bluuebunny/crossref_metadata_2025 huggingface dataset:
Transanal endoscopic microsurgery: The first 50 cases
Authors: Farmer K. Chip , Wale Roger , Winnett Jason , Cunningham Ian , Grossberg Peter , Polglase Adrian
Published: March 2003

Background:  Transanal endoscopic microsurgery is a form of minimally invasive rectal surgery first used at Cabrini Hospital in April 1997. This paper presents a prospective analysis of the first 50 cases with a median follow up of 33 months (range 20−48 months).

Methods:  Prospective data was obtained from all cases between April 1997 and June 2000.

Results:  Forty‐nine patients (30 men and 19 women) underwent 50 procedures. Thirty‐six had benign lesions and 14 malignant. The mean distance of the lower edge of the lesion from the anal verge was 8.7 cm. Three cases were converted to traditional transanal or transabdominal operations. Full‐thickness excision was performed on 26 patients and the rectal wound was closed in 13 cases. The mean duration of transanal endoscopic microsurgery was 67 min (range 20−175), with a mean blood loss of 24 mL (0−300). The mean diameter and area of the fixed specimen was 3.7 cm (1.5−9.8) and 11.4 cm2 (0.8−18.9), respectively. Complications included postoperative fever (3), urinary retention (1) and per rectum bleeding (1). There was one death. The mean length of stay was 4 days. Histology confirmed complete excision in 39 (78%) cases and there have been two instances of local recurrence of adenoma (5%).

Conclusions:  Transanal endoscopic microsurgery is an effective, safe and cost‐beneficial procedure for local excision of selected lesions in the middle and upper thirds of the rectum.
STATISTICAL INVESTIGATION OF THE EFFECT OF LABORATORY AIR ON THE FATIGUE BEHAVIOUR OF A CARBON STEEL
Authors: Goto M
Published: March 2003

In order to clarify the effect of the atmospheric conditions on fatigue damage, rotary bending fatigue tests were carried out on smooth specimens of a normalized 0.37% carbon steel in controlled laboratory air. The air conditions used in the tests were moist air at 20 °C, moist air at 35 °C and dry air at 35 °C. The influence of atmosphere on crack initiation and propagation behaviour was investigated in detail based on successive observations of the surface. Experimental results showed that the fatigue life was superior at 20 °C compared to 35 °C by a factor of 2, while the effect of moisture was small compared to that of temperature. The statistical investigation of crack initiation and propagation behaviour indicated that the temperature strongly affects the crack initiation process; conversely, moisture plays an important role in the propagation process of cracks smaller than 0.3 mm. Moreover, the distribution characteristics of crack initiation life, crack propagation life, fatigue life and crack growth rate were analysed by assuming either a Weibull distribution or a log‐normal distribution.
ENGINEERING ESTIMATION OF THE LOWER BOUND TOUGHNESS IN THE TRANSITION REGIME OF FERRITIC STEELS
Authors: Zerbst  , Heerens  , Pfuff  , Wittkowsky  , Schwalbe
Published: March 2003

A simple engineering method for estimating a lower bound fracture toughness in the ductile‐to‐brittle transition region is presented. It is based on empirical evidence that the lower tail of the failure probability versus fracture toughness curve tends to be a straight line rather than a Weibull curve. Fitting the lower tail by a straight line, however, gives an engineering lower bound at a theoretical failure probability of zero. The method enables one to obtain lower bounds using small data sets of three or four specimens.
CYCLIC FATIGUE CRACK GROWTH AND CLOSURE BEHAVIOUR IN ALUMINA CERAMICS
Authors: Huh  , Song
Published: March 2003

Cyclic fatigue crack growth behaviour in alumina ceramics is investigated and the effect of grain size discussed. Special attention is given to crack closure effects. Cyclic fatigue tests were carried out using four‐point bend specimens, and the load–strain and load–differential strain curves were monitored. These curves show hysteretic behaviour probably related to frictional sliding of bridging grains, and also include non‐linearities due to crack closure. The crack opening load is determined from the load–differential strain curve by using a method introduced in this study. Growth rates can be successfully described by the relationship da/dN = C[ΔKeff /(1 − Kmax /KIC )]m which is proposed in this study to account for the effects of crack closure and the maximum stress intensity factor. Irrespective of grain size, growth rates can be well represented by the above relationship, implying that the grain size exerts an influence on growth rates not only because of crack closure behaviour but also the material fracture toughness. The growth rate curve based on the proposed relationship shows a sigmoidal form for ceramic materials, which is similar to metals.
A FATIGUE LIFE ESTIMATION OF SPECIMENS EXCESSIVELY PRESTRAINED IN TENSION
Authors: Uemura T
Published: March 2003

Fatigue tests were carried out on a shipbuilding‐grade rolled steel, prestrained to various degrees up to 85% of its static tensile fracture strain. It is observed that prestraining degrades the fatigue life in the domain of low‐cycle fatigue, but this effect is not apparent in the medium‐to‐high cycle fatigue regime. A set of equations has been developed to assess the behaviour of tensile prestrained materials for the entire range from low‐to‐high cycle fatigue. The data acquired in this study validate the authenticity of these formulae sufficiently well.
INFLUENCE FUNCTIONS FOR INCLINED EDGE CRACKS
Authors: Rayaprolu DB , Rooke DP
Published: March 2003

