bluuebunny/crossref_metadata_2025 huggingface dataset:
Photodimerization of the α′-polymorph of ortho-ethoxy-trans-cinnamic acid in the solid state. I. Monitoring the reaction at 293 K
Authors: Fernandes M. A. , Levendis D. C.
Published: May 2004

Structural changes that occur during the [2 + 2] photodimerization of the metastable α′-polymorph of ortho-ethoxy-trans-cinnamic acid at 293 K are presented here. Crystals of the α′-polymorph were first stabilized by exposing the α-polymorph to UV light for a short period of time at 343 K. The photodimerization reaction was then carried out at 293 K and observed in situ by single-crystal X-ray diffraction. The α′-polymorph contains three molecules in the asymmetric unit, labelled A, B and C, which are arranged to form two potential reaction sites. The intermolecular distance between the C=C bonds of molecules A and B (making up the AB site) is 3.6 Å, and these were observed to undergo photodimerization at 293 K. The corresponding distance between centrosymmetrically related C=C bonds in the CC site (made up of C molecules) is 4.6 Å, and these remain unreacted even after 60 h irradiation at 293 K. The crystal of the final product, which corresponds to a 66.7% conversion (only two out of three molecules in the asymmetric unit take part in the photodimerization reaction at 293 K), contains an ordered arrangement of the photodimer and unreacted monomer. The crystal retains many structural features of the original monomer crystal, including carboxylic acid hydrogen bonds and C—H...O interactions. Single-crystal X-ray diffraction was used to monitor changes in the unit-cell parameters, reacting molecules and molecular conformations as the reaction progressed. The conformation of the photodimer obtained from the solid-state reaction differs from that of the photodimer obtained by recrystallization from solution.
A new polymorph of ortho-ethoxy-trans-cinnamic acid: single-to-single-crystal phase transformation and mechanism
Authors: Fernandes Manuel A. , Levendis Demetrius C. , Schoening F. R. Ludwig
Published: May 2004

The α-polymorph of ortho-ethoxy-trans-cinnamic acid (OETCA) undergoes a reversible single-crystal-to-single-crystal phase transformation at 333 K. The new high-temperature polymorph (α′-OETCA) is stable between 333 and 393 K with three molecules in the asymmetric unit (Z′ = 3), space group P\bar 1. Unlike the other polymorphs (and solvate) of OETCA recently reported, two of the molecules in α′-OETCA deviate significantly from planarity. This conformational change results in the corrugated sheet-type structure of α′-OETCA. The sheets are made up of ribbons, each composed of R_2 ^2 (8) hydrogen-bonded pairs (via the —COOH groups), which are further connected by CH...O interactions. When exposed to UV radiation the α′-OETCA polymorph can be stabilized below 333 K with ca 8% of the monomer converted into the photodimer. The crystal structures of α′-OETCA are reported at two temperatures above the phase transition point (at 345 and 375 K) as well as the stabilized forms at 173 and 293 K. A mechanism for the phase transition involving a cooperative conformational transformation coupled with a shift of layers of OETCA molecules is proposed. The α′-OETCA polymorph is also an example of a cinnamic acid derivative where two different potentially photoreactive environments exist in one crystal in which each unit cell has two non-centrosymmetric predimer sites and one centrosymmetric predimer site.
Mg1 + x
Ir1 − x
(x = 0, 0.037 and 0.054), a binary intermetallic compound with a new orthorhombic structure type determined from powder and single-crystal X-ray diffraction
Authors: Černý Radovan , Renaudin Guillaume , Favre-Nicolin Vincent , Hlukhyy Viktor , Pöttgen Rainer
Published: May 2004

The new binary compound Mg1 + x
Ir1 − x
(x = 0–0.054) was prepared by melting the elements in the Mg:Ir ratio 2:3 in a sealed tantalum tube under an argon atmosphere in an induction furnace (single crystals) or by annealing cold-pressed pellets of the starting composition Mg:Ir 1:1 in an autoclave under an argon atmosphere (powder sample). The structure was independently solved from high-resolution synchrotron powder and single-crystal X-ray data: Pearson symbol oC304, space group Cmca, lattice parameters from synchrotron powder data a = 18.46948 (6), b = 16.17450 (5), c = 16.82131 (5) Å. Mg1 + x
Ir1 − x
is a topologically close-packed phase, containing 13 Ir and 12 Mg atoms in the asymmetric unit, and has a narrow homogeneity range. Nearly all the atoms have Frank–Kasper-related coordination polyhedra, with the exception of two Ir atoms, and this compound contains the shortest Ir—Ir distances ever observed. The solution of a rather complex crystal structure from powder diffraction, which was fully confirmed by the single-crystal method, shows the power of powder diffraction in combination with the high-resolution data and the global optimization method.
Web‐based discussion groups at stake: the profile of museum professionals online
Authors: Bernier Roxane , Bowen Jonathan P.
Published: May 2004

