Bennett et al., Abundance, rarity and invasion debt among exotic species in a patchy
ecosystem
Electronic Supplementary Material 1. Study patches, sampling protocol and patch sizes
Fig. ES1: Map showing location of study patches with respect to Vancouver Island, BC (inset,
top), and detail of the northern (inset, A) and southern (B) study patch locations. Patch sizes are
given in Table S1 below.
1
Quadrat Sampling Protocol
Quadrats for intra-patch surveys were established using a stratified-random sampling protocol, in
which the number of quadrats was scaled by area. Patches were divided a priori into grids based
on UTM coordinates in site maps. Patches <1 ha were divided into 25-m grids; patches 1-5 ha
were divided into 50-m grids; and patches >5 ha were divided into 100-m grids. In the field,
sample points were navigated to using a handheld GPS. As soon as the UTM coordinates for an
exact grid intersection point were displayed on the GPS (e.g. UTM northing ending in “00”,
easting ending in “00”), a plot was established. Spatial error on the initial GPS readings (±~10m)
and navigation to the first GPS reading showing specific grid points introduced randomness,
while ensuring adequate spatial coverage. Quadrats were placed on as many grid intersections as
possible within sites. Locations that had >50% cover rock, had slope >45 degrees, or were
obscured by shrub cover >1.5 m high were rejected.
Table ES1: Patch numbers and sizes. Italicized sites were included in the subset of 22
isolated/least disturbed small-island patches.
Site
Site
Number Area (ha) Number
Area (ha)
1
0.32
35
0.77
2
6.52
36
1.22
3
1.84
37
1.07
4
5.03
38
0.62
5
0.39
39
0.64
6
0.3
40
0.63
7
5.89
41
1.1
8
1.17
42
0.57
9
3.48
43
0.34
10
1.2
44
0.26
11
1.35
45
0.34
12
1.27
46
0.59
13
3.19
47
1.96
14
5.88
48
1.62
15
2.03
49
1.26
16
1.31
50
0.56
17
1.15
51
0.68
18
1.48
52
3.37
19
16.38
53
3.83
20
0.18
54
0.17
21
0.6
55
4.02
22
2.77
56
1.93
23
8.72
57
0.42
24
17.68
58
0.59
2
25
26
27
28
29
30
31
32
33
34
8.82
1.22
1.73
1.11
4.43
4.48
2.15
1.55
0.49
0.72
59
60
61
62
63
64
65
66
67
0.84
3.72
2.84
3.81
3.83
1.07
3.01
11.54
3.66
3
Bennett et al., Abundance, rarity and invasion debt among exotic species in a patchy
ecosystem
Electronic Supplementary Material 2. Phylogenetic Analyses
Creation of Phylogenetic Tree
We created a phylogenetic tree of our species using the Angiosperm Phylogeny Group III (2009)
phylogeny. Where there was no sub-family phylogenetic information, species within genera were
assumed to be more closely related than genera within families. Internal nodes were dated using
fossil evidence where available (Wikstrom et al. 2001), and the branch lengths for the tree were
scaled to the dated nodes and made ultrametric via Bladj software (Webb 2000). Phylogenetic
distances among species were subsequently used to test intra- versus inter-group distances and to
test for a phylogenetic signal in abundance differences.
Tests for Phylogenetic Relatedness Within and Among Groups
We tested for significant differences in intra- versus inter-group phylogenetic distances using
permutation tests (permuting group identities 10 000 times) of mean within-group distances
versus means of all other distances. Apart from native long dispersers, selected groups exhibited
lower intra-group than inter-group phylogenetic distances (Table S3). As reported in the main
article, we also tested for a phylogenetic signal in abundance differences at both scales, using
Mantel tests.
4
Table ES2: Permutation test results for intra- versus inter-group phylogenetic distances
Group
Intra-Group vs.
