bluuebunny/crossref_metadata_2025 huggingface dataset:
S‐(2,3‐Dichlorotriazinyl)glutathione
Authors: Kotzia Georgia A. , Labrou Nikolaos E.
Published: August 2004

S‐(2,3‐Dichlorotriazinyl)glutathione (SDTG) was synthesized and shown to be an effective alkylating affinity label for recombinant maize glutathione S‐transferase I (GST I). Inactivation of GST I by SDTG at pH 6.5 followed biphasic pseudo‐first‐order saturation kinetics. The biphasic kinetics can be described in terms of a fast initial phase of inactivation followed by a slower phase, leading to 42 ± 3% residual activity. The rate of inactivation for both phases exhibits nonlinear dependence on SDTG concentration, consistent with the formation of a reversible complex with the enzyme (Kd 107.9 ± 2.1 µm for the fast phase, and 224.5 ± 4.2 µm for the slow phase) before irreversible modification with maximum rate constants of 0.049 ± 0.002 min−1 and 0.0153 ± 0.001 min−1 for the fast and slow phases, respectively. Protection from inactivation was afforded by substrate analogues, demonstrating the specificity of the reaction. When the enzyme was inactivated (42% residual activity), ≈ 1 mol SDTG per mol dimeric enzyme was incorporated. Amino‐acid analysis, molecular modelling, and site‐directed mutagenesis studies suggested that the modifying residue is Met121, which is located at the end of α‐helix H′′′3 and forms part of the xenobiotic‐binding site. The results reveal an unexpected structural communication between subunits, which consists of mutually exclusive modification of Met residues across enzyme subunits. Thus, modification of Met121 on one subunit prevents modification of Met121 on the other subunit. This communication is governed by Phe51, which is located at the dimer interface and forms part of the hydrophobic lock‐and‐key intersubunit motif. The ability of SDTG to inactivate other glutathione‐binding enzymes and GST isoenzymes was also investigated, and it was concluded that this new reagent may have general applicability as an affinity reagent for other enzymes with glutathione‐binding sites.
New insights into conformational and functional stability of human α‐thrombin probed by high hydrostatic pressure
Authors: Lima Luis Mauricio T. R. , Zingali Russolina B. , Foguel Débora , Monteiro Robson Q.
Published: August 2004

The effects of high hydrostatic pressure (HHP) and urea on conformational transitions of human α‐thrombin structure were studied by fluorescence spectroscopy and by measuring the catalytic activity of the enzyme. Treatment of thrombin with urea produced a progressive red shift in the center of mass of the intrinsic fluorescence emission spectrum, with a maximum displacement of 650 cm−1. HHP (270 MPa) shifted the centre of mass by only 370 cm−1. HHP combined with a subdenaturing urea concentration (1.5 m) displaced the centre of mass by ≈ 750 cm−1. The binding of the fluorescent probe bis(8‐anilinonaphthalene‐1‐sulfonate) to thrombin was increased by 1.8‐, 4.0‐, and 2.7‐fold after treatment with high urea concentration, HHP or HHP combined with urea, respectively, thus suggesting that all treatments convert the enzyme to partially folded intermediates with exposed hydrophobic regions. On the other hand, treatment of thrombin with urea (but not HHP) combined with dithiothreitol progressively displaced the fluorescent probe, thus suggesting that this condition converts the enzyme to a completely unfolded state. Urea and HHP also led to different conformations when changes in the thrombin catalytic site environment were assessed using the fluorescence emission of fluorescein‐d‐Phe‐Pro‐Arg‐cloromethylketone‐α‐thrombin: addition of urea up to 2 m gradually decreased the fluorescence emission of the probe to 65% of the initial intensity, whereas HHP caused a progressive increase in fluorescence. Hydrolysis of the synthetic substrate S‐2238 was enhanced (35%) in 2 m urea and gradually abolished at higher concentrations, while HHP (270 MPa) inhibited the enzyme's catalytic activity by 45% and abolished it when 1.5 m urea was also present. Altogether, analysis of urea and HHP effects on thrombin structure and activity indicates the formation of dissimilar intermediate states during denaturation by these agents.
Processing of the 24 kDa subunit mitochondrial import signal is not required for assembly of functional complex I in Yarrowia lipolytica
Authors: Kerscher Stefan , Bénit Paule , Abdrakhmanova Albina , Zwicker Klaus , Rais Isam , Karas Michael , Rustin Pierre , Brandt Ulrich
Published: August 2004