Online forums help in stimulating debates and reflection on a wide range of cultural topics, as well as providing answers for museum professionals working in specialised areas. The main objective of this paper is to concentrate on the relevance of individuals interacting virtually within an informal knowledge setting, from which to judge the value of Web‐based discussion groups. However, little is known about how museum‐related forums target their audience and which subjects are of real interest to them. Arising from the statistical results of an international survey of users of online museum forums, the authors have investigated the users’ socio‐demographic profile, their content preference, and favourite Web‐based discussions (e.g. e‐mail lists, newsgroups, forums). The outcome of the collected data should be useful in further binding together the worldwide museum community, as there is great scope for enlivening interactions and empowering individual knowledge in various fields of expertise.
Assessing the business and employee benefits resulting from the implementation of NVQs
Authors: McAdam Rodney , Crowe Julie
Published: May 2004

National Vocational Qualifications (NVQs) have been introduced and developed within a competency framework by successive UK governments. Potential benefits are listed as improved skills, less skills shortages and more appropriate job‐employee fit. However, there has been considerable and sustained criticism of NVQs from employers, employees and academics. Criticisms include excessive bureaucracy, overly complex terminology and a lack of credibility of the competence concept. This case‐based study examines the implementation of NVQs in an organisation based on 60 semi‐structured interviews with those involved. The findings reveal that NVQ is seen as a training regime within the organisation and that there are no clear links to improved business performance or employee morale. Moreover, there were contextual problems in applying the standard.
BPR: alive and well in the public sector
Authors: MacIntosh Robert
Published: May 2004

This paper examines three business process re‐engineering (BPR) projects, one conducted in the private sector and two conducted in the UK's higher education sector. The broad aim of the paper is to compare public and private sector applications of BPR. The paper begins with a brief overview of BPR and identifies three unresolved issues from the literature (the choice of modelling techniques used to describe business processes, whether to use generic or context specific process maps and whether to aim for radical or incremental change). An overview of each project is given and the paper considers how each of the unresolved theoretical issues was addressed in the cases before making a public vs private sector comparison. The paper illustrates differences and similarities between private sector usage of BPR and the two public sector examples given here and concludes that the techniques of BPR are highly applicable in the public sector.
New Web Browser Applications
Authors: Riggs Colby
Published: May 2004

Summarises new and developing Web browser technologies. Describes three browsers, one with a “tabbed browsing” capability, another which includes a new productivity tool called a “search information manager”, and a voice operated browser which is still in development.
Outpatient appointment scheduling with urgent clients in a dynamic, multi‐period environment
Authors: Klassen Kenneth J. , Rohleder Thomas R.
Published: May 2004

Time waiting for service is a major concern for consumers, and excessive waiting for a pre‐scheduled appointment is especially annoying. This is an on‐going problem because appointment scheduling is a challenging task, mainly due to the uncertainties associated with service times. Prior studies have focused mainly on a single scheduling period (i.e. either a morning or afternoon); this paper uses a more realistic model that represents an on‐going, multi‐period scheduling environment where clients can be scheduled days or even weeks into the future. Two main objectives will be considered; the best scheduling rule to use in a multi‐period environment, and the best placement of appointment slots that are left open for urgent clients. Both of these have been studied in a single period environment, and results here will be compared to those. It will be shown that in some cases earlier findings from the one‐period environment are robust and perform well in a multi‐period environment, while in other cases the one‐period findings do not apply.
Self‐service with a smile?
Authors: Pujari Devashish
Published: May 2004

This paper investigates self‐service technology (SST) encounters among Canadian B2B (business‐to‐business) customers. It provides an understanding of key determinants of satisfaction and dissatisfaction. This research also explores issues relating to service recovery in case of SST failure and effects of favorable/ unfavorable SST encounters on business relationships. The study finds that B2B customers experience satisfaction from different sources as compared to B2C customers. These sources include speed, process efficiency and cost savings. Service recovery has been found to be a critical problem with regards to SST.
Identification with leader
Authors: Connaughton Stacey L. , Daly John A.
Published: May 2004

Geographically dispersed teams have become common in many industries and organizations. Yet previous research on distanced leadership often is done from the perspective of the leader, not the team members. This study examines identification with team leader among distanced and proximate employees in geographically dispersed teams. Through survey research, the study examines the relationship between members' identification with their team leader and four other relevant variables – trust, isolation, accessibility, and information equity. Specifically, the study finds that identification and trust are closely related constructs in both distanced and proximate settings; that perceived isolation is inversely related with leader identification in proximate settings, but not in distanced ones; that accessibility is positively related to identification with leader in both distanced and proximate settings; and that perceived information equity is positively related with leader identification in distanced and proximate settings. Implications for leadership in distanced settings are discussed.
Challenges in collaborative writing in the contemporary corporation
Authors: Colen Kerryn , Petelin Roslyn
Published: May 2004

