Supplementary Material
Appendix S2: Stable isotope analyses
Stable isotope analyses are a useful tool to quantify trophic niche and specialization of
consumers in wild populations (Newsome et al. 2009; Layman et al. 2012). Specifically, the
stable isotopes of nitrogen (δ15N) and carbon (δ15N) depict the trophic position of the
consumers and the origin of the trophic resource, respectively (Post 2002; Fry 2006).
Moreover, stable isotope analyses permit to integrate dietary information through time. For
instance, the stable isotope values in fish fin samples provide dietary information over 4 to 6
weeks (Boecklen et al. 2011). Stable isotope analyses can be used in conjunction with
individual tagging and multiple recaptures (e.g. Cunjak et al. 2005; Cucherousset, Paillisson
& Roussel 2013) to provide unique information about individual trophic specialization
through longitudinal monitoring (Araújo, Bolnick & Layman 2011).
δ13C and δ15N values were measured on fin samples from individual fish. Specifically,
all recaptured individuals were analyzed for each sampling season (93 individuals with two
samples per individual, n = 186) and when possible, additional fish only captured in
September were analyzed (n = 111 individuals) to reach a minimum of 15 individuals per
studied site (Figure S2).
The stable isotope values of potential prey were analyzed in each studied site and
during each fish sampling (April and September) to inform on the diet of fish during the
period of their maximal growth rate (i.e. summer period). For each studied site, prey items
were collected along the stream and in different places randomly selected and prey samples
for stable isotope analyses were composed of pooled items to account for potential spatial
variability within-site (n = 3-30 individuals per samples, e.g. Cucherousset et al. 2011).
According Jardine et al. (2005), guts were removed for predators. These prey were selected
according to their abundance in the sites, identified to the lowest possible taxon and finally
categorized into five trophic groups: aquatic herbivore (Glossosomatidae, Heptageneidae),
aquatic
predators
(Perlidae),
aquatic
detritivores
(Gammaridae,
Nemouridae,
Sericostomatidae), terrestrial herbivores (Orthoptera, Coleoptera) and terrestrial predators
(Aranea, Diptera). Following the recommendations of Philips, Newsome & Gregg (2005),
this procedure was performed to obtain functionally and isotopically coherent isotopic groups
to reduced the number of putative prey in mixing models. This was confirmed by the facts
that functional groups did not overlap in the 2-D isotopic space (Figure S2) and that, for each
season and each site, between-group variability of prey stable isotope values (δ13C and δ15N)
was much higher than the within-group variability (April: meaninter δ13C = 83.07% (± 6.72
SE), meanintra δ13C = 16.93% (± 6.72 SE), meaninter δ15N = 79.60% (± 3.51 SE), meanintra δ15N
= 20.40% (± 3.51 SE); September: meaninter δ13C = 83.74% (± 6.28 SE), meanintra δ13C =
16.26% (± 6.28 SE), meaninter δ15N = 80.46% (± 2.75 SE), meanintra δ15N = 19.54% (± 2.75
SE). Therefore, these functional and isotopic groups were used for subsequent analyses and
within-group variability was incorporated in the mixing models (Parnell et al. 2010).
Since the C:N ratio of prey were upper (aquatic herbivore: mean = 9.31 ± 0.95 SE;
aquatic predators: 4.05 ± 0.05; aquatic detritivores: 5.97 ± 0.12; terrestrial herbivores: 4.89 ±
0.15; terrestrial predators: 4.48 ± 0.13) than the suggested limits (3.5 and 4 for aquatic and
terrestrial organisms, respectively; Post et al. 2007), the stable isotope values of prey were
lipid-corrected following Post et al. (2007). The mean magnitude of lipid corrections in April
and in September for aquatic herbivores, aquatic predators, aquatic detritivores, terrestrial
herbivores and terrestrial predators are 1.33 (± 0.06 SE), 0.65 (± 0.06), 2.76 (± 0.11), 1.51 (±
0.18), 0.90 (± 0.14) and 1.08 (± 0.06), 0.72 (± 0.07), 2.44 (± 0.23), 1.56 (± 0.17), 1.11 (±
0.19), respectively. No significant differences in δ13C lipid correction between sites were
observed (ANOVAs, F < 3.33, P > 0.05).
