Probabilistic patterns of interaction: the effects of link-strength variability on food web structure

Patterns of species interactions affect the dynamics of food webs. An important component of species interactions that is rarely considered with respect to food webs is the strengths of interactions, which may affect both structure and dynamics. In natural systems, these strengths are variable, and can be quantified as probability distributions. We examined how variation in strengths of interactions can be described hierarchically, and how this variation impacts the structure of species interactions in predator-prey networks, both of which are important components of ecological food webs. The stable isotope ratios of predator and prey species may be particularly useful for quantifying this variability, and we show how these data can be used to build probabilistic predator-prey networks. Moreover, the distribution of variation in strengths among interactions can be estimated from a limited number of observations. This distribution informs network structure, especially the key role of dietary specialization, which may be useful for predicting structural properties in systems that are difficult to observe. Finally, using three mammalian predator-prey networks ( two African and one Canadian) quantified from stable isotope data, we show that exclusion of link-strength variability results in biased estimates of nestedness and modularity within food webs, whereas the inclusion of body size constraints only marginally increases the predictive accuracy of the isotope-based network. We find that modularity is the consequence of strong link-strengths in both African systems, while nestedness is not significantly present in any of the three predator-prey networks.

Assessment of trophic transfer of benzo(a)pyrene genotoxicity from the post-larval pink shrimp F. brasiliensis to the juvenile Florida pompano T. carolinus

In the present study, the polycyclic aromatic hydrocarbon (PAH) genotoxicity was investigated in a one-step predator-prey relationship with the trophic-related marine species. Florida pompanos were fed for 5 and 10 days with pink shrimp post larvae previously exposed to benzo(a)pyrene (BaP) concentrations. Parent BaP body burden was measured in samples of Farfantepenaeus brasiliensis. BaP metabolites were determined in bile samples of Trachinotus carolinus and DNA damage was assessed through the comet and erythrocyte nuclear abnormalities (ENAs) assays in fish erythrocytes. BaP body burden increased significantly with the PAH concentration in pink shrimp PLs as well as the fish bile BaP metabolites. Both, comet and ENAs assays indicated significant increase on erythrocyte DNA damage of Florida pompanos fed with BaP-exposed pink shrimp on both feeding periods. The trophic route of BaP genotoxicity is discussed as well as the PAH biotransformation as the inducing mechanism for the DNA damages observed.

The occurrence of defensive alkaloids in non-integumentary tissues of the Brazilian red-belly toad Melanophryniscus simplex (Bufonidae)

The red-belly toads (Melanophryniscus) of southern South America secrete defensive alkaloids from dermal granular glands. To date, all information on Melanophryniscus alkaloids has been obtained by extraction from either skins or whole organisms; however, in other amphibians, tetrodotoxins, samandarines, and bufadienolides have been detected in both skin and other organs, which raise the possibility that lipophilic alkaloids may occur in non-integumentary tissues in Melanophryniscus as well. To test this hypothesis, we studied the distribution of alkaloids in the skin, skeletal muscle, liver, and mature oocytes of the red-belly toad M. simplex from three localities in southern Brazil. Gas chromatography and mass spectrometry of skin extracts from 11 individuals of M. simplex resulted in the detection of 47 alkaloids (including isomers), 9 unclassified and 38 from 12 known structural classes. Each alkaloid that was present in the skin of an individual was also present in the same relative proportion in that individual's skeletal muscle, liver, and oocytes. The most abundant and widely distributed alkaloids were the pumiliotoxins 251D, 267C, and 323A, 5,8-disubstituted indolizidines 207A and 223D, 5,6,8-trisubstituted indolizidine 231B, 3,5-disubstituted pyrrolizidines cis-223B and cis- and trans-251K, and izidine 211C. We report the first record of piperidines in Melanophryniscus, bringing the total number of alkaloid classes detected in this genus to 16. Alkaloid composition differed significantly among the three study sites. The functional significance of defensive chemicals in non-integumentary tissues is unknown.

