bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential allele-specific accumulation of bovine kappa-casein mRNA throughout lactation
Authors: Vachon Dominic , Britten Michel , Morisset Jean , Petitclerc Denis , Robitaille Gilles
Published: November 2004

A differential allele-specific accumulation of κ-casein mRNA that is not linked to the κ-casein protein variants is described in Holstein cows. Actually, cows genotyped κ-casein AB were a mixed population. For the first group of κ-casein AB cows, allele A-specific κ-casein mRNA contents within mammary epithelial cells were lower than the allele B-specific ones (cows LH), suggesting that the allele A-specific κ-casein gene was expressed with lower efficiency in mRNA. For the other group of κ-casein AB cows, allele A- and B-specific κ-casein mRNA accumulated to a similar level within mammary epithelial cells (cows HH). The objective of this study was to determine whether the accumulation of allele-specific κ-casein mRNA remained constant throughout lactation for the two groups of cows. Quantitative RT-PCR was used to monitor Holstein cows κ-casein AB genotyped HH and LH throughout lactation for the proportion of allele B-specific mRNA accumulation relative to the total κ-casein encoded mRNA within mammary epithelial cells: RNA was extracted from milk somatic cells known to contain a small proportion of mammary epithelial cells. Mean values of allele B-specific mRNA content were 50·6±0·5 and 54·0±0·9%, for cows HH and cows LH, respectively, and did not vary during lactation (P>0·10). This suggests that the phenotypic expression of the genetic mutation that causes the differential allele-specific accumulation of κ-casein mRNA was not affected by physiological and environmental factors, which tend to vary considerably throughout lactation.
Susceptibility of plasmin and chymosin in Cheddar cheese to inactivation by high pressure
Authors: Huppertz Thom , Fox Patrick F , Kelly Alan L
Published: November 2004

High pressure (HP) processing has attracted considerable interest in dairy research in recent years; its effects on cheese have been reviewed by O'Reilly et al. (2001). HP treatment of cheese may influence several of its properties, e.g., for hard and semi-hard cheeses, such as Cheddar and Gouda, the most notable effects are on the texture and rate of ripening. HP treatment increased elasticity and improved organoleptic properties of Gouda cheese (Kolakowski et al. 1998). Messens et al. (2000) reported that, immediately after treatment at 400 MPa, Gouda cheese was less rigid and solid-like and more viscoelastic than untreated cheese. HP treatment also enhances the functional properties of Mozzarella cheese (Johnston & Darcy, 2000; O'Reilly et al. 2002).
Complete parameter identification of parallel manipulators with partial pose information using a new measurement device
Authors: Rauf Abdul , Kim Sung-Gaun , Ryu Jeha
Published: November 2004

A new measurement device is proposed for the calibration of parallel manipulators that can be used to indentify all kinematic parameters with partial pose measurements. The device while restricting the motion of the end-effector to five degree-of-freedom measures three components of posture. A study is performed for a six degree-of-freedom fully parallel Hexa Slide Manipulator. Intrinsic inaccuracies of the measurement device are modeled with two additional identification parameters. Computer simulations show that all parameters, including the additional parameters, can be identified. Results show a significant error reduction, even with noisy measurements, and reveal that the identification is robust against errors in initial guess.
Components of simultaneous interpreting: Comparing interpreting with shadowing and paraphrasing
Authors: CHRISTOFFELS INGRID K. , DE GROOT ANNETTE M. B.
Published: November 2004

Simultaneous interpreting is a complex task where the interpreter is routinely involved in comprehending, translating and producing language at the same time. This study assessed two components that are likely to be major sources of complexity in SI: The simultaneity of comprehension and production, and transformation of the input. Furthermore, within the transformation component, we tried to separate reformulation from language-switching. We compared repeating sentences (shadowing), reformulating sentences in the same language (paraphrasing), and translating sentences (interpreting) of auditorily presented sentences, in a simultaneous and a delayed condition. Output performance and ear–voice span suggest that both the simultaneity of comprehension and production and the transformation component affect performance but that especially the combination of these components results in a marked drop in performance. General lower recall following a simultaneous condition than after a delayed condition suggests that articulation of speech may interfere with memory in SI.
On the probability distributions of SuperDARN Doppler spectral width measurements inside and outside the cusp
Authors: Freeman M. P. , Chisham G.
Published: November 2004

The Doppler spectral width of backscatter from the SuperDARN HF radars has been routinely used to identify the ionospheric cusp. The probability distribution of spectral width values has been described as Gaussian (normal) in the cusp and exponential equatorward of it. Here we re‐examine the empirical distributions and show that they are better described by a log‐Lévy distribution in both the cusp and non‐cusp regions, with the same Lévy index a ≈ 1.85 but varying Lévy location parameter. The spectral width distribution may also be log‐Lévy at other magnetic local times, but with generally different parameters.
Limited diversity of HLA‐DRB1*02 alleles and DRB1–DRB5 haplotype associations in four United States population groups
Authors: Baldassarre L.A. , Steiner N.K. , Jones P. , Tang T. , Slack R. , Ng J. , Hartzman R.J. , Hurley C.K.
Published: November 2004