Prior to analyses, all stable isotope samples were oven-dried at 60°C for 48h and
subsequently analyzed at the Cornell Isotope Laboratory (COIL, Ithaca, New York, USA).
The analytical precision for all samples, calculated as the standard deviation of an internal
Mink standard, was 0.15 and 0.27 ‰ for δ13C and δ15N, respectively.
Streams are composed of mixed carbon source (terrestrial plant litter vs autochthonous
primary producers) with distinct isotopic signature (13C-depleted and
13
C-enriched,
respectively, Hoeinghaus & Zeug 2008). Therefore, the δ13C values of aquatic prey should
change in response to canopy openness. Consequently, the δ13C range of aquatic prey was
calculated using the difference between the maximum and the minimum δ13C values of
aquatic detritivores, herbivores and predators (Layman et al. 2007). As expected, a significant
hump-shaped curve was found between the δ13C rage of aquatic prey and the gradient of
canopy openness (R² = 0.52, linear term: P = 0.029, quadratic term: P = 0.032), indicating
that carbon source used by aquatic prey in intermediate site were more diverse than in
extreme sites.
Cited references
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Ecology Letters, 14, 948–958.
Boecklen, W.J., Yarnes, C.T., Cook, B.A. & James, A.C. (2011) On the use of stable isotopes in
trophic ecology. Annual Review of Ecology, Evolution, and Systematics, 42, 411–440.
Cucherousset, J., Acou, A., Blanchet, S., Britton, J.R., Beaumont, W.R.C. & Gozlan, R.E. (2011)
Fitness consequences of individual specialization in resource use and trophic morphology in
European eels. Oecologia, 167, 75–84.
Cucherousset, J., Paillisson, J.-M. & Roussel, J.-M. (2013) Natal departure timing from spatially
varying environments is dependent of individual ontogenetic status. Naturwissenschaften, 100, 761–
768.
Cunjak, R.A., Roussel, J-M., Gray, M.A., Dietrich, J.P., Catwright, D.F., Munkittrick, K.R. & Jardine,
T.D. (2005) Using stable isotope analysis with telemetry or mark-recapture data to identify fish
movement and foraging. Oecologia, 144, 636–646.
Fry, B. (2006) Stable Isotope Ecology. Springer.
Hoeinghaus, D.J. & Zeug, S.C. (2008) Can stable isotope ratios provide for community-wide measures
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Jardine, T.D., Curry, R.A., Heard, K.S. & Cunjak, R.A. (2005) High fidelity: isotopic relationship
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Layman, C.A., Arrington, D.A., Montaña, C.G. & Post, D.M. (2007) Can stable isotope ratios provide
for community-wide measures of trophic structure? Ecology, 88, 42–48
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sea otters (Enhydra lutris nereis). Ecology, 90, 961–974.
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assumptions. Ecology, 83, 703–718.
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Getting to the fat of the matter: models, methods and assumptions for dealing with lipids in
stable isotope analyses. Oecologia, 152, 179–189.