Behavioral analysis of the interaction between the spitting spider Scytodes globula (Araneae: Scytodidae) and the harvestman Discocyrtus invalidus (Opiliones: Gonyleptidae)

Spitting spiders (Scytodidae) have a distinct predatory strategy in which they eject a sticky secretion from their cheliceral fangs to immobilize prey. This behavior could potentially allow the spider not only to avoid defensive secretions but also to bite specific vulnerable spots of a potential prey such as a harvestman. We used an ethogram, a fluxogram and an experiment to analyze the interaction between the harvestman Discocyrtus invalidus Piza 1938 (Arachnida: Opiliones) and the syntopic spider Scytodes globula (Nicolet 1849) (Arachnida: Araneae). These spiders, while readily taking crickets as prey, seldom spat at and never bit the harvestmen, which apparently did not exude repugnatorial secretions. We therefore tested, by clogging the glands and using appropriate controls, whether non-visible amounts of secretions could cause the rejection, but the harvestmen were still refused. This is the first detailed and quantified description of an interaction between a spitting spider and a harvestman. The general conclusions are that S. globula avoids preying on D. invalidus, S. globula behaves differently when attacking harvestmen and crickets and the scent gland secretions of D. invalidus do not play a direct role in this predator-prey interaction.

Bifurcation effects on the plasma edge of tokamaks with ergodic limiter.

In the present paper, we solve a twist symplectic map for the action of an ergodic magnetic limiter in a large aspect-ratio tokamak. In this model, we study the bifurcation scenarios that occur in the remnants regular islands that co-exist with chaotic magnetic surfaces. The onset of atypical local bifurcations created by secondary shearless tori are identified through numerical profiles of internal rotation number and we observe that their rupture can reduce the usual magnetic field line escape at the tokamak plasma edge.

The role of chemotactile cues in interspecific interactions among Central-European arthropod communities

In einem Ökosystem beeinflussen sich Tiere gegenseitig in erster Linie durch direkte Interaktionen. Ihr Verhalten kann aber auch indirekt durch chemotaktile Stoffe die andere Tiere in der Umwelt hinterlassen beeinflusst werden. Vergleichbar zu direkten Interaktionen können indirekt ausgelöste Verhaltensänderungen einen starken Einfluss auf Populationsdynamiken und Gemeinschaftsstrukturen eines Ökosystems haben. Obwohl das daran gehegte Interesse der Ökologen in den letzten Jahrzenten stark gestiegen ist, fehlen immer noch Studien, welche über mehrere Arten hinweg versuchen die übergreifende Relevanz von chemotaktilen Stoffen herauszufinden. Im Rahmen meiner Doktorarbeit untersuchte ich daher wie sich mehrere mitteleuropäische Arthropodenarten, abhängig von deren interspezifischen Räuber-Beute- und Konkurrenzbeziehungen, mittels chemotaktiler Stoffe beeinflussen können. Mithilfe unterschiedlicher Verhaltensversuche konnte ich empirisch nachweisen, dass verschiedene Arthropoden chemotaktile Stoffe zu ihrem eigenen Vorteil nutzen können. Außerdem zeigen meine Ergebnisse, dass die Verhaltensänderungen artspezifisch und abhängig von den jeweiligen Lebenszyklen und den damit verbundenen Eigenschaften (z.B. Körpergröße, Häufigkeit oder Rangordnung) der beteiligten Arten sind. Ich vermute daher, dass Arthropoden chemotaktile Stoffe ihrer Gegenspieler wahrnehmen und interpretieren können. Eine Verhaltensänderung scheint jedoch nur dann statt zu finden wenn ein Nichtreagieren starke Fitnesskosten mit sich führen würde. Zusammenfassend zeigen die Ergebnisse meiner Doktorarbeit, wie wichtig es ist, die Bedeutung von chemotaktilen Stoffen innerhalb vieler Arten einer Gemeinschaft zu testen, um die den Verhaltensänderungen zugrundeliegenden Ursachen identifizieren zu können. Dies wiederum stellt die Grundlage, um die ökologische Relevanz von chemotaktilen Stoffen und deren mögliche Effekte auf Ökosystemfunktionen besser zu verstehen.

