Variable δ15N Diet-Tissue Discrimination Factors among Sharks: Implications for Trophic Position, Diet and Food Web Models

The application of stable isotopes to characterize the complexities of a species foraging behavior and trophic relationships is dependent on assumptions of δ(15)N diet-tissue discrimination factors (∆(15)N). As ∆(15)N values have been experimentally shown to vary amongst consumers, tissues and diet composition, resolving appropriate species-specific ∆(15)N values can be complex. Given the logistical and ethical challenges of controlled feeding experiments for determining ∆(15)N values for large and/or endangered species, our objective was to conduct an assessment of a range of reported ∆(15)N values that can hypothetically serve as surrogates for describing the predator-prey relationships of four shark species that feed on prey from different trophic levels (i.e., different mean δ(15)N dietary values). Overall, the most suitable species-specific ∆(15)N values decreased with increasing dietary-δ(15)N values based on stable isotope Bayesian ellipse overlap estimates of shark and the principal prey functional groups contributing to the diet determined from stomach content analyses. Thus, a single ∆(15)N value was not supported for this speciose group of marine predatory fishes. For example, the ∆(15)N value of 3.7‰ provided the highest percent overlap between prey and predator isotope ellipses for the bonnethead shark (mean diet δ(15)N = 9‰) whereas a ∆(15)N value < 2.3‰ provided the highest percent overlap between prey and predator isotope ellipses for the white shark (mean diet δ(15)N = 15‰). These data corroborate the previously reported inverse ∆(15)N-dietary δ(15)N relationship when both isotope ellipses of principal prey functional groups and the broader identified diet of each species were considered supporting the adoption of different ∆(15)N values that reflect the predators' δ(15)N-dietary value. These findings are critical for refining the application of stable isotope modeling approaches as inferences regarding a species' ecological role in their community will be influenced with consequences for conservation and management actions

Are carrion resources as scarce as we think?

As humans, we tend to focus on the greener, living aspects of the environment and often forget the other side filled with death and decay. Carrion, the decaying flesh of dead animals, is a nutrient-rich, spatially patchy ephemeral resource, relied upon as a food by a variety of organisms. As a patchy and finite resource, carrion\u27s availability and distribution are unpredictable. Some factors that can influence the availability and production of carrion include predation, old age, and anthropogenic causes. Feeding on these resources are many scavengers, both facultative and obligate, vertebrate and arthropod. A primary consumer of carrion are blow flies (Diptera: Calliphoridae); often the first organisms to arrive at a decaying carcass. There are at least 11 blow fly species in SW Ontario, all requiring carrion resources for immature larval development yet manage to co-exist on what has been stated to be a rare, patchy ephemeral resource. My thesis will be testing the hypothesis that carrion resources are not as rare as previously considered and may be predicted using land-use attributes. Specifically, I will be using geospatial technology to model land-use attributes in the urban and rural areas of Essex County, Ontario. Some distinct elements of land-use being examined include farm, residential, commercial, and conservation. Following this, sites will be randomly chosen to trap blow flies across the gradient of land-use predicted to influence carrion availability, measuring blow fly species diversity along this gradient. This knowledge furthers our understanding of blow fly co-existence across a spatial and temporal landscape

Spatial Variability and Application of Ratios between BTEX in Two Canadian Cities

Spatial monitoring campaigns of volatile organic compounds were carried out in two similarly sized urban industrial cities, Windsor and Sarnia, ON, Canada. For Windsor, data were obtained for all four seasons at approximately 50 sites in each season (winter, spring, summer, and fall) over a three-year period (2004, 2005, and 2006) for a total of 12 sampling sessions. Sampling in Sarnia took place at 37 monitoring sites in fall 2005. In both cities, passive sampling was done using 3M 3500 organic vapor samplers. This paper characterizes benzene, toluene, ethylbenzene, o, and (m + p)-xylene (BTEX) concentrations and relationships among BTEX species in the two cities during the fall sampling periods. BTEX concentration levels and rank order among the species were similar between the two cities. In Sarnia, the relationships between the BTEX species varied depending on location. Correlation analysis between land use and concentration ratios showed a strong influence from local industries. Use one of the ratios between the BTEX species to diagnose photochemical age may be biased due to point source emissions, for example, 53 tonnes of benzene and 86 tonnes of toluene in Sarnia. However, considering multiple ratios leads to better conclusions regarding photochemical aging. Ratios obtained in the sampling campaigns showed significant deviation from those obtained at central monitoring stations, with less difference in the (m + p)/E ratio but better overall agreement in Windsor than in Sarnia

Possible Ballast Water Transfer of Lionfish to the Eastern Pacific Ocean

The Indo-Pacific Red Lionfish was first reported off the Florida coast in 1985, following which it has spread across much of the SE USA, Gulf of Mexico, and Caribbean Sea. Lionfish negatively impact fish and invertebrate assemblages and abundances, thus further spread is cause for concern. To date, the fish has not been reported on the Pacific coast of North or Central America. Here we examine the possibility of ballast water transfer of lionfish from colonized areas in the Atlantic Ocean to USA ports on the Pacific coast. Over an eight-year period, we documented 27 commercial vessel-trips in which ballast water was loaded in colonized sites and later discharged untreated into Pacific coast ports in the USA. California had the highest number of discharges including San Francisco Bay and Los Angeles-Long Beach. A species distribution model suggests that the probability of lionfish establishment is low for the western USA, Colombia and Panama, low to medium for Costa Rica, Nicaragua, El Salvador and Guatemala, medium to high for mainland Ecuador, and very high for western Mexico, Peru and the Galapagos Islands. Given the species’ intolerance of freshwater conditions, we propose that ballast water exchange be conducted in Gatún Lake, Panama for western-bound vessels carrying ‘risky’ ballast water to prevent invasion of the eastern Pacific Ocean