Collaborative writing is pervasive in the contemporary corporate workplace. North American research reports that nine out of ten business professionals produce some of their documents as part of a team. As workplace writers seek to meet the business goals of their employers, and further their own careers, they require sophisticated skills in joining with other writers to collaboratively produce documents. Taking advantage of the benefits, and meeting the challenges of this demand, requires corporate and academic communities to collaborate: to address gaps in the knowledge about collaborative writing and to train and develop competent collaborative writers.
The role of company image as brand equity
Authors: Ross‐Wooldridge Barbara , Brown Mark P. , Minsky Barbara D.
Published: May 2004

Proposes that benefits would accrue as a result of the development of a halo marketing campaign for firms forced to serve unprofitable markets, and the pharmaceutical industry is used as an example. Halo marketing should allow firms to garner increased positive firm image and/or increased brand equity from serving these markets, as opposed to the unavailable traditional benefit of profit. Utilizes the international tourism literature to illustrate how firms may effectively use halo marketing since this literature has a history of applying halo marketing to increase travel to tourist destinations. Also integrates the corporate reputation literature base. Presents five research propositions regarding how these concepts could be applied to firms serving unprofitable markets.
A model of bovine tuberculosis in the badger Meles meles: an evaluation of different vaccination strategies
Authors: WILKINSON D. , SMITH G. C. , DELAHAY R. J. , CHEESEMAN C. L.
Published: May 2004

In recent years bovine tuberculosis (TB) incidence in cattle has been increasing in south‐west England. The European badger Meles meles is implicated in the transmission of TB to cattle and has been the subject of culling operations in an attempt to control the disease.

An individual‐based, spatial, stochastic, simulation model was used to investigate the control of TB in the badger by various badger‐vaccination strategies. Nearly all population and epidemiological parameters were derived from a single long‐term study site. Heterogeneous carrying capacities (the maximum number of breeding females per badger social group) and different sized badger territories were used to simulate natural heterogeneity. The model included the transmission of TB from badgers to cattle to allow reactive vaccination of badgers, i.e. in response to positive cattle TB test results.

The model predicted that badger populations with reduced contiguity (e.g. natural barriers) between social group territories would have a lower TB prevalence.

In the absence of information on the true prevalence of TB in badger social groups, vaccinating 80% of groups at a low vaccine probability (10% successfully immunized) was more effective in the model at reducing prevalence of TB in badgers, than vaccinating 10% of the groups at a higher probability (80% successfully immunized).

Although a lower cost option, vaccinating badgers purely in reaction to cattle herd infections took longer to reduce badger TB prevalence to 50% than proactive strategies (7–20 years compared with 3–5 years). Simulations suggested that at least 40% of healthy badgers need to be immunized each year to eradicate TB in the badger. The model indicated that vaccination of badgers is a viable alternative to badger culling for the control of TB in cattle. Combined control policies were not investigated.

Synthesis and applications. Widespread proactive vaccination appears to be the most effective strategy for disease control. Initial proactive vaccination followed by localized reactive vaccination can lead to a greater reduction in disease prevalence for less effort. This is likely to be a global finding for the control of wildlife diseases, although the optimal duration for a proactive campaign will depend upon specific circumstances (e.g. detection rate of disease).
On the loss of saltmarshes in south‐east England and methods for their restoration
Authors: HUGHES R. G. , PARAMOR O. A. L.
Published: May 2004

The saltmarshes of south‐east England have been eroding rapidly for about the last 50 years, at a continuing rate of about 40 ha year−1, with deleterious consequences for conservation and coastal flood defence. The possible reasons for this erosion and suitability of methods of saltmarsh restoration are discussed.

The prevailing hypothesis that the saltmarsh erosion is due to coastal squeeze, where sea walls prevent a landward migration of saltmarsh in response to sea level rise, is rejected because: (i) as the sea level rises saltmarshes accrete vertically as well, at least at the same rate, and may even extend seaward; (ii) in recent decades the rate of rise in sea level has been no higher than in the past when the saltmarshes developed; (iii) the pattern of vegetation loss, mostly of pioneer zone species, is opposite to that predicted by coastal squeeze, where the upper marsh plants should disappear first.

 Alternative explanations and hypotheses are proposed that relate the recent saltmarsh erosion to changes to the intertidal biota, an increase in abundance of the infaunal polychaete Nereis diversicolor, and a decrease in abundance of intertidal seagrasses. Bioturbation and herbivory by Nereis cause the loss of pioneer zone plants, increase sediment instability and exacerbate the erosion of saltmarsh creeks. The erosion of the seaward edge of some marshes may also be due to increased wave action, and increased tidal current speeds in estuaries, following the loss of intertidal seagrasses since the 1930s through wasting disease.