A small deletion in the second intron of human NDUFV2 (IVS2+5_+8delGTAA) has been shown to cause hypertrophic cardiomyopathy and encephalomyopathy [Bénit, P., Beugnot, R., Chretien, D., Giurgea, I., de Lonlay‐Debeney, P., Issartel, J.P., Kerscher, S., Rustin, P., Rötig, A. & Munnich, A. (2003) Human Mutat.21, 582–586]. Skipping of exon 2 results in a partial deletion of the mitochondrial targeting sequence of the precursor for the 24 kDa subunit of respiratory chain complex I. Immunoreactivity of the 24 kDa subunit and complex I activity, both present at 30–50% of normal levels in patient mitochondria, raised the question of how the mutant 24 kDa subunit precursor can be imported and assembled into functional complex I. In the present study, we have remodelled the human NDUFV2 mutation by deleting codons 17–32 from the orthologous NUHM gene of the obligate aerobic yeast Yarrowia lipolytica. The resulting mutant enzyme was indistinguishable from parental complex I with regard to activity, inhibitor sensitivity and EPR signature. Size, isoelectric point and presumably also N‐terminal acetylation were altered, indicating that the residual targeting sequence was retained on the mature 24 kDa protein. Complete removal of the NUHM presequence resulted in the absence of complex I activity, strongly arguing against the presence of an internal mitochondrial targeting sequence within the 24 kDa protein.
The proteasome inhibitor, MG132, promotes the reprogramming of translation in C2C12 myoblasts and facilitates the association of hsp25 with the eIF4F complex
Authors: Cowan Joanne L. , Morley Simon J.
Published: August 2004

The eukaryotic translation initiation factor (eIF) 4E, is regulated by modulating both its phosphorylation and its availability to interact with the scaffold protein, eIF4G, to form the mature eIF4F complex. Here we show that treatment of C2C12 myoblasts with the proteasomal inhibitor, MG132 (N‐carbobenzoxyl‐Leu‐Leu‐leucinal), resulted in an early decrease in protein synthesis rates followed by a partial recovery, reflecting the reprogramming of translation. The early inhibition of protein synthesis was preceded by a transient increase in eIF2α phosphorylation, followed by a sustained increase in eIF4E phosphorylation. Inhibition of eIF4E phosphorylation with CGP57380 failed to prevent translational reprogramming or the moderate decrease in eIF4F complexes at later times. Prolonged incubation with MG132 resulted in the increased expression of heat shock protein (hsp)25, αB‐crystallin and hsp70, with a population of hsp25 associating with the eIF4F complex in a p38 mitogen‐activated protein kinase‐dependent manner. Under these conditions, eIF4GI, and to a lesser extent eIF4E, re‐localized from a predominantly cytoplasmic distribution to a more perinuclear and granular staining. Although MG132 had little effect on the colocalization of eIF4E and eIF4GI, it promoted the SB203580‐sensitive association of eIF4GI and hsp25, an effect not observed with αB‐crystallin. Addition of recombinant hsp25 to an in vitro translation assay resulted in stimulation of on‐going translation and a moderate decrease in de novo translation, indicating that this modified eIF4F complex containing hsp25 has a role to play in recovery of mRNA translation following cellular stress.
Trophic links’ length and slope in the Tuesday Lake food web with species’ body mass and numerical abundance
Authors: REUMAN DANIEL C. , COHEN JOEL E.
Published: August 2004

Previously unnoticed patterns emerged in the lengths and slopes of trophic links of the food web of Tuesday Lake, Michigan, USA, when species were plotted on axes of log body mass (vertical) vs. log numerical abundance (horizontal). Link length was defined as equal to the number of orders of magnitude difference in mean body size between predator and prey plus the number of orders of magnitude difference in numerical abundance between predator and prey.

The average length over all trophic links was 6·2 [SD (standard deviation) = 2·8] orders of magnitude in 1984, and 5·8 (SD = 2·6) in 1986. Thus, for the average link, the ratio of the mean body mass of predator to prey, times the ratio of the numerical abundance of prey to predator, was about one million (106 ±). To a first approximation the typical predator was 10 times as long as its prey but 1000 times less numerically abundant. Link length distributions were approximately normal. Mean link lengths in 1984 and 1986 were not statistically different, but were more than an order of magnitude larger than the mean distance between all possible ordered pairs of species in each year. Ordered pairs of species that were between 9 and 11 orders of magnitude apart were the most likely to be links in both years.

