bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel dissociation mechanism of a polychaetous annelid extracellular haemoglobin
Authors: Rousselot Morgane , Le Guen Dominique , Chabasse Christine , Zal Franck
Published: February 2006

The extracellular haemoglobin of the marine polychaete, Arenicola marina, is a hexagonal bilayer haemoglobin of ≈ 3600 kDa, formed by the covalent and noncovalent association of many copies of both globin subunits (monomer and trimer) and nonglobin or ‘linker’ subunits. In order to analyse the interactions between globin and linker subunits, dissociation and reassociation experiments were carried out under whereby Arenicola hexagonal bilayer haemoglobin was exposed to urea and alkaline pH and the effect was followed by gel filtration, SDS/PAGE, UV‐visible spectrophotometry, electrospray‐ionization MS, multiangle laser light scattering and transmission electron microscopy. The analysis of Arenicola haemoglobin dissociation indicates a novel and complex mechanism of dissociation compared with other annelid extracellular haemoglobins studied to date. Even though the chemically induced dissociation triggers partial degradation of some subunits, spontaneous reassociation was observed, to some extent. Parallel dissociation of Lumbricus haemoglobin under similar conditions shows striking differences that allow us to propose a hypothesis on the nature of the intersubunit contacts that are essential to form and to hold such a complex quaternary structure.
Prediction of coenzyme specificity in dehydrogenases/ reductases
Authors: Kallberg Yvonne , Persson Bengt
Published: February 2006

Dehydrogenases and reductases are enzymes of fundamental metabolic importance that often adopt a specific structure known as the Rossmann fold. This fold, consisting of a six‐stranded β‐sheet surrounded by α‐helices, is responsible for coenzyme binding. We have developed a method to identify Rossmann folds and predict their coenzyme specificity (NAD, NADP or FAD) using only the amino acid sequence as input. The method is based upon hidden Markov models and sequence pattern analysis. The prediction sensitivity is 79% and the selectivity close to 100%. The method was applied on a set of 68 genomes, representing the three kingdoms archaea, bacteria and eukaryota. In prokaryotes, 3% of the genes were found to code for Rossmann‐fold proteins, while the corresponding ratio in eukaryotes is only around 1%. In all genomes, NAD is the most preferred cofactor (41–49%), followed by NADP with 30–38%, while FAD is the least preferred cofactor (21%). However, the NAD preponderance over NADP is most pronounced in archaea, and least in eukaryotes. In all three kingdoms, only 3–8% of the Rossmann proteins are predicted to have more than one membrane‐spanning segment, which is much lower than the frequency of membrane proteins in general. Analysis of the major protein types in eukaryotes reveals that the most common type (26%) of the Rossmann proteins are short‐chain dehydrogenases/reductases. In addition, the identified Rossmann proteins were analyzed with respect to further protein types, enzyme classes and redundancy. The described method is available at http://www.ifm.liu.se/bioinfo, where the preferred coenzyme and its binding region are predicted given an amino acid sequence as input.
Pentose phosphates in nucleoside interconversion and catabolism
Authors: Tozzi Maria G. , Camici Marcella , Mascia Laura , Sgarrella Francesco , Ipata Piero L.
Published: February 2006

Ribose phosphates are either synthesized through the oxidative branch of the pentose phosphate pathway, or are supplied by nucleoside phosphorylases. The two main pentose phosphates, ribose‐5‐phosphate and ribose‐1‐phosphate, are readily interconverted by the action of phosphopentomutase. Ribose‐5‐phosphate is the direct precursor of 5‐phosphoribosyl‐1‐pyrophosphate, for both de novo and ‘salvage’ synthesis of nucleotides. Phosphorolysis of deoxyribonucleosides is the main source of deoxyribose phosphates, which are interconvertible, through the action of phosphopentomutase. The pentose moiety of all nucleosides can serve as a carbon and energy source. During the past decade, extensive advances have been made in elucidating the pathways by which the pentose phosphates, arising from nucleoside phosphorolysis, are either recycled, without opening of their furanosidic ring, or catabolized as a carbon and energy source. We review herein the experimental knowledge on the molecular mechanisms by which (a) ribose‐1‐phosphate, produced by purine nucleoside phosphorylase acting catabolically, is either anabolized for pyrimidine salvage and 5‐fluorouracil activation, with uridine phosphorylase acting anabolically, or recycled for nucleoside and base interconversion; (b) the nucleosides can be regarded, both in bacteria and in eukaryotic cells, as carriers of sugars, that are made available though the action of nucleoside phosphorylases. In bacteria, catabolism of nucleosides, when suitable carbon and energy sources are not available, is accomplished by a battery of nucleoside transporters and of inducible catabolic enzymes for purine and pyrimidine nucleosides and for pentose phosphates. In eukaryotic cells, the modulation of pentose phosphate production by nucleoside catabolism seems to be affected by developmental and physiological factors on enzyme levels.
On the correlation of short gamma-ray bursts and clusters of galaxies
Authors: Ghirlanda G. , Magliocchetti M. , Ghisellini G. , Guzzo L.
Published: February 2006