Abstract:  At least 60 DRB1*02 positive individuals from each of four US population groups found within a hematopoietic stem cell volunteer donor registry – Caucasoids, African Americans, Asians/Pacific Islanders, and Hispanics – were randomly selected from a database of 82,979 individuals. DRB1*02 alleles were identified by DNA sequencing. A total of five of 23 known DRB1*02 alleles were detected. DRB1*15011 was the predominant DRB1*02 allele in Caucasoids and Hispanics. The most common DRB1*02 allele observed in African Americans was DRB1*1503, and DRB1*15021 in Asians/Pacific Islanders. Caucasoids were found to be the least diversified; only DRB1*15011 and DRB1*16011 were observed. A subset of individuals was also typed for DRB5 alleles by DNA sequencing. DRB5*01011, DRB5*0102, DRB5*0103, DRB5*0108N and DRB5*0202 were detected and nine DRB1‐DRB5 haplotypes defined.
High‐throughput peptide synthesis and peptide purification strategy at the low micromol‐scale using the 96‐well format
Authors: Pipkorn R. , Boenke C. , Gehrke M. , Hoffmann R.
Published: November 2004

Abstract: The increasing demand for short‐ and medium‐sized peptides in many fields of biological, medical and pharmaceutical research requires optimized and universally applicable high‐throughput synthesis and purification techniques at the low‐µmol scale. Here, we describe a continuous peptide synthesis/purification approach using the 96‐well format. First, a µmol scale peptide synthesis on resin beads was optimized on a novel miniaturized 96‐reaction vessel block employing standard Fmoc/tBu‐chemistry. Almost 90% of the synthesized peptides contained the target sequence as the main component, as judged from matrix‐assisted laser desorption/ionization (MALDI) mass spectra. Impurities were mostly related to partially protected peptides. Second, we tested the applicability of ion pair reversed‐phase solid‐phase extraction (IP–RP–SPE) to purify individual peptides. Depending on the length and predicted hydrophobicity of the peptides, elution was performed with 25 or 35% aqueous acetonitrile in the presence of 0.1% trifluoroacetic acid (TFA). Thus, scavengers used during TFA cleavage and partially protected peptides carrying very hydrophobic protecting groups were effectively removed. Using a narrow step gradient, the target peptides were even separated from deleted sequences and protected peptides with similar hydrophobicities. Third, we combined the µmol‐scale synthesis in the 96‐well format with purification by IP–RP–SPE on a 96‐well micro‐extraction plate format. This simple, fast and parallel approach was tested on 12‐mer and 15‐mer peptides to map epitopes of T‐ and B‐cell clones, respectively. Approximately 80% of all peptides were obtained at purities > 90% without purification by RP–HPLC. In summary, this novel approach has several advantages: (i) the µmol‐scale reduced the cost of peptide synthesis, (ii) large numbers of peptides were purified faster, (iii) the volumes of eluents and waste were significantly reduced, and (iv) the RP–HPLC column was not contaminated with hydrophobic impurities.
Detergent‐assisted oxidative folding of δ‐conotoxins
Authors: DeLa Cruz R. , Whitby F. G. , Buczek O. , Bulaj G.
Published: November 2004

Conotoxins comprise a diverse group of disulfide‐rich peptides found in venoms of predatory Conus species. The native conformation of these peptides is marginally stable in comparison with alternative conformations, often resulting in low folding yields. The oxidative folding of hydrophobic δ‐conotoxins was found to produce less than 1% of the native peptide [Bulaj, G. et al. (2001) Biochemistry 40, 13201]. In order to identify factors that might improve folding yields, we screened a number of additives including water‐soluble polymers, detergents and osmolytes for their ability to increase steady‐state accumulation of the native δ‐conotoxin PVIA. The presence of a non‐ionic detergent Tween and low temperature appeared to be the most effective factors in improving the oxidative folding. The detergent was also effective in promoting folding of other hydrophobic δ‐conotoxins. Based on our findings, we discuss a possible mechanism for detergent‐assisted folding and the general applicability of this mechanism to facilitating the proper folding of hydrophobic, cysteine‐rich peptides.
Position Paper of the Ethics Committee of the International Xenotransplantation Association
Authors: Sykes Megan , D'Apice Anthony , Sandrin Mauro
Published: November 2004

Abstract: Xenotransplantation (XTx) provides a potential solution to the shortage of human organs and tissues, and has several advantages over other possible solutions to this problem. However, a number of scientific and ethical barriers exist, and need to be addressed in order to advance the field of XTx in a manner that optimizes its potential to benefit society and minimizes its risk. Some of the most pressing ethical issues are discussed, and the position of the Ethics Committee of the International Xenotransplantation Association is presented.
A therapeutic concept for the combined orthodontic surgical correction of angle Class II deformities with short‐face syndrome: Surgical lengthening of the lower face
Authors: Watted Nezar , Witt Emil , Bill Josip S.
Published: November 2004