Herbivore identity mediates the strength of trophic cascades on individual plants

The strength of top-down indirect effects of carnivores on plants (trophic cascades) varies greatly and may depend on the identity of the intermediate (herbivore) species. If the effect strength is linked to functional traits of the herbivores then this would allow for more general predictions. Due to the generally sub-lethal effects of herbivory in terrestrial systems, trophic cascades manifest themselves in the first instance in the fitness of individual plants, affecting both their numerical and genetic contributions to the population. We directly compare the indirect predator effects on growth and reproductive output of individual Vicia faba plants mediated by the presence of two aphid species: Acyrtosiphon pisum is characterised by a boom and bust strategy whereby colonies grow fast and overexploit their host plant individual while Megoura viciae appear to follow a more prudent strategy that avoids over-exploitation and death of the host plant.Plants in the field were infested with A. pisum, M. viciae or both and half the plants were protected from predators. Exposure to predators had a strong impact on the biomass of individual plants and the strength of this effect differed significantly between the different herbivore treatments.A. pisum had a greater direct impact on plants and this was coupled with a significantly stronger indirect predator effect on plant biomass.Although the direct impact of predators was strongest on M. viciae, this was not transmitted to the plant level, indicating that the predator-prey interactions strength is not as important as the plant-herbivore link for the magnitude of the indirect predator impact. At the individual plant level, the indirect predator effect was purely due to consumptive effects on herbivore densities with no evidence for increased herbivore dispersal in response to presence of predators. The nature of plant-herbivore interactions is the key to terrestrial trophic cascade strength. The two herbivores that we compared were similar in feeding mode and body size but differed their way how they exploit host plants, which was the important trait explaining the strength of the trophic cascade.

Plasma DNA is Elevated in Patients with Deep Vein Thrombosis

OBJECTIVE To investigate if plasma DNA is elevated in patients with deep vein thrombosis (DVT) and to determine whether there is a correlation with other biomarkers of DVT. BACKGROUND Leukocytes release DNA to form extracellular traps (ETs), which have recently been linked to experimental DVT. In baboons and mice, extracellular DNA co-localized with von Willebrand factor (VWF) in the thrombus and DNA appeared in circulation at the time of thrombus formation. ETs have not been associated with clinical DVT. SETTING From December 2008 to August 2010, patients were screened through the University of Michigan Diagnostic Vascular Unit and were divided into three distinct groups: 1) the DVT positive group, consisting of patients who were symptomatic for DVT, which was confirmed by compression duplex ultrasound (n=47); 2) the DVT negative group, consisting of patients that present with swelling and leg pain but had a negative compression duplex ultrasound, (n=28); and 3) a control group of healthy non-pregnant volunteers without signs or symptoms of active or previous DVT (n=19). Patients were excluded if they were less than 18 years of age, unwillingness to consent, pregnant, on an anticoagulant therapy, or diagnosed with isolated calf vein thrombosis. METHODS Blood was collected for circulating DNA, CRP, D-dimer, VWF activity, myeloperoxidase (MPO), ADAMTS13 and VWF. The Wells score for a patient's risk of DVT was assessed. The Receiver Operating Characteristic (ROC) curve was generated to determine the strength of the relationship between circulating DNA levels and the presence of DVT. A Spearman correlation was performed to determine the relationship between the DNA levels and the biomarkers and the Wells score. Additionally the ratio of ADAMTS13/VWF was assessed. RESULTS Our results showed that circulating DNA (a surrogate marker for NETs) was significantly elevated in DVT patients, compared to both DVT negative patients (57.7±6.3 vs. 17.9±3.5ng/mL, P<.01) and controls (57.7±6.3 vs. 23.9±2.1ng/mL, P<.01). There was a strong positive correlation with CRP (P<.01), D-dimer (P<.01), VWF (P<.01), Wells score (P<.01) and myeloperoxidase (MPO) (P<.01), along with a strong negative correlation with ADAMTS13 (P<.01) and the ADAMTS13/VWF ratio. The logistic regression model showed a strong association between plasma DNA and the presence of DVT (ROC curve was determined to be 0.814). CONCLUSIONS Plasma DNA is elevated in patients with deep vein thrombosis and correlates with biomarkers of DVT. A strong correlation between circulating DNA and MPO suggests that neutrophils may be a source of plasma DNA in patients with DVT.