We cross-correlate gamma-ray bursts (GRBs) and X-ray selected clusters of galaxies at z≤ 0.45. We find a positive 2σ signal for the angular cross-correlation function wbc(θ) on scales θ≤ 3° between short GRBs and clusters. Conversely, no correlation is found between clusters and the population of long GRBs. The comparison with the cluster autocorrelation function shows that short GRBs do not trace the cluster distribution, as not all short GRBs are found in clusters. A higher signal in wbc(θ) is found if we only consider the cluster population up to z= 0.1. By comparing the short-burst autocorrelation function with model predictions, we then constrain short bursts to mostly originate within ∼270 Mpc (i.e. z≤ 0.06). Our analysis also reveals that short GRBs are better correlated with ‘normal’ galaxies. The double compact-object merger model for short GRBs would associate them preferentially with early-type galaxies, but the present statistics do not allow us to exclude that at least a fraction of these events might also take place in late-type galaxies, in agreement with recent evidence.
A spectral slope versus perihelion distance correlation for planet-crossing asteroids
Authors: Marchi S. , Magrin S. , Nesvorný D. , Paolicchi P. , Lazzarin M.
Published: February 2006

The spectral slope of sunlight reflected by an asteroid surface may change with time as a result of several physical processes acting on the surface layer known as ‘space weathering’. The effects of space weathering are important for asteroid studies because they may help us to explain the paucity of spectroscopic analogues of ordinary chondrites (OCs) among the main belt asteroids.

In this Letter we report a new result that may be used to understand better how asteroid surfaces evolve with time. Using a large data set of spectroscopic observations of planet-crossing asteroids (near-Earth objects and Mars-crossers), we have found a statistically significant correlation between their spectral slope and the perihelion distance. We have also determined that the Q- and Sq-type planet-crossing asteroids are more abundant (relative to more space-weathered S-type asteroids) at small perihelion distances that characterize dynamically evolved orbits.

We take these results as evidence for some (so far neglected) process that modifies surfaces of planet-crossing asteroids. As originally proposed by Nesvorný et al., the close encounters of these objects with the terrestrial planets may produce tidal perturbations to their surfaces that may partially, or even completely, remove the old and weathered layers and expose non-weathered OC-like material. Our findings may provide new evidence for this process because standard models for the dynamical evolution of asteroids show that planet-crossing asteroids with small perihelion distances have undergone more frequent planetary encounters than those residing in more distant orbits. Therefore, if planetary encounters are important, the distribution of Q-type asteroids in the planet-crossing space should show a correlation with the perihelion distance, exactly as we have found here.
Consumer Credit Risk and Pricing
Authors: GETTER DARRYL E.
Published: February 2006

Previous academic studies viewed borrower rejection as a sign of market imperfections in the consumer credit markets, but this view was based upon the assumption that differences in the levels of borrower creditworthiness could not be accurately identified. Today, it is possible to differentiate between types of borrowers, and riskier borrowers can participate in credit markets if they are willing to pay relatively higher borrowing costs. Hence, a more critical issue concerning the performance of these markets should be whether loan prices correctly reflect the level of borrower credit risk. This paper reexamines consumer participation in credit markets looking specifically at issues related to the pricing of borrowers of different credit risk.
Understanding Parental Beliefs and Attitudes about Children's Sexual Behavior: Insights from Parental Style
Authors: CARLSON LES , TANNER JOHN F.
Published: February 2006

Parental style theory is used to explore how parents differ with regard to parental roles, attitudes, and perceptions about the consequences of teens engaging in sex. Findings from a survey of 150 parents indicate that parental style influences parents’ attitudes and beliefs concerning teen sex. Also, since parents do not have confidence about conveying sex‐related information to children, an opportunity may exist for empowering parents on how to discuss these topics with them. Such empowerment may be accomplished by provision of information to parents through health organizations and the government on how to engage in such conversations with children.
Defining the Consumer Interest: Challenges for Advocates
Authors: BROBECK STEPHEN
Published: February 2006