A theoretical technique is developed for determining both KI and KII from influence functions for angled edge cracks subjected to arbitrary distributions of normal and tangential contact stresses. Numerical results are presented which indicate the effect of crack length and crack angle on four influence functions, from which KI and KII can be readily determined for specified distributions of tangential or normal contact stresses. In order to illustrate the use of the influence functions, a worked example is presented which shows the variation of KI and KII with crack length and crack angle calculated for an assumed parabolic distribution of tangential stress under a fretting pad. Corresponding values of KI and KII for other distributions of tangential and normal stresses may be determined by the same simple summation techniques used in this report.
Manufacturing and ultimate mechanical performance of carbon fibre‐reinforced epoxy composite suspension push‐rods for a Formula 1 racing car
Authors: Gilchrist M.D. , Curley L.
Published: March 2003

The contemporary Formula 1 racing car makes extensive use of advanced composite materials in its construction. The design, manufacture and ultimate performance under compression of composite suspension push‐rods, that typically could be used in a Grand Prix racing car, are described in this present paper. An aerofoil cross‐section has been used based on different lay‐ups of carbon/epoxy composite. One push‐rod was manufactured using a uniform layup of unidirectional and woven cross‐ply prepreg, whilst a further three push‐rods were manufactured with a tapered layup of unidirectional and woven cross‐ply prepreg. Failure mechanisms including fibre microbuckling, fibre kinking and fibre fracture were observed, whilst comparisons have been made between the experimentally observed failure strains and those that were predicted using simple buckling theory. The ultimate compressive strength of the structural component was significantly less than that of the carbon/epoxy composite.
Fatigue striation formation in an Fe–3%Si alloy—effects of crystallographic orientation and neighbouring grains
Authors: Shimojo  , Uchida  , Turuoka  , Higo
Published: March 2003

In order to know the criterion of fatigue striation formation, fatigue fracture surfaces and crack paths were investigated in Fe–3%Si single and bicrystals having various crystallographic orientations. On single crystals, striations were formed when the loading direction was close to a 〈110〉 direction. In this direction, the crack grew perpendicular to the loading direction. When the loading direction was near a 〈111〉 direction and the crack grew along an inclined plane, no striations were observed. Even in this orientation, when the crack grew perpendicular by necessity using bicrystals, striations were observed. This suggests that striations are not formed on a special crystallographic plane, but are formed when the fatigue crack plane is perpendicular to the loading direction regardless of crystallographic orientation.
Application of focused ion beam (FIB) microscopy to the study of crack profiles
Authors: Wang  , Revie  , Phaneuf  , Li
Published: March 2003

Focused ion beam (FIB) microscopy is used to form an image similar to that formed in a conventional scanning electron microscope (SEM), but with greatly enhanced grain contrast due to the use of a primary ion beam as opposed to a beam of primary electrons as found in the SEM. In addition, by increasing the current of the positively charged gallium ion beam, it can be used as a precision, essentially stress‐free milling machine on a scale of tens of nanometres to several hundred microns. In this paper, the application of FIB microscopy to the study of crack profiles is reported. Samples of a Grade 448 (X‐65) pipeline steel were cyclically loaded in a dilute simulated groundwater solution of near neutral pH. Cracks that initiated on these samples were imaged in plan view and were locally cross‐sectioned using a high‐current focused gallium ion beam at different locations along the cracks. Samples were then tilted in situ to permit imaging of the crack profile, the grain structures around the crack tip and accurate measurement of the crack depth using the same ion beam at lower currents. The transgranular crack path and other microstructural features associated with crack development were clearly illustrated, and crack aspect ratio (depth/length) could be obtained. The capability of the FIB for enhanced imaging of grain structures, combined with its precision‐sectioning capability, make it a novel new tool for the study of cracks.
Effect of particle size on fatigue behaviour in SiC particulate‐reinforced aluminium alloy composites
Authors: Tokaji  , Shiota  , Kobayashi
Published: March 2003

The effect of particle size on rotary bending fatigue behaviour was studied for powder metallurgy 2024 aluminium alloy composites reinforced with 10 wt% silicon carbide particles (SiCp ). Average particle sizes of 5, 20 and 60 μm were evaluated. Particle size had a significant influence on fatigue strength, indicating an increased fatigue strength with decreasing particle size. The composite with 5 μm SiC particles showed higher fatigue strength than the unreinforced alloy. The incorporation of 20 μm SiC particles led to an increase in fatigue strength at a high stress level, but the improvement diminished with decreasing stress level, and a slightly decreased fatigue strength was observed at low stress level, as compared with the unreinforced alloy. The composite with 60 μm SiC particles exhibited a considerable decrease in fatigue strength. Fatigue cracks initiated at several different microstructural features, e.g. surface defects, inclusions and particle–matrix interfaces, and crack initiation was considerably affected by particle size. Fatigue strength was found to depend strongly on the resistance to crack initiation, because there was no discernible difference in small crack growth between the unreinforced alloy and the composites, particularly at a low maximum stress intensity factor.
Probabilities of occurrence and detection of damage in airframe materials
Authors: Harlow D. G. , Wei R. P.
Published: March 2003

