Fig. S1. The highly dynamic nature of algal assemblages on rocky shores at the scale of
individual plots. (a) Total cover and (b) taxon richness of macroalgal assemblages (mean +
s.e.m., n = 4) in our uncaged unmanipulated procedural control plots on each algal census.
Fig. S2. Standardised effect sizes based on the instantaneous difference between experimental
treatments and the corresponding treatment with no species removals for those components of
stability that could be quantified separately for each algal survey: (a) the number of algal
secondary extinctions, (b) the number of algal invasions and (c) the resistance of algal
assemblages to experimental perturbations. The inverse of resistance is shown in (c) so that all
positive effect sizes correspond to reductions in stability.
Fig. S3. Effects of primary consumer species loss on the volume of ellipsoids in
multidimensional stability space. Pairwise differences in ellipsoid volume for random
permutations of the data (grey histogram) and observed treatments (Grazers lost–No primary
consumers lost [red line]: P = 0.1; Mussels lost–No primary consumers lost [turquoise line]: P =
0.095; Grazers lost–Mussels lost [purple line]: P = 0.95).
Table S1. Results of ANOVAs testing for effects of our experimental perturbations on the
stability of macroalgal assemblages. Significant effects (P < 0.05) are highlighted in bold.
Response variable
Source of variation
df
MS
F
P
Temporal variability
Loss of predators, P
2
207.18
0.6
0.56
Loss of primary consumers, C
2
7571.28
21.95
≤0.0001
P*C
4
1561.62
4.53
0.006
Residual
27
344.94
Loss of predators, P
2
681.66
0.37
0.71
Loss of primary consumers, C
2
11564.58
145.43
0.0002
Month, M
2
181.93
0.39
0.68
P*C
4
2912.75
5.43
0.021
P*M
4
1856.93
3.96
0.0055
C*M
4
79.52
0.17
0.95
P*C*M
8
536.75
1.14
0.34
Residual
21
468.83
Loss of predators, P
2
1.07
8.91
0.0011
Loss of primary consumers, C
2
0.41
3.41
0.048
P*C
4
0.46
3.81
0.014
Residual
27
0.12
Loss of predators, P
2
2.53
1.84
0.18
Loss of primary consumers, C
2
11.03
8.05
0.0018
Compositional turnover
Number of extinctions†
Number of invasions
Spatial variability†
Resistance
†
P*C
4
0.69
0.51
0.73
Residual
27
1.37
Loss of predators, P
2
1.14
0.27
0.77
Loss of primary consumers, C
2
36.34
8.47
0.001
P*C
4
3
0.7
0.6
Residual
27
4.29
Loss of predators, P
2
1236.08
7
0.004
Loss of primary consumers, C
2
233.59
1.32
0.28
P*C
4
567.56
3.21
0.028
Residual
27
176.68
Dependent variable was square-root transformed to stabilise heterogeneous variances
Table S2. Results of ANOVAs testing for effects of experimental perturbations on detrended
temporal and spatial variability of total algal cover. Significant effects (P < 0.05) are highlighted
in bold.
Response variable
Source of variation
df
MS
F
P
Temporal variability†
Loss of predators, P
2
0.26
0.16
0.85
Loss of primary consumers, C
2
50.1
30.37
≤0.0001
P*C
4
7.1
4.3
0.008
Residual
27
1.65
Loss of predators, P
2
41992.09
1.97
0.16
Loss of primary consumers, C
2
97767.19
4.58
0.019
P*C
4
54692.2
2.56
0.07
Residual
27
21353.1
Spatial variability‡
†
Dependent variable was square-root transformed to stabilise heterogeneous variances.
The dependent variable had heterogeneous variances that could not be stabilised by transformation. These data
were analysed untransformed based upon the relative robustness of ANOVA to heterogeneous variances in
particular when sample size is balanced (Underwood 1997).
‡
Table S3. Macroalgal taxa found in experimental plots over the duration of the experiment.
