bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of preindustrial biomass‐burning emissions on the oxidation pathways of tropospheric sulfur and nitrogen
Authors: Alexander B. , Savarino J. , Kreutz K. J. , Thiemens M. H.
Published: April 2004

Ice core measurements (H2O2and CH4/HCHO) and modeling studies indicate a change in the oxidation capacity of the atmosphere since the onset of the Industrial Revolution due to increases in fossil fuel burning emissions [e.g.,Lelieveld et al., 2002;Hauglustaine and Brasseur, 2001;Wang and Jacob, 1998;Staffelbach et al., 1991]. The mass‐independent fractionation (MIF) in the oxygen isotopes of sulfate and nitrate from a Greenland ice core reveal that biomass‐burning events in North America just prior to the Industrial Revolution significantly impacted the oxidation pathways of sulfur and nitrogen species deposited in Greenland ice. This finding highlights the importance of biomass‐burning emissions for atmospheric chemistry in preindustrial North America and warrants the inclusion of this impact in modeling studies estimating changes in atmospheric oxidant chemistry since the Industrial Revolution, particularly when using paleo‐oxidant data as a reference for model evaluation.
Eight‐hundred‐year temperature variability from the Norwegian continental margin and the North Atlantic thermohaline circulation
Authors: Kristensen D. Klitgaard , Sejrup H. P. , Haflidason H. , Berstad I. M. , Mikalsen G.
Published: April 2004

Four cores raised from the eastern Norwegian Sea and adjacent Norwegian fjords at sites influenced by Atlantic water have been investigated. Oxygen isotope analyses in benthic and planktonic foraminifera are used as a proxy for the paleotemperature development spanning the last 800 years. The cores have been dated using a combination of 210Pb and radiocarbon dates yielding time resolutions of 2–5 years for the last century and 9–25 years beyond this. The proxy records have been compared with instrumental time series covering the last 100 years in order to validate the oxygen isotope measurements as a proxy for paleotemperature. The comparison shows that the paleotemperature variability derived from the oxygen isotope analyses is generally similar to the amplitudes and trends seen in the instrumental time series. In particular, a cooling around 1905–1925 followed by a warming until 1955 is evident in all proxy records as well as in the instrumental time series. Beyond the last century the proxy records show two periods from ∼1225–1450 and ∼1650–1905(25) when temperatures were 1.3–1.6°C lower than present separated by a period of temperatures periodically comparable to present. The last 80 years represent the modern warming and appear to be the warmest period of the last 800 years. We find that that the ocean temperature variability is comparable to terrestrial reconstructions from the region implying a strong link in the ocean‐atmosphere climate system. This suggests that the climate variability in this region beyond the period covered by instrumental time series was also associated with changes in the thermohaline circulation.
Nonideal transport of solute and colloidal tracers through reactive zeolite/iron pellets
Authors: Zhang Pengfei , Šimůnek Jirka , Bowman Robert S.
Published: April 2004

Solute and colloidal tracer tests were conducted in laboratory columns to examine the hydraulic properties of a foamed zeolite/iron pellet material that was developed for in situ remediation of contaminated groundwater. The colloidal tracer (1 μm polystyrene microspheres) moved through the columns much faster than the nonreactive solute tracer tritiated water, reflecting the interpellet preferential flow paths in the packed material. Flow interruption experiments with tritium and bromide showed concentration rebound of both tracers after the interruption (during elution), indicating the existence of nonadvective zones inside the pellets. Inverse modeling of microsphere data using a physical nonequilibrium transport model yielded immobile water content (θim) equivalent to the intrapellet porosity (0.40), suggesting that the microspheres were excluded from the small intrapellet pores and could only move through the large interpellet pore spaces. Inverse modeling of tritium data using physical nonequilibrium and dual‐permeability dual‐porosity models yielded θim values of 0.1–0.2, confirming the existence of nonadvective zones inside the pellets as suggested by the flow interruption experiments. The dual‐permeability dual‐porosity model also indicated that 6–11% of the total porosity was preferential flow porosity, consistent with the observation of enhanced microsphere transport with respect to tritiated water. Forward modeling with the dual‐permeability dual‐porosity model suggested that the immobile water in the pellets would not significantly affect the removal efficiency of contaminants subject to sorption and reduction. In contrast, the preferential flow porosity would drastically lower the contaminant removal efficiency.
Upper mantle P‐wave velocity structure from PASSCAL teleseismic transects across Idaho, Wyoming and Colorado
Authors: Dueker Ken , Yuan Huaiyu
Published: April 2004

