Ecological Archives A025-011-A1

Mireia Bartrons, Claudio Gratton, Brian J. Spiesman, and M. Jake Vander Zanden. 2015. Taking the trophic bypass: aquatic-terrestrial linkage reduces methylmercury in a terrestrial food web. Ecological Applications 25:151159. http://dx.doi.org/10.1890/14-0038.1

Appendix A. Path diagrams and models output showing the direct and indirect effects of aquatic reliance (δ13C) and trophic position on MeHg.

FigA1

Fig. A1. Path diagrams showing the direct and indirect effects of aquatic reliance (δ13C) and trophic position on MeHg. Path diagrams for (A) Linyphiidae, (B) Lycosidae, (C) Opiliones, and (D) Acari. Arrow widths are scaled to standardized path coefficients.  Dashed gray lines indicate negative effects. Gray hairlines represent nonsignificant (NS) pathways. *P < 0.05, **P < 0.01, and ***P < 0.0001. R² values are given in the upper right corner of variable boxes where appropriate. Path coefficients and p-values are given in Table A2.


 

Table A1. Trophic position of primary consumers from the four habitat types (Mývatn 200m from shore, Mývatn 5 m from shore, Helluvaðstj’rn 200m from shore, Helluvaðstj’rn 5 m from shore) and from the two lakes (Mývatn and Helluvaðstj’rn):

Herbivore trophic position

Mývatn 5 m from shore

Mývatn 200m from shore

Helluvaðstj’rn 5 m from shore

Helluvaðstj’rn 200m from shore

Tingidae

2.0

2.0

2.1

2.2

 

Mývatn

 

Helluvaðstj’rn

 

Chironomidae

1.9

 

2.3

 

 

Table A2. Absolute and standardized path coefficients for all taxa combined and each family separately.

Taxa

Path

Estimate (absolute)

SE

Estimate (standardized)

P

All combined

(Fig. 3)

δ13C → Trophic position

-0.0100

0.0018

-0.5309

0.0003

δ13C → MeHg

-0.0374

0.0098

-0.3825

0.0007

Trophic position → MeHg

1.9764

0.5210

0.3800

0.0005

 

 

 

 

 

 

Linyphiidae

(Fig. A1A)

δ13C → Trophic position

-0.0132

0.0052

-0.4665

0.0253

δ13C → MeHg

-0.0838

0.0179

-0.7199

0.004

Trophic position → MeHg

0.3048

0.6342

0.0740

0.6287

 

 

 

 

 

 

Lycosidae

(Fig. A1B)

δ13C → Trophic position

-0.0065

0.0024

-0.4926

0.0170

δ13C → MeHg

-0.0521

0.0092

-0.8101

0.0003

Trophic position → MeHg

-0.0845

0.6997

-0.0173

0.9131

 

 

 

 

 

 

Opiliones

(Fig. A1C)

δ13C → Trophic position

-0.0179

0.0028

-0.8730

0.0005

δ13C → MeHg

-0.0609

0.0200

-0.9737

0.0140

Trophic position → MeHg

-0.5255

0.9719

-0.1728

0.6296

 

 

 

 

 

 

Acari

(Fig. A1D)

δ13C → Trophic position

-0.0137

0.0036

-0.6996

0.0045

δ13C → MeHg

-0.0460

0.0167

-0.6458

0.0223

Trophic position → MeHg

0.5619

0.8488

0.1548

0.5230

 

Table A3. AIC-based model selection. The path structure of the saturated model is as depicted in Fig. 1. The path from trophic position to MeHg is removed in the reduced model.

A. Linyphiidae model

K

log-likelihood

AIC

ΔAIC

Reduced

5

-0.115

10.23

0.00

Saturated

6

0.00

12.00

1.77

 

 

 

   

B. Lycosidae model

K

log-likelihood

AIC

ΔAIC

Reduced

5

-0.010

10.02

0.00

Saturated

6

0.00

12.00

1.98

 

 

 

   

C. Opiliones model

K

log-likelihood

AIC

ΔAIC

Reduced

5

-0.145

10.29

0.00

Saturated

6

0.00

12.00

1.71

 

 

 

   

D. Acari model

K

log-likelihood

AIC

ΔAIC

Reduced

5

-0.215

10.43

0.00

Saturated

6

0.00

12.00

1.57


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