Proceedings of the Seventeenth Annual Biochemical Engineering Symposium

This is the seventeenth of a series of symposia devoted to talks by students about their biochemical engineering research. The first, third, fifth, ninth, twelfth, and sixteenth were at Kansas State University, the second and fourth were at the University of Nebraska-Lincoln, the sixth was in Kansas City and was hosted by Iowa State University, the seventh, tenth, thirteenth, and seventeenth were at Iowa State University, the eighth and fourteenth were at the University of Missouri–Columbia, and the eleventh and fifteenth were at Colorado State University. Next year's symposium will be at the University of Colorado. Symposium proceedings are edited by faculty of the host institution. Because final publication usually takes place elsewhere, papers here are brief, and often cover work in progress. ContentsThe Effect of Polymer Dosage Conditions on the Properties of ProteinPolyelectrolyte Precipitates, K. H. Clark and C. E. Glatz, Iowa State University An Immobilized Enzyme Reactor/Separator for the Hydrolysis of Casein by Subtilisin Carlsberg, A. J. Bream, R. A. Yoshisato, and G. R. Carmichael, University of Iowa Cell Density Measurements in Hollow Fiber Bioreactors, Thomas Blute, Colorado State University The Hydrodynamics in an Air-Lift Reactor, Peter Sohn, George Y. Preckshot, and Rakesh K. Bajpai, University of Missouri–Columbia Local Liquid Velocity Measurements in a Split Cylinder Airlift Column, G. Travis Jones, Kansas State University Fluidized Bed Solid Substrate Trichoderma reesei Fermentation, S. Adisasmito, H. N. Karim, and R. P. Tengerdy, Colorado State University The Effect of 2,4-D Concentration on the Growth of Streptanthus tortuosis Cells in Shake Flask and Air-Lift Permenter Culture, I. C. Kong, R. D. Sjolund, and R. A. Yoshisato, University of Iowa Protein Engineering of Aspergillus niger Glucoamylase, Michael R. Sierks, Iowa State University Structured Kinetic Modeling of Hybidoma Growth and Monoclonal Antibody Production in Suspension Cultures, Brian C. Batt and Dhinakar S. Kampala, University of Colorado Modelling and Control of a Zymomonas mobilis Fermentation, John F. Kramer, M. N. Karim, and J. Linden, Colorado State University Modeling of Brettanomyces clausenii Fermentation on Mixtures of Glucose and Cellobiose, Max T. Bynum and Dhinakar S. Kampala, University of Colorado, Karel Grohmann and Charles E. Yyman, Solar Energy Research Institute Master Equation Modeling and Monte Carlo Simulation of Predator-Prey Interactions, R. 0. Fox, Y. Y. Huang, and L. T. Fan, Kansas State University Kinetics and Equilibria of Condensation Reactions Between Two Different Monosaccharides Catalyzed by Aspergillus niger Glucoamylase, Sabine Pestlin, Iowa State University Biodegradation of Metalworking Fluids, S. M. Lee, Ayush Gupta, L. E. Erickson, and L. T. Fan, Kansas State University Redox Potential, Toxicity and Oscillations in Solvent Fermentations, Kim Joong, Rakesh Bajpai, and Eugene L. Iannotti, University of Missouri–Columbia Using Structured Kinetic Models for Analyzing Instability in Recombinant Bacterial Cultures, William E. Bentley and Dhinakar S. Kompala, University of Colorado