In today's society not only facial esthetics have become important, but also the information on ways to correct adult orthodontic problems is readily available. Subsequently, increasing number of adults seek orthodontic treatment merely to change their facial appearance. In general, these adult patients exhibit such a severe skeletal deformity that it is noticeable even by non‐experts. The nature of these adult deformities is such that the only promising treatment is the combined orthodontic‐surgical approach. A stable and functional occlusion with a physiologic position for the condyle is the common goal of orthodontic treatment. In patients with skeletal deformities, however, improvement of facial esthetics takes paramount importance. They judge the success of treatment by extraoral appearance. Accordingly, the clinician must assess both the dental and facial appearance, and then inform the patient of different treatment possibilities. In this scenario, patient's input into the decision making process is critical for a mutually satisfactory result. This clinical report describes a concept of systematic approach to treatment of Class II deformities with skeletal deep bite and short lower face (short‐face syndrome). This approach emphasizes the soft tissue analysis.
The development of a tactile graphic version of IOTN for visually impaired patients
Authors: AlSarheed M , Bedi R , Hunt Np
Published: November 2004

The Index of Orthodontic Treatment Need (IOTN) is a visual‐based index and has been widely used. This paper describes the development and evaluation of tactile graphics representing the aesthetic component (AC) of IOTN for the use of visually impaired patients (VI). Four tactile graphics were produced corresponding to IOTN photographs 1 (graphic 1, no treatment – mild need), 5 (graphic 2, moderate need), 8 (graphic 3, severe need; increased overjet) and 10 (graphic 4, severe need). Nine (30–50 years) expert consumers from the Royal National Institute for the Blind (RNIB) and 13 VI schoolchildren (11–16 years) evaluated the graphics. The evaluation was in terms of design features, complexity of information and ease of use. Each individual was asked to arrange the graphics in order of severity of malocclusion. The procedure was repeated after 30 min to test individual reliability (http://www.clinorthodres.com/cor‐c‐084/).  The consumer group was able to identify the main features in each graphic and found them easy to use. Six had arranged the graphics correctly at the first attempt and five on their second. The children were able to distinguish the different oral features, except the overjet presentation in graphic 2. Nine children arranged the graphics correctly at the first attempt, but only six at the second. The confusion centred for both groups on presenting an increased overjet with graphic 2. A modification was undertaken to enhance the anterior–posterior nature of the image. Fifteen VI schoolchildren reassessed the modified graphics, 14 arranged them correctly at the first attempt and 13 at the second. The study concluded that IOTN tactile graphics were well accepted and showed a good reliability.
Modeling of structure, quality, and function in the orthodontic patient
Authors: Maki K , Inou N , Takanishi A , Miller AJ
Published: November 2004

Authors– Maki K, Inou N, Takanishi A, Miller AJ

The advantages of three‐dimensional (3‐D) imaging technology and solid modeling make it possible to visualize the morphological information. However, lacking in this ‘digital patient’ is the motion and mechanical properties observed in the living patient. Functional diagnostic techniques such as electromyography and motion analysis could complement the morphological characteristics to be applied in orthodontics. In this review, new computer‐assisted analyzing methods are introduced which include visualization of: 1) the 3‐D structure and bone density distribution; 2) masticatory‐generated forces by using automated finite element modeling (FEM); and 3) the 3‐D jaw movement and its motion analysis. In each study, the data from X‐ray computed tomography scanning, electromyograms, biting pressure, and digital jaw movement analysis (six axes) are used for calculation. By using these applications, growing changes in bone mineral density distribution of the mandibular cortical bone have been clarified, automated finite element modeling has indicated stress distribution in the craniofacial skeleton, and patient‐specific 3‐D images of the mandible have been depicted as a motion picture. These studies were completed in 124 living subjects (75 females, 49 males) between 8 and 33 years of age. From these results, malfunctions during mastication were evaluated clearly with the individual patient craniofacial structures and its characteristics. These computer‐based visualization techniques can be used to derive much clinically useful information, and to improve the combined evaluation of both static characteristics and dynamic function.
Three‐dimensional visualization of the craniofacial patient: volume segmentation, data integration and animation
Authors: Enciso R , Memon A , Mah J
Published: November 2004

Authors–Enciso R, Memon A, Mah J

The research goal at the Craniofacial Virtual Reality Laboratory of the School of Dentistry in conjunction with the Integrated Media Systems Center, School of Engineering, University of Southern California, is to develop computer methods to accurately visualize patients in three dimensions using advanced imaging and data acquisition devices such as cone‐beam computerized tomography (CT) and mandibular motion capture. Data from these devices were integrated for three‐dimensional (3D) patient‐specific visualization, modeling and animation. Generic methods are in development that can be used with common CT image format (DICOM), mesh format (STL) and motion data (3D position over time).