Synthesis and applications. The current strategy for saltmarsh creation is based on managed realignment, where some sea walls are breached to provide new intertidal habitat. The conclusion that the causes of saltmarsh loss are not related to sea level rise calls into question this dependence on management realignment as the most appropriate means of saltmarsh creation, not least because many realignment areas are unlikely to develop vegetation. Other methods should be considered for creating new marshes and for reducing/reversing marsh erosion. These include, alone or in combinations, exclusion of the infauna, use of dredged material for strategic intertidal recharge, and transplantation of intertidal seagrasses.
The effects of bioturbation and herbivory by the polychaete Nereis diversicolor on loss of saltmarsh in south‐east England
Authors: PARAMOR O. A. L. , HUGHES R. G.
Published: May 2004

The saltmarshes of south‐east England are eroding rapidly. Field and laboratory experiments were used to test the hypotheses that: (i) at the mudflat–saltmarsh boundary there are two alternative states, one dominated by pioneer zone vegetation that excludes burrowing infauna, and the other dominated by infaunal invertebrates that exclude vegetation; and (ii) the major cause of the loss of saltmarshes in south‐east England is internal creek erosion, which is exacerbated by bioturbation and herbivory by the infaunal polychaete Nereis diversicolor.

In laboratory experiments Nereis ate the seeds and seedlings of Salicornia spp., and Salicornia deterred burrowing by Nereis. In field experiments, at Tollesbury in Essex, UK, exclusion of Nereis from the sediment surface increased the density of Salicornia, but only when a source of seeds was close by. In the Tollesbury saltmarsh the plants and Nereis had mutually exclusive distributions within a vertical zone of overlap. The recently vegetated area of the managed realignment site at Tollesbury contained no Nereis, but Nereis colonized areas where Salicornia had been removed. These observations and data support the first hypothesis.

Much of the loss of the Tollesbury saltmarsh is by lateral erosion of the internal creeks. Physical factors alone cannot be responsible for this erosion because experimental exclusion of Nereis led to sediment accretion. These results support the second hypothesis. Creek erosion may create a positive feedback where creek enlargement leads to faster tidal currents and further erosion until creeks have widened to their new equilibrium morphology.

Synthesis and applications. We conclude that the infauna are a major cause of reduction in area of saltmarsh vegetation and this has implications for the management of saltmarsh restoration. These results call into question the assumption that saltmarsh erosion in south‐east England is due to sea level rise and coastal squeeze, and demands re‐examination of the role of management realignment in the regeneration of saltmarshes. Reducing the rates of saltmarsh creek erosion, by exclusion of the infauna, and/or by reducing current velocities in the saltmarsh creeks, would reduce the need to replace eroded marshes by managed realignment, and would reduce future erosion of existing sea walls by wave action.
Taxation of the Global Arms Trade? An Overview of the Issues
Authors: Brzoska Michael
Published: May 2004

A number of proposals for a tax on the international trade with weapons have been made during the last 25 years, most recently prior to the G‐8 summit in Lyon, France, in June 2003. Originally, the major objectives were both to reduce the level of trade in arms and raise money for purposes such as development and disarmament. Later proposals included the compensation of victims of the use of specific types of weapons. Various objections have been raised against the suggestions for an international arms trade tax. Major points include the difficulties of achieving sufficient levels of compliance, tax evasion through increases in domestic production and a stimulation of the illicit trade in arms. There are also fundamental objections against demeritorizing arms transfers only, and not also domestic production of arms. In order for an international arms trade tax to work, the level of transparency in the international arms trade would need to increase. A major part of the tax burden would be borne by buyers of arms, who are predominantly developing countries. However, these are currently also major beneficiaries of large‐scale subsidies on arms exports. An international arms trade tax will lead, using available estimates of price elasticities, to an increase in expenditures on arms import. Transfers from a fund fed by an arms trade tax should be spent in those countries which substantially reduce their spending on arms imports. In general, an arms trade tax makes more sense as a measure for disarmament than as a measure for development.
The Price of Bodies: A Hedonic Pricing Model of Avatar Attributes in a Synthetic World
Authors: Castronova Edward
Published: May 2004

This paper explores a unique new source of social valuation: a market for bodies. The internet hosts a number of large synthetic worlds which users can visit by piloting a computer‐generated body, known as an avatar. Avatars can have an asset value, in that users can spend time to increase their skills; these asset values can be directly observed in online markets. Auction data for avatars from the synthetic fantasy world of EverQuest are used here to explore a number of questions involving the relative value of different body characteristics. Hedonic analysis of the auction price data suggests that the ‘level’, a game‐design metric that indicates the overall functionality or power of the avatar, is by far the most important attribute of the body. Other attributes that show significant price effects include: sex and class (i.e. being a wizard rather than warrior type of character). The male‐female price difference is interesting because there are actually no sex‐based differences in the abilities of the avatar bodies, by design. Price differences here must be caused by some other aspect of buyer preferences, ones unrelated to power or functionality of the avatar itself.
What Do We Know about Ourselves? on the Economics of Economics
Authors: Coupé Tom
Published: May 2004