From its birth, The Journal of Consumer Affairs has provided a forum for government officials, consumer activists, and academics to discuss the definition of the consumer interest and how best to pursue it. In the inaugural issue of JCA, published in the summer of 1967, three of the first four articles were titled “The View from Washington” (by Deputy Assistant Secretary of Labor David Swankin), “Is It Time to Re‐Evaluate the Consumer Protection Activities of the Federal Government?” (by Consumers Union president Colston E. Warne), and “The Consumer Interest—the Real Issue” (by Professor of Marketing Robert D. Schooler). When JCA began publication in 1967, a few landmark pieces of consumer legislation had already been passed concerning pharmaceuticals, cigarettes, and motor vehicles, but the heyday of the consumer movement—and consumer research—was just beginning. In his article, Warne wrote: “The time has come, I think, for consumers and consumer movements to face some highly unpleasant problems” (p. 24). Schooler chastised the federal government for being “misdirected toward real but secondary issues” (p. 40). Swankin called for an organization and a professional journal capable of creating “an intellectual climate in which the phrases ‘consumer interest,’‘consumer economics,’ and, yes, ‘consumer information’ can be developed and can flourish” (pp. 9–10). Nearly forty years later, and long after the zenith of the U.S. consumer movement, we still face a host of consumer problems and a federal government disinclined to address them. We do, however, have a respected journal in whose pages the consumer interest and consumer policy can be examined. On April 25, 2005, the University of Utah hosted a symposium on consumer policy in honor of the retirement of Dr. John R. Burton. John, who established the consumer studies program at the University of Utah, has devoted his career to teaching, research, and service that advance the consumer interest. Seven nationally renowned speakers, including professors Monroe Friedman, Loren Geistfeld, Jeanne Hogarth, Jean Lown, and Ivan Preston, presented papers pertaining to the consumer interest. Two of the seven papers are reproduced here. The first is by Stephen Brobeck, long‐time executive director of the Consumer Federation of America (CFA) and the editor of The Encyclopedia of the Consumer Movement. Dr. Brobeck's article examines how a major consumer advocacy organization like CFA decides what public policy positions are in the consumer interest. The article applies a general framework to the specific issue of automobile fuel economy standards. In the companion piece to this article, Michael Burton, an assistant professor of political science at Ohio University and the son of the symposium's honoree, draws on his experience as a congressional aide and vice presidential staff member to describe and defend the art of compromise as it applies to consumer politics.

–Robert N. Mayer, University of Utah
“When to Hold ‘Em; When to Fold ‘Em”: Choosing Consumer Protection Battles
Authors: BURTON MICHAEL JOHN
Published: February 2006

On April 25, 2005, the University of Utah hosted a symposium on consumer policy in honor of the retirement of Dr. John R. Burton. All seven of the papers presented addressed, either directly or indirectly, the nature of the consumer interest. In the companion piece to this article, Dr. Stephen Brobeck, executive director of the Consumer Federation of America (CFA), describes how a major consumer advocacy organization like CFA decides what public policy positions are in the consumer interest. In this article, Michael Burton, an assistant professor of political science at Ohio University and the son of the symposium's honoree, draws on his experience on the staffs of Congressman Paul E. Kanjorski (1991–93) and Vice President Al Gore (1993–98) to describe and defend the art of compromise in advancing the consumer interest.

–Robert N. Mayer, University of Utah
The impact of nurse‐directed patient education on quality of life and functional capacity in people with heart failure
Authors: Kutzleb Judith , Reiner Dana
Published: February 2006

Purpose: The purpose of this research was to evaluate the impact of a nurse‐directed approach to patient education, which focused on lifestyle modification, daily weight management, diet, and medication compliance to improve the quality of life (QOL) and functional capacity in people with heart failure.

Data sources: This was a prospective quasiexperimental multicenter research study of 23 patients comparing a nurse‐directed care (NC) group (n= 13), which received comprehensive disease management education and weekly telephone follow‐up, and the routine care (RC) group (n= 10) that received protocol‐driven medical management. The study length was 12 months.

Conclusions: Analysis of covariance (ANCOVA) was used to test for equality of variance–covariance matrices in the study population over time. ANCOVA measured baseline and two data intervals for a total of 9 months between the control and experimental (NC and RC) groups. There was statistically significant improvement in the NC group for the domains of total QOL: F= 3.569, p= 0.000; health and function: F= 3.995, p= 0.003; social and economic: F= 14.109, p= 0.000; psychological and spiritual: F= 13.212, p= 0.000; and family: F= 2.384, p= 0.048. Functional capacity was not significantly impacted by the study team interventions (F= 0.228, p= 0.949).

Implications for practice: Results indicate that nurse‐directed patient education was effective in improving QOL. A nurse‐directed treatment strategy significantly improves patients’ role in symptom control and disease self‐management.
The use of the nicotine inhaler in smoking cessation
Authors: Burkett Jenny Sigel
Published: February 2006

Purpose: To raise awareness among nurse practitioners (NPs) about the nicotine inhaler by providing clinical and practical information about the use of the nicotine inhaler as a treatment option for smoking cessation.

Data sources: This included data‐based and review articles in the medical literature, tobacco use and dependence clinical practice guideline, and Medline and Cinahl search engines. Criteria for search keywords were “nicotine inhaler” and “nicotine replacement therapy.” Initial search was done in December 2004.

Conclusions: The nicotine inhaler has been tested as safe and efficacious in the treatment of tobacco cessation. Clinical trials show the nicotine inhaler to be useful alone or as an adjunct to other pharmacological therapies. Current national guidelines recommend that the nicotine inhaler be used in smoking cessation therapy.

Implications for practice: The nicotine inhaler is appropriate for many different smokers, including certain types of cardiac patients. NPs can include the nicotine inhaler in a group of nicotine replacement therapies to ensure that smokers are successful in tobacco cessation.
Disorders of glucose metabolism in the context of human immunodeficiency virus infection
Authors: Larson Ruth , Capili Bernadette , Eckert‐Norton Margaret , Colagreco Joseph P. , Anastasi Joyce K.
Published: February 2006

Purpose: To discuss the pathophysiology and the current treatment approaches for the dysregulation of glucose metabolism in the context of human immunodeficiency virus (HIV) infection.