Inter-Group
Difference (%)
Z
P
Exotic Long
Dispersers
-3.1
-7.82
<0.0001
Exotic Short
Dispersers
-5.9
-8.55
<0.0001
Native Long
Dispersers
0.2
0.53
0.60
Native Short
Dispersers
-1.0
-3.01
0.0032
References
Angiosperm Phylogeny Group III phylogeny (2009) An update of the Angiosperm Phylogeny
Group classification for the orders and families of flowering plants: APG III. Bot J Linn
Soc 161:105–21
Wikstrom, N, Savolainen V, Chase, MW (2001) Evolution of the angiosperms: calibrating the
family tree. Proc R Soc Lond Ser B 268:2211–2220
Webb, CO (2000) Exploring the phylogenetic structure of ecological communities: an example
for rain forest trees. Am Nat 156:145-155
5
Bennett et al., Abundance, rarity and invasion debt among exotic species in a patchy
ecosystem
Electronic Supplementary Material 3. Tests for all variables from most parsimonious
models
Table ES3: Significant and non-significant coefficients from the most parsimonious models for
numbers of occurrences and forms of rarity/commonness. P<0.1 are italicized; P<0.05 are
bolded and italicized.
Response Variable
Predictor
Variables
Final
Model
Coefficient
Coefficient
Value
Standard
Error
T
P
EL
ES
NL
NS
EL
ES
NL
NS
EL
ES
NL
NS
EL
ES
NL
NS
0.364
-0.756
-0.010
0.081
0.626
-1.109
-0.202
0.271
0.510
-1.626
-0.047
0.434
-1.008
0.334
0.385
0.211
0.169
0.192
0.143
0.254
0.368
0.418
0.312
0.553
0.397
0.472
0.362
0.649
0.365
0.411
0.302
0.518
2.161
3.948
0.070
0.321
1.698
2.654
0.649
0.490
1.283
3.443
0.129
0.669
2.765
0.812
1.276
0.407
0.0342
0.0003
0.9443
0.7491
0.0940
0.0114
0.5176
0.6256
0.2037
0.0014
0.8979
0.5053
0.0073
0.4216
0.2047
0.6853
Number of Occurrences in
Patches
O, D, Gf
O×D
Number of Occurrences in
Quadrats
O, D, Gf
O×D
Commonness on Both Interand Intra-Patch Scales
O, D, Gf
O×D
Rarity on Both Inter- and
Intra-Patch Scales
O, D, Gf
O×D
D, Gf, Ta
D + Ta
Ta
-0.453
0.103
4.399 <0.0001
D, Gf, Ta
D + Ta
Ta
-1.479
0.280
5.275
<0.0001
D, Gf, Ta
D + Ta
Ta
-0.210
0.095
2.218
0.0292
EL
ES
NL
NS
EL
ES
NL
NS
0.326
-1.500
0.207
0.217
0.385
-2.003
0.223
0.398
0.225
0.259
0.194
0.346
0.425
0.484
0.362
0.644
1.448
5.798
1.066
0.629
0.906
4.135
0.616
0.618
0.1522
<0.0001
0.2888
0.5312
0.3682
0.0002
0.5391
0.5383
6
Number of Occurrences in
Full Surveys (Exotic spp.
only; including estim. time
since arrival)
Number of Occurrences in
Quadrats (Exotic spp. only;
including estim. time since
arrival)
Minimum Convex Polygon
Size (Exotic spp. only;
including estim. time since
arrival)
Number of Occurrences on
Patches (22 Small-Island
Patches Only)
O, D, Gf
O×D
Number of Occurrences in
Quadrats (22 Small-Island
Patches Only
O, D, Gf
O×D
Notes:
-Predictor variables: O = origin (native or exotic); D = dispersal ability (short or long); Gf =
growth form (forb, grass, shrub, tree); Ta = estimated time since arrival
-Predictor variable categories: E = exotic; N = Native; S = short dispersers; L = long dispersers
(i.e., EL = coefficient for exotic long dispersers in O×D interaction term)
7
Bennett et al., Abundance, rarity and invasion debt among exotic species in a patchy
ecosystem
Electronic Supplementary Material 4. Patch-level analysis using mean proportion of
quadrats occupied per patch.