Since quite some time, economists have been aware of the fact that also the behavior of economists generates questions that need to be answered. Why, for example, do economists use an alphabetic ordering of names when they co‐author an article? And what determines the success of an academic economist? Or, how does studying economics affect behavior? At the same time, economists have also noticed that the economics profession generates data that can be used to test theoretical ideas proposed by economists. In this paper, the author gives an overview of such research that takes economists and their behavior as a subject of study. He will focus on three topics: the education of economists, the publication habits of economists and the labor market of economists.
Take or Leave? Distribution in Asymmetric One‐Off Conflict
Authors: de Jasay Anthony , Güth Werner , Kliemt Hartmut , Ockenfels Axel
Published: May 2004

Most social scientists' views of conflict and cooperation in society are shaped by very elementary, one‐off, two by two symmetric simultaneous move games like prisoner's dilemma, chicken, assurance or stag hunt. We think that this diet of examples leads to biased accounts in particular of distributional conflict, and therefore suggest that asymmetry in payoffs and move structure be taken into account systematically. In this paper a new paradigm of asymmetric games to study basic distributional conflicts is introduced, illustrated numerically and discussed theoretically. The results of exploratory experiments on the empirical side of the matter are also reported.
Quality of Government Services and the Civic Duty to Pay Taxes in the Czech and Slovak Republics, and other Transition Countries
Authors: Hanousek Jan , Palda Filip
Published: May 2004

This paper analyses a 2002 survey of the Czech and Slovak Republics, and more limited surveys of Hungary and Poland to conclude that tax evasion is lowest among those who believe that they are getting good quality government services for the taxes they pay. A 20% increase in perceived quality of government services could lead to a 13% drop in the frequency of tax evasion. The present analysis is the first of this sort to indicate that quality of government services influences the willingness to pay taxes. Governments in transition countries who suffer from weak tax collection apparatus may wish to transmit clear information on the quality of their services in order to cut down on evasion.
Industry Matters for Poverty: A Critique of Agricultural Fundamentalism
Authors: Hasan Rana , Quibria M. G.
Published: May 2004

We use a recently constructed cross‐country data set on absolute poverty to examine whether there is regional and sectoral variation in the relationship between poverty and economic growth. We find that the poverty‐growth linkage is strongest in East Asia and that this linkage is essentially driven by growth in the industrial sector. By contrast, industrial growth has had little positive impact on poverty reduction in any other region. These findings are consistent with the notion that East Asia's greater success in poverty reduction lies in its greater openness and market orientation, which created a pattern of labor‐intensive industrial growth that led to a rapid growth in employment and poverty reduction.
The Euro Cash Changeover Process
Authors: Stenkula Mikael
Published: May 2004

This article describes and analyzes the Euro cash changeover process. The European Monetary Union, EMU, is a unique event in history, although other monetary unions were formed and existed long before. Still, this giant experiment makes it possible to study changes in the monetary environment from a unique and new position. The article tries to find factors that can help to explain the different pace of transition between the countries participating in the third stage of the EMU. Even though it was common knowledge that the national currency would lose its status as legal tender at a predetermined point in time, the speed of acceptance of the new monetary standard could not be directly controlled by the relevant authorities. Hence, the whole changeover process was formed as much by the authorities as by the public. The paper focuses on four types of factors that may help to explain the differences in the pace of transition pattern between the countries: network related reasons, technical and logistic reasons, characteristics of the financial and payment systems and psychological reasons. It is found that the initial supply of Euro bank notes (so‐called frontloading), the size of the population of the country, the length of the period when the national currency and Euro bank notes were used side by side, and the number of bank branches (per capita) together can help to explain a large part of the variation in the pace of adoption of the new monetary standard across the countries. The first two of these factors support the idea that currency is a network good. Psychological factors, such as nationalism, have not been found to significantly influence the outcome.
The Economics of the FIFA Football Worldcup
Authors: Torgler Benno
Published: May 2004

The expansion of economics to ‘non‐market topics’ has received increased attention in recent years. The economics of sports (football) is such a sub‐field. This paper reports empirical evidence of team and referee performances in the FIFA World Cup 2002. The results reveal that being a hosting nation has a significant impact on the probability of winning a game. Furthermore, the strength of a team measured with the FIFA World Ranking does not play the important role presumed, which indicates that the element of uncertainty is working. The findings also indicate that the influence of a referee on the game result should not be neglected. Finally, the previous World Cup experiences seem to have the strongest impact on referees' performances during the game.
Multivariate control of plant species richness and community biomass in blackland prairie
Authors: Weiher Evan , Forbes Sarah , Schauwecker Timothy , B. Grace James
Published: May 2004