Data sources: Selected research, clinical studies, clinical guidelines, and review articles.

Conclusions: In HIV infection, multiple factors are associated with the pathogenesis of glucose dysregulation. Studies suggest that protease inhibitors, a class of antiretroviral agent, as well as viral factors, lipodystrophy, hepatitis C infection, injection drug use, and second‐generation antipsychotics have been implicated in the development of glucose disorders and diabetes. Current treatment recommendations are based on extrapolated data from non‐HIV diabetic patients. More research is needed to establish the most appropriate management for the disorders of glucose metabolism in the context of HIV infection.

Implications for practice: If left untreated, patients are at increased risk for cardiovascular disease and complications associated with untreated diabetes.
Improving patient outcomes with ambulatory blood pressure monitoring in elderly with hypertension
Authors: Frost Brandy K. , Hajjar Ihab M.
Published: February 2006

Purpose: The purpose of this article is to review the current knowledge regarding ambulatory blood pressure monitoring (ABPM) use in clinical practice and to provide example cases for its use in a hypertension (HTN) specialty clinic.

Data sources: Published research trials, medical literature, and cases from the Center for Senior Hypertension.

Conclusions: The knowledge of ABPM benefits to using ABPM are substantial and improves the care and management of many conditions, including white coat HTN, white coat normotension, resistant, borderline, episodic, paroxysmal HTN, and finally orthostatic hypotension. Third‐party payers only cover ABPM for “white coat” HTN.

Implications for practice: This article reviews previous studies and explains the benefit to changing our current practice to match the knowledge we have gained through research through case studies.
Concordance of provider recommendations with American Diabetes Association's Guidelines
Authors: Morritt Taub Leslie‐Faith
Published: February 2006

Purpose: To determine if selected client characteristics were factors influencing the provision of provider advice for diet, exercise, smoking cessation, alcohol cessation, eye and foot care, and influenza and pneumonia vaccine for those told by a provider that they had diabetes.

Data sources: Data from the 2001 National Health Interview Survey were used in a secondary analysis to answer the research question. This study used a subsample who self‐reported having provider‐diagnosed diabetes; the subsample comprised 2287 unweighted subjects that, when weighted, represent 6.38% of the civilian noninstitutionalized individuals with diabetes in the United States.

Conclusions: This study suggests that many patients are not receiving all the eight processes of care studied, particularly those with new onset diabetes, elders, black people, and Hispanics.

Implications for practice: This study suggests that the present paradigm is not early prevention but treatment of established disease. Changes in entrenched thinking about clinical care need to be addressed. Patients with diabetes need to have an awareness that there is a standard of optimal care, and they should be encouraged to seek those who provide this care. Further, system changes may be required to address changes that are not easily made at the provider level.
Breathing pattern and kinematics in normal subjects during speech, singing and loud whispering
Authors: Binazzi B. , Lanini B. , Bianchi R. , Romagnoli I. , Nerini M. , Gigliotti F. , Duranti R. , Milic‐Emili J. , Scano G.
Published: February 2006

Aims:  We used for the first time a non‐invasive optoelectronic plethysmography to assess breathing movements and to provide a quantitative description of chest wall kinematics during phonation.

Methods:  Volumes of different chest wall compartments (abdomen and lung apposed to rib cage and abdomen) were assessed using optoelectronic plethysmography in 16 normal Italians (eight men) during reading, singing and high‐effort whispering (HW).

Results:  During phonation the breathing pattern was different from quiet breathing and exercise. (1) During phonation, tidal volume and expiratory time increased while inspiratory time decreased. The expiratory volume changes and flows during HW were considerably greater than during vocalization. During HW, the overall end‐expiratory thoracic volume significantly decreased as a result of decreased volume of all compartments and essentially impinged on the maximal expiratory flow‐volume curve. (2) While, as previously shown, during exercise the expired volume is due entirely to the abdomen, during phonation all three chest wall compartments contribute to it. Under all conditions studied breathing was, on average, more costal in females than in males but this was mainly related to different size rather than gender per se.

Conclusions:  Physical characteristics have a greater importance than gender in determining breathing pattern and chest wall kinematics during phonation. The activity of the control of expiration during phonation is more complex than during exercise.
Localization of tubular uptake segment of filtered Cystatin C and Aprotinin in the rat kidney
Authors: Baran D. , Tenstad O. , Aukland K.
Published: February 2006

Aim:  The renal tubular uptake of 125I‐Aprotinin (*Ap) is on average located more superficially than its filtration site, causing transfer of some of *Ap filtered in deep to more superficial cortical zones. 125I‐Cystatin C (*Cy) showed less uptake in deep cortical zones than Ap, suggesting a longer and/or a more superficial tubular uptake site. To test that hypothesis and to quantify the outward transfer of the filtered polypeptides, we estimated the tubular uptake pattern of the tracers in perfusion fixed rat kidneys after intravenous injection of *Cy and *Ap.