Isotopic geochemistry of granitoids in the Jinshajiang suture zone, SW China

The Jinshajiang suture zone, located in the eastern part of the Tethyan tectonic domain, is noticeable for a large-scale distribution of Late Jurassic to Triassic granitoids. These granitoids were genetically related to the evolution of the Paleo-Tethys Ocean. The Beiwu, Linong and Lunong granitoids occur in the middle zone of the Jinshajiang Suture Zone, and possess similar geochemical features, indicating they share a common magma source. SIMS zircon U-Pb dating reveals the Beiwu, Linong and Lunong granitic intrusions were emplaced at 233.9±1.4 Ma (2 sigma), 233.1 ±1.4 Ma (2 sigma) and 231.0±1.6 Ma (2 sigma), respectively. All of these granitoids are enriched in abundances of Si (SiO2 =65.2-73.5 wt.%), and large-ion-lithophile-elements (LILEs), but depleted in high-field-strength-elements contents (HFSEs, e.g., Nb, Ta, Ti). In addition, they have low P2O5 contents (0.06-0.11 wt.%), A/CNK values ([molecular Al2O3/(CaO+Na2O+K2O)], mostly<1.1) and 10000Ga/Al ratios (1.7-2.2), consistent with the characteristics of I-type granites. In terms of isotopic compositions, these granitoids have high initial 87Sr/86Sr ratios (0.7078-0.7148), Pb isotopic compositions [(206Pb/204Pb)t=18.213-18.598, (207Pb/204Pb)t=15.637-15.730 and (208Pb/204Pb)t=38.323-38.791], zircon d18O values (7. per mil-9.3 per mil) and negative eNd(t) values (-5.1 to -6.7), suggesting they were predominantly derived from the continental crust. Their Nb/Ta ratios (average value=8.6) are consistent with those of the lower continental crust (LCC). However, variable ?Hf(t) values (-8.6 to +2.8) and the occurrences of mafic microgranular enclaves (MMEs) suggest that mantle-derived melts and lower crustal magmas were involved in the generation of these granitoids. Moreover, the high Pb isotopic ratios and elevated zircon d18O values of these rocks indicate a significant contribution of the upper crustal composition. We propose a model in which the Beiwu, Linong and Lunong granitoids were generated under a late collisional or post-collisional setting. It is possible that this collision was completed before Late Triassic. Decompression induced mantle-derived magmas underplated and provided the heat for the anatexis of the crust. Hybrid melts including mantle-derived and the lower crustal magmas were then generated. The hybrid melts thereafter ascended to a shallow depth and resulted in some degree of sedimentary rocks assimilation. Such three-component mixing magmas source and subsequent fractional crystallization could be responsible for the formation of the Beiwu, Linong and Lunong granitoids.

Gas hydrates at DSDP Leg 84

On DSDP Leg 84, gas hydrates were found at three sites (565, 568, and 570) and were inferred, on the basis of inorganic and organic geochemical evidence, to be present at two sites (566 and 569); no evidence for gas hydrates was observed at Site 567. Recovered gas hydrates appeared as solid pieces of white, icelike material occupying fractures in mudstone or as coarse-grained sediment in which the pore space exhibited rapid outgassing. Also a 1.05-m-long core of massive gas hydrate was obtained at Site 570. Downhole logging indicated that this hydrate was actually 3 to 4 m thick. Measurements of the amount of methane released during the decomposition of these recovered samples clearly showed that gas hydrates had been found. The distribution of evolved hydrocarbon gases indicated that Structure I gas hydrates were present because of the apparent inclusion of methane and ethane and exclusion of propane and higher molecular weight gases. The water composing the gas hydrates was fresh, having chlorinities ranging from 0.5 to 3.2 per mil. At Sites 565, 568, and 570, where gas hydrates were observed, the chlorinity of pore water squeezed from the sediment decreased with sediment depth. The chlorinity profiles may indicate that gas hydrates can often occur finely dispersed in sediments but that these gas hydrates are not recovered because they do not survive the drilling and recovery process. Methane in the gas hydrates found on Leg 84 was mainly derived in situ by biogenic processes, whereas the accompanying small amounts of ethane likely resulted from low-temperature diagenetic processes. Finding gas hydrates on Leg 84 expands observations made earlier on Leg 66 and particularly Leg 67. The results of all of these legs show that gas hydrates are common in landward slope sediments of the Middle American Trench from Mexico to Costa Rica.