The reliability of airworthiness assessment and the effective management of ageing fleets of aircraft depend critically on the quality of tools for predicting damage nucleation and accumulation and its detection, i.e. on the interrelationship between the probabilities of occurrence and detection. To illustrate these interrelationships, a mechanistically based probability approach involving localized pitting corrosion and subsequent fatigue cracking is presented. A probability of detection based on a typical state‐of‐the‐art technique for non‐destructive evaluation is used for comparison and probabilistic assessment. The results suggest that the probability of detection is inadequate, and information on damage size should be included as part of an effective airworthiness assurance methodology. An appropriate target for detecting and sizing damage of ≈ 0.10 mm with a probability of detection and a confidence level of at least 90% is suggested, versus the current capability of 1.27 mm at only 50%
A stochastic damage accumulation model for crack initiation in high‐cycle fatigue
Authors: Ihara  , Tanaka
Published: March 2003

A stochastic damage accumulation model for crack initiation in high‐cycle fatigue is proposed. It is assumed that the fatigue damage is accumulated in the form of dislocations under the repeated stress and that the slip band crack is initiated when the strain energy due to a local pile‐up of dislocations exceeds a critical value. The size of an initiating crack is the cell size, derived from a probabilistic argument and its depth is determined in relation to the stored dislocation energy. Our theoretical results are compared with the experimental data from a low‐carbon steel S20C in order to examine the consistency of our model.
The effect of overload on the fatigue crack growth behaviour of 304 stainless steel in hydrogen
Authors: Kelestemur M. H. , Chaki T. K.
Published: March 2003

Fatigue crack growth (FCG) behaviour and its characteristics following tensile overloads were investigated for AISI 304 stainless steel in three different atmospheres; namely dry argon, moist air and hydrogen. The FCG tests were performed by MTS 810 servohydraulic machine. CT specimens were used for the tests and crack closure measurements were made using an extensometer. FCG rates of 304 stainless steel at both dry argon and moist air atmospheres have shown almost the same behaviour. In other words, the effect of moisture on FCG of this material is very small. However, in a hydrogen atmosphere, the material showed considerably higher crack growth rate in all regimes. In general, for all environments, the initial effect of overloads was to accelerate the FCG rate for a short distance (less than a mm) after which retardation occurred for a considerable amount of time. The main causes for retardation were found as crack blunting and a long reinitiation period for the fatigue crack. Regarding the environmental effect, the overload retardation was lowest in a hydrogen atmosphere. This low degree of retardation was explained by a hydrogen embrittlement mechanism. In a general sense, hydrogen may cause a different crack closure mechanism and hydrogen induced crack closure has come in to the picture. Scanning electron microscope and light microscope examinations agreed well with the above results.
Fatigue crack growth of a welded tube–flange connection under bending and torsional loading
Authors: Amstutz H. , Störzel K. , Seeger T.
Published: March 2003

In this contribution the results of an experimental investigation into the fatigue crack growth of welded tube‐to‐plate specimens of steel StE 460 under bending, torsion, and combined in‐phase and out‐of‐phase bending/torsion loading are presented. The tests were performed at stress ratios of R = −1 and R = 0. The residual stresses were reduced by thermal stress relief. The fatigue crack development is compared with the prediction on the crack growth rates of Paris. Individual stress intensity factors for the semielliptical surface cracks in the tube‐flange specimens are approximated on a weight function analogy using the published solutions of other workers.
Crack growth mechanism in precracked torsional fatigue specimens
Authors: Makabe C. , Socie D. F.
Published: March 2003

The mechanism of crack growth of precracked materials was investigated under cyclic torsion loading with and without axial static stress using 4340 steel. During the crack growth, branching of the crack was observed. The length of the crack between the first branching points was dependent on loading conditions. This length was longer when the applied shear amplitude and the static axial stress level were higher. When the crack tips were opened by the tension loads, the crack had the tendency to grow in a shear mode during cyclic torsion. It was found that friction of the crack surfaces prevented shear mode crack growth. Furthermore, at higher stresses the initiation of new microcracks was observed in front of the main crack and their density was dependent on loading conditions. This helped the crack grow in a shear mode before and after branching.
Fatigue strength CAE system for three‐dimensional welded structures
Authors: TANAKA K , OKAJIMA H , KOIBUCHI K
Published: March 2003

ABSTRACT Fatigue strength assessment methods are applied to practical arc‐welded structural features that have complex three‐dimensional geometry. Two methods are investigated in the present research. The criterion of the first method is cyclic plastic zone size, which is calculated from stress singularity parameters. The criterion of the second method is hot spot stress. These fatigue strength criteria are proved to be applicable to the fatigue strength assessment of practical arc‐welded structural features. These criteria enable a critical point at which fatigue cracks are most likely to initiate to be specified for each type of welded joint and load. Consequently, the critical point simplifies the classification of various welded joints. Furthermore, a fatigue strength computer‐aided engineering system, which includes functional engines for the evaluation of the fatigue strength of a designed shape, is proposed.
Fatigue behaviour and life prediction of fibre reinforced metal laminates under constant and variable amplitude loading
Authors: WU X. R. , GUO Y. J.
Published: March 2003