This paper presents preliminary descriptive studies on: 1) segmentation of the lower and upper jaws with two types of CT data – (a) traditional whole head CT data and (b) the new dental Newtom CT; 2) manual integration of accurate 3D tooth crowns with the segmented lower jaw 3D model; 3) realistic patient‐specific 3D animation of the lower jaw.
Craniofacial imaging informatics and technology development
Authors: Vannier MW
Published: November 2004

Structured Abstract

Author– Vannier MW

Purpose – ‘Craniofacial imaging informatics’ refers to image and related scientific data from the dentomaxillofacial complex, and application of ‘informatics techniques’ (derived from disciplines such as applied mathematics, computer science and statistics) to understand and organize the information associated with the data.

Method – Major trends in information technology determine the progress made in craniofacial imaging and informatics. These trends include industry consolidation, disruptive technologies, Moore's law, electronic atlases and on‐line databases. Each of these trends is explained and documented, relative to their influence on craniofacial imaging.

Results – Craniofacial imaging is influenced by major trends that affect all medical imaging and related informatics applications. The introduction of cone beam craniofacial computed tomography scanners is an example of a disruptive technology entering the field. An important opportunity lies in the integration of biologic knowledge repositories with craniofacial images.

Conclusion – The progress of craniofacial imaging will continue subject to limitations imposed by the underlying technologies, especially imaging informatics. Disruptive technologies will play a major role in the evolution of this field.
Image file interoperability for data protection, communication and trans‐system connectivity
Authors: Farman AG , Lapp RP
Published: November 2004

Authors –
Farman AG, Lapp RP

DICOM (Digital Imaging and Communication in Medicine) is a set of international imaging standards developed for medicine and extended to incorporate other professions. These standards encompass primary digital and secondary capture images made for dental diagnostic procedures. The standards provide a basis of interoperability for digital system outputs, providing portability and reducing the danger of obsolescence that would render valuable diagnostic information impossible to display. The American Dental Association, through the activities of its Working Group 12.1, is promoting interoperability within DICOM as the industry standard for digital imaging in dentistry.
Lessons learned from a randomised controlled trial on web learning
Authors: Canegallo L. , Pinelli I. , Beccalli M. G. , Lodi G. , Bez C. , Demarosi F. , Sardella A. , Esposito A. , Visioli S. , Zannini L. , Carrassi A.
Published: November 2004

The web‐based course in Oral Pathology ran its third edition during the academic year 2001–2002. To encourage the independence in the selection of contents, site structure supports not only a ‘guided’ and sequential, but also a ‘free’ usage of the learning material. Qualitative evaluations conducted during the last 2 years through questionnaires and interviews reported a positive feedback from students. However, due to lack of quantitative data regarding the added value of a dual‐mode web‐based course versus the in‐class teaching course, we decided to undertake a pilot randomised control trial (RCT) to measure the learning gain of students who had access to the web support. The aim of this work is to present difficulties emerged in the design of such a study. Authors point out their experience about the following aspects: appropriateness of outcomes considered (pre‐ and post‐test and questionnaires were distributed to assess learning and skills developed in hypothetical deductive reasoning; final examination marks were also considered); methods of randomisation and groups' matching (students were assigned randomly to a test and control group; a later analysis of pre‐tests and questionnaires showed that the two groups were comparable); study design (study design had to be a cross‐evaluation, but due to practice difficulties we could not cross the groups); control of the web access (only the test group received a password to log in), duration of the trial (it was not possible to limit the site access for several months; therefore, trial lasted 5 weeks); influence of formal teaching (in order to record the teacher's behaviour during in‐class teaching activities an external observer, pedagogist, attended all lectures).

We can conclude that previously mentioned difficulties will limit the possibility to draw affordable results from this first attempt of RCT on web learning, even if data collected are still under analysis. However, the authors hope their experience will be helpful when planning and setting up similar evaluations in other European Faculties' web based courses.
Constitutive activation of STAT transcription factors in acute myelogenous leukemia
Authors: Spiekermann K. , Biethahn S. , Wilde S. , Hiddemann W. , Alves F.
Published: November 2004

