Ecological Archives E096-183-A3

Jeffrey P. Stephens, Keith A. Berven, Scott D. Tiegs, and Thomas R. Raffel. 2015. Ecological stoichiometry quantitatively predicts responses of tadpoles to a food quality gradient. Ecology 96:20702076. http://dx.doi.org/10.1890/14-2439.1

Appendix C. Supplemental tables and figures presenting: leaf litter composition measurements, model parameters and variables, model optimization results, generalized linear model results, sensitivity analysis, sources of algal C and N values, treatment effects on amphibian traits, and gut contents analysis results.

Table C1. Chemistry of each litter mixture used in the experiment. Mixture C:N was calculated by dividing total C by total N. Molar amounts of C and N were used for modeling purposes.

Mixture

Mixture Chemistry

% Fraxinus

% Acer

 

C

N

C:N

molar C:N

0

100

52.13

0.43

120.12

140.20

25

75

50.61

0.79

64.23

74.97

50

50

49.09

1.14

42.99

50.17

75

25

47.57

1.50

31.80

37.12

100

0

46.05

1.85

24.89

29.05

 

Table C2. Parameters and variables used in the tadpole growth model.

Model Parameter

 

Meaning

Units

Value

Source

QC

Concentration of carbon bound in consumer mass

mmol C ∙ mg-1 tadpole dry mass

3.75 × 10-2a 3.06 × 10-2b

Stephens et al. 2013
Vanni et al. 2002

QN

Concentration of nitrogen bound in consumer mass

mmol N ∙ mg-1 tadpole dry mass

7.99 × 10-3a  4.78 × 10-3b

Stephens et al. 2013
Vanni et al. 2002

SN

Nitrogen Assimilation Efficiency; the percent of nitrogen that passes the gut lumen relative to the amount consumed

Dimensionless fraction from one to zero

1.00

Sterner and Elser 2002

LN

Minimal loss rate of      nitrogen

mmol N lost ∙ mmol N  tadpole-1 ∙ day-1

1.25 × 10-2a 2.19 × x10-2b

Munro 1952

I

 

Food intake rate

mg food ∙ mg-1 tadpole ∙ day-1

0.79a      0.84b

Richardson 2002

Model Variable

 

 

 

 

 

AC

Concentration of carbon bound in food mass

mmol C ∙ mg-1 leaf litter dry mass

Variable

Measured

AN

Concentration of nitrogen bound in food mass

mmol N ∙ mg-1 leaf litter dry mass

Variable

Measured

gC

Specific rate of tadpole growth based on carbon

mmol C ∙ mg-1 tadpole dry mass ∙ day-1

Variable

Measured & calculated

 

 

 

 

 

 

a = Wood frog values, b = American toad values


 

Table C3. Results of model optimization for growth rates of wood frogs in low light, using the “nls” function in Program R. Parameters whose values were obtained from the literature were not included as degrees of freedom in AIC calculations.

Model

I value

LN value

AIC

Literature

0.79

0.0125

-494.48

I optimized

0.78

0.0125

-494.52

LN optimized

0.79

0.0142

-494.68

I and LN optimized

0.85

0.0214

-494.98

 

Table C4. Results of the general linear models conducted on amphibian traits. Type II sums of squares were used for this analysis.

Trait

Predictors

Coef.

 

Statistic

 

    P

Mass

Nitrogen

-69.67

F1,66

=

0.42

0.518

Nitrogen2 a

121.01

F1,66

=

6.88

0.011

Light

5.25

F1,66

=

0.16

0.695

Amphibian

-244.49

F1,66

=

154.83

<0.001

Block

11.53

F1,66

=

3.73

0.058

Nitrogen*Light

8.20

F1,66

=

0.09

0.763

Nitrogen*Amphibian

-28.76

F1,66

=

78.39

<0.001

Light*Amphibian

-28.76

F1,66

=

1.15

0.288

 

Nitrogen*Light*Amphibian

-72.81

 

F1,66

=

1.83

 

0.181

Larval Period

Nitrogen

-11.53

F1,67

=

61.66

<0.001

Light

-8.20

F1,67

=

46.92

<0.001

Amphibian

-18.30

F1,67

=

155.38

<0.001

Block

1.49

F1,67

=

5.67

0.020

Nitrogen*Light

1.46

F1,67

=

0.38

0.540

Nitrogen*Amphibian

14.71

F1,67

=

38.56

<0.001

Light*Amphibian

-4.69

F1,67

=

3.96

0.050

 

Nitrogen*Light*Amphibian

4.51

 

F1,67

=

0.90

 

0.345

Survival

Nitrogen

14.00

F1,67

=

55.23

<0.001

Light

2.99

F1,67

=

2.19

0.144

Amphibian

1.81

F1,67

=

0.74

0.391

Block

0.40

F1,67

=

0.23

0.635

Nitrogen*Light

3.34

F1,67

=

0.87

0.353

Nitrogen*Amphibian

-10.87

F1,67

=

9.23

0.003

Light*Amphibian

16.82

F1,67

=

22.37

<0.001

Nitrogen*Light*Amphibian

-8.03

F1,67

=

1.26

0.266

a Represents the polynomial term used in the general linear models conducted for mass at metamorphosis.