Phylum
Taxon
Ochrophyta
Fucus serratus
Leathesia difformis
Chlorophyta
Enteromorpha intestinalis
Ulva lactuca
Rhodophyta
Ceramium rubrum
Chondrus crispus
Corallina officinalis
Ectocarpus spp.
Gelidium pusillum
Gracilaria gracilis
Lithothamnion spp.
Nemalion helminthoides
Osmundea pinnatifida
Palmaria palmata
Polysiphonia fucoides
Porphyra umbilicalis
Table S4. Results of analyses testing for effects of experimental cages on each of the temporal
variability of total algal cover (ANOVA), compositional turnover of algal assemblages
(ANOVA), number of extinctions of algal taxa (ANOVA), invasions of algal taxa (ANOVA),
spatial variability of total algal cover (ANOVA) and the structure of algal assemblages
(PERMANOVA, based on a Bray-Curtis similarity matrix calculated from log(x + 1)transformed algal cover data and done with 9999 permutations of the residuals under a reduced
model). Although the design of the cages used to maintain our experimental treatments has been
used extensively and successfully to manipulate consumer presence on rocky shores with no
consequences for algal community structure (O'Connor & Crowe 2005; O’Connor & Donohue
2013), we tested for experimental artefacts caused by the presence of the cages by comparing the
structure and stability of macroalgal communities in caged treatments that had no experimental
species removals to that in equivalent uncaged and unmanipulated procedural control plots at the
experimental site.
Response variable
Source of variation
df
MS
F
P
Temporal variability
Cage
1
157.59
0.22
0.66
Residual
6
723.06
Cage, C
1
558.58
0.93
0.44
Month, M
2
3155.93
8.11
0.003
C*M
2
601.29
1.55
0.24
Residual
18
388.95
Compositional turnover†
Number of extinctions
Number of invasions
Spatial variability
Assemblage structure
†
Cage
1
0.13
0.16
0.7
Residual
6
0.79
Cage
1
0.5
0.32
0.59
Residual
6
1.58
Cage
1
5.71
0.02
0.9
Residual
6
365.56
Cage, C
1
1497.3
4.16‡
0.86
Month, M
3
2228.2
0.88‡
0.59
C*M
3
360.3
0.14‡
0.99
Residual
24
2539.5
The dependent variable had heterogeneous variances that could not be stabilised by transformation. These data
were analysed untransformed based upon the relative robustness of ANOVA to heterogeneous variances in
particular when sample size is balanced (Underwood 1997).
‡
Pseudo-F ratio.
Table S5. Results of PERMANOVAs testing for effects of consumer species loss on algal
assemblage structure four, seven, ten and fourteen months after the commencement of the
experiment. Significant effects (P < 0.05) are highlighted in bold.
Month
Source of variation
df
MS
Pseudo-F
P
4
Loss of predators, P
2
1646.2
0.8
0.61
Loss of primary consumers, C
2
7105.6
3.46
0.001
P*C
4
1007.9
0.49
0.93
Residual
27
2055.9
Loss of predators, P
2
1178
1.38
0.26
Loss of primary consumers, C
2
19353
22.72
≤0.0001
P*C
4
2539.9
2.98
0.005
Residual
27
851.97
Loss of predators, P
2
1282.2
1.97
0.077
Loss of primary consumers, C
2
19503
29.97
≤0.0001
P*C
4
2272.9
3.49
0.0005
Residual
27
650.86
Loss of predators, P
2
2082.1
1.15
0.32
Loss of primary consumers, C
2
19611
10.8
≤0.0001
P*C
4
1630.8
0.9
0.61
Residual
27
1815.7
7
10
14
References
O'Connor N.E. & Crowe T.P. (2005). Biodiversity loss and ecosystem functioning:
distinguishing between number and identity of species. Ecology, 86, 1783-1796.
O'Connor N.E. & Donohue I. (2013). Environmental context determines multi-trophic effects of
consumer species loss. Global Change Biology, 19, XXX-XXX.
Underwood A.J. (1997). Experiments in ecology: their logical design and interpretation using
analysis of variance. Cambridge University Press, Cambridge, UK.