Inversion of teleseismic P‐time residuals along two linear seismic arrays provides well‐resolved inverse images of the upper mantle. Low velocity bodies beneath the Yellowstone Hotspot Track and the Grand Mesa volcanic field in western Colorado are similar in shape and magnitude. In the two places where our transects cross the 1.78 Ga Archean‐Proterozoic Cheyenne suture, high velocities are imaged to 150 km. Beneath the Leucite Hills volcanic field in Wyoming a small upper mantle low velocity body is imaged. Whether these anomalies are lithospheric or asthenospheric in origin is poorly constrained, but the consistent high velocities beneath the Cheyenne suture suggest a lithospheric origin. Likewise, the lack of extension beneath the western Colorado volcanic fields suggests that a low‐solidus lithosphere is being disturbed by a regional heating event.
The importance of NO2and volatile organic compounds in the urban air from the viewpoint of the OH reactivity
Authors: Sadanaga Y. , Yoshino A. , Kato S. , Yoshioka A. , Watanabe K. , Miyakawa Y. , Hayashi I. , Ichikawa M. , Matsumoto J. , Nishiyama A. , Akiyama N. , Kanaya Y. , Kajii Y.
Published: April 2004

Total OH reactivity was measured in the suburban area, Tokyo, in July and August 2003, by use of a laser‐induced pump and probe technique. More than 90% of the measured data of the OH loss rates were higher than the calculated values with simultaneously measured concentrations of various trace species. The maximum difference between the measured and calculated values is 34.3%. However, this difference was reduced to be 24.6% when using the rate coefficient of the OH + NO2reaction recommended by IUPAC 1997, which is 40% larger than the most recently recommended value (JPL 2002). We concluded that this disagreement is due to the uncertainty of the OH + NO2rate coefficient as well as existence of unmeasured VOCs. VOCs were quantitatively important as contribution to the OH loss processes.
The Günther’s formalism in classical field theory: momentum map and reduction
Authors: Munteanu Florian , Rey Angel M. , Salgado Modesto
Published: April 2004

The polysymplectic formalism in local field theory, developed by Günther [J. Diff. Geom. 25, 23 (1987)], is revised. A new approach and new results on momentum maps and reduction are given.
Group averaging in the (p,q) oscillator representation of SL(2,R)
Authors: Louko Jorma , Molgado Alberto
Published: April 2004

We investigate refined algebraic quantization with group averaging in a finite-dimensional constrained Hamiltonian system that provides a simplified model of general relativity. The classical theory has gauge group SL(2,R) and a distinguished o(p,q) observable algebra. The gauge group of the quantum theory is the double cover of SL(2,R), and its representation on the auxiliary Hilbert space is isomorphic to the (p,q) oscillator representation. When p⩾2, q⩾2 and p+q≡0 (mod 2), we obtain a physical Hilbert space with a nontrivial representation of the o(p,q) quantum observable algebra. For p=q=1, the system provides the first example known to us where group averaging converges to an indefinite sesquilinear form.
On diffusion dynamics for continuous systems with singular superstable interaction
Authors: Kondratiev Yuri G. , Rebenko Alexei L. , Röckner Michael
Published: April 2004

We consider the time evolution of states for continuous infinite particle systems which corresponds to nonequilibrium diffusion dynamics. For initial states μ0 which are perturbations of the equilibrium we obtain a bound for finite volume nonequilibrium correlation functions and their continuity in time uniformly in volume for any finite time interval. This gives the possibility to construct the time evolution of correlation functions and corresponding states in the thermodynamic limit.
Locality and orthomodular structure of compound systems
Authors: Watanabe Teppei
Published: April 2004

A P-lattice is defined as a σ-complete, orthomodular atomic lattice ℒ which is formed by the set of propositions of a physical system. A composition of physical systems in the framework of P-lattices is considered and some notions of locality are given. It is shown that the following statements about compound systems are equivalent. (a) All atoms of a compound system are reducible to those of its subsystems. (b) All pure states of a compound system are separable into those of its subsystems. (c) A compound system has statistical property independence. (d) At least one of the subsystems is classical. (e) Bell-type inequalities hold.
On the generalized function calculus for infrared and ultraviolet singular quantum fields
Authors: Soloviev M. A.
Published: April 2004

New theorems on properties of the generalized functions defined on Gelfand–Shilov’s spaces Sα0 are established. These functional classes are universal for the operator realization of quantum field theories whose infrared or/and ultraviolet behavior is more singular than that of the standard Wightman quantum field theories (QFT’s). The leading role in these applications is played by the notion of a carrier cone of analytic functional which generalizes and replaces the notion of support of distribution. An explicit representation for the generalized functions with a given carrier cone is obtained. It is proved that the restrictions of functionals defined on Sα0 to the spaces with smaller subscripts have the same carrier cones. The precise characterization of the relation between the carrier cones of multilinear forms with respect to their arguments and the carrier cones of their associated generalized functions is given. Applications of the obtained results to indefinite metric QFT and to nonlocal models are discussed.
Integrable and superintegrable quantum systems in a magnetic field
Authors: Bérubé Josée , Winternitz Pavel
Published: April 2004

Integrable quantum mechanical systems with magnetic fields are constructed in two-dimensional Euclidean space. The integral of motion is assumed to be a first or second order Hermitian operator. Contrary to the case of purely scalar potentials, quadratic integrability does not imply the separation of variables in the Schrödinger equation. Moreover, quantum and classical integrable systems do not necessarily coincide: the Hamiltonian can depend on the Planck constant ℏ in a nontrivial manner.
A statistical complexity measure with nonextensive entropy and quasi-multiplicativity
Authors: Yamano Takuya
Published: April 2004