Table ES4: Significant and non-significant coefficients from the most parsimonious models for
numbers of occurrences and forms of rarity/commonness. P<0.1 are italicized; P<0.05 are
bolded and italicized.
Response Variable
Predictor
Variables
Final
Model
Coefficient
EL
ES
NL
Commonness
O, D, Gf
O × D + Gf
NS
F
G
S
T
Coefficient
Value
0.015
-0.023
-0.009
0.010
-0.005
0.047
-0.012
-0.020
Standard
Error
0.012
0.014
0.010
0.018
0.003
0.013
0.014
0.020
T
P
1.212
1.690
0.907
0.582
1.628
3.721
0.860
0.979
0.229
0.099
0.367
0.562
0.105
0.001
0.396
0.344
8
Bennett et al., Abundance, rarity and invasion debt among exotic species in a patchy
ecosystem
Electronic Supplementary Material 5. Alternate forms of rarity/commonness
Conservative estimate (fewer common, more rare):
Common (patch-level) = 20 or more patches
Rare (patch-level) = 4 or fewer patches
Common (quadrat-level) = greater than one occurrence in quadrats from at least one patch
Rare (quadrat-level) = never found in more than one quadrat per patch
Liberal estimate (more common, fewer rare):
Common (patch-level) = 10 or more patches
Rare (patch-level) = 1 or 0 patches
Common (quadrat-level) = greater than one occurrence in quadrats from at least one patch
Rare (quadrat-level) = never found in more than one quadrat per patch
Table ES5a: Coefficients from most parsimonious models for rarity/commonness (conservative
estimate)
Response Variable
Predictor
Variables
Final
Model
Commonness
O, D, Gf
O × D + Gf
Rarity
O, D, Gf
O×D
Coefficient
EL
ES
NL
NS
F
G
S
T
EL
ES
NL
NS
Coefficient
Value
Standard
Error
0.389
-1.330
-0.066
0.413
-0.198
0.760
0.563
-0.375
-0.803
0.448
0.334
0.045
0.414
0.490
0.374
0.669
0.095
0.324
0.374
0.642
0.311
0.352
0.260
0.456
T
0.940
2.714
0.177
0.617
2.080
2.343
1.504
0.584
2.580
1.274
1.281
0.098
P
0.3507
0.0098
0.8601
0.5393
0.0388
0.0244
0.1432
0.5686
0.0120
0.2099
0.2032
0.9221
9
Table ES5b: Most parsimonious models for rarity/commonness (liberal estimate)
Response Variable
Predictor
Variables
Final
Model
Commonness
O, D, Gf
O × D + Gf
Rarity
O, D, Gf
O
Coefficient
EL
ES
NL
NS
F
G
S
T
E
N
Coefficient
Value
Standard
Error
0.433
-1.342
-0.163
0.499
-0.180
0.757
0.567
-0.605
-0.536
0.322
0.380
0.446
0.339
0.605
0.093
0.321
0.365
0.638
0.207
0.124
T
1.141
3.009
0.481
0.825
1.943
2.355
1.554
0.948
2.587
2.587
P
0.2576
0.0045
0.6316
0.4115
0.0534
0.0238
0.1307
0.3590
0.0110
0.0105
Notes:
-Predictor variables: O = origin (native or exotic); D = dispersal ability (short or long); Gf =
growth form (forb, graminoid, shrub, tree)
-Predictor variable categories: E = exotic; N = native; S = short dispersers; L = long dispersers; F
= forb; G = graminoid; S = shrub; T = tree
10
Bennett et al., Abundance, rarity and invasion debt among exotic species in a patchy
ecosystem
Electronic Supplementary Material 6. Patterns on small-island patches.
Fig. ES1. Frequencies of long- and short-dispersing exotic and native species in the subset of 22
small-island patches. a) number of patches per species in full patch surveys; b) number of
quadrats per species in quadrat-level surveys. Error bars indicate ±1 standard error.
11