Table C5. Sensitivity analysis of the optimized parameters. We chose to conduct this analysis using an AN and AC of 1.26 × 10-3 and 3.86 × 10-2 respectively yielding a C:N of 30.6. Each parameter was then independently increased or decreased by 20% and the resulting growth rate was then compared to the original.

Parameter

Starting parameter value

Initial gc

% change in gc after ± 20% change in parameter

I

0.79

0.00421

22.23%

LN

0.0125

0.00421

2.23%

AN

1.26x10-3

0.00421

22.23%

 

Table C6. Literature sources of C and N values for periphyton dry mass used in the meta-analysis, indicating the number of values taken from each source.

Source

Journal

 

Number of
values harvested

Bowman et al. 2005

Freshwater Biology

 

9

Rothlisberger et al. 2008

JNABS

4

Stelzer and Lamberti 2002

Ecology

4

Frost et al. 2007

Freshwater Biology

 

16

Drake et al. 2012

Limnology

20

Evans-White and Lamberti 2005

Freshwater Biology

 

3

Evans-White and Lamberti 2006

Ecology Letters

 

12

 

 

 

 

FigC1

Fig. C1. Mixture N and light alter amphibian traits: (a,b) mass at metamorphosis, (c,d) larval period, and (e,f) larval survival. Open and closed circles represent wood frogs and American toads respectively. Each point represents the treatment mean ± 1 SE. Results of general linear models are given in Table C4.


 

 

FigC2

Fig. C2. Results of colon contents analysis. One new metamorph was randomly selected from each of the 100% ash and 100% maple mesocosm at both high and low light. Colons were then dissected and emptied for gut content screening. Contents were spread evenly on a microscope slide. We estimated the proportion of a representative field of view at 400x magnification that contained algae or bacteria/fungi/fine detritus (a). Toad colon contents (b) contained algal and biofilm detritus (green in color) with no signs of leaf fragments. We also recorded whether or not leaf litter fragments (c) were present in the colon contents of each animal (d) Wood frog colons contained coarser detritus composed of leaf vasculature (c), in addition to algae and bacterial detritus.


 

Literature cited

Bowman, M. F., P. A. Chambers, and D. W. Schindler. 2005. Changes in stoichiometric constraints on epilithon and benthic macroinvertebrates in response to slight nutrient enrichment of mountain rivers. Freshwater Biology 50:1836–1852.

Drake, W., J. T. Scott, M. Evans-White, B. Haggard, A. Sharpley, C. W. Rogers, and E. M. Grantz. 2012. The effect of periphyton stoichiometry and light on biological phosphorus immobilization and release in streams. Limnology 13:97–106.

Evans‐White, M. A., and G. A. Lamberti. 2006. Stoichiometry of consumer‐driven nutrient recycling across nutrient regimes in streams. Ecology Letters 9:1186–1197.

Evans-White, M. A., R. S. Stelzer, and G. A. Lamberti. 2005. Taxonomic and regional patterns in benthic macroinvertebrate elemental composition in streams. Freshwater Biology 50:1786–1799.

Frost, P. C., C. T. Cherrier, J. H. Larson, S. Bridgham, and G. A. Lamberti. 2007. Effects of dissolved organic matter and ultraviolet radiation on the accrual, stoichiometry and algal taxonomy of stream periphyton. Freshwater Biology 52:319–330.

Munro, A. F. 1953. The ammonia and urea excretion of different species of Amphibia during their development and metamorphosis. The Biochemical journal 54:29–36.

Richardson, J. M. 2002. A comparative study of phenotypic traits related to resource utilization in anuran communities. Evolutionary Ecology 16:101–122.

Rothlisberger, J. D., M. A. Baker, and P. C. Frost. 2008. Effects of periphyton stoichiometry on mayfly excretion rates and nutrient ratios. Journal of the North American Benthological Society 27:497–508.

Stelzer, R. S., and G. A. Lamberti. 2002. Ecological stoichiometry in running waters: periphyton chemical composition and snail growth. Ecology 83:1039–1051.

Stephens, J. P., K. A. Berven, and S. D. Tiegs. 2013. Anthropogenic changes to litter input affect the fitness of a larval amphibian. Freshwater Biology 58:1631–1646.

Sterner, R. W., and J. J. Elser. 2002. Ecological stoichiometry: the biology of elements from molecules to the biosphere. Princeton University Press, Princeton, New Jersey, USA.

Vanni, M. J. 2002. Nutrient cycling by animals in freshwater ecosystems. Annual Review of Ecology and Systematics :341–370.


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