The angle of a (non‐cannibalistic) link was defined so that an angle of 135° indicates that the predator was larger than the prey by exactly as many orders of magnitude as the prey was numerically more abundant than the predator, and so that the biomass (mean body mass times numerical abundance) of predator and prey were equal. For all non‐cannibalistic links, the median angle was 132° in 1984 and 129° in 1986. Both of these angles were significantly less than 135°. Angle deviated much from its median value only for short links. When the link was short or had the median angle, the predator species’ biomass was probably greater than that of the prey species.

Several models of food web structure failed to reproduce the observed normal distribution of link lengths. Observed predation matrices with species ordered by body mass had links arranged in blocks suggesting functional groups. Models that incorporated this block structure reproduced the normal link length distribution, but a model that forced a normal link length distribution did not produce blocks. The cascade model explained the median angle of trophic links.
Understanding demography in an advective environment: modelling Calanus finmarchicus in the Norwegian Sea
Authors: SPEIRS DOUGLAS C. , GURNEY WILLIAM S. C. , HOLMES STEVEN J. , HEATH MICHAEL R. , WOOD SIMON N. , CLARKE ELIZABETH D. , HARMS INGO H. , HIRCHE HANS‐JURGEN , McKENZIE EDDIE
Published: August 2004

Attempts to understand the demography of natural populations from time‐series can be hampered by the fact that changes due to births and deaths may be confounded with those due to movement in and out of the sampling area.

We illustrate the problem using a stage‐structured time‐series of the marine copepod Calanus finmarchicus sampled in the vicinity of a fixed location but where the demography is shown to be inconsistent with the assumption of a closed population.

By combining a realistic simulation of the hydrodynamic environment with a model of phenology we infer the time and location at which the stages observed in each sample were recruited as eggs. This yields a spatial and temporal map of the recruitment history required to produce the observed densities.

Using an empirical relationship between C. finmarchicus egg production and the abundance of phytoplanktonic food, the spatio‐temporal patterns in chlorophyll a can be inferred. The distributions during the spring bloom are spatially heterogeneous, and we estimate that the phytoplankton patches are of the order of 30 km across. This result is robust to substantial variations in the assumed stage‐dependent mortalities.

We conclude that information on advective transport can be used to make testable predictions about the scale of spatial heterogeneities. These, in turn, imply the appropriate spatial scale over which time‐series might be replicated in order to obtain more information about unknown processes such as mortality.
Individual differences in microhabitat use in a Caribbean cleaning goby: a buffer effect in a marine species?
Authors: WHITEMAN ELIZABETH A. , CÔTÉ ISABELLE M.
Published: August 2004

Buffer effects occur when changes in population size result in the disproportionate use of poor‐quality habitats. Thus, at low population sizes high‐quality habitats are used preferentially. As population size increases an increasing proportion of the population uses poorer‐quality habitats. Assessment of the temporal and spatial variation in patterns of habitat occupancy can therefore shed light on the differences in quality between habitats and the individual fitness consequences of habitat choice.

We provide the first evidence of the potential operation of a buffer effect for a site‐attached marine species. Caribbean cleaning gobies Elacatinus prochilos (Böhlke & Robins) occupy coral and sponge on fringing reefs in Barbados. For adult gobies, resource selection indices suggested a preference for sponge. However, as cleaning goby population size increased, the number of adult cleaning gobies occupying sponge increased more rapidly than the number occupying coral. In contrast, adults preferentially re‐colonized coral following experimental removals and at these low population densities the rate of population increase was greater on coral. Our results suggest that coral may be the preferred habitat, but in Barbados this habitat becomes saturated at very low population densities as a consequence of low client densities and ectoparasite loads. Thus, a larger proportion of the population occupies sponge at most observed population densities.

Patterns of habitat occupancy with population size for recruits and juveniles suggest only a small difference in habitat quality between sponge and coral. Indeed, recruits and juveniles do not discriminate between sponge and coral. The population shift towards sponge rather than coral occupancy between recruitment and maturity may arise as a combination of differing survival of recruits and juveniles on coral and sponge and active movement of individuals towards sponge.