ABSTRACT Fatigue crack growth of fibre reinforced metal laminates (FRMLs) under constant and variable amplitude loading was studied through analysis and experiments. The distribution of the bridging stress along the crackline in centre‐cracked tension (CCT) specimen of FRMLs was modelled numerically, and the main factors affecting the bridging stress were identified. A test method for determining the delamination growth rates in a modified double cracked lap shear (DCLS) specimen was presented. Two models, one being fatigue‐mechanism‐based and the other phenomenological, were developed for predicting the fatigue life under constant amplitude loading. The fatigue behaviour, including crack growth and delamination growth, of glass fibre reinforced aluminium laminates (GLARE) under constant amplitude loading following a single overload was investigated experimentally, and the mechanisms for the effect of a single overload on the crack growth rates and the delamination growth rates were identified. An equivalent closure model for predicting crack‐growth in FRMLs under variable amplitude loading and spectrum loading was presented. All the models presented in this paper were verified by applying to GLARE under constant amplitude loading and Mini‐transport aircraft wing structures (TWIST) load sequence. The predicted crack growth rates are in good agreement with test results.
Failure analysis of gas turbine last stage bucket made of Udimet 500 superalloy
Authors: Mazur Z. , Kubiak J. , Mariño‐Lopez C.
Published: March 2003

ABSTRACT This study presents the failure analysis of the 37.5 MW gas turbine third stage buckets made of Udimet 500 (U‐500) superalloy. The buckets experienced repetitive integral tip shroud fractures assisted by a low temperature (type II) hot corrosion. A detailed analysis of all elements which had an influence on the failure initiation was carried out, namely: the commensurate loss of a load bearing cross‐sectional area of the bucket tip shroud by the conversion of metal to the corrosion product (scale) and related increase in stress; the influence of the tip shroud microstructure, e.g. a presence of equiaxed and columnar grains, their distribution and orientation; evidence of the transgranular fracture initiation and intergranular creep mechanism fracture propagation. Finally, the most probable mechanism for bucket damage, conclusions and recommendations to prevent failures of the buckets are presented.
Effect on fatigue crack growth of interactions between overloads
Authors: POMMIER S. , DE FREITAS M.
Published: March 2003

ABSTRACT Various types of interactions between overloads were studied in a 0.38% C low carbon steel. The retarding effect due to consecutive overloads is found to increase with the number of overloads, until it reaches a maximum. Similarly, it is found that a critical distance between overloads ensures the highest retarding effect, while shorter or longer spacing are less efficient for retarding crack growth. These effects are successfully explained using FEM calculations of the effective stress intensity factor. The kinematic hardening of the alloy, which is very efficient in ferritic–pearlitic steels, is shown to be mostly responsible for those effects. Taking into account the amplitude of kinematic hardening allows qualitative explanation of the observed effects. The order of application of the cycles during variable amplitude fatigue is thus important and should be taken into account for predicting fatigue lives.
Fatigue of clamped connections with application to a stem‐handlebar assembly for off‐road bicycles
Authors: McKENNA S. P. , HILL M. R. , HULL M. L.
Published: March 2003

The objectives of this study were: (i) to determine the stresses as a result of assembly and the stress concentration of a clamped connection, (ii) to demonstrate the importance of the effects of assembly in fatigue life predictions and (iii) to verify the accuracy of fatigue life predictions by measuring fatigue life experimentally. A stem‐handlebar assembly used in off‐road bicycles was chosen for the study because it is a critical assembly for which structural reliability must be insured to prevent serious injury. Assembly stresses in the handlebar exceeded 200 MPa and stress concentration because of the attached stem increased the applied stress by 40%. A stress‐life prediction indicated that assembly effects would reduce predicted fatigue life of the handlebar by a factor of approximately 20. The measured fatigue lifetime of the handlebar was longer than that predicted by using the stress‐life approach, but was much shorter than that predicted when assembly effects were ignored. Therefore, assembly effects have a significant effect on fatigue life predictions and should be included in lifetime assessments for clamped mechanical assemblies.
Fretting fatigue crack initiation mechanism in Ti–6Al–4V
Authors: NAMJOSHI S. A. , MALL S. , JAIN V. K. , JIN O.
Published: March 2003

Fretting fatigue crack initiation in titanium alloy, Ti−6Al−4V, was investigated experimentally and analytically by using finite element analysis (FEA). Various types of fretting pads were used in order to determine the effects of contact geometries. Crack initiation location and crack angle orientation along the contact surface were determined by using microscopy. Finite element analysis was used in order to obtain stress state for the experimental conditions used during fretting fatigue tests. These were then used in order to investigate several critical plane based multiaxial fatigue parameters. These parameters were evaluated based on their ability to predict crack initiation location, crack orientation angle along the contact surface and the number of cycles to fretting fatigue crack initiation independent of geometry of fretting pad. These predictions were compared with their experimental counterparts in order to characterize the role of normal and shear stresses on fretting fatigue crack initiation. From these comparisons, fretting fatigue crack initiation mechanism in the tested titanium alloy appears to be governed by shear stress on the critical plane. However, normal stress on the critical plane also seems to play a role in fretting fatigue life. At present, the individual contributions/importance of shear and normal stresses in the crack initiation appears to be unclear; however, it is clear that any critical plane describing fretting fatigue crack initiation behaviour independent of geometry needs to include components of both shear and normal stresses.
The dependence of heterotrophic consumption and C accumulation on autotrophic nutrient content in ecosystems
Authors: Cebrián  , Williams  , McClelland  , Valiela
Published: March 2003

