1. Testing trophic niche partitioning in sibling species:
A stable isotope study of Dysdera spiders in the
Eastern Canary islands
Departamento de Biologia animal
Estudiante: Antonio Sanna
Directores: Carolina Sanpera Trigueros Miquel Arnedo Lombarte
Màster de Biodiversitat 2014 / 2015

2. • Dysdera : >250 species Circum-Mediterranean distribution (Central Asia –
Macaronesian Islands)
• ground-dwelling ,nocturnal wandering, hunter spiders (isopodos)
• Important diversification in the Canary Islands (>50 endemics)
The spider genus Dysdera in the Eastern
Canary Islands
Some in
sympatry

3. The studied species
D.alegranzaensis
D.nesiotes
D.mahan
No morphological differences , except for genitalia

4. Objective of the study
• Testing resource partitioning in similar sympatric species:
D.alegranzaensis and D.nesiotes
• Testing the use of resources from marine origin in the
species with coastal habitat D.mahan

5. The stable isotope analysis
The stable isotopes used :
• The δ15N ( 15N/14N): (3-4 ‰) trophic level shift
It depends on the base of food wed (isotopic baseline)
• The δ 13C (13C/12C): (0.5 ‰) lower change with trophic level
Major changes related to carbon source:
terrestrial < marine environment
C3 plants (-27 ‰) < C4 plants (-12‰)
Use of δ15N and δ 13C as biomarkers of ecological dimensions

6. HYPOTHESIS
Hypothesis 1: DA and DN should have different isotopic signatures
(nitrogen /carbon)

7. Hypothesis 2: difference in isotopic signature between sympatric and
allopatric populations (nitrogen)
2 A Differences in mean values between allopatric and sympatric
populations (niche shift)
2 B Lower variance in sympatry (niche narrowing)
Niche shift(2 A)
Niche narrowing (2B)
allopatry sympatry

8. Hypothesis 3: Carbon isotope signature of D.mahan should be higher than
the other two species, reflecting the use of resources from marine origin
C3 plants
-27‰
seagrasses
-10‰
CAM plants
-10 to-28‰
C4 plants
-12‰
macroalgae
-15‰
phytoplankton -22‰
Zooplancton -20‰

9. Materials and methods
The study site
Los Ajaches
Femés
Mña. Blanca
Mña Tinache
B.Co Elv. Sanchez
Catalina Cabr.
La Graciosa
Mña. Clara

10. Sample collection
Locality Habitat DA DN DM Type Total
Bco.Elv.Sanchez
s
Mount. 13 (5♂,5♀,3j)
3J)
Allopatry 13
Catalina Cabrera Beach 7(j) Allopatry 7
Femés Mount. 1 (♂) 14 (3♂,4♀,7j) Sympatry 15
La Graciosa Mount. 10 (1♂,4♀,5j) Allopatry 10
Los Ajaches Mount. 4 (1♂,3j) Allopatry 4
Montaña Blanca Mount. 10 (2♂,5♀,3j) 10 (4♂,4♀,2j) Sympatry 20
Montaña Clara Mount. 9 (3♂,5♀,1j) 10 (2♂,5♀,3j) Sympatry 19
Mont. Tinache Mount. 20 (1♂,5♀,14j) 13 (5♂,5♀,3j) Sympatry 33
Total 54 60 7 121
Originally done for other studies (2002-2005)

11. Isotopic analysis
• Measured (prosoma width)
• prosoma and legs for all individuals
• Dried 60 °C
• Homogenized
• Stable isotope analysis with mass spectrometer at Serveis Científico-tècnics
de la UB
• δ15N and δ 13C
Statistical analysis
• General lineal models (ANOVA and t-student test)
• Levene test (variance)

12. Results
NAIVE APPROACH
We had results for our hypothesis, but there were biases:
1)Differences in isotopic baseline of localities
2)Sample size too small
3)Heterogeneity of the sample
δ15N
Da Dn Da Dn Da Dn Da Dn Da Dn Da Dn Da Dn Da Dn Da Dn

13. Factors F-stat p-value
Model 1
SEX 1.76 0.2746
LOC 33.33 0.0084
SEX * LOC 1.85 0.1633
Model 2
SEX 2.74 0.1094
LOC 61.38 <0.0001
PROSOMA WIDTH 0.63 0.4352
Model 3
SEX 2.68 0.1134
LOC 60.79 <0.0001
C:N RATIO 0.29 0.5938
Selected Model
SEX 2.46 0.1280
LOC 64.62 <0.0001
95% CI estimated differences
male-female -0.29 - 2.18
Femés-Tinache 2.47 - 5.76
Mña. Blanca-Tinache 0.30 - 3.59
Mña. Clara-Tinache 9.63 - 13.10
(adults from 4 sympatric
localities, n=33)
MODELLING APPROACH: account for parameters
related to isotopic values
δ15N in D.nesiotes