The properties of a statistical complexity measure that are characterized by nonextensivity in entropy have been investigated, which is of so-called disequilibrium type. Considering the composition law for two systems with different nonextensivities (quasi-multiplicativity), a nontrivial relation between the nonextensive parameters and the fluctuating bit number in information theory has been mentioned. To see the time evolution of the nonextensive complexity measure, we examine systems having a lognormal distribution, the underlying dynamics for which is known to obey a random multiplicative process in the presence of a boundary constraint.
Associated Bessel functions and the discrete approximation of the free-particle time evolution operator in cylindrical coordinates
Authors: Nash Patrick L. , López-Mobilia Rafael
Published: April 2004

A central finite difference approximation for the radial contribution Δr to the Laplacian ∇2=Δr+Δr⊥(r) is considered in a three-dimensional cylindrical coordinate system (r,θ,z). A free-particle Schrödinger time evolution operator is constructed by exponentiation, e(i/2)ξ∇2=⋯e−(1/2)ξ2[Δr,Δr⊥(r)] e(i/2)ξΔr⊥(r) e(i/2)ξΔr→⋯e(i/2)ξΔr. Denoting the central finite difference approximation of Δr by (1/Δr2) T, the matrix S≡e(i/2)λT, with λ=ξ/Δr2, is shown to be similar to a particular unitary representation UVK of the group of motions on Euclidean three-space that has been described by Vilenkin and Klimyk. The matrix elements of UVK generalize the Bessel function and provide an approximation of the leading term in the radial contribution to the evolution operator.
Integrable mixing of An−1 type vertex models
Authors: Grillo S. , Montani H.
Published: April 2004

Given a family of monodromy matrices T0,T1,…,TK−1 corresponding to integrable anisotropic vertex models of Anμ−1 type, μ=0,1,…,K−1, we built up a related mixed vertex model by means of gluing the lattices on which they are defined, in such a way that integrability property is preserved. The gluing process is implemented through one-dimensional representations of rectangular quantum matrix algebras A(Rnμ−1:Rnμ), namely, the gluing matrices ζμ. Algebraic Bethe ansatz is applied on a pseudovacuum space with a selected basis and, for each element of this basis, it yields a set of nested Bethe ansatz equations matching up to the ones corresponding to an Am−1 quasiperiodic model, with m equal to minμ∈ZK{rank ζμ}.
Persistence of an extreme sex-ratio bias in a natural population
Authors: Dyson Emily A. , Hurst Gregory D. D.
Published: April 2004

The sex ratio is a key parameter in the evolution and ecology of a species. Selfish genetic elements that bias the sex ratio of affected individuals are well known and characterized, but their effect on populations has been considered limited, because either the element does not achieve high prevalence or the host rapidly evolves resistance to the distorting element, reducing its prevalence. We tested whether the host necessarily prevails by using a butterfly system where records from the early part of the 20th century reported extreme sex-ratio bias in nature. We reexamined this population and found the bias was present today, 400 generations after the original record, with a population sex ratio of 100 females per male. The sex-ratio bias was associated with the presence of a heritable male-killing
Wolbachia
infection in 99% of adult females, against which the host butterfly has failed to evolve resistance. The resultant dearth of males causes an average 57% reduction in the reproductive output of adult females. Persistence of the population despite the very high frequency of the sex-ratio distorter appears to be associated with the ability of males to mate >50 times in their life combined with a high intrinsic rate of increase of the species.
Infant negative emotionality and attachment: Implications for preschool intelligence
Authors: Karrass Jan , Braungart-Rieker Julia M.
Published: April 2004

This longitudinal study examined the extent to which dimensions of infant negative temperament in the first year predicted IQ at age 3, and whether these associations depended on the quality of the infant–mother attachment relationship. In a sample of 63 infant–mother dyads, mothers completed Rothbart’s (1981) IBQ when infants were 4 and 12 months, mothers and infants participated in Ainsworth and Wittig’s (1969) Strange Situation at 12 months, and children completed the Stanford-Binet (Thorndike, Hagen, & Sattler, 1986) when they were 36 months of age. Hierarchical multiple regression analyses indicated that 4- or 12-month distress to limitations was not predictive of later IQ, but infants with greater distress to novelty at 4 months had higher IQs at 36 months. Furthermore, greater distress to novelty at 12 months predicted higher IQs but only for infants whose attachment was insecure. Differential implications of temperamental fear versus anger for social influences on cognitive development are discussed.
Bringing Buprenorphine‐Naloxone Detoxification to Community Treatment Providers: The NIDA Clinical Trials Network Field Experience
Authors: Amass Leslie , Ling Walter , Freese Thomas E. , Reiber Chris , Annon Jeffrey J. , Cohen Allan J. , McCarty Dennis , Reid Malcolm S. , Brown Lawrence S. , Clark Cynthia , Ziedonis Douglas M. , Krejci Jonathan , Stine Susan , Winhusen Theresa , Brigham Greg , Babcock Dean , Muir Joan A. , Buchan Betty J. , Horton Terry
Published: April 2004