Primary producers with high nutrient contents typically exhibit high herbivory rates and fast decomposition rates. These tendencies, however, have not been generalized across ecosystems with contrasting herbivore characteristics and abiotic properties. Here we demonstrate that ecosystem types dominated by richer autotrophs (i.e. higher nutrient contents) are subject to higher rates of herbivory and decomposition in spite of differences in herbivore characteristics and environmental conditions. We further show that, as a result of these tendencies, ecosystems with richer autotrophs accumulate less carbon. These results identify autotrophic nutrient content as a main control of heterotrophic consumption and carbon accumulation in ecosystems. They also provide a basis to evaluate changes in these ecosystem properties following anthropogenic eutrophication.
Predation risk alters interactions among species: competition and facilitation between ants and nesting birds in a boreal forest
Authors: Haemig
Published: March 2003

Although interactions between species are often assumed to be fixed, theory and empirical evidence suggest that they may be quite variable, changing in the presence of other species or environmental conditions. The interaction between ants and nesting birds exhibits such variability, ants sometimes being predators of bird nests and other times protectors of them. Hypothesizing that predation risk might be a critical factor in altering the interaction of ants with birds, I investigated the interaction of wood ants Formica aquilonia with nesting birds under different levels of predation risk. In a controlled field experiment, I allowed tits (Parus major, P. caeruleus, P. ater) and pied flycatchers (Ficedula hypoleuca) to select nest boxes in trees with ants (ant trees) or trees without ants. I found that birds usually nested in trees without ants, apparently to avoid the danger of injury from encounters with ants. Nesting in ant trees occurred mainly in the habitat where risk of predation was highest (along the forest edge), and with the bird taxa that lost nests most frequently in trees without ants (tits). Tits nesting on the forest edge achieved significantly greater nesting success, and fledged significantly more young, in ant trees compared with trees without ants. As the season progressed, ant traffic increased in trees without nesting birds, but decreased in trees with nesting birds, indicating that the outcome of interference competition between ants and nesting birds was reversed under increased predation risk. These results support the idea that predation risk can shift species interactions from predominately competitive processes to predominately facilitative processes.
A roadmap for metapopulation research
Authors: Holyoak M. , Ray C.
Published: March 2003

The theory of metapopulation dynamics now embraces a diversity of spatially structured populations. New and increasingly realistic models address important details of population and community dynamics. But general results are difficult to glean from such realistic models. Discovering the general behaviour of these models will require meaningful comparison of metapopulations with very diverse structures. A simple parameter space can be constructed to facilitate such comparisons. The axes defining this space determine both the structure of metapopulations and the potential for action of various persistence mechanisms. This exercise clarifies the relationship between metapopulation structure and dynamics, and illustrates future research opportunities.
Fertility control of overabundant species; Can it work for feral rabbits?
Authors: Twigg L.E. , Kent Williams C.
Published: March 2003

Demographic changes were monitored in free‐ranging European rabbit (Oryctolagus cuniculus) populations in Australia following the surgical imposition of four levels of female sterility (0%, 40%, 60%, 80%). Rabbit productivity decreased with increasing sterility level, but a greater proportion of offspring were recruited into populations with high levels of sterility. Adult rabbits, particularly sterile females, also survived better in the high sterility populations. Thus we were able to experimentally demonstrate that two density‐dependent processes were operating on our rabbit populations: one was acting on juvenile survival, the other on the survival of infertile adult rabbits. However, these compensatory mechanisms were insufficient to overcome the effects of sterility in the high sterility populations and the seasonal abundance of rabbits decreased. Female sterility levels of 60%–80% would benefit rabbit control programs by reducing the peaks of rabbit abundance. This effect is likely to be enhanced if fertility control could be integrated with other pest control strategies.
The impact of herbivore type and grazing pressure on benthic microalgal diversity
Authors: Sommer U.
Published: March 2003

Benthic microalgae and the herbivores Idothea chelipes (Isopoda) and Littorina littorea (Gastropoda) were used as an experimental model system to study the effect of herbivore type on primary producer diversity. Both herbivores enhanced diversity at intermediate grazing pressures, the enhancing effect being stronger with Littorina. This difference is explained by differences in the spatial heterogeneity of the grazed microalgal biofilm caused by behavioural differences in spatial grazing patterns. Idothea spreads its grazing pressure rather evenly in space (“lawn‐mower” type), whereas Littorina creates pronounced spatial heterogeneity by moving slowly over the biofilm and decimating it within the grazing tracks (“bulldozer” type). Idothea grazing did not enhance biomass patchiness beyond the level of ungrazed controls (maximum/minimum from 1.7 to 5.5), whereas Littorina strongly increased patchiness (maximum/minimum from 45 to 850).
Periodic travelling waves in cyclic predator–prey systems
Authors: Sherratt J.A.
Published: March 2003

