhizal fungi and induction on relative growth rate of both caterpillar species separately for each plant species. We found significant mycorrhizal fungi × induction interactions in several plant and caterpillar species, but no general pattern. For example, we found that for both caterpillars, plants of Artemisia biennis were more able to induce resistance in the absence of mycorrhizal fungi. In contrast, in plants of Solidago canadensis induction had a more negative effect on the caterpillar species S. littoralis in the presence of mycorrhizal fungi. We conclude that the interactions of microbes and herbivores with invasive and non-invasive species do not follow a general pattern but differ idiosyncratically between species.
When we analysed herbivores feeding on mycorrhized plant only, we were also able to test whether the invasive or non-invasive species of a certain genus was generally more defended
(i.e. herbivores performed worse) or more able to induce resistance. Therefore, in data of the mycorrhizal fungal treatment only, we analysed each species group separately. In four speciesgroups herbivore performance differed significantly between the non-invasive and the invasive species (Table S4, Fig. S1): caterpillars feeding on the invasive species of the genus Artemisia ,
Bidens and Erigeron performed better than caterpillars feeding on their non-invasive congener.
In contrast, caterpillars feeding on the invasive Fallopia japonica performed worse than on the confamiliar non-invasive species Polygonum orientale . Additionally, in three species-groups, we observed that the ability to induce resistance differed between the non-invasive and the invasive species (significant induction × status interaction, Table S4, Fig. S1): the invasive species
Erigeron annuus , Solidago canadensis and Solidago gigantea were less able to induce resistances than their non-invasive congeners Erigeron karvinskianus , Solidago rugosa and
Solidago graminifolia . In contrast, the invasive Fallopia japonica was more able to induce resistance than its confamiliar Polygonum orientale . In two species-groups the two generalist herbivores responded differently to induction (significant induction × herbivore interaction,
Table S4, Fig. S1): in the genus Bidens the caterpillar S. littoralis was negatively affected by previous induction whereas M. brassicae was not affected. The opposite was the case in the genus Solidago . We conclude, that dominant invasive alien species are not generally more able
2

to induce resistance against herbivores than non-invasive alien species and also do not differ generally in their constitutive resistance against herbivores. Although induced resistance might be a useful trait for some species, it is not very likely that it is responsible for the dominance of most invaders.
3

Table S2 F-Values and significances of the results of an ANOVA using either the mean larval growth rate of both herbivore species, of S. littoralis only and of M. brassica only, as dependent variable. ANOVAS were calculated separately for each plant species of which we had data on both mycorrhizal fungal treatments. Significance levels of the effects are denoted with
(
*
)
P <
0.1, *P < 0.05, **P < 0.01 and ***P < 0.001
Artemisia biennis
Artemisia verlotiorum
Bidens bipinnata
Bidens frondosa
Lepidium
virginicum
Lepidium neglectum
F-Value
Fallopia japonica
Senecio inaequidens
Senecio vernalis
Erigeron annuus
Solidago
canadensis
Solidago gigantea
Solidago
rugosa
Both
Induction
Mycorrhiza
I x M
Spodoptera
Induction
Mycorrhiza
I x M
Mamestra
Induction
Mycorrhiza
I x M
3.387
(
*
)
4.040
(
*
)
16.257 **
1.666
4.630
7.055 *
2.181
0.317
(
*
)
5.765 *
0.273
2.448
0.348
0.430
1.952
3.185
< 0.001
3.338
0.013
0.050
2.439
0.138
1.521
8.599 *
5.612
1.006
6.054
0.300
(
*
)
(
*
)
0.719
0.081
0.097
0.259
0.023
0.264
0.778
0.927
3.210
0.157
2.914
(
*
(
*
)
6.023 *
0.312
4.051
(
*
)
0.527
0.127
6.026 * 0.725
)
0.502
0.063
0.321
0.031
0.400
3.195
(
*
)
0.874
0.003
0.097
7.006 *
3.302
0.105
3.337
0.308
0.979
6.206
3.522
1.108
( * )
( * )
0.644
0.417
1.907
0.001
0.191
0.376
2.574
0.403
2.511
0.754
0.645
0.036
-
-
-
0.326
0.881
0.003
0.038
1.457
2.043
0.484
0.010
1.631
0.003
2.262
0.442
2.302
0.978
1.086
6.228 *
3.851
(
*
)
3.271
(
*
)
5.847 *
0.651
0.266
0.013
0.008
0.003
0.009
4.261
0.080
0.075
0.931
0.114
(
*
)
1.336
0.023
2.168
0.019
0.043
1.313
1.608
0.004
6.887 *
4

Table S3 Results of linear mixed effect models using the relative growth rate of the caterpillars as dependent variable. Presented are estimates ± SE, separately for each species group. Data are from the mycorrhizal fungal treatment only. Significance levels of the effects are denoted with
(
*
)
P < 0.1, *P < 0.05, **P < 0.01 and ***P < 0.001
Artemisia
Fixed factors
Induction
Status
Herbivore
Induction × Status
Induction × Herbivore
Status × Herbivore
Induction × Status × Herbivore -
-
-
-
-
-
0.481 ± 0.29
(
*
)
Random factors
Block
Species
0.007
0.05
Bidens
0.3028 ± 0.228
0.440 ± 0.274
(
*
)
0.855 ± 0.222**
-
-0.571 ± 0.294*
-
-
< 0.0001
0.027
Erigeron Lepidium
-0.218 ± 0.114
0.686 ± 0.199*
0.422 ± 0.118
0.392 ± 0.162*
-
-0.57 ± 0.162***
-
Estimates ± SE
-
-
-0.303 ± 1.011**
-
-
-
-
0.007
0.008
Variance
0.019
0.025
Polygonaceae
0.135 ± 0.17
-0.145 ± 0.245
(
*
)
-
-0.508 ± 0.23*
-
-
-
0.006
0.017
Solidago
-1.254 ± 0.213** 0.272 ± 0.110*
-0.432 ± 0.228
-0.271 ± 0.191
0.775 ± 0.279*
1.264 ± 0.285***
0.084 ± 0.26
-0.751 ± 0.381*
-
-
-
-
0.238 ± 0.110*
-
0.021
0.017
Senecio
< 0.0001
0.008
5

1.0
0.5
0.0
1.5
Fallopia japonica
Polygonum orientale
Lepidium virginicum
Lepidium neglectum
Erigeron annuus
Erigeron karvinskianus
Artemisia verlotiorum
Artemisia biennis
Artemisia annua
1.0
0.5
0.0
-0.5
-1.0
1.5
-I
Bidens frondosa
+I -I
Bidens bipinnata
+I -I +I
Senecio inaequidens
-I
Senecio vernalis
+I
S. littoralis
M. brassicae
-I
Solidago gigantea
+I -I +I
Solidago canadensis
-I
Solidago rugosa
+I -I
Solidago graminifolia
+I -I +I
-0.5
-1.0
-I +I -I +I -I +I -I +I -I +I -I +I -I +I -I +I
Figure S1 Relative growth rate ± SE of S. littoralis and M. brassicae feeding on undamaged (-I) and damaged (+I) plants (plants from the mycorrhizal fungal treatment only).
6