Methods:  Autoradiographs were made from 10 μm thick slices of Microfil nephron casts from outer (OC), middle (MC) and inner (IC) cortical zones to quantify cortical border‐crossing *Ap transfer. Single nephron glomerular filtration rate (snGFR) was estimated as the zonal uptake of *Ap corrected for *Ap transfer, divided by its time‐integrated plasma concentration and the zonal number of glomeruli.

Results:  *Ap and *Cy uptake fell exponentially along the proximal convoluted tubule (PCT), indicating an uptake proportional to luminal concentration. Uptake in IC exceededx that in MC and OC nephrons. The per cent PCT length with *Cy uptake (67.2 ± 1.6) exceeded that of *Ap (54.6 ± 1.8). The zonal border‐crossing PCT length (29–34% of total PCT) from deep to more superficial cortical zones transferred 4–6% more *Cy than *Ap.

Conclusion:  Greater tubular uptake length of *Cy than of *Ap causes more cortical border‐crossing of *Cy. The zonal snGFR estimated from Aprotinin uptake corrected for border‐crossing agreed well with that obtained with the Hanssen ferrocyanide technique.
Energy input and species diversity patterns in microcosms
Authors: Warren Philip H. , Weatherby Anita J.
Published: February 2006

Numerous studies document some form of relationship between the energy input to a community (or some surrogate for energy input), and the species richness of all, or part, of the community. Although not consistently so, the relationship is commonly either unimodal or positive. However covariation of energy with other environmental factors, in both field and experimental studies, and the timescale of expected population responses to variation in energy, means that testing the patterns is difficult. Here we use laboratory microcosm systems, of protists and bacteria, to examine the response of artificially constructed communities to an energy gradient (6 levels), on a long timescale (up to 421 days), while in parallel examining the responses of each species individually to the environmental conditions across the gradient. The species richness of individual communities (α‐diversity) showed positive responses initially, but after longer periods either no relationship, or a modestly unimodal one. When all replicate communities were considered together at each energy level (γ‐diversity), there was a more consistently positive relationship, an effect generated by the fact that at low energy the species composition of replicate communities was almost identical, while at high energy there was considerable variation among replicates. Although when each species used in the multispecies systems was exposed to the same energy gradient individually, there were distinct differences in the their responses to the gradient, the patterns of community composition and diversity seen in the multispecies systems could not be explained simply by the individual species’ responses to the environmental conditions along the gradient.
Two ecologically‐divergent generalist predators have different responses to landscape fragmentation
Authors: Marshall Samuel D. , Walker Sean E. , Rypstra Ann L.
Published: February 2006

We conducted three replicated field experiments to test the population response of two ecologically‐divergent wolf spider species (Hogna helluo and Pardosa milvina) to three correlates of landscape fragmentation: area reduction, spatial subdivision, and increased edge to core ratio. We selected these two species because they differ in vagility and habitat selectivity. Hogna helluo is relatively large, averse to disturbed substrata, and has poor colonization abilities. Conversely, Pardosa is small, vagile, and will use barren, disturbed areas. In a test for the effect of area reduction on populations of the two wolf spiders, we destroyed 0%, 20% or 80% of randomly selected habitat islands in replicated experimental landscapes. We found that population densities of Hogna declined significantly, even at the lowest level of area reduction (20%), and that there was an increase in numbers of Pardosa. In a test for the response to an increase in landscape subdivision, we created four levels of habitat fragmentation in replicate plots. We found a significant decline in Hogna populations with increasing fragmentation. Pardosa populations did not respond to the fragmentation. In the third experiment we kept landscape area and subdivision constant, but manipulated the edge‐to‐core ratio. We found that populations of Hogna declined sharply with increasing edge, and that populations of Pardosa did not respond. These two syntopic wolf spiders have distinctly different responses to landscape fragmentation.
Functional and numerical responses of four lemming predators in high arctic Greenland
Authors: Gilg Olivier , Sittler Benoît , Sabard Brigitte , Hurstel Arnaud , Sané Raphaël , Delattre Pierre , Hanski Ilkka
Published: February 2006