Abstract: Hematopoietic growth factors (HGF) are essential for proliferation and differentiation of hematopoietic precursors and activate a distinct set of JAK‐STAT (Janus kinases‐signal transducers and activators of transcription) proteins. Previous results from our group have shown a strong expression of JAK‐STAT proteins in primary acute myelogenous leukemia (AML) blasts and AML cell lines. Here, we asked whether a constitutive activation of the JAK‐STAT pathway might be involved in the pathogenesis of AML. We could demonstrate a constitutive activation of STAT1, 3 and 5 by immunoprecipitation of the tyrosine phosphorylated proteins in different human AML cell lines. Three patterns of STAT activation were found: (I) activation of only STAT1, (II) activation of STAT1 in combination with STAT3, and (III) activation of STAT1, 3 and 5. Furthermore, STAT1 and 3 formed stable heterodimers only in cell lines with constitutive STAT3 activation. In all cell lines analyzed, tyrosine phosphorylation of the four known Janus kinases could not be detected, although JAK1 was stably associated with STAT3. To further analyze whether a constitutive activation of tyrosine kinases might contribute to the autonomous growth of AML blasts, inhibitor studies were performed. The tyrphostin AG490, an inhibitor of the JAK‐STAT pathway, but not A1, an inactive tyrphostin induced a time‐ and dose‐dependent growth arrest without overt morphological signs of differentiation in AML cell lines. Our results show that STAT transcription factors are constitutively activated in human AML cell lines and might contribute to the autonomous proliferation of AML blasts. Inhibition of this pathway might be of interest for the establishment of more specific antileukemic strategies.
The effects of supraphysiological doses of corticosteroids in hypotensive liver failure
Authors: Harry Rachael , Auzinger Georg , Wendon Julia
Published: November 2004

Abstract: Background: In septic shock, supraphysiological doses of corticosteroids reduce norepinephrine requirements. We reviewed our experience of this treatment in hypotensive liver failure.

Methods: We retrospectively analysed 20 patients with liver failure who were treated with supraphysiological doses of hydrocortisone because of norepinephrine dependence. We compared their norepinephrine requirements, outcome, microbiology and incidence of gastrointestinal bleeding to an historical control group treated with norepinephrine but not corticosteroids.

Results: After 48 h of steroid treatment, the median norepinephrine dose was reduced (0.14 µg/kg/min to 0.08 µg/kg/min; P < 0.05) while the blood pressure over the same period of time did not change significantly (67.3 mm Hg to 70 mm Hg). Duration of ITU stay was longer in the steroid treated group (13.5 days vs 3 days; P < 0.05) but survival was similar in both groups. There were 23 episodes of positive bacterial cultures after norepinephrine was started in the steroid treated group, compared with 18 episodes in the control group. More of the positive cultures were due to resistant organisms in the steroid treated group (65% vs 17% in the control group; P < 0.002). There was no significant bleeding due to gastrointestinal inflammation in either group.

Conclusions: Supraphysiological doses of corticosteroids reduce norepinephrine requirements in hypotensive liver failure. They do not improve survival but may extend time to find a suitable donor in those awaiting urgent liver transplantation.
Does predation maintain tit community diversity?
Authors: Kullberg Cecilia , Ekman Jan
Published: November 2004

European tits of the genus Parus constitute a complex group of
coexisting boreal birds. Here we present a survey of the distribution of
three coniferous‐living Parus species and one of their main
predators, the pygmy owl (Glaucidium passerinum), on nine isolated
islands in Scandinavia. On all islands the coal tit (Parus ater)
is the sole tit species when the pygmy owl is absent. The two larger
species, the willow tit (P. montanus) and the crested tit (P.
cristatus), only coexist with the coal tit when pygmy owls are present. We suggest that the coexistence of willow tits, crested tits and coal tits is the result of a combination of competition for food and predator‐safe foraging sites. The smaller coal tit is superior in exploitation competition for food, while the two larger species have an advantage in interference competition for predator‐safe foraging sites. The association between the distribution of the pygmy owl and the two larger tit species on isolated islands in Scandinavia is consistent with the idea that the pygmy owl is a keystone predator.
Immobilization of tissue iron on calcareous soil: differences between calcicole and calcifuge plants
Authors: Zohlen Angelika , Tyler Germund
Published: November 2004

Deficiency of P and sometimes of micronutrients, especially Fe, is of importance to the calcicole–calcifuge behaviour of plants. Calcifuge species are unable to solubilize these elements or keep them metabolically active in sufficient amounts on calcareous soils. To demonstrate if calcicole, calcifuge and ‘soil indifferent’ species differ in Fe nutrition dynamics, samples of such species were transplanted on a slightly acid silicate soil (pH BaCl2 ca
4.0) and on a calcareous soil (pH BaCl2 ca 7.2). Plants were
grown in a computer‐controlled greenhouse at a soil moisture content of
50–60% water holding capacity and with additional light (ca 160
μE s−1 m−2, 12 h
d−1) if ambient light was <120 μE
s−1 m−2.  The calcifuge species developed chlorosis when grown on the calcareous soil, whereas the other species did not. Calcareous‐soil grown plants had less 1,10‐phenanthroline extractable Fe in their leaf tissues than the silicate‐grown plants whereas total leaf Fe showed more species specific properties. The ratio of 1,10‐phenanthroline extractable to total Fe in the leaves was significantly lower in the calcifuges than in the calcicoles when grown on the calcareous soil. ‘Soil indifferent’ species did not differ much from the calcicoles. Root Fe, fractioned as DCB extractable ‘plaque’ on the root surface and Fe remaining in the root after DCB extraction, showed no distinct pattern of DCB‐Fe related to the different categories, but remaining root Fe tended to be lower in the calcifuges compared to the two other categories. Leaf colour estimated by a colour scale correlated well with chlorophyll a+b content measured in the leaves of two calcifuges. Leaf P concentrations did not differ between the different categories but were more species dependent.  We conclude that chlorosis in calcifuge species is related to an immobilization of Fe in physiologically less active forms in the tissue, if plants are forced to grow on a calcareous soil, whereas calcicole and ‘soil indifferent’ species are able to retain a much higher share of their leaf Fe in metabolically active form. This probably decreases the vitality and may exclude calcifuge plants from calcareous soil. We consider this property, previously almost unconsidered in an ecological context, as important to the calcifuge–calcicole behaviour of plants.
Conflicting interests of plants and the natural enemies of herbivores
Authors: Van Der Meijden Ed , Klinkhamer Peter G. L.
Published: November 2004