In October 2002, the U.S. Food and Drug Administration approved buprenorphine‐naloxone (Suboxone®) sublingual tablets as an opioid dependence treatment available for use outside traditionally licensed opioid treatment programs. The NIDA Center for Clinical Trials Network (CTN) sponsored two clinical trials assessing buprenorphine‐naloxone for short‐term opioid detoxification. These trials provided an unprecedented field test of its use in twelve diverse community‐based treatment programs. Opioid‐dependent men and women were randomized to a thirteen‐day buprenorphine‐naloxone taper regimen for short‐term opioid detoxification. The 234 buprenorphine‐naloxone patients averaged 37 years old and used mostly intravenous heroin. Direct and rapid induction onto buprenorphine‐naloxone was safe and well tolerated. Most patients (83%) received 8 mg buprenorphine‐2 mg naloxone on the first day and 90% successfully completed induction and reached a target dose of 16mg buprenorphine‐4 mg naloxone in three days. Medication compliance and treatment engagement was high. An average of 81% of available doses was ingested, and 68% of patients completed the detoxification. Most (80.3%) patients received some ancillary medications with an average of 2.3 withdrawal symptoms treated. The safety profile of buprenorphine‐naloxone was excellent. Of eighteen serious adverse events reported, only one was possibly related to buprenorphine‐naloxone. All providers successfully integrated buprenorphine‐naloxone into their existing treatment milieus. Overall, data from the CTN field experience suggest that buprenorphine‐naloxone is practical and safe for use in diverse community treatment settings, including those with minimal experience providing opioid‐based pharmacotherapy and/ or medical detoxification for opioid dependence.
The effects of mandatory and optional use on students’ ratings of a computer‐based learning package
Authors: Garland Kate , Noyes Jan
Published: April 2004

Continuing developments in educational technology and increasing undergraduate numbers in the UK have facilitated the use of computer‐based learning packages. One of the effects of the increasing use of these packages is the shift in teaching of material from being primarily lecturer‐led to student‐driven. This has a number of implications concerning using the package, since it is quite likely that students will be working in isolation, and the use of the package may be mandatory or optional. In this study we report on the usefulness ratings of a software package for undergraduate use within the context of whether or not students choose to use it. Level 1 students and lecturers in Economics were surveyed at three UK universities. Findings indicate that students whose use was mandatory rated the learning package as more useful than those whose use was optional. Reasons for non‐use centred on lack of instruction and on student apathy. These results have important implications for the use of computer‐based learning packages and for understanding user attitudes.
Automated finger spelling by highly realistic 3D animation
Authors: Adamo‐Villani Nicoletta , Beni Gerardo
Published: April 2004

We present the design of a new 3D animation tool for self‐teaching (signing and reading) finger spelling—the first basic component in learning any sign language. We have designed a highly realistic hand with natural animation of the finger motions. Smoothness of motion (in real time) is achieved via programmable blending of animation segments. The hand is utilised by a programme that automatically converts text to finger spelling with controllable playback speed and playback views. The programme can be operated in two modes for two basic applications: learning to read (finger spelling) and learning to sign. For both modes, multi‐sided views are provided. In addition, for the signing mode, a mirror view is provided for the common technique of using a mirror for feedback in practising finger spelling. An additional view revealing the joint structure of the hand allows the signer to practise the subjective view without having to guess the position of the fingers. This is the first example of highly realistic 3D animation that can be used practically to teach a basic aspect of sign language. The method is applicable more generally to sign language, and this finger‐spelling application should be regarded as a first step toward the extension of highly realistic 3D animation to sign language in general.
International outsourcing when labour markets are unionized
Authors: Skaksen Jan Rose
Published: April 2004

Abstract.  We consider the implications of international outsourcing in a simple general equilibrium model where the wage rate is the outcome of negotiations between a firm and a trade union. The effects of potential, but non‐realized, international outsourcing, is a reduction in the wage rate and an increase in employment. Aggregate welfare increases, but the trade union becomes worse off while owners of capital become better off. Realized international outsourcing gives rise to an increase in the wage rate and a reduction in employment. Aggregate welfare decreases, but the trade union becomes better off, while owners of capital become worse off.
Antidumping law as a collusive device
Authors: Zanardi Maurizio
Published: April 2004

Abstract.  In the United States many antidumping petitions are withdrawn before the investigations are completed. Prusa (1992) argues that petitions are used by domestic industries to induce foreign industries into collusive agreements. In his model, all antidumping petitions should be withdrawn, which is not the case. This paper provides a model in which only some petitions are withdrawn. Withdrawal depends on two key parameters: coordination cost and bargaining power of domestic and foreign industries. A new data set is constructed to test the model on the U.S. experience for the period 1980–97. The econometric analysis supports the theoretical conclusions of the model. JEL classification: F13; D43
Escaping the poverty trap in a developing rural economy
Authors: Manh Hung Nguyen , Makdissi Paul
Published: April 2004

Abstract. In this paper, we examine the economic policies that might allow a developing rural economy to escape from the poverty trap characterized by a subsistence level of per capita consumption in the long run. In our model where labour is combined to land available in fixed quantity to produce a homogeneous good, saving could be made through only having children, the number of which is an endogenous decision. We provide conditions under which the economy runs into a poverty trap, and proceed to analyse the relevant policies in this case. We demonstrate that an escape from this poverty trap is possible through a suitable technology transfer, or an appropriate child‐rearing tax, but not with a foreign manufacturing sector, which increases only temporarily the labour income in this rural economy. JEL classification: J11, O11, O40
Large predators and their prey in a southern African savanna: a predator's size determines its prey size range
Authors: Radloff Frans G. T. , Du Toit Johan T.
Published: April 2004

A long‐term (13‐year) data set, based on > 4000 kills, was used to test whether a sympatric group of large predators adheres to the theoretical predictions that (1) mean prey body size and (2) prey diversity increase as functions of predator body size.