The high‐arctic tundra ecosystem has the world's simplest vertebrate predator–prey community, with only four predators preying upon one rodent species, the collared lemming (Dicrostonyx groenlandicus). We document the functional and numerical responses of all the four predators in NE Greenland. Using these data, we assess the impact of predation on the dynamics of the collared lemming with a 4 yr cycle and >100‐fold difference between maximum and minimum densities. All predator species feed mostly (>90%) on lemmings when lemming density is >1 ha−1, but the shapes of the predators’ responses vary greatly. The snowy owl (Nyctea scandiaca) is present and breeds only when lemming densities at snowmelt are >2 ha−1, giving rise to a step‐like numerical response. The long‐tailed skua (Stercorarius longicaudus) has a type III functional response and shifts from alternate food (mainly berries and insects) to lemmings with increasing lemming density. The skua surpasses all the other predators in summer by its total response. The type III functional response of the Arctic fox (Alopex lagopus) starts to increase at much lower lemming densities than the responses of the avian predators, but it has only a weak numerical response. Finally, the stoat (Mustela erminea) is the most specialized predator and the only one with a clearly delayed numerical response. According to their specific functional and numerical responses, each predator plays a key role at some point of the lemming cycle, but only the stoat has the potential to drive the lemming cycle. Stoat predation is greatly reduced in the winter preceding the lemming peak, and it reaches a maximum in the winter preceding the lowest lemming summer density. Stoat predation appears to maintain low lemming densities for at least two successive years. Our study provides empirical support for the specialist predator hypothesis about small mammal population cycles.
A mutualism's indirect costs: the most aggressive plant bodyguards also deter pollinators
Authors: Ness Joshua H.
Published: February 2006

Plant defenses against herbivores may be costly if they exclude mutualists. Here, I test the hypothesis that aggressive ant bodyguards of plants deter pollinators, and explore mechanisms by which Ferocactus wislizeni, an extrafloral nectary bearing cactus, limits conflicts between its pollinators and bodyguards. Flower visitation by ants and pollinating bees differed among plants tended by four different ant species. The ant species most rarely found in flowers showed the strongest aversion to F. wislizeni flower petals in laboratory assays, suggesting that those structures may include an ant‐deterrent. Species‐specific estimates of mean ant abundance within flowers and aggressiveness towards other arthropods were used to distinguish the relative threat of ant attack in flowers on plants tended by each ant species. Pollinator surveys in 2003 and 2004 demonstrated that bee visitation rates and the duration of flower occupation differed among plants with different ant associates, decreasing as the threat of ant attack increased. Flowers on plants tended by Solenopsis xyloni, the best ant bodyguard, were more dangerous than those on plants tended by three milder species, due to that ants’ greater aggressiveness and abundance within flowers. These flowers were visited by pollinators least frequently and for less time per visit, and produced fruits with significantly lower total seed mass, fewer seeds, and lighter individual seeds, relative to fruits from similarly‐sized plants tended by three other ant species. As a result, the best bodyguard may indirectly constrain plant reproduction in some settings. Conflicts between mutualistic guilds may be particularly common in generalized systems, where there is variation in partner quality and in the relative importance of the protection and pollination mutualisms.
Early‐successional plants regulate grassland productivity and species composition: a removal experiment
Authors: Wayne Polley H. , J. Wilsey Brian , D. Derner Justin , B. Johnson Hyrum , Sanabria Joaquin
Published: February 2006

Grime's (1998)“mass‐ratio” hypothesis holds that ecosystem processes depend in the short term on functional properties of dominant plants and in the longer term on how resident species influence the recruitment of dominants. The latter of these effects may be especially important among early‐successional species in disturbed ecosystems, but experimental tests are few. We removed two groups of early‐successional species, an annual forb Gutierrezia dracunculoides (DC.) S. F. Blake and annual species (mostly grasses) that complete growth early in the growing season [early‐season (ES) species], from a heavily‐grazed grassland in central Texas, USA dominated by a C4 perennial grass. We sought to determine effects of annuals on grassland functioning [productivity, water balance, soil and plant nitrogen (N)] and composition. Removals did not impact N retention in the soil/plant system during the two years of this study, but removing ES annuals increased the amount of water between 30 and 120 cm in the soil profile early in each growing season. Production and N accumulation by vegetation declined following the removal of ES annuals in approximate proportion to the contribution of annuals to aboveground biomass and N, consistent with the mass‐ratio hypothesis. By the second year, production and N uptake by initially sub‐dominant species increased to fully compensate for the loss of annuals. These results are consistent with the view that ecosystem functions are more strongly linked to species attributes than to diversity per se. Longer‐term effects of annuals on grassland composition were evident in a dramatic increase in biomass of perennial forbs after annuals were removed. Because perennial forbs differ from the dominant grass in this grassland in traits that influence ecosystem functioning, ES annuals may affect grassland functioning more by regulating the composition of vegetation than by directly affecting process rates.
Tolerance of understory plants subject to herbivory by roe deer
Authors: Moser Barbara , Schütz Martin
Published: February 2006

Current understanding of plant–herbivore interactions postulates that forest understory species are less tolerant to herbivory by large mammals than grassland species. As yet, research on forest species has focused on extensive biomass loss. However, forest dwelling ungulates are often selective browsers, hence biomass loss experienced by forage species is mostly limited to specific plant modules. We investigated the impact of herbivory on common forage species of roe deer Capreolus capreolus by simulating browsing on wild transplants of the two herbs Geum urbanum and Prenanthes purpurea, and the two graminoids Carex sylvatica and Luzula luzuloides. Two clipping regimes simulated different browsing frequencies, whereas shading and full day light represented light conditions in closed forests and gaps, respectively. Single clipping did not affect above ground biomass production of any species, independent of light conditions. Repeated biomass loss led to undercompensation in L. luzuloides, marginal compensation in C. sylvatica, and full compensation in G. urbanum and P. purpurea measured as above ground biomass production. The change in root biomass after clipping was positively correlated with the change in above ground biomass production in all four species. In contrast, nitrogen concentration was negatively correlated with above ground biomass in the graminoids, whereas no relationship between nitrogen and biomass was found in the herbs. Although light conditions and plant provenance affected biomass production, we found no effect of light conditions on plant reactions to herbivory. These results suggest that forest understory species, graminoids as well as herbs, are tolerant to herbivory by selective browsers such as roe deer. As in grassland ecosystems, the degree of compensatory growth depends on amount and frequency of biomass loss.
Evolving dispersal and age at death
Authors: Dytham Calvin , M. J. Travis Justin
Published: February 2006

