Quantifying biodiversity trade-offs in the face of widespread renewable and unconventional energy development

The challenge of balancing biodiversity protection with economic growth is epitomized by the development of renewable and unconventional energy, whose adoption is aimed at stemming the impacts of global climate change, yet has outpaced our understanding of biodiversity impacts. We evaluated the potential conflict between biodiversity protection and future electricity generation from renewable (wind farms, run-of-river hydro) and non-renewable (shale gas) sources in British Columbia (BC), Canada using three metrics: greenhouse gas (GHG) emissions, electricity cost, and overlap between future development and conservation priorities for several fish and wildlife groups - small-bodied vertebrates, large mammals, freshwater fish - and undisturbed landscapes. Sharp trade-offs in global versus regional biodiversity conservation exist for all energy technologies, and in BC they are currently smallest for wind energy: low GHG emissions, low-moderate overlap with top conservation priorities, and competitive energy cost. GHG emissions from shale gas are 1000 times higher than those from renewable sources, and run-of-river hydro has high overlap with conservation priorities for small-bodied vertebrates. When all species groups were considered simultaneously, run-of-river hydro had moderate overlap (0.56), while shale gas and onshore wind had low overlap with top conservation priorities (0.23 and 0.24, respectively). The unintended cost of distributed energy sources for regional biodiversity suggest that trade-offs based on more diverse metrics must be incorporated into energy planning.Peer reviewe

Predator-Driven Nutrient Recycling in California Stream Ecosystems

Nutrient recycling by consumers in streams can influence ecosystem nutrient availability and the assemblage and growth of photoautotrophs. Stream fishes can play a large role in nutrient recycling, but contributions by other vertebrates to overall recycling rates remain poorly studied. In tributaries of the Pacific Northwest, coastal giant salamanders (Dicamptodon tenebrosus) occur at high densities alongside steelhead trout (Oncorhynchus mykiss) and are top aquatic predators. We surveyed the density and body size distributions of D. tenebrosus and O. mykiss in a California tributary stream, combined with a field study to determine mass-specific excretion rates of ammonium (N) and total dissolved phosphorus (P) for D. tenebrosus. We estimated O. mykiss excretion rates (N, P) by bioenergetics using field-collected data on the nutrient composition of O. mykiss diets from the same system. Despite lower abundance, D. tenebrosus biomass was 2.5 times higher than O. mykiss. Mass-specific excretion summed over 170 m of stream revealed that O. mykiss recycle 1.7 times more N, and 1.2 times more P than D. tenebrosus, and had a higher N:P ratio (8.7) than that of D. tenebrosus (6.0), or the two species combined (7.5). Through simulated trade-offs in biomass, we estimate that shifts from salamander biomass toward fish biomass have the potential to ease nutrient limitation in forested tributary streams. These results suggest that natural and anthropogenic heterogeneity in the relative abundance of these vertebrates and variation in the uptake rates across river networks can affect broad-scale patterns of nutrient limitation

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

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