All kills observed by safari guides are documented routinely in Mala Mala Private Game Reserve, South Africa. We analysed these records for lion (Panthera leo, Linnaeus), leopard (Panthera pardus, Linnaeus), cheetah (Acinonyx jubatus, Schreber) and African wild dog (Lycaon pictus, Temminck). Males and females of the sexually dimorphic felid species were treated as functionally distinct predator types. Prey types were classified by species, sex and age class.

Prey profiles were compared among predator types in terms of richness and evenness to consider how both the range of prey types used and the dominance of particular prey types within each range may be influenced by predator size. No significant size‐dependent relationships were found, so factors separate from or additional to body size must explain variation in prey diversity across sympatric predators.

A statistically strong relationship was found between mean prey mass and predator mass (r2 = 0·86, P= 0·002), although pairwise comparisons showed that most predators killed similar prey despite wide differences in predator size. Also, minimum prey mass was independent of predator mass while maximum prey mass was strongly dependent on predator mass (r2 = 0·71, P= 0·017). The ecological significance is that larger predators do not specialize on larger prey, but exploit a wider range of prey sizes.
Predator–prey body size, interaction strength and the stability of a real food web
Authors: Emmerson Mark C. , Raffaelli Dave
Published: April 2004

We examined the empirical relationship between predator–prey body size ratio and interaction strength in the Ythan Estuary food web.

We have refined a previously published version of the food web and explored how size‐based predatory effects might affect food web dynamics. To do so, we used four predatory speciesCrangon crangon(Linnaeus),Carcinus maenas(Linnaeus),Pomatoschistus microps(Krøyer) andPlatichthys flesus(Linnaeus) and one common prey speciesCorophium volutator(Pallas) from the food web.

All predators and prey were sorted into small, medium and large size classes and placed into mesocosms in all possible pairwise combinations of size and species identity to determine per capita effects of predators on prey (aij).

Using Lotka–Volterra dynamics the empirical body size relationships obtained from these experiments and other relationships already available for the Ythan Estuary, we parameterized a food web model for this system. The local stability properties of the resulting food web models were then determined.

We found that by choosing interaction strengths using an empirically defined scaling law, the resulting food web models are always dynamically stable, despite the residual uncertainties in the modelling approach. This contrasts with the statistical expectation that random webs with random parameters have a vanishingly improbable chance of stability.

The patterning of predator and prey body sizes in real ecosystems affects the arrangement of interaction strengths, which in turn determines food web stability.
Estimating the density of ground‐dwelling arthropods with pitfall traps using a nested‐cross array
Authors: Perner Jörg , Schueler Silvio
Published: April 2004

A new procedure for estimating the population densities of ground‐dwelling arthropods with pitfall trapping is described. It couples the fitting of single hyperbolic functions to trap data with the use of a ‘nested‐cross array’, a cross‐shaped trap arrangement with distances between traps doubling with increasing distance from the central trap.

We used individual‐based simulation modelling to test the method's reliability given changes in population density, turning rate, trapping period, beetle distribution and intertrap distance.

Simulations show that function fits are more likely, and density estimates more accurate, with greater body size and therefore with net displacement, increasing population density, decreasing aggregation and increased turning rate.

Simulation indicates that the method is a promising procedure for density estimation that is worth testing in the field. Reliable density estimates are possible if the traps contain a neutral preservative, arrays are established in nearly homogeneous parts of habitat and the arms of the nested‐cross array are distant from habitat edges.
Looks are important: parasitic assemblages of agromyzid leafminers (Diptera) in relation to mine shape and contrast
Authors: Salvo Adriana , Valladares Graciela R.
Published: April 2004

We test the hypothesis that leaf mine appearance can affect the risk of leafminers being discovered by parasitoids, and therefore influence parasitic assemblages, using a comparative study of parasitic complexes associated with 28 agromyzid species in Central Argentina. Analyses were based on size, structure (defined as the number of species in host‐range categories) and impact (percentage parasitism) of parasitic complexes on leafminers. Mine appearance was defined in terms of shape (linear, linear‐blotch, blotch) and colour (high or low contrast with the leaf lamina).

Irrespective of the agromyzid species involved, significant differences were found in the structure of the parasitoid complexes: specialists were more abundant and generalists rarer than expected in blotch and cryptically coloured mines.