In the literature there is a persistent temptation to accept at face value the hypothesis that plants manipulate the natural enemies of their herbivores. This hypothesis has received a lot of attention both theoretically and in reductionist laboratory experiments, but evidence that plants actually benefit from the active attraction of natural enemies in the field is virtually absent. Especially for parasitoids the validity of this 'evolutionary enlistment hypothesis’ should be questioned. In this paper we discuss conditions that may select for active attraction by plants of the third trophic level and formulate a number of questions that should be answered before we can accept this hypothesis.
Combined effects of shade and drought on tulip poplar seedlings: trade‐off in tolerance or facilitation?
Authors: Holmgren Milena
Published: November 2004

It has been hypothesised that many natural plant distribution patterns can be explained by a trade‐off between shade and drought tolerance which would make plants more sensitive to shade under dry conditions. On the other hand, shading by nurse plants is often observed to enhance growth and survival of smaller plants in dry areas. This paper describes an experiment designed to address the interactive effects of drought and shade on growth and physiology of tulip poplar seedlings (Liriodendron
tulipifera) grown in shade houses under different combinations of irradiance (1%, 5%, 12%, 17%, and 27% of ambient PAR) and soil water content (5–9%, 11–15%, and>20%). The results show no evidence that higher PAR levels compensate for the negative effects of drought on photosynthesis and growth. Rather, rates of estimated daily shoot carbon gain decreased with PAR under dry conditions. Daily xylem sapflow patterns indicated that this was associated with a strong reduction in stomatal conductance in plants growing in dry soil and high PAR conditions. Whole‐shoot light compensation points were higher for plants raised under higher PAR conditions, but were not significantly influenced by the water treatments. Shoot dark respiration rates decreased under drier conditions. These results do not support the hypothesis of a trade‐off between shade and drought tolerance. Instead, they indicate mechanisms that can lead to positive effects of shading by neighbouring plants under dry conditions. Indeed, such facilitation is thought to be important in many plant communities.
Spatial proximity between two host plant species influences oviposition and larval distribution in a leaf beetle
Authors: Ballabeni Pierluigi , Conconi Davide , Gateff Sophie , Rahier Martine
Published: November 2004

Everything else being equal, insect herbivores can be expected to oviposit on host plants that provide the qualitatively and quantitatively best food for larvae. However, the selection of a plant for oviposition may be influenced by such ecological factors as natural enemies, host distribution, host patch size or host patch density. We performed a field study to test whether spatial proximity between two host plant species influences the oviposition patterns and larval distribution of the alpine leaf beetle Oreina elongata. In the population studied, O. elongata oviposits and feeds on two host plants, that belong to the same family (Asteraceae): Adenostyles alliariae and Cirsiumspinosissimum. The first species contains pyrrolizidine alkaloids that are sequestered by the beetle as a chemical defence, whereas the second plant does not contain any alkaloids but has hairy and spiny leaves that might give some mechanical protection to beetle larvae. 
During two consecutive summers, we quantified oviposition and larval distribution on randomly chosen C. spinosissimum that grew spatially isolated from A. alliariae, on C. spinosissimum that grew in leaf contact with A. alliariae and on A. alliariae that grew in leaf contact with C. spinosissimum (isolated A. alliariae was not considered, because it is rare in the study population). In both years, more eggs were laid on C. spinosissimum than on A. alliariae and more on those C. spinosissimum that were growing close to A. alliariae than on those growing isolated. Large numbers of larvae moved from C. spinosissimum to A. alliariae during the season. Patch size did not influence egg and larval numbers. Eggs survived better on C. spinosissimum than on A. alliariae in the field. The data suggest that C. spinosissimum may provide eggs with better protection against stormy weather. In a separate study of the same population, we found that larval performance was better on A. alliariae than on C. spinosissimum. Our present data suggest that O. elongata preferentially oviposits on plants of the species that maximizes egg survival and that grow in close proximity to plants of the species that provides better food and chemical defence.
Short‐term versus long‐term effects of food intake on reproductive output in a viviparous snake, Vipera aspis
Authors: Bonnet X. , Naulleau G. , Shine R. , Lourdais O.
Published: November 2004