Recent studies have shown that patterns of plant species richness and community biomass are best understood in a multivariate context. The objective of this study was to develop and evaluate a multivariate hypothesis about how herbaceous biomass and richness relate to gradients in soil conditions and woody plant cover in blackland prairies. Structural equation modeling was used to investigate how soil characteristics and shade by scatteredJuniperus virginianatrees relate to standing biomass and species richness in 99 0.25 m2quadrats collected in eastern Mississippi, USA. Analysis proceeded in two stages. In the first stage, we evaluated the hypothesis that correlations among soil parameters could be represented by two underlying (latent) soil factors, mineral content and organic content. In the second stage, we evaluated the hypothesis that richness and biomass were related to (1) soil properties, (2) tree canopy extent, and (3) each other (i.e. reciprocal effects between richness and biomass). With some modification to the details of the original model, it was found that soil properties could be represented as two latent variables. In the overall model, 51% and 53% of the observed variation in richness and biomass were explained. The order of importance for variables explaining variations in richness was (1) soil organic content, (2) soil mineral content, (3) community biomass, and (4) tree canopy extent. The order of importance for variables explaining biomass was (1) tree canopy and (2) soil organic content, with neither soil mineral content nor species richness explaining significant variation in biomass. Based on these findings, we conclude that variations in richness are uniquely related to both variations in soil conditions and variations in herbaceous biomass. We further conclude that there is no evidence in these data for effects of species richness on biomass.
Responses to competition effects of two anuran tadpoles according to life‐history traits
Authors: Richter‐Boix Alex , Llorente Gustavo A. , Montori Albert
Published: May 2004

Experimental manipulations of the densities of two larval anurans, Pelodytes punctatus and Bufo bufo, showed that these species compete asymmetrically in semi‐natural conditions. Growth, mass at metamorphosis, date of metamorphosis, and survival were used as measures of response to interspecific competition. A mechanistic approach was used to collect information on the behaviour of the two species in different conditions. The competitive superiority of Pelodytes at individual level was correlated with a larger body, faster growth rate, increased per capita competitive impact on conspecifics, and greater reduction in the availability of trophic and spatial resources. In the presence of Pelodytes, Bufo showed slower growth, smaller size at metamorphosis and reduced survival. In the interspecific treatments Bufo individuals modified their behaviour by increasing activity and use of the water column while Pelodytes did not change their foraging activity or space use in the aquaria. However, the presence of Bufo resulted in a reduced larval period and smaller size at metamorphosis. We hypothesise that the presence of Bufo act as a signal of environmental degradation and shorten the larval period of Pelodytes, a typical temporal pond breeder. The smaller Bufo tadpoles are potentially stronger competitors at population level because they use relatively large amounts of energy (greater densities and higher metabolic rates). Consequently, they use larger proportions of the shared resources than their larger competitor. A possible evolutionary response for larger tadpoles is the development of interference mechanisms or “escaping” from ephemeral ponds where mortality by drying represent a high risk.
Allee effect in an invasive alien plant, pale swallow‐wortVincetoxicum rossicum(Asclepiadaceae)
Authors: Cappuccino Naomi
Published: May 2004

I tested for the presence of an Allee effect in pale swallow‐wortVincetoxicum rossicum, an invasive alien vine, by planting 1‐, 9‐ and 81‐plant patches in an old field. Biomass and seed set of central "target" plants were significantly higher in the 81‐plant patches than in the 1‐ and 9‐plant patches. Biomass of roots did not differ significantly among treatments. The nine central plants of the 81‐plant patches also had higher biomass and produced more seeds than the nine plants of the 9‐plant treatment. Unlike most other examples of Allee effects in plants, the effect inV. rossicumwas not due to differences in pollinator visitation rates. Instead,V. rossicumappears to suppress background vegetation more effectively when growing in larger patches. Like many other invasives,V. rossicumhas been present in North America for years before it attained pest status. The Allee effect is one of several mechanisms that may contribute to such a latency period.
Comparative dynamics of small mammal populations in treefall gaps and surrounding understorey within Amazonian rainforest
Authors: Beck Harald , Gaines Michael S. , Hines James E. , Nichols James D.
Published: May 2004