There were no differences in average parasitoid species richness and parasitism rates among differently coloured or shaped galleries. However, mine appearance significantly affected parasitic assemblage structure, with shape driving generalist species richness and contrast influencing that of specialists. Mine shape also affected parasitism rates, which were highest for generalists in linear mines, and for specialists in blotch mines. The existence of a gradient of discovery from the cryptically coloured blotch mines to the most apparent highly contrasting linear ones was supported by significant correlations of this gradient with richness and parasitism rates of generalist and specialist parasitoids.

Taxonomic composition of parasitic complexes (analysed through parasitoid species abundance) was separated significantly according to host mine shape. An even more significant classification of assemblages was achieved when the combination of mine shape and colour was considered in the discoverability gradient.

Our results suggest that despite leaf mines being an ecologically homogeneous resource, their morphology might offer varying degrees of refuge against different parasitoids.
Foraging trip duration and density of megachilid bees, eumenid wasps and pompilid wasps in tropical agroforestry systems
Authors: Klein Alexandra‐Maria , Steffan‐Dewenter Ingolf , Tscharntke Teja
Published: April 2004

Most animals have to bridge some distances in space and time to provide all resources necessary for survival. Little is known about how the local and regional management of tropical agroforestry systems, differing in the availability of food resources and suitable nesting sites, determine foraging trip duration and density of bees and wasps (Hymenoptera Aculeata).

In this study, foraging trip duration and brood‐cell density (in trap nests exposed for a 15‐month period) were analysed for three species, which represent three guilds in 24 agroforestry systems in Central Sulawesi (Indonesia): the pollinator Heriades sp. aff. fulvescens (Apidae), the cacao caterpillar‐hunting predator Rhynchium haemorrhoidale umeroatrum (Eumenidae) and the spider‐hunting predator Auplopus levicarinatus (Pompilidae). The agroforestry systems were characterized by plant species richness, blossom cover of herbs, light intensity and distance from the nearest natural forest.

The correlation of foraging time to bee and wasp density showed the relative importance of food and nest‐site availability for the pollinator and the spider‐hunting predator, because both parameters are correlated with light intensity in the agroforestry systems. In contrast, foraging time and nest density of the eumenid predator were not correlated because of the distance between high quantities of food resources (in sites with dense cacao plants) and nesting sites (in adjacent natural forests).

The eumenid response to local and regional agroforestry management illustrates that species may survive only in landscapes that permit access to a multiple set of resources. Accordingly, habitat evaluations using only foraging time may lead to wrong conclusions, as key drivers of population dynamics may not be inside but outside the local systems, emphasizing the need for a landscape approach.
Parasitoid–host metapopulation dynamics: the causes and consequences of phenological asynchrony
Authors: Van Nouhuys Saskya , Lei Guangchun
Published: April 2004

The strength of interaction between the specialist parasitoidCotesia melitaearumand the host butterflyMelitaea cinxiais influenced by the coincidence of the adult stage of the parasitoid with the larval stage of the host.

We show that there is great variation in this developmental synchrony among local populations and among years, ranging from complete synchrony to complete asynchrony.

The causal mechanism is early spring temperature, which affects parasitoid development differently than the development of the host.

At cool air temperatures the dark‐coloured and mobile host larvae benefit from basking in the sun, while the white and immobile parasitoid cocoons develop slowly in shaded microclimates, becoming adults after hosts have pupated and are no longer available for parasitism. At warm temperatures many adult wasps emerge in time to parasitize host larvae.

We show that the host–parasitoid synchrony influences subsequent parasitoid population size and the rate of colonization of previously uninhabited host populations, contributing to parasitoid metapopulation dynamics.

We detected no direct effect of the phenological synchrony on local host population size, but the synchrony is likely to be important for overall host metapopulation dynamics via variation in the rate of colonization by the parasitoid.
Invertebrate community assembly along proglacial chronosequences in the high Arctic
Authors: Hodkinson Ian D. , Coulson Stephen J. , Webb Nigel R.
Published: April 2004

Invertebrate community assembly is described for two contrasting proglacial chronosequences (over 1900 years) at Kongsfjord, W. Spitsbergen, Svalbard.

Three hypotheses were tested: (1) community assembly is deterministic, directional and predictable; (2) succession is inextricably linked to plant community and soil development; and (3) dispersal is a rate‐limiting factor for community assembly.

Communities, dominated by omnivores and detritivores, are more complex than supposed previously. Herbivore species were few but predators, parasitoids and hyperparasitoids were abundant.

Species fell within one of eight defined groups with respect to colonization. This relates to ecophysiological tolerances, need for facilitation or dependence on other species. Spiders, surface‐active Collembola and drought‐resistant cryptostigmatic mites arrived before vascular plants established and soils developed. Later colonizers required site facilitation through soil development or host availability.

Comparisons between the proglacial area of Midtre Lovénbre, a land‐terminating glacier, and three Lovén Islands, released from beneath a tidewater glacier, showed similarities in community composition and species abundance with respect to successional stage, suggesting determinism and direction in community development.