Feeding rates influence reproductive output in many kinds of animals, but we need to understand the timescale of this influence before we can compare reproductive energy allocation to energy intake. A central issue is the extent to which reproduction is fuelled by long‐term energy stores (“capital” breeding) versus recently‐acquired resources (“income” breeding). Our data on free‐living aspic vipers show that there is no simple answer to this question: reproductive frequency is determined by long‐term energy stores, offspring size is influenced by maternal food intake immediately before ovulation, and litter size is influenced by both long‐term stores and short‐term energy acquisition. Thus, offspring size in free‐living vipers reflects the mother's energy balance over the preceding year (via a trade‐off between litter size and offspring size) as well as her energy balance in the current breeding season. Hence, different components of a given reproductive output (litter) are not only functionally linked, but also respond to different temporal scales of prey availability. A female's body size has little effect on her reproductive output. Attempts to quantify reproductive energy allocation must take into account the fact that different reproductive traits (such as offspring size versus number) may respond to energy availability over different timespans. Thus, although the aspic viper is a typical “capital breeder” in terms of its reliance on stored reserves for maternal “decisions” concerning reproductive frequency, it is to some degree a facultative “income breeder” with respect to the determination of offspring size and litter size.
The changing place of theory in 20th century ecology: from universal laws to array of methodologies
Authors: Ghilarov Alexei M.
Published: November 2004

From the beginning of the 20th century ecologists have tried to do self‐sufficient hard science that possesses real theory and laws. Early mathematical models were partly borrowed from physics and chemistry. For a long time they were the characteristic feature of theoretical ecology despite the striking absence of supporting empirical data. In the late 1960s a growing disappointment in “classical” theoretical foundations of ecology forced some researchers to propose “pattern‐oriented” models that were derived from observation of real populations, communities and ecosystems, rather than from common sense written in mathematical language. However, this view had its own shortcomings, and in the 1980s it was supplemented by a “mechanistic” approach aimed at understanding basic processes and constraints. This shift of attention from general “laws” to “patterns” and later to “mechanisms” corresponds to an evident weakening of demands for theoretical rigour. Although there are great doubts about the existence of universal laws in ecology, ecologists continue to search for generalities. This search has resulted in an elaboration of methodologies that describe post hoc changes in populations, communities and ecosystems, with limited predictive ability.
Horizontally acquired mutualisms, an unsolved problem in ecology?
Authors: Wilkinson David M. , Sherratt Thomas N.
Published: November 2004

Current models of the evolution and maintenance of mutualism stress the importance of vertical transmission and the genetic uniformity of symbionts to evolutionary stability. Here we point out that many well‐known mutualistic relationships involve symbionts that are neither vertically transmitted nor genetically uniform. We have therefore re‐examined some of the existing models in an attempt to identify general conditions under which horizontally acquired mutualisms might be evolutionarily stable.
A general model of site‐dependent population regulation: population‐level regulation without individual‐level interactions
Authors: McPeek Mark A. , Rodenhouse Nicholas L. , Holmes Richard T. , Sherry Thomas W.
Published: November 2004

In this paper, we use a modeling approach to explore the population regulatory consequences of individual choices for where to breed in heterogeneous environments. In contrast to standard models, we focus on individuals that interact only indirectly through their choices of breeding sites (i.e., individuals preempt the occupation of a breeding site by others when they choose to breed there). We consider the consequences of individuals choosing breeding sites either randomly or sequentially from best to worst. Our analysis shows that average per‐capita fecundity of the population is independent of the number of occupied breeding sites if individuals choose sites at random and that variation in average per‐capita fecundity increases as population size declines. In contrast, if individuals choose breeding sites sequentially from highest to lowest quality, then as population size increases average per‐capita fecundity declines and variation in average per‐capita fecundity increases. Consequently, aggregate population‐level demographic rates can change in ways that generate population regulation, even when change in population size does not change the demographic performance of any individual on any particular breeding site. However, such regulation occurs only when individuals make adaptive choices of where to breed. Because variation in average per‐capita fecundity decreases when population size declines, populations regulated in a site‐dependent manner should be much less susceptible to the vicissitudes of small population size than those which choose breeding sites at random.
Mineral diversity in wild plants: benefits and bane for moose
Authors: Ohlson Mikael , Staaland Hans
Published: November 2004

