1
Table S1. Correlation matrix of variables used in the structural equation modeling to explain the spatial
2
distribution of tadpoles in rice fields. The Pearson correlation coefficient is calculated by treating the
3
survey year and modernization of ditch as dummy variables (year: 2009 = 0 and 2010 = 1, modernization:
4
unlined drainage ditch = 0 and lined with concrete = 1). Relative densities of six predator/competitor
5
species groups are log (x + 0.5)-transformed to normalize their distributions.
6
Variable
1
2
3
4
5
6
7
8
9
－
1. Year
－
2. Modernization
0.00
－
3. Flood period
0.35**
-0.46***
－
4. Egret
0.06
-0.53***
0.22*
－
5. Adult loach
0.17
-0.38***
0.33**
0.27*
－
6. Young loach
0.28*
-0.54***
0.40***
0.55***
0.38***
－
7. Crayfish
0.13
-0.52***
0.30*
0.20
0.31**
0.30*
－
8. Insect predators
-0.15
0.44***
-0.35***
-0.43***
-0.22*
-0.28*
-0.14
－
9. Insect consumers
0.26*
0.07
0.02
-0.09
-0.11
-0.06
0.13
0.01
7
*P < 0.05; **P < 0.005; ***P < 0.0005, indicating a significant correlation between variables.
8
1
9
Table S2. Results of the final model of structural equation modeling examining the direct, indirect and
10
total effects of three abiotic (survey year, modernization of ditch and flood-irrigation period) and six biotic
11
(relative densities of egret, adult and young loach, crayfish, insect predators and consumers) variables on
12
the density of Japanese tree frog tadpoles in rice fields. P value of direct paths is also shown. Details for
13
the calculation of direct, indirect and total effects are shown in the main text.
14
Path from
Year
Modernization
To
Effects
Direct
Total
P
Young loach
0.27
0.27
<0.001
Insect consumers
0.26
0.26
<0.01
Egret
-0.53
-0.53
<0.001
Adult loach
-0.28
-0.28
<0.01
Young loach
-0.54
-0.54
<0.001
Crayfish
-0.52
-0.52
<0.001
0.35
0.35
<0.001
Insect predators
Tadpoles
Flood period
Indirect
Adult loach
Insect predators
0.12
0.12
0.20
0.20
0.05
-0.21
-0.21
<0.05
0.33
<0.001
Tadpoles
0.41
-0.08
Adult loach
Tadpoles
-0.18
-0.18
0.07
Insect predators
Tadpoles
0.20
0.20
<0.05
15
16
2
17
Table S3. Results of the general linear model examining the relationship between mean body size of the
18
tree frog tadpoles and the flood-irrigation period in the rice fields in 2009 and 2010. 16 and 10 out of 48
19
fields in each year were removed for the analysis because no tadpole was captured by the traps and thus
20
body size could not be calculated. The response variable was the mean body size (cm) of tadpoles in each
21
field and the explanatory variables were the flood-irrigation period and the survey year (2009 = 0 and
22
2010 = 1). Scatter plot is shown in Fig. S3.
23
Variable
Coeff.
SE
P
Intercept
1.21
0.48
Year
0.41
0.13
<0.005
Flood period
0.04
0.01
<0.005
24
25
3
26
Figure S1. The study site lies along the southern shore of Lake Kasumigaura in Ibaraki Prefecture, Kanto
27
region, central Japan (36°02′N, 140°17′E). The location of four areas for tadpole surveys was shown with
28
black-line boxes. As an example, rice fields for the surveys (diagonally lined areas) in four blocks
29
(black-line boxes) in Area 2 are also shown in the inset.
30
“Area”
0
N
1km
0
10km N
Pacific
Ocean
Study site
Lake Kasumigaura
1
Kanto region
2
3
“Block”
Lake
Kasumigaura
0
4
200m N
Towns and mountains
Key
Rice paddy region
Rice fields for sampling
31
32
Breeding colony of egrets
4
33
Figure S2. The periods of flood-irrigation (i.e., the number of days from the flood-irrigation date to the
34
survey date of tadpoles) in 48 rice fields in 2009 (white bars) and 2010 (black bars). Tadpole surveys in
35
the fields were conducted on 25–26 May 2009 and 27–28 May 2010. On the Y axis the fields were sorted
36
by the type of cultivation (M: modern field; T: traditional field) and chronologically from the beginning of
37
the flood-irrigation in 2010.
38
39
40
41
42
43
44
45
46
47
48
49
5
50
Figure S3. Frequency histograms of body size distributions for dojo loach, crayfish and Japanese tree frog
51
tadpoles in rice fields in late May 2009 (white bars) and 2010 (black bars). Dojo loach was counted by the
52
night-time census, and the other two species were captured by the minnow traps (for more details please
53
see the main text).
54
250
Dojo loach
2009
2010
200
Number of individuals
150
55
56
100
50
0
1.1 - 2.1 - 3.1 - 4.1 - 5.1 - 6.1 - 7.1 - 8.1 - 9.1 - 10.1 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 14.0
Total length (cm)
25
Crayfish
1000
20
800
15
600
10
400
5
200
0
0
01.0 - 2.0 - 3.0 0.9
1.9
2.9
3.9
Carapace length (cm)
Tadpole
1.0 - 2.0 - 3.0 - 4.0 1.9
2.9
3.9
5.0
Total length (cm)
6
57
Figure S4. Moran's correlograms for residuals of the six biotic variables in the best model in 2009 (circle
58
and solid line) and 2010 (square and dotted line). The abscissa is distance classes, which were defined at
59
100 m intervals to confirm the presence of patch structure at a small spatial scale. The ordinate is Moran’s
60
coefficients estimated for different distance classes. Moran’s coefficients usually range from -1 (indicating
61
regular distribution of loach at the spatial scale) to 1 (clumped distribution). Zero value indicates a random
62
spatial distribution. Filled circles/squares indicate significant coefficients for each distance class, which
63
was tested by performing 1000 permutations of the original data with Bonferroni correction.
1
64
65
Adult loach
0.5
0.5
0
0
-0.5
-0.5
100
69
70
71
Moran’s coefficients
68
300
500
700
1
67
100
900
Egret
300
500
1
0.5
0.5
0
0
-0.5
-0.5
700
900
Crayfish
-1
-1
100
300
1
500
700
100
900
Predatory insects
0.5
0
0
-0.5
-0.5
-1
300
500
700
900
Consumer
insects
1
0.5
-1
100
300
500
700
1
72
Young loach
-1
-1
66
1
900
100
Tadpole
0.5
300
500
700
900
2009
2010
0
73
74
-0.5
-1
100
300
500
700
900
Spatial scale (m)
7
75
Figure S5. Scatter plot on the relationship between the mean body size (cm) of tree frog tadpoles and the
76
flood-irrigation period in the 32 and 40 rice fields in 2009 and 2010, respectively. General linear model
77
showed that their mean body size in each field is positively correlated with the flood-irrigation period (see
78
Table S3).
Mean body size (cm)
79
4
3
2
2009
1
2010
0
20
30
40
50
Flood period (number of date)
8