Most common species on Midtre Lovénbre colonized the Lovén Islands rapidly, suggesting that dispersal does not seriously restrict community development on the time scales involved. Some minor species associated with older soils appear not yet to have reached the islands.
Temperature‐dependent interactions explain unexpected responses to environmental warming in communities of competitors
Authors: Jiang Lin , Morin Peter J.
Published: April 2004

Predictions about how species will respond to climate warming are based commonly on eco‐physiological models or niche models. One critique of this practice is that it ignores interspecific interactions.

We examined how resource competition affects the responses of two ciliate species, Colpidium striatum Stein and Paramecium tetraurelia Sonneborn, to warming in laboratory microcosms.

We found that warming had a negative effect on Colpidium abundance and a negligible effect on Paramecium abundance in the absence of interspecific competition. When Colpidium and Paramecium competed, however, Paramecium coexisted with Colpidium at low and high temperatures, and was competitively excluded at intermediate temperatures.

Temperature‐dependent strength of the interaction between Colpidium and Paramecium may explain the unexpected responses of Paramecium, which were inconsistent with its response to temperature in the absence of Colpidium.

Our results provide further support for the important role of species interactions in understanding how species respond to environmental warming, and suggest that the complex interplay between species interactions and climate may make it extremely difficult to predict accurately how species embedded in complex communities will respond to climate warming.
Ontogenetic changes in metabolism may determine diet shifts for a sit‐and‐wait predator
Authors: Jackson Angus C. , Rundle Simon D. , Attrill Martin J. , Cotton Peter A.
Published: April 2004

Body size is a central parameter in determining prey selection, and where animals exhibit large increases in size, ontogenetic diet shifts are common. Optimal foraging models have proved to be useful tools in predicting changes in diet, but previous applications have been limited to those associated with changes in external drivers such as habitat use.

We conducted laboratory and field experiments to parameterize an optimal foraging model to test whether prey choice can be determined by internal mechanisms such as metabolism.

Model predictions were made for Pomatoschistus microps, the common goby (Pisces: Gobiidae), a sit‐and‐wait predator that exhibits a shift in prey choice independently of external drivers. The model predicted a change in diet at a fish length of 30 mm, which agrees well with existing empirical observations. This is the first time the link between metabolism and prey choice has been considered as a major determinant of diet shifts.

P. microps, using a sit‐and‐wait foraging mode, were expected to act as cost‐minimizers but the model indicated that gobies were typically not time‐limited and that prey selection maximized energy intake rates both before and after the diet shift.

Prey size range and mean prey length were determined primarily by the presence or absence of meiofauna in the diet, supporting the observation that the diet shift occurs between the two ecologically distinct groups of benthic meiofauna and macrofauna.
Interaction strengths in food webs: issues and opportunities
Authors: Berlow Eric L. , Neutel Anje‐Margiet , Cohen Joel E. , De Ruiter Peter C. , Ebenman Bo , Emmerson Mark , Fox Jeremy W. , Jansen Vincent A. A. , Iwan Jones J. , Kokkoris Giorgos D. , Logofet Dmitrii O. , McKane Alan J. , Montoya Jose M. , Petchey Owen
Published: April 2004

Recent efforts to understand how the patterning of interaction strength affects both structure and dynamics in food webs have highlighted several obstacles to productive synthesis. Issues arise with respect to goals and driving questions, methods and approaches, and placing results in the context of broader ecological theory.

Much confusion stems from lack of clarity about whether the questions posed relate to community‐level patterns or to species dynamics, and to what authors actually mean by the term ‘interaction strength’. Here, we describe the various ways in which this term has been applied and discuss the implications of loose terminology and definition for the development of this field.

Of particular concern is the clear gap between theoretical and empirical investigations of interaction strengths and food web dynamics. The ecological community urgently needs to explore new ways to estimate biologically reasonable model coefficients from empirical data, such as foraging rates, body size, metabolic rate, biomass distribution and other species traits.

Combining numerical and analytical modelling approaches should allow exploration of the conditions under which different interaction strengths metrics are interchangeable with regard to relative magnitude, system responses, and species identity.

Finally, the prime focus on predator–prey links in much of the research to date on interaction strengths in food webs has meant that the potential significance of non‐trophic interactions, such as competition, facilitation and biotic disturbance, has been largely ignored by the food web community. Such interactions may be important dynamically and should be routinely included in future food web research programmes.
Lateral inhibition and habituation of the human auditory cortex
Authors: Pantev C. , Okamoto H. , Ross B. , Stoll W. , Ciurlia‐Guy E. , Kakigi R. , Kubo T.
Published: April 2004