Predation is an established cause of cycling in prey species. Here, the ability of predation to explain periodic travelling waves in prey populations, which have recently been found in a number of spatiotemporal field studies, is examined. The nature of periodic waves in these systems, and the way in which they can be generated by the invasion of predators into a prey population is discussed. A theoretical calculation that predicts, as a function of two parameter ratios, whether such an invasion will lead to a stable periodic travelling wave that would be observed in practice is presented ‐ the alternative outcome is spatiotemporal chaos. The calculation also predicts quantitative details of the periodic waves, such as speed and amplitude. The results give new insights into the types of predator‐prey systems in which one would expect to see periodic travelling waves following an invasion by predators.
Maternal effects in Daphnia: what mothers are telling their offspring and do they listen?
Authors: LaMontagne J.M. , McCauley E.
Published: March 2003

Maternal effects can significantly impact offspring performance. Provisioning of offspring with energy stores can quantitatively alter their growth rates, survivorship, and future fecundity, and influence population regulatory mechanisms. In this paper, we show that maternal effects can also qualitatively affect offspring reproduction (i.e. their mode of reproduction). The freshwater herbivore Daphnia pulex can change the amount of energy allocated between asexual and ephippial egg production. Our experiments on individuals, experiencing “step‐up” or “step‐down” food manipulations, reveal that offspring qualitatively shift their energy allocation away from asexual reproduction to ephippial egg production when there is a simple mismatch between maternal and offspring food environments. We show that the response is asymmetric with respect to changes in food level, ephippial egg production is higher with a greater mismatch between environments, and that the effect can be observed in dynamic experimental populations. These results point to a “generational memory” that could challenge our interpretation of field patterns and mechanisms influencing population dynamics in Daphnia–algal systems.
Compensatory growth and competitive ability of an invasive weed are enhanced by soil fungi and native neighbours
Authors: Callaway Ragan , Newingham Beth , Zabinski Cathy A. , Mahall Bruce E.
Published: March 2003

Compensatory responses to herbivory by invasive weeds may foil attempts to arrest their spread with biological controls. We conducted an experiment to study the effects of defoliation and soil fungi on interactions between Centaurea melitensis, an invasive annual from Eurasia, and Nassella pulchra, a native Californian bunchgrass. Defoliation of C. melitensis reduced its final biomass in all species–fungicide treatments, except when C. melitensis was grown with both Nassella and non‐treated soil fungi at the same time. In this treatment, the biomass of clipped C. melitensis plants was equal to that of unclipped plants, indicating that soil fungi and Nassella promoted a compensatory response in the weed. Overall, the biomass of C. melitensis was 44% lower when soil fungi were reduced. However, in soil not treated with fungicide, the total biomass of C. melitensis increased in the presence of Nassella, but decreased when it was grown alone. When stressed by defoliation, C. melitensis may benefit from a form of mycorrhizae‐mediated parasitism through a common mycorrhizal network, or Nassella may alter the fungal community in a way that enhances the positive direct effects of soil fungi on Centaurea.
Food or sex; pollinator–prey conflict in carnivorous plants
Authors: Anderson B. , Midgley J.J.
Published: March 2003

Carnivorous plants potentially trap their own pollinators and it has been argued that considerable spatial separation of flowers and traps has evolved to protect pollinators. We investigated flower‐trap separation of Drosera and Utricularia. Short Drosera had a greater element of floral–trap separation than tall Drosera. Such a relationship is unexpected for plants whose peduncles were evolved to protect their pollinators. Utricularia can not trap pollinators but this genus still produces exceptionally long peduncles. We propose that flower‐trap separation evolved because carnivorous plants are often short and need to project their flowers well above ground level to make them more attractive to pollinators.
Linearity in the aggregate effects of multiple predators in a food web
Authors: Schmitz Oswald J. , Sokol‐Hessner Lauge
Published: March 2003

Theory in community ecology often assumes that predator species have similar indirect effects and thus can be treated mathematically as a single functional unit (e.g. guild or trophic level). This assumption is questionable biologically because predator species typically differ in their effects, creating the potential for nonlinearities when they coexist. We evaluated the nature of indirect effects caused by three species of hunting spider predators, singly and in multiple species combinations, on grass and herb plants in experimental old‐field food webs. Despite the potential for nonlinearity, indirect effects in different multiple predator combinations consistently did not differ significantly from the respective means of the single species effects. Thus, for this experimental system, the whole was simply the average of the parts. Consequently, models which abstract predator species as single trophic levels would successfully predict indirect effects in this system regardless of the composition of the predator fauna.
An introduced invertebrate predator (Bythotrephes) reduces zooplankton species richness
Authors: Yan Norman D. , Girard Robert , Boudreau Stephanie
Published: March 2003