We studied the mineral nutrition ecology of moose, Alces alces, by a comprehensive examination of concentration levels of 18 elements in browsing plants, and in rumen and distal colon contents, respectively. The plants, in total 14 species, included deciduous and evergreen trees, shrubs, herbs, grasses and aquatic macrophytes. Our study was done in four sites in southern Norway and the plants were sampled in spring, summer, autumn and winter to document seasonal trends. The plants were generally characterized by low concentrations of major elements, very low phosphorus: calcium ratios, and the willow Salix aurita– a preferred browse – had high cadmium concentrations, up to 9 ppm (dry mass). Sodium concentrations in terrestrial plants were significantly under the dietary requirement, while levels were sufficient in aquatic plants, which, however, had high concentrations of toxic heavy metals. We suggest that the moose experience a nutritional dilemma as a strong physiological need for sodium results in an overintake of heavy metals. A selective intake of plants rich in heavy metals was corroborated by high heavy metal concentrations in rumen and distal colon. Over all, the plants were characterized by a marked mineral diversity due to element concentration levels that were highly variable between species and sites. Thus, there is a strong link between plant species diversity and mineral diversity, which has a pivotal role for herbivores. It is concluded that a diversity of plant species is a prerequisite for the mineral diversity that the moose needs to obtain essential minerals, not only in sufficient amounts, but also in physiologically balanced proportions.
Size constraints in a real food web: predator, parasite and prey body‐size relationships
Authors: Leaper Rebecca , Huxham Mark
Published: November 2004

In the absence of well‐resolved food webs that include both information on predators and parasites, body‐size has been proposed as the biological mechanism underlying the assumption of a trophic hierarchy in the cascade model and its variants. We show that parasites consume prey larger than themselves, and therefore the logical conclusion is that the trophic hierarchy cannot be justified on the basis of body‐size when food webs include parasites. Two other assumptions central to the cascade model and its variants, the link‐species scaling law and the probability of predation, are not supported by the empirical data presented here. We show that linkage density is scale‐dependent rather than independent, but that the relationship between linkage density and web size is far from clear. Specifically, the webs that exclude parasites examined here, overestimate the values of linkage density and connectance by more than one order of magnitude. There is little evidence for a relationship between predator generalisation (the number of prey exploited by a predator), prey vulnerability (the number of predators exploiting a prey) and trophic position within each web, when trophic position corresponds to an ordering by size. Therefore the probability of predation neither remains constant as assumed under the original cascade model, nor increases with trophic position (increasing body‐size) as assumed under some of its variants. The present study however, does show some support for the notion that the cascade model's assumption of constant predation probability should be replaced by heterogeneous predation probabilities. We also examined the relationship between the morphological niche of consumers, a metric where resources falling within a defined size are always taken, and a parameter that may be closely linked to the connectance of whole food webs, but rarely examined in empirical webs. Although we could find no evidence for trends in morphological niche with trophic position, further investigation of the consequences of individual or species‐level feeding constraints on the connectance of webs may repay further investigation. We contend that the organisms often most neglected in food web studies e.g. parasites and pathogens, must be included in food webs if we are able to make more realistic descriptions of the trophic structure of natural communities, and to develop mechanistic explanations for the structure of natural food webs.
The impact of a sit‐and‐wait predator: separating consumption and prey emigration
Authors: Woodward Guy , Hildrew Alan G.
Published: November 2004

Reviews of the impact of invertebrate predators in enclosure/exclosure experiments suggest that much of the apparent depletion of prey is due to prey emigration induced by the predators. However, these generalisations derive mainly from studies of invertebrate predators that are predominantly active searchers (usually stoneflies) and of prey with strong avoidance responses (mainly mayflies).

We examined the impact of a large sit‐and‐wait predator, the nymph of the dragonflyCordulegaster boltonii, which has recently invaded Broadstone Stream as a new top predator. Field enclosure/exclosure experiments were conducted to assess the impact of the invader on the benthos. Depletion of prey varied seasonally and among taxa, and was highest when prey density and encounter rates were high. Mobile prey, although least likely to show a statistically significant response because of high exchange rates, were those most strongly depleted.

Experimental channels were used to separate the relative contribution of consumption and emigration to total impact for the two most depleted prey species. Depletion of prey was due solely to consumption and predators did not induce emigration. We therefore urge caution in making generalisations about the impacts of invertebrate predators, since sit‐and‐wait and searching predators potentially have very different impacts.
Extinctions in simple and complex communities
Authors: Fowler Mike S. , Lindström Jan
Published: November 2004

Disagreement exists between the results of theoretical and empirical exploration into the effect of increasing community complexity on the stability of multispecies ecosystems. A recent return to interest in this area suggests previous results should be re‐assessed, from both experimental studies and models, to understand where this discrepancy arises from. Here we propose various simple extensions to a standard multispecies community model that each increase the complexity of the system in a different way. We find that increasing the number of species in a community leads to a decrease in community persistence after the system is perturbed, and go on to show that increasing the dynamical diversity of the community members leads to an increase in stability through a reduction in extinction events, relative to the less complex form of the model. Our results suggest that different forms of complexity lead to different outcomes in the stability properties of the community. While aspects of this work agree with previous empirical findings that more complex communities are more robust to perturbation, we stress that the type of complexity included and the measure of stability used in community models must be properly defined, to allow objective comparisons to be made with previous and future work.