Traditional, and often competing, theories on ageing agree that a programmed age at death must have arisen as a side effect of natural selection, and that it can have no adaptive value of its own. However, theoretical models suggest that ageing and programmed death can be adaptive. Travis J. M. J. suggested that if fecundity declines with age, a programmed age of death evolves through kin selection and that the nature of dispersal is crucial as it determines the degree of spatial structure and hence the strength of kin selection. Here, using a similar model, we consider the interplay between dispersal and age of death. We incorporate more realistic dispersal kernels and allow both dispersal and age of death to evolve. Our results show each trait can evolve in response to the other: earlier age of death evolves when individuals disperse less and greater dispersal distances evolve when individuals are programmed to die later. When we allow dispersal and age of death to evolve at the same time we typically find that dispersal evolves more rapidly, and that ageing then evolves in response to the new dispersal regime. The cost of dispersal is crucial in determining the evolution of both traits. We argue both that ageing is an overlooked ecological process, and that the field of gerontology could learn a lot from evolutionary ecology. We suggest that it is time to develop the field of ecological gerontology and we highlight a few areas where future work might be particularly rewarding.
A hump‐shaped density–area relationship for island lizards
Authors: B. Buckley Lauren , Roughgarden Joan
Published: February 2006

We evaluated the density ofAnolislizards as a function of island area, habitat diversity, and topographic diversity on the Grenadines islands. We found a hump‐shaped density–area relationship. Density at sea level increased with island area until an island was sufficiently large to contain multiple habitat types. Beyond this area threshold, average sea level density declined with island area. Increased species interactions on larger islands may explain the density decline.
Avoid your neighbours: size‐determined spatial distribution patterns among northern pike individuals
Authors: Anders Nilsson P.
Published: February 2006

The spatial distribution of individual animals may both cause and be caused by intra‐ and/or interspecific interactions. This work aims primarily on effects of intraspecific interactions. Agonistic and unequally strong interactions among conspecifics should make the within‐population distribution of individuals to be characterised by spatial avoidance of potentially risky conspecifics, according to the individual risks perceived. This process should affect individual performance and involve individual tradeoffs, as failing to adequately avoid risky conspecifics could incur unnecessary costs, while, at the same time, successful conspecific avoidance may reduce access to patches favourable for e.g. foraging or sheltering. Intraspecific agonistic behaviours, such as cannibalism and competition, are likely to have prominent effects in size‐structured populations. It is therefore reasonable to assume spatial avoidance of intraspecific risks according to individuals’ size relationships in such populations. With this field investigation I show that individuals of northern pike spatially avoid larger conspecifics. This avoidance creates a size‐influenced and spatially clumped distribution pattern among pike individuals. At low pike densities, however, distances between individuals increase, allowing for an even distribution pattern to appear. The spatial distribution patterns among piscivore individuals should affect both the individual performance of predators and the potential for spatial anti‐predatory responses of their prey, and hence be a factor in consumer–resource interactions.
Alternative stable states, trait dispersion and ecological restoration
Authors: Fukami Tadashi , Lee William G.
Published: February 2006

Didham et al. suggested that abiotically structured communities showing trait under‐dispersion are more likely to exhibit alternative stable states than are competitively structured communities showing trait over‐dispersion. We argue that the opposite is the logical expectation, and discuss implications for ecological restoration at local and regional scales.
Are morphology–performance relationships invariant across different seasons? A test with the green anole lizard (Anolis carolinensis)
Authors: Irschick Duncan J. , Ramos Margarita , Buckley Christine , Elstrott Justin , Carlisle Elizabeth , Lailvaux Simon P. , Bloch Natasha , Herrel Anthony , Vanhooydonck Bieke
Published: February 2006