Rarely do ecologists have the data needed to assess the impacts of invading species on biodiversity, i.e. pre‐ and post‐invasion census information from both invaded and control sites. Using a 21‐year time series, we demonstrate that the invasion of Harp Lake, Ontario, Canada, by the Eurasian spiny water flea, Bythotrephes longimanus, a zooplanktivore, was accompanied by a rapid and long‐lasting reduction in the average species richness of crustacean zooplankton, particularly of cladoceran taxa. No such reduction was observed in seven nearby un‐invaded lakes over the same two decades. If the Harp Lake results are typical, we predict a widespread reduction in crustacean zooplankton richness on the Canadian Shield for three reasons. Shield lakes provide the invader with good habitat. Its dispersal rates and colonization success are high. Zooplankton richness in Harp Lake is now unusually low for a Shield Lake of its size and acidity.
Micro‐fungi and invertebrate herbivores on birch trees: fungal mediated plant–herbivore interactions or responses to host quality?
Authors: Ahlholm Jouni , Helander Marjo , Elamo Pirjo , Saloniemi Irma , Neuvonen Seppo , Hanhimäki Sinikka , Saikkonen Kari
Published: March 2003

We studied interactions between microfungi and herbivores sharing a host tree. In a series of experiments and field observations over a 3‐year period, we compared phenotypic and genetic correlations of fungal frequencies and performance of invertebrate herbivores growing on mature half‐sib progenies of mountain birches (Betula pubescens ssp. czerepanovii) in two environments, a forested river valley and an adjacent higher‐elevation mountain birch woodland. We found little support for direct relation between fungal frequencies and performance of herbivore species. Instead, genetic correlations, particularly between autumnal moth (Epirrita autumnata) and rust fungus (Melampsoridium betulinum), suggest that herbivore performance may be caused by (1) genetic differences in plant quality for fungi and herbivores, or (2) genetic differences in responses to environmental conditions.
Temperature checks the Red Queen? Resistance and virulence in a fluctuating environment
Authors: Blanford Simon , Thomas Matthew B. , Pugh Clare , Pell Judy K.
Published: March 2003

Numerous studies have revealed genetic variation in resistance and susceptibility in host–parasite interactions and therefore the potential for frequency‐dependent selection (Red Queen dynamics). Few studies, if any, have considered the abiotic environment as a mediating factor in these interactions. Using the pea aphid, Acyrthosiphon pisum, and its fungal pathogen, Erynia neoaphidis, as a model host–parasite system, we demonstrate how temperature can mediate the expression of genotypic variation for susceptibility and virulence. Whilst previous studies have revealed among‐clone variation in aphid resistance to this pathogen, we show that resistance rankings derived from assessments at one temperature, are not conserved across differing temperature regimes. We suggest that variation in environmental temperature, through its nonlinear impact on parasite virulence and host defence, may contribute to the general lack of evidence for frequency‐dependent selection in field systems.
How accurate are population models? Lessons from landscape‐scale tests in a fragmented system
Authors: Lindenmayer D. B. , Possingham H. P. , Lacy R. C. , McCarthy M. A. , Pope M. L.
Published: March 2003

There is a growing debate about the ability of Population Viability Analysis (PVA) to predict the risk of extinction. Previously, the debate has focused largely on models where spatial variation and species movement are ignored. We present a synthesis of the key results for an array of different species for which detailed tests of the accuracy of PVA models were completed. These models included spatial variation in habitat quality and the movement of individuals across a landscape. The models were good approximations for some species, but poor for others. Predictive ability was limited by complex processes typically overlooked in spatial population models, these being interactions between landscape structure and life history attributes. Accuracy of models could not be determined a priori, although model tests indicated how they might be improved. Importantly, model predictions were poor for some species that are among the best‐studied vertebrates in Australia. This indicated that although the availability of good life history data is a key part of PVA other factors also influence model accuracy. We were also able to draw broad conclusions about the sorts of populations and life history characteristics where model predictions are likely to be less accurate. Predictions of extinction risk are often essential for real‐world population management. Therefore, we believe that although PVA has been shown to be less than perfect, it remains a useful tool particularly in the absence of alternative approaches. Hence, tests of PVA models should be motivated by the cycle of testing and improvement.
Stoichiometric tracking of soil nutrients by a desert insect herbivore
Authors: Schade John D. , Kyle Marcia , Hobbie S. E. , Fagan W. F. , Elser J. J.
Published: March 2003

Abstract Biogeochemistry and population biology have developed independently, with few attempts at linkage, almost none of which were mechanistically based. We hypothesize that biogeochemical cycling is linked to herbivore population dynamics through the influence of soil nutrient availability on foliar nutrient content, which constrains herbivore investment in phosphorus (P)‐rich molecules necessary for growth. We show that variation in desert soil P availability is linked to abundance of an insect herbivore (Sabinia setosa) through the influence of soil P on the C:P ratio of the host plant (Prosopis velutina). Low P availability increases C:P ratio of Prosopis leaves, leading to a decline in body %P, %RNA and abundance of Sabinia. Tight association between soil, plant and herbivore P provides the first evidence of a mechanistic pathway linking P biogeochemistry to terrestrial food webs by altering the supply of dietary P to herbivores, thus limiting their capacity for growth by constraining the production of P‐rich cellular ribosomal RNA (rRNA).
Bumblebee workers from different sire groups vary in susceptibility to parasite infection
Authors: Baer Boris , Schmid‐Hempel Paul
Published: March 2003