Variation in food resource availability can have profound effects on habitat selection and dynamics of populations. Previous studies reported higher food resource availability and fruit removal in treefall gaps than in the understorey. Therefore, gaps have been considered “keystone habitat” for Neotropical frugivore birds. Here we test if this prediction would also hold for terrestrial small mammals. In the Amazon, we quantified food resource availability in eleven treefall gaps and paired understorey habitats and used feeding experiments to test if two common terrestrial rodents (Oryzomys megacephalusandProechimysspp.) would perceive differences between habitats. We live‐trapped small mammals in eleven gaps and understorey sites for two years, and compared abundance, fitness components (survival and per capita recruitment) and dispersal of these two rodent species across gaps and understorey and seasons (rainy and dry). Our data indicated no differences in resource availability and consumption rate between habitats. Treefall gaps may represent a sink habitat forOryzomyswhere individuals had lower fitness, apparently because of habitat‐specific ant predation on early life stages, than in the understorey, the source habitat. Conversely, gaps may be source habitat forProechimyswhere individuals had higher fitness, than in the understorey, the sink habitat. Our results suggest the presence of source‐sink dynamics in a tropical gap‐understorey landscape, where two rodent species perceive habitats differently. This may be a mechanism for their coexistence in a heterogeneous and species‐diverse system.
Effects of plant diversity on Collembola in an experimental grassland ecosystem
Authors: Salamon Jörg‐Alfred , Schaefer Matthias , Alphei Jörn , Schmid Bernhard , Scheu Stefan
Published: May 2004

The response of species numbers and density of Collembola to manipulation of plant species richness (1, 2, 4, 8, 32 species) and number of plant functional groups (grasses, legumes and non‐legume herbs) was studied in an experimental grassland at the Swiss BIODEPTH site (Lupsingen, Switzerland) in October 1997. Plant species richness or number of plant functional groups did not affect total diversity of Collembola, however, the number of Collembola species increased in the presence of legumes and the grassTrisetum flavescens. The abundance ofProtaphorura armataincreased but that of Hypogastruridae/Neanuridae significantly decreased with increasing number of plant functional groups. Other groups including the herbivorous Symphypleona did not respond to plant species richness and plant functional groups. Possibly, Hypogastruridae/Neanuridae species are weak competitors declining in density if the density of other Collembola groups increase. In general, the effect of the number of plant functional groups on the densities of collembolan taxa was stronger than that of plant species richness. Changes in Collembola density and diversity in part was likely caused by increased soil microbial and fine root biomass in treatments with higher plant functional group diversity. The presence of legumes resulted in an increase in the densities of total Collembola, Symphypleona/Neelipleona and Isotomidae indicating that they benefited from the high litter quality and the increased microbial biomass in the rhizosphere of legumes. The results suggest that microbivorous soil invertebrates are controlled by food quality rather than quantity. Furthermore, they indicate that presence of certain plant species and functional groups may be more important for collembolan community structure than the diversity of plant species and functional groups per se.
Patch based predation in a southern Appalachian stream
Authors: Gibson C. A. , Ratajczak Jr. R. E. , Grossman G. D.
Published: May 2004

Streams are characterized by high degrees of patchiness that could influence the role of predators in these systems. Here we assess the impact of predatory benthic fishes on benthic macroinvertebrate density, biomass, and community structure at the patch scale in a fourth order stream in the southern Appalachians. We tested the role of predation in two different patch types: patches inhabited by adult mottled sculpin (Cottus bairdi) and random patches. We placed 30 basket pairs (one open to fish predation, and one from which fish predators were excluded) in the streambed at each patch type. We also tested for potential basket effects by setting up a basket control area. Although there was some evidence of basket artifacts on macroinvertebrate density in sculpin patches, these artifacts were not consistent and we do not feel that they affected our results because predators did not affect macroinvertebrate density. In random patches, predation did not significantly affect macroinvertebrate density or biomass. Predators significantly reduced macroinvertebrate biomass in sculpin patches but did not affect prey density. When the data‐set was size‐limited to exclude macroinvertebrates too large for consumption by sculpin, macroinvertebrate biomass did not differ significantly between exclusion and open baskets. This suggests that sculpin can reduce macroinvertebrate biomass through a combination of consumption and by predator‐induced emigration of large macroinvertebrates into areas that are protected from sculpin. In addition, invertebrate predator biomass was higher in predator exclusion baskets in sculpin patches indicating that predation pressure remained high in the exclusion baskets despite fish exclusion. These results illustrate the heterogeneity of streams and the effect of small‐scale differences (e.g. location of predators’ territories) on local processes. Experiments that utilize these differences can provide insights into these stream processes.
Amphipod crustacean size spectra: new insights in the relationship between size and oxygen
Authors: Chapelle Gauthier , Peck Lloyd S.
Published: May 2004

