Impacts on excretion of simulated tradeoffs between predator biomasses.

<p>Estimated total recycled N (NH₄) and P (SRP) excretion (g·day⁻¹) in Fox Cr. due to simulated changes in the relative abundance (by biomass) of <i>O. mykiss</i> and <i>D. tenebrosus</i>. Simulations assumed a fixed total biomass of predators (6275 g) within the study reach, and estimated total excretion rates (left y-axis) and ratios (right y-axis) by bootstrapped re-sampling of surveyed individuals. Predator relative abundance (x-axis) varies by 10% increments from 100% <i>O. mykiss</i> composition to 100% <i>D. tenebrosus</i> composition, expressed as the proportion of predator biomass (salamander:fish). Vertical line indicates the observed ratio of predators in Fox Cr.</p

Density and biomass (abundance survey) and average wet weight elemental composition of diets (diet survey) for <i>O. mykiss</i> and <i>D. tenebrosus</i> in Fox Creek, California.

<p>Values calculated using total area of the study reach.</p

Excretion rates of <i>D. tenebrosus</i>.

<p>Nitrogen (NH₄) and phosphorus (SRP) nutrient excretion rates (ug·min⁻¹) of <i>D. tenebrosus</i>. Lines represent the fit of the top model selected by AICc for P (<i>log₁₀</i>[µg_P·min⁻¹] = −3.12+1.60(<i>log</i>₁₀[mass]), r² = 0.31, P = 0.01), and N excretion rates (<i>log₁₀</i>[µg_N·min⁻¹] = −2.04+1.41(<i>log</i>₁₀[mass]), r² = 0.79, P<<0.001).</p

Histograms of size and mass of predators in our study reach.

<p>Size- and mass-frequency distributions for <i>O. mykiss</i> and <i>D. tenebrosus</i> from a 1 km study reach of Fox Creek. Standard length (mm) was used for fish (n = 528) and snout-vent length (mm) for salamanders (n = 348) to exclude the size variability generated by tail injuries. Note differences in y-axis scales.</p

Estimates of excreted N:P ratio for predators in our study reach.

<p>Estimates of the ratio of excreted N:P for <i>O. mykiss</i> (filled), <i>D. tenebrosus</i> (grey), and both predators combined (open). Bars represent mean ±95%CI.</p

Daily excretion estimates for predators in our study reach.

<p>Estimated total daily excreted N (NH₄) and P (SRP) by <i>O. mykiss</i> (filled), <i>D. tenebrosus</i> (grey), and both predators combined (open) within the Fox Cr. study reach. Bars represent mean ±95%CI. Note the log scaled y-axis.</p

Average elemental body composition (by dry mass) of common <i>O. mykiss</i> and <i>D. tenebrosus</i> diet items* by order.

<p>Elemental composition estimates from the literature for orders Lepidoptera and Hymenoptera did not include estimates of variability.</p><p>Footnotes: *Unaccounted for percentage of diet was comprised of diet items not covered by invertebrate CNP survey and for which values could not be found in literature. Contributions by these uncommon items were deemed inconsequential due to their small individual proportion of the wet mass of diets. Large and/or unique diet items (orders comprising <0.5% of total items) were discounted in diets so as not to bias elemental estimates.</p>1<p>Frost PC, Tank SE, Turner MA, Elser JJ (2010) Elemental composition of littoral invertebrates from oligotrophic and eutrophic Canadian lakes. Journal of the North American Benthological Society 22:51–62.</p>2<p>Elser JJ (2003) Biological stoichiometry: a theoretical framework connecting ecosystem ecology, evolution, and biochemistry for application in astrobiology. International Journal of Astrobiology 2:185–193.</p>3<p>Woods HA, Fagan WF, and Elser JJ (2004) Allometric and phylogenetic variation in insect phosphorus content. Functional Ecology 18:103–108.</p>4<p>Elser JJ, Fagan FF, Denno RF, Dobberfuhl DR, Folarin A, Huberty A, Interlandi S, Kilham SS, McCauley E, Schulz KL, Siemann EH, Sterner RW (2000) Nutritional constraints in terrestrial and freshwater food-webs. Nature 408:578–580.</p>5<p>Slansky Jr. F, and Feeny P (1977). Stabilization of the rate of nitrogen accumulation by larvae of the cabbage butterfly on wild and cultivated food plants. Ecological Monographs 47:209–228.</p>6<p>Cross WF, Benstead JP, Rosemond AD, and Wallace JB (2003) Consumer-resource stoichiometry in detritus-based streams. Ecology Letters 6:721–732.</p