Abstract Female multiple mating with different males (polyandry) can be advantageous because the resulting genetic heterogeneity among offspring reduces the effects of parasitism. However, the underlying assumption that offspring fathered by different males vary in their susceptibility to parasites is so far only supported indirectly. Here we tested this crucial assumption using data from a study on the bumblebee Bombus terrestris L. with queens inseminated with sperm of either one or several males that originated from different sire groups (i.e. groups of brothers). We found that, under field conditions, workers from different sire groups, forming a patriline within a given colony, indeed differ in their susceptibility to the common intestinal parasite, Crithidia bombi, and do so independently of queen mating frequency.
Hydrogen sulphide demand of long‐lived vestimentiferan tube worm aggregations modifies the chemical environment at deep‐sea hydrocarbon seeps
Authors: Cordes Erik E. , Bergquist Derk C. , Shea Katriona , Fisher Charles R.
Published: March 2003

Abstract Lamellibrachia luymesi is a long‐lived vestimentiferan polychaete that produces biogenic habitat at hydrocarbon seeps on the upper Louisiana slope of the Gulf of Mexico. Lamellibrachia luymesi relies on endosymbiotic, chemoautotrophic bacteria for nutrition which are supplied with hydrogen sulphide acquired from seep sediments by the tube worms. In this study, an individual‐based model is developed for L. luymesi aggregations. The results show that aggregations can persist for centuries because of extremely low mortality rates. Recruitment patterns reflect intraspecific competition for settlement space, with the recruitment period estimated between 11 and 68 years. Substantial hydrogen sulphide requirements are estimated for large aggregations of L. luymesi, exceeding 30 mmol h−1. In addition to modifying habitat through physical structure, L. luymesi may be considered to be an ecosystem engineer because of its profound effect on the chemical environment at hydrocarbon seep sites.
Anaerobic utilization of alkylbenzenes and n‐alkanes from crude oil in an enrichment culture of denitrifying bacteria affiliating with the β‐subclass of Proteobacteria
Authors: Rabus  , Wilkes  , Schramm  , Harms  , Behrends  , Amann  , Widdel
Published: March 2003

Denitrifying bacteria were enriched from freshwater sediment with added nitrate as electron acceptor and crude oil as the only source of organic substrates. The enrichment cultures were used as laboratory model systems for studying the degradative potential of denitrifying bacteria with respect to crude oil constituents, and the phylogenetic affiliation of denitrifiers that are selectively enriched with crude oil. The enrichment culture exhibited two distinct growth phases. During the first phase, bacteria grew homogeneously in the aqueous phase, while various C1–C3 alkylbenzenes, but no alkanes, were utilized from the crude oil. During the second phase, bacteria also grew that formed aggregates, adhered to the crude oil layer and emulsified the oil, while utilization of n‐alkanes (C5 to C12) from the crude oil was observed. During growth, several alkylbenzoates accumulated in the aqueous phase, which were presumably formed from alkylbenzenes. Application of a newly designed, fluorescently labelled 16S rRNA‐targeted oligonucleotide probe specific for the Azoarcus/Thauera group within the β‐subclass of Proteobacteria revealed that the majority of the enriched denitrifiers affiliated with this phylogenetic group.
Inhibition of photosynthesis and bleaching of zooxanthellae by the coral pathogen Vibrio shiloi
Authors: Ben‐Haim Yael , Banim Ehud , Kushmaro Ariel , Loya Yossi , Rosenberg Eugene
Published: March 2003

Vibrio shiloi is the causative agent of bleaching (loss of endosymbiotic zooxanthellae) of the coral Oculina patagonica in the Mediterranean Sea. To obtain information on the mechanism of bleaching, we examined the effect of secreted material (AK1‐S) produced by V. shiloi on zooxanthellae isolated from corals. AK1‐S caused a rapid inhibition of photosynthesis of the algae, as measured with a Mini‐PAM fluorometer. The inhibition of photosynthesis was caused by (i) ammonia produced during the growth of V. shiloi on protein‐containing media and (ii) a non‐dialysable heat‐resistant factor. This latter material did not inhibit photosynthesis of the algae by itself but, when added to different concentrations of NH4Cl, enhanced the inhibition approximately two‐ to threefold. Ammonia and the enhancer were effective to different degrees on zooxanthellae isolated from four species of coral examined. In addition to the rapid inhibition of photosynthesis, AK1‐S caused bleaching (loss of pigmentation) and lysis of zooxanthellae. Bleaching was more rapid than lysis, reaching a peak (25% bleached algae) after 6 h. The factors in AK1‐S responsible for bleaching and lysis were different from those responsible for the inhibition of photosynthesis, because they were heat sensitive, non‐dialysable and active in the dark. Thus, the coral pathogen V. shiloi produces an array of extracellular materials that can inhibit photosynthesis, bleach and lyse zooxanthellae.