Oxygen availability limits the maximum potential size attainable in benthic gammaridean amphipods from the suborder to the generic level, while also influencing size within species. In this paper we investigate the effect of oxygen on 15 size spectra worldwide, established by compiling maximum length data of more than 2000 amphipod species. We used TS95/5 as a proxy for maximum size and defined this as the threshold size between the 95% smallest and the 5% largest species at any given site. Our data show that beside TS95/5, minimum, mean and modal sizes, as well as all 10% increment threshold sizes (from TS10/90 to TS90/10) also vary significantly with oxygen concentration. Size distributions are very similar in shape from one geographical area to another, whatever the width of the spectrum, hence if overall numbers of species stay constant more small species should coexist at low than at high latitudes. No amphipod species were found in water with an oxygen content lower than the minimum requirement predicted (175 mmol O2 kg−1). Our data also show that minimum adult amphipod size is probably limited by the minimum possible egg size, whereas maximum size is set by the physico‐chemic ceiling of oxygen availability.
Vole preference forSalix caprea,S. repens, and their F1, F2, and backcross hybrids
Authors: Hallgren Per , Hjältén Joakim
Published: May 2004

In recent years, the influence of plant hybridization on plant–animal interactions has become an important issue; however, these studies have mainly focused on insects or slugs and to a large degree ignored mammalian herbivores despite their importance in many ecosystems. This study aims to determine the preference of voles for pureSalix caprea,S. repens, and their F1, F2, and backcross hybrids to evaluate whether voles select against hybrids in natural willow populations. To address this, we conducted two field studies and a cafeteria experiment in the laboratory with bank voles (Clethrionomys glareolus). We found no strong indications of reduced resistance in any of the hybrid taxa. Voles damaged moreS. repensthanS. capreaindividuals. There was a general decreasing trend of utilization from pureS. repensto pureS. caprea, hybrid taxa being intermediate between the parents. Thus, voles seemingly do not have a more detrimental effect on hybrid fitness than on the fitness of pure individuals and probably will not select against hybrids in these willows populations.
Predators indirectly protect tundra plants by reducing herbivore abundance
Authors: Hambäck Peter A. , Oksanen Lauri , Ekerholm Per , Lindgren Åsa , Oksanen Tarja , Schneider Michael
Published: May 2004

The role of predators in controlling herbivores and indirectly affecting plant abundance is controversial, and some have argued that such trophic cascades are rare in terrestrial habitats. To examine the potential of trophic cascades in a shrubby tundra ecosystem, vole densities, plant damage and plant cover were examined in areas with and without small mammal predators. On islands without predators, vole densities and plant damage were upto five times higher compared with predator‐rich mainland habitats. As a consequence, the abundance of three out of five dwarf shrub species was substantially reduced on predator‐free islands, providing evidence for strong cascading effects in a rather large‐scale terrestrial system. Herbs on the other hand were not affected by the increased herbivory on islands. This suggests that the strength of trophic cascades also depends on the interaction between plant type and seasonality.
Small‐scale variation in growing season length affects size structure of scarlet monkeyflower
Authors: Williams Jennifer L. , Levine Jonathan M.
Published: May 2004

Growing season length can control plant size over altitudinal and biogeographic scales, but its effect at the scale of meters is largely unexplored. Within the riparian zone of a northern California river, scarlet monkeyflower, Mimulus cardinalis, grows significantly larger at sites high in the channel as compared to sites low in the channel, and even larger where tributaries meet the main stem of the river. We explored the hypothesis that markedly different growing season length controls this size variation. Due to the very gradual retreat of the water level following winter flooding, emergence time is three months longer for plants growing at tributary confluences than for plants growing at low elevations in the channel. Consistent with the growing season length hypothesis, we found no difference in transplant growth between river and tributary confluence sites in an experiment where we equalized growing season length at these locations. Moreover, a second experiment showed that individuals planted earlier in the year gain a distinct size advantage over those planted later, even though growing conditions are less ideal. These results suggest that emergence time may be a key determinant of plant size structure along rivers, an important result considering forecasted variation in water flows with climate change.
Dispersal limits natural recruitment of African mahoganies
Authors: Makana Jean‐Remy , C. Thomas Sean
Published: May 2004

The abundance of forest tree species may be locally limited by the inability of species to disperse to all sites suitable for germination and establishment. This phenomenon of “dispersal limitation” has been suggested to promote the maintenance of high species diversity in tropical forests by slowing down competitive exclusion. We present the first direct experimental evaluation of dispersal limitation in tropical forests, and of its importance relative to other factors affecting recruitment. Seed addition, litter removal and light availability effects on seedling establishment were evaluated in a full factorial experiment on two African mahogany species, Entandrophragma utile and Khaya anthotheca. Seedling recruitment after 18 months, was ∼22 times greater in seed addition treatments (with addition rates corresponding to the tail of seed shadows of large reproductive trees) compared to controls. This seed addition effect was an order of magnitude greater than either gap or litter removal effects, with similar results observed in both logged and primary forest locations. We conclude that dispersal limitation strongly limits seedling establishment for the two species studied. An important “applied corollary” of this result is that seed supplementation may substantially increase local abundance of valuable or rare species in disturbed or managed tropical forests.