Whale sightings, group sizes and krill biomass in West Greenland in 2005

This study combined data on fin whale Balaenoptera physalus, humpback whale Megaptera novaeangliae, minke whale B. acutorostrata, and sei whale B. borealis sightings from large-scale visual aerial and ship-based surveys (248 and 157 sightings, respectively) with synoptic acoustic sampling of krill Meganyctiphanes norvegica and Thysanoessa sp. abundance in September 2005 in West Greenland to examine the relationships between whales and their prey. Krill densities were obtained by converting relationships of volume backscattering strengths at multiple frequencies to a numerical density using an estimate of krill target strength. Krill data were vertically integrated in 25 m depth bins between 0 and 300 m to obtain water column biomass (g/m**2) and translated to density surfaces using ordinary kriging. Standard regression models (Generalized Additive Modeling, GAM, and Generalized Linear Modeling, GLM) were developed to identify important explanatory variables relating the presence, absence, and density of large whales to the physical and biological environment and different survey platforms. Large baleen whales were concentrated in 3 focal areas: (1) the northern edge of Lille Hellefiske bank between 65 and 67°N, (2) north of Paamiut at 63°N, and (3) in South Greenland between 60 and 61° N. There was a bimodal pattern of mean krill density between depths, with one peak between 50 and 75 m (mean 0.75 g/m**2, SD 2.74) and another between 225 and 275 m (mean 1.2 to 1.3 g/m**2, SD 23 to 19). Water column krill biomass was 3 times higher in South Greenland than at any other site along the coast. Total depth-integrated krill biomass was 1.3 x 10**9 (CV 0.11). Models indicated the most important parameter in predicting large baleen whale presence was integrated krill abundance, although this relationship was only significant for sightings obtained on the ship survey. This suggests that a high degree of spatio-temporal synchrony in observations is necessary for quantifying predator-prey relationships. Krill biomass was most predictive of whale presence at depths >150 m, suggesting a threshold depth below which it is energetically optimal for baleen whales to forage on krill in West Greenland.

Amount and patterns of beluga sightings in the eastern Beaufort Sea

An understanding of the adaptability of belugas (Delphinapterus leucas) to changing ice conditions is required to interpret and predict possible changes in habitat selection in response to projected loss of sea ice throughout the circumpolar Arctic. We analyzed beluga observations made during spring aerial surveys for ringed seals conducted from 1975 to 1979 in the eastern Beaufort Sea. Despite interannual variability in the extent and distribution of sea ice, belugas consistently selected areas with water depths of 200-500 m and heavy ice concentrations (8/10 to 10/10) while areas of open water to light ice concentrations (0/10 to 1/10) were not selected. Belugas were also found in proximity to regions with >0.5 degrees seafloor slope which include the continental slope and other areas with the potential for oceanographic upwellings. In most years (4 of 5), fast-ice edges and coastal areas were not selected. In the lightest ice year analyzed, belugas showed less specificity in habitat selection as their distribution expanded and shifted shoreward to fast-ice edges. The observed distribution is discussed in terms of predator-prey relationships particularly with reference to beluga feeding on polar cod (Boreogadus saida). More research is required to examine and compare possible changes in distribution since the late 1970s and to investigate the factors driving the patterns described.