A Signal Model for Forensic DNA Mixtures

For forensic purposes, short tandem repeat allele signals are used as DNA fingerprints. The interpretation of signals measured from samples has traditionally been conducted by applying thresholding. More quantitative approaches have recently been developed, but not for the purposes of identifying an appropriate signal model. By analyzing data from 643 single person samples, we develop such a signal model. Three standard classes of two-parameter distributions, one symmetric (normal) and two right-skewed (gamma and log-normal), were investigated for their ability to adequately describe the data. Our analysis suggests that additive noise is well modeled via the log-normal distribution class and that variability in peak heights is well described by the gamma distribution class. This is a crucial step towards the development of principled techniques for mixed sample signal deconvolution

Variable δ15N Diet-Tissue Discrimination Factors among Sharks: Implications for Trophic Position, Diet and Food Web Models

The application of stable isotopes to characterize the complexities of a species foraging behavior and trophic relationships is dependent on assumptions of δ15N diet-tissue discrimination factors (∆15N). As ∆15N values have been experimentally shown to vary amongst consumers, tissues and diet composition, resolving appropriate speciesspecific ∆15N values can be complex. Given the logistical and ethical challenges of controlled feeding experiments for determining ∆ 15N values for large and/or endangered species, our objective was to conduct an assessment of a range of reported ∆ 15N values that can hypothetically serve as surrogates for describing the predator-prey relationships of four shark species that feed on prey from different trophic levels (i.e., different mean δ 15N dietary values). Overall, the most suitable species-specific ∆ 15N values decreased with increasing dietary-δ 15N values based on stable isotope Bayesian ellipse overlap estimates of shark and the principal prey functional groups contributing to the diet determined from stomach content analyses. Thus, a single ∆ 15N value was not supported for this speciose group of marine predatory fishes. For example, the ∆ 15N value of 3.7‰ provided the highest percent overlap between prey and predator isotope ellipses for the bonnethead shark (mean diet δ 15N = 9‰) whereas a ∆ 15N value \u3c 2.3‰ provided the highest percent overlap between prey and predator isotope ellipses for the white shark (mean diet δ 15N = 15‰). These data corroborate the previously reported inverse ∆ 15N-dietary δ 15N relationship when both isotope ellipses of principal prey functional groups and the broader identified diet of each species were considered supporting the adoption of different ∆ 15N values that reflect the predators’ δ 15N-dietary value. These findings are critical for refining the application of stable isotope modeling approaches as inferences regarding a species’ ecological role in their community will be influenced with consequences for conservation and management actions

A hierarchical porous microstructure for improving long-term stability of Ni1-xCux/SDC anode-supported IT-SOFCs fueled with dry methane

A series of Ni1-xCux/Sm-doped ceria (Ni1-xCux/SDC) anodes have been prepared through introducing a soluble pore former with the co-pressing and co-sintering process. Uniform hierarchical porous microstructures are formed in Ni0.9Cu0.1/SDC anode with interconnected large pores of 2–5 μm and 100–300 nm small pores on the wall. The solid oxide fuel cell (SOFC) based on such anode exhibits exceptional electrochemical catalytic activity for dry CH4 oxidation and a maximum power density of 379 mW cm−2 is acquired at 600 °C. Durability test results show only 2.4% power density drop is observed after 72 h operation under a constant cell voltage of 0.5 V. The results have demonstrated that the optimization of anode microstructures is an effective way to improve the performance and long-term stability of Ni1-xCux alloy-based anode-supported SOFC

Anodes for solid oxide fuel cell (SOFC) systems operating in multiple fuel environments: Effects of microstructure and composition

This work examined several cermet materials as possible anode materials for solid oxide fuel cell (SOFC) systems operating in multiple fuel environments. In particular, these materials consisted of two phase M-YSZ (M = Ni, Cu or Co, YSZ = yttria stabilized zirconia) cermets synthesized via the gel-precipitation method. Relations between synthesis conditions and cermet structure/performance dominated the first section of this work. SOFC anode performance was correlated back to original synthesis conditions, whereby dM/dYSZ was controlled via the production of a crystalline intermediate. Electrochemical characterization of Ni- and Co-YSZ anodes in H2 and H2S/H2 fuels was performed and each arc observed in the impedance curves was ascribed to a specific process. The high- and mid-frequency arcs were related to transport and charge transfer processes respectively. Non-traditional relationships between inverse Tafel (Lefat) slopes and temperature were observed. This resulted in a change in charge transfer coefficients with respect to temperature. By evaluating this dependence, a charge transfer coefficient of 1.5 for hydrogen oxidation on Ni-, Co- and NiS-anodes was determined. CoS-anodes resulted in a charge transfer coefficient of 0.2. NiS- and CoS-anodes were stable in sour gas environments and selective towards the electrochemical oxidation of H2 over H2S as suggested by open circuit voltage and mass spectrometry. Cell performances of and CoS-anodes in sour gas environments were stable over a 6 day period and showed no signs of deterioration. However, H 2S was required in the fuel stream to maintain optimal performance of these anodes. Once H2S was removed, the CoS-anodes reverted to Co-YSZ. For CoS-based anodes, optimum cell performance was maintained at a H2S content >1v/v%. Investigations of bimetallic NiCu- and NiCo-anodes were also performed. The addition of Cu to Ni-based anodes resulted in larger metal particle sizes and decreased anode activity for hydrogen oxidation. Small additions of Co to Ni-based anodes showed a marked improvement in hydrogen oxidation activity. The bimetallic anodes were also tested in H2S/CH4 mixtures and showed good activity for all anodes tested over a 15 hour period