Aquatic predators
Aquatic herbivores
September
April
7
(a)
7
5
MOUS
5
(b)
3
3
1
c
p
a
h
-1
p
s
c
p
1
-1
a
a
h
s
s
n
ga
gl
n
-3
-3
ga
gl
n
ga
i
-5
-5
-29
-27
Terrestrial predators
Terrestrial herbivores
Aquatic detritivores
-25
-23
-29
-21
7
(c)
7
5
FRAI
5
-27
-25
-23
(d)
d
c
c
3
p
3
p
h
1
a
s
a
-1
ga
n
s
s
a
gl
-3
n
ga
n
ga
-3
-30
δ15N
p
h
h
1
gl
-1
-21
-28
-26
-24
-22
-30
6
(e)
6
4
PESQ
4
-2
p
h
gl
s
h
ga
-2
a
a
s
m
m
n
-22
p
0
m
gl
-24
(f)
a
h
0
-26
2
p
2
-28
n
ga
ga
n
-4
-4
-31
-29
-27
-25
-31
-23
9
9
(g)
7
LAMP
-29
-27
-25
-23
(h)
d
7
5
5
3
3
a
1
p
h
-1
ga
c
s
s
h
n
n
-3
gl
a
p
h
-1
s
n
-3
a
p
1
c
ga
gl
ga
-5
-5
-33
-31
6
(i)
4
PEYR
-29
-27
-25
6
-31
-29
-25
-23
p
2
p
a
h
s
h
d
n
-2
m
-4
-28
-26
-24
-22
ga
n
ga
m
-4
-30
s
s
gl
ga
n
a
a
h
0
gl
-2
-32
-27
(j)
4
p
2
0
-33
-23
-32
δ13C
-30
-28
-26
-24
-22
Aquatic predators
Aquatic herbivores
Terrestrial predators
Terrestrial herbivores
Aquatic detritivores
September
April
9
(k)
9
7
ORBI
7
(l)
p
h
5
5
p
h
3
a
p
h
3
gl
1
gl
1
ga
n
-1
a
a
d
n
ga
n
ga
-1
or
or
-3
-3
-34
6
4
-30
-26
-22
-34
(m)
6
BRG1
4
p
2
-30
-26
-22
(n)
2
p
p
a
a
a
0
0
s
-2
m
n
gl
or
-2
ga
ga
m
n
gl
ga
-4
-4
-34
-30
-26
-34
-22
7
(o)
7
5
LINO
5
3
δ15N
h
h
h
-30
3
-1
-3
h
gl
-1
-ga
n
gl
p
p
a
1
s
h
-22
d
a
p
1
-26
(p)
s
h
n
a
s
n
ga
ga
-3
or
or
-5
-5
-37
-33
-29
-25
-21
-37
7
(q)
7
5
BRG2
5
-33
-29
p
1
h
s
-1
p
a
p
1
gl
-3
a
a
h
h
s
or
gl
-1
ga
n
ga
s
n
n
ga
-3
or
-21
(r)
3
3
-25
or
-5
-5
-32
-30
-28
-26
-24
-32
-22
6
(s)
6
4
BERN
4
-30
-28
c
p
0
s
h
-2
p
-4
p
s
d
n
-2
gl
n
-22
a
2
c
0
-24
(t)
a
a
2
-26
s
h
h
gl
n
-4
-28
-26
-24
-22
-28
-26
-24
-22
δ13C
Figure S2: δ13C and δ15N values of individual fish (diamonds) and putative prey (circles)
analyzed in April (left panels) and September (right panels) in the ten studied stream sites:
MOUS (a, b), FRAI (c, d), PESQ (e, f), LAMP (g, h), PEYR (i, j), ORBI (k, l), BRG1 (m, n),
LINO (o, p), BRG2 (q, r) and BERN (s, t). Open diamonds represent individuals tagged in
April and recaptured in September while black diamonds represent additional individuals
sampled in September. Small circles represent single prey composed of pooled items (n = 3 –
30 individuals). Large circles represent prey trophic groups (mean ± SE): aquatic herbivores
(gl: Glossosomatidae, h: Heptageneidae), aquatic predators (p: Perlidae), aquatic detritivores
(ga: Gammaridae, n: Nemouridae, s: Sericostomatidae), terrestrial herbivores (c: Coleoptera,
or: Orthoptera, m: mixed) and terrestrial predators (a: Aranea, d: Diptera).