14. PARAMETERS RELATED TO δ 13C in D.nesiotes
Factors F-stat p-value
Model 1
SEX 6.69 0.0761
LOC 3.84 0.1490
SEX * LOC 0.84 0.4853
Model 2
SEX 5.34 0.0287
LOC 3.62 0.0256
PROSOMA WIDTH 0.00 0.9496
Model 3
SEX 2.13 0.1562
LOC 3.92 0.0190
C:N RATIO 4.86 0.0362
Selected Model
LOC 3.38 0.0319
CNRATIO 8.76 0.0062
95% CI estimated differences
Femés-Tinache -0.42 - 1.14
Mña. Blanca-Tinache 0.02 - 1.58
Mña. Clara-Tinache 0.36 - 1.99
1 unit on C:N ratio -4.31 - -0.78

15. PARAMETERS RELATED TO δ15N and δ 13C in D.alegranzaensis
δ15N F-stat p-value
Model 1
LOC 51.38 <0.0001
PROSOMA WIDTH 4.59 0.0553
Model 2
LOC 39.29 <0.0001
CNRATIO 1.30 0.2783
Selected Model
LOC 41.45 <0.0001
95% CI estimated differences
Mña. Blanca-Tinache 0.91 - 6.62
Mña. Clara-Tinache 8.83 - 14.54
δ13C F-stat p-value
Model 1
LOC 9.69 0.0037
PROSOMA WITDTH 0.00 0.9498
Model 2
LOC 10.52 0.0028
CNRATIO 0.00 0.9850
Selected Model
LOC 13.91 0.0007
95% CI estimated differences
Mña. Blanca-Tinache -0.22 - 2.21
Mña. Clara-Tinache 1.68 - 4.10
Only females from 3 sympatric localities (n=15)

16. HYPOTHESIS 1 : differences in isotopic mean values
between Da and Dn
Adults from 3 sympatric localities
Estimated mean values of δ15N according to species, locality and sex.
For Nitrogen

17. Model for Hypothesis 1 (nitrogen)
Selected Model
SP 9.09 0.0044
SEX 9.01 0.0046
LOC 140.81 <0.0001
95% CI estimated differences
D.alegrazaensis-D.nesiotes 0.56 - 2.83
female-male 0.57 - 2.89
Mña. Blanca-Tinache 1.24 - 3.95
Mña. Clara-Tinache 9.52 - 12.24
Shift between
Da and Dn
0.56-2.83 ‰
Trophic segregation from moderate to high

18. HYPOTHESIS 1 : differences mean values between DA
and DN
Range for C: 4 ‰; for N : 15 ‰
Rather similar
carbon
signature
For
Carbon

19. 2a In mean values –not evaluable
2b In variability ( locality adjusted variance)
HYPOTHESIS 2 : differences between sympatric and
allopatric populations
N Locs Condition
Inter-individual
variance
Among localities
variance
D. alegrazaensis
Juv. 21 4 Sympatry 8.02 6.13
5 1 Allopatry 44.21 n.e.
♀ 15 3 Sympatry 4.29 34.72
4 3 Allopatry n.e. 0.28
♂ 8 5 Sympatry 0.30 9.49
1 1 Allopatry n.e. n.e.
Adults (♀+♂) 23 5 Sympatry 4.40 15.69
5 3 Allopatry 0.01 0.30
D. nesiotes
Juv. 14 4 Sympatry 2.25 12.52
3 1 Allopatry 0.02 n.e.
♀ 18 4 Sympatry 3.34 25.41
5 1 Allopatry 0.90 n.e.
♂ 15 4 Sympatry 1.74 22.60
5 1 Allopatry 5.30 n.e.-
Adults (♀+♂) 33 4 Sympatry 3.02 25.20
10 1 Allopatry 2.81 n.e.
tested only
on N

20. HYPOTHESIS 3
Use of resources of marine origin in D.mahan
D.Mahan was higher in
δ 13C by 7-8 ‰
(2 times the difference
among localities)
Tested only on juveniles

21. Conclusions
We found that Da feeds at a higher trophic level than Dn (clear shift in N)
(Hyp 1)
To Compare individuals from different habitats it’s necessasary to calculate
the isotopic baseline of each habitat (Hyp 2°a)
Lower variance in some sub-groups of sympatric populations (Hyp 2b).
Dm has a significative higher value of carbon signature, reflecting the use of
resources of marine origine (Hyp 3)
Remarkabe differences among localities for nitrogen (not for carbon)
Isotopes inform on trophic level or habitat use, but for the species
composition of the diet molecular studies are required

22. • THANK YOU!