The goal of this study was to compare the lateral inhibition and the habituation in the human auditory cortex, two important physiological effects during auditory processing that can be reliably measured by means of magnetoencephalography when recording auditory evoked fields. Applying 40‐Hz amplitude‐modulated stimuli allowed us to record simultaneously the slow transient evoked and the steady‐state fields and thus to characterize the lateral inhibition and the habituation effect in primary and non‐primary auditory cortical structures. The main finding of the study is that the lateral inhibition effect of non‐primary auditory areas as measured on the major component of the slow transient auditory evoked field (N1) is significantly stronger than the corresponding habituation effect. By contrast, this effect was not observed for the 40‐Hz steady‐state fields, characterizing the activation of the primary auditory cortex in humans. The results might be interpreted as (i) evidence that the inhibition mediated by lateral connections is stronger than the habituation of excitatory neurons in the non‐primary auditory cortex and (ii) the processing hierarchy in the human auditory cortex is demonstrated by the different behaviour of lateral inhibition and habituation in primary and non‐primary auditory cortical structures.
Comparative analysis of CNS populations in knockout mice with altered growth hormone responsiveness
Authors: Ransome Mark I. , Goldshmit Yona , Bartlett Perry F. , Waters Michael J. , Turnley Ann M.
Published: April 2004

Recently we have shown that growth hormone (GH) inhibits neuronal differentiation and that this process is blocked by suppressor of cytokine signalling‐2 (SOCS2). Here we examine several cortical and subcortical neuronal populations in GH hyper‐responsive SOCS2 null (−/−) mice and GH non‐responsive GH receptor null (GHR−/−) mice. While SOCS2−/− mice showed a 30% decrease in density of NeuN positive neurons in cortex compared to wildtype, GHR−/− mice showed a 25% increase even though brain size was decreased. Interneuron sub‐populations were variably affected, with a slight decrease in cortical parvalbumin expressing interneurons in SOCS2−/− mice and an increase in cortical calbindin and calretinin and striatal cholinergic neuron density in GHR−/− mice. Analysis of glial cell numbers in cresyl violet or glial fibrillary acidic protein (GFAP) stained sections of cortex showed that the neuron : glia ratio was increased in GHR−/− mice and decreased in SOCS2−/− mice. The astrocytes in GHR−/− mice appeared smaller, while they were larger in SOCS2−/− mice. Neuronal soma size also varied in the different genotypes, with smaller striatal cholinergic neurons in GHR−/− mice. While the size of layer 5 pyramidal neurons was not significantly different from wildtype, SOCS2−/− neurons were larger than GHR−/− neurons. In addition, primary dendritic length was similar in all genotypes but dendritic branching of pyramidal neurons in the cortex appeared sparser in GHR−/− and SOCS2−/− mice. These results suggest that GH, possibly regulated by SOCS2, has multiple effects on central nervous system (CNS) development and maturation, regulating the number and size of multiple neuronal and glial cell types.
Hippocampal theta rhythm is reduced by suppression of the H‐current in septohippocampal GABAergic neurons
Authors: Xu Changqing , Datta Subimal , Wu Min , Alreja Meenakshi
Published: April 2004

Hippocampal learning and memory tasks are tightly coupled to the hippocampal theta rhythm, which is critically dependent on the medial septum/diagonal band of Broca (MSDB) although the underlying mechanisms remain unclear. The MSDB sends both cholinergic and GABAergic projections to the hippocampus. Here we show that: (i) septo‐hippocampal GABAergic but not cholinergic neurons have a pacemaking current, the H‐current, and that its selective blockade by ZD7288 reduces their spontaneous firing in rat brain slices; and (ii), local infusions of ZD7288 into the MSDB reduce exploration and sensory evoked hippocampal theta bursts in behaving rats. Thus, the H‐current in septohippocampal GABAergic neurons modulates the hippocampal theta rhythm.
Purinergic modulation of synaptic input to Purkinje neurons in rat cerebellar brain slices
Authors: Brockhaus Johannes , Dressel Diana , Herold Sabine , Deitmer Joachim W.
Published: April 2004

Adenosine triphosphate (ATP) is a cotransmitter and an extracellular neuromodulator in nervous systems, and it influences neural circuits and synaptic strength. We have studied a stimulating effect of ATP (100 µm) on the synaptic input of Purkinje neurons in acute cerebellar brain slices of juvenile rats (p14–19). Bath application of ATP increased the frequency of spontaneous postsynaptic currents (sPSCs) almost twofold, and increased their amplitude. These effects were fully suppressed by the P2 receptor antagonist pyridoxalphosphate‐6‐azophenyl‐2′4′‐disulphonic acid (PPADS; 10 µm), or after blocking action potentials with tetrodotoxin (TTX; 0.5 µm), but were not impaired by inhibiting ionotropic, non‐NMDA glutamate receptors with 2,3‐dioxo‐6‐nitro‐1,2,3,4,‐tetrahydrobenzo[f]quinoxaline‐7‐sulphonamide (NBQX; 5 µm). The frequency of sPSCs was reduced by 35% by PPADS and increased by 50% after inhibiting ectonucleotidase with ARL67156 (50 µm), suggesting intrinsic, ‘tonic’, stimulation of synaptic activity via P2 receptors. The pharmacological profile indicated that the ATP effect was mediated by both P2X and P2Y receptors, most probably of the P2X5– and P2Y2,4–like subtypes. The action potential frequency in the inhibitory basket cells was increased by 65%, and decreased in Purkinje neurons by 25%, in the presence of ATP. Our results suggest that ATP continuously modulates the cerebellar circuit by increasing the activity of inhibitory input to Purkinje neurons, and thus decreasing the main cerebellar output activity, which contributes to locomotor coordination.