A key assumption in ecomorphological studies is that morphology–function relationships are invariant due to underlying biomechanical principles. We tested the hypothesis that morphology–performance relationships are invariant across different seasons by examining how a key performance trait, bite force, and two aspects of morphology (head shape and dewlap size) changed seasonally in the field and in the laboratory in the green anole lizard Anolis carolinensis. We found that not only did bite force change seasonally (up to 80% within the same individual), but relationships between morphology and bite force are highly plastic. Of the three traits examined (bite force, head shape, and dewlap area), only head shape did not change seasonally. We noted opposing trends for how bite force and dewlap area changed seasonally; whereas dewlap areas were large in the spring, and small in the winter, bite forces were low in the spring and high in the winter. This pattern occurred because of a tradeoff at the individual level: individuals in the spring with large dewlaps and high bite forces diminish their dewlaps (but not bite force), whereas individuals with small dewlaps and low bite forces in the spring increase their bite forces (but not dewlap size). We also show that this trend was apparent both in the field (comparing different individuals) and the laboratory (comparing the same set of individuals under standardized conditions). Finally, seasonal changes were not consistent among individuals for either bite force or dewlap area, as individuals changed seasonally in proportion to their initial state. These findings cast doubt on the widely held view of invariant morphology–performance relationships, and offer a cautionary note for eco‐morphological studies.
The role of stochastic processes in producing nested patterns of species distributions
Authors: L. Higgins Christopher , R. Willig Michael , E. Strauss Richard
Published: February 2006

Nestedness has received considerable attention in community ecology and conservation biology from both theoretical and empirical perspectives. This has lead to the creation of various metrics and null models to analyze nested subsets, all of which rely on the random placement of species to assess significance. However, if immigration and extinction are the processes that underlie species distributions on island systems, then null models might be better determined on the basis of randomly placed individuals. Consequently, we examined the effects of species–abundance distributions (uniform, dominance–decay, random–assortment, and dominance–preemption), island–size distributions (uniform and linear decrease), and total abundances (128, 256, 512, 1024, 2048, 4096 and 8192) on the degree of nestedness and its significance. Generally, matrices of species presence and absence created from the random placement of individuals were nested significantly according to null models based on the random placement of species. Island size and abundance had less of an effect on nestedness in systems dominated by only a few species than in systems in which abundances were distributed more evenly. Stochastic processes, such as the random placement of individuals, predispose systems to evince patterns of nestedness at the species level, which may account, in part, for the ubiquity of nestedness in nature.
Predicting local–regional richness relationships using island biogeography models
Authors: W. Fox J. , Srivastava D.
Published: February 2006

Local species richness frequently is linearly related to the richness of the regional species pool from which the local community was presumably assembled. What, if anything, does this pattern imply about the relative importance of species interactions and dispersal as determinants of local species richness? Two recent papers by Hugueny and Cornell and He et al. propose that the classical island biogeography model of MacArthur and Wilson can help answer this question, by serving as a null model of the relationship between local (island) and regional (mainland) species richness in the absence of local species interactions. The two models make very different predictions, despite being derived from apparently‐similar assumptions. Here we reinterpret these two models and show that their contrasting predictions can be regarded as arising from different, implicit assumptions about how species abundances vary with species richness on the mainland. We derive a more general island biogeography model of local–regional richness relationships that explicitly incorporates mainland species abundance and subsumes the two previous models as limiting cases. The new model predicts that the local–regional richness relationship can range from nearly linear to strongly curvilinear, depending on how species abundances on the mainland vary with mainland richness, as well as on rates of immigration to and extinction from islands. Local species interactions are not necessary for producing curvilinear local–regional richness relationships. We discuss the implications of our new model for the interpretation of local–regional richness relationships.
Nitric oxide and noradrenaline contribute to the temperature threshold of the axon reflex response to gradual local heating in human skin
Authors: Houghton Belinda L. , Meendering Jessica R. , Wong Brett J. , Minson Christopher T.
Published: February 2006

The initial skin blood flow response to rapid local heating is an axon reflex, which may be mediated by calcitonin gene‐related peptide and substance P released from C‐fibres. We investigated the role of nitric oxide (NO) and noradrenaline on the temperature threshold for the axon reflex during gradual local heating. 36 subjects participated in two studies. Using microdialysis, we examined the following interventions: NO synthase inhibition (10 mmNG‐nitro‐l‐arginine methyl ester, l‐NAME); low‐dose NO infusion (1.0 μm sodium nitroprusside, SNP); adrenergic blockade (10 mm bretylium tosylate); and low‐dose (0.1 μm) noradrenaline infusion. Laser‐Doppler flowmetry was used to measure red blood cell flux. Skin was heated at a rate of 0.1°C min−1 from 33°C to 40°C. Compared to control skin sites, the axon reflex response was shifted to a higher temperature in 4 subjects in the l‐NAME sites (control, 37.0 ± 0.3°C, n= 16; l‐NAME, 39.8 ± 0.1°C, n= 4; P < 0.001) and absent in 12 subjects. The response was also absent in l‐NAME plus low‐dose SNP sites and not altered by low‐dose SNP infusion alone. Adrenergic blockade, with and without low‐dose noradrenaline infusion, also abolished the axon reflex response in all subjects. Low‐dose noradrenaline infusion alone shifted the axon reflex to a significantly lower temperature threshold compared to control sites (control, 38.2 ± 0.5°C; noradrenaline, 37.7 ± 0.4°C, P < 0.05, n= 5). These results suggest that endogenous NO and noradrenaline contribute to the temperature threshold of the axon reflex response during gradual local heating of the skin.