Our results demonstrate that interactions among individuals are an integral part of population distribution and dynamics and are therefore important in future studies of habitat choice and its associated fitness consequences.
Determining trophic niche width: a novel approach using stable isotope analysis
Authors: BEARHOP STUART , ADAMS COLIN E. , WALDRON SUSAN , FULLER RICHARD A. , MACLEOD HAZEL
Published: August 2004

Although conceptually robust, it has proven difficult to find practical measures of niche width that are simple to obtain, yet provide an adequate descriptor of the ecological position of the population examined.

Trophic niche has proven more tractable than other niche dimensions. However, indices used as a proxy for trophic niche width often suffer from the following difficulties. Such indices rarely lie along a single scale making comparisons between populations or species difficult; have difficulty in combining dietary prey diversity and evenness in an ecologically meaningful way; and fail to integrate diet over ecological time‐scales thus usually only comprise single snapshots of niche width.

We propose an alternative novel method for the comparison of trophic niche width: the use of variance of tissue stable isotope ratios, especially those of nitrogen and carbon.

This approach is a potentially powerful method of measuring trophic niche width, particularly if combined with conventional approaches, because: it provides a single measure on a continuous axis that is common to all species; it integrates information on only assimilated prey over time; the integration period changes with choice of tissue sampled; and data production is theoretically fast and testing among populations simple.

Empirical studies are now required to test the benefits of using isotopic variance as a measure of niche width, and in doing so help refine this approach.
The importance of habitat heterogeneity, biotic interactions and dispersal in abundance–occupancy relationships
Authors: HOLT ALISON R. , WARREN PHILIP H. , GASTON KEVIN J.
Published: August 2004

In simple microcosm systems, the form of interspecific abundance–occupancy relationships has been found to be dependent on biotic interactions. However, in more complex systems such effects may be obscured by those of habitat heterogeneity. Here we test this proposal using laboratory microcosms of protists and bacteria.

The independent effects of species interactions and heterogeneity were tested by comparison of the abundance–occupancy relationship formed in multiple habitat patch systems containing all species together, with that relationship formed by combining data from equivalent systems containing each protist species alone and between homogeneous and heterogeneous environments.

There was more residual variation about positive interspecific abundance–occupancy relationships formed in heterogeneous environments in interacting and non‐interacting communities as the majority of species were more restricted in the number of patches they could occupy compared to homogeneous landscapes.

Abundance–occupancy relationships in interacting communities were better defined than those in non‐interacting communities. The inclusion of interspecific interactions caused a reduction in the abundance and occupancy of the majority of species and changed the position of species within the relationship.

Our results show that biotic interactions influence the abundance–occupancy relationships even with imposed environmental heterogeneity. However, in heterogeneous environments, for some species these processes occurred in fewer patches, causing increased residual variation about positive interspecific abundance–occupancy relationships compared to homogeneous environments.
Adaptations of animals to commensal habitats: population dynamics of house mice Mus musculus domesticus on farms
Authors: POCOCK MICHAEL J. O. , SEARLE JEREMY B. , WHITE PIRAN C. L.
Published: August 2004

Commensal mammals live in habitats that appear to provide both benefits and costs compared with natural and semi‐natural (non‐commensal) habitats. These commensal habitats offer potentially rich food resources but are also characterized by instability in time and space. We expected to demonstrate that animals in these habitats have high reproductive rates to counter high mortality rates and show flexibility in spatial organization. House mice (Mus musculus domesticus) are unusual because they are able to persist entirely in both commensal and non‐commensal habitats, and so can provide a test of the distinctiveness of commensal populations.

We studied populations of commensal house mice on two neighbouring farms in North Yorkshire, UK, for 2 years by capture–mark–recapture using the robust design. A total of 568 house mice were captured, with a total of 1053 recaptures. Population size varied from nine to 93 individuals, estimated with closed population models. Apparent survival was surprisingly low (0·54 per month) and was best modelled as constant across age, sex and time.

In situ reproductive recruitment occurred throughout the study and was numerically more important than immigration. Immigration was important during only two intervals and was probably from untrappable areas within the study site. Breeding throughout the year allowed the population to persist despite low survival rates. The results suggested that births and deaths had more influence on the overall population dynamics than movement.

The population was divided into subgroups to represent the territorial, demic structure known to be present in commensal house mouse populations. Dispersal between subgroups within the population was limited, representing only 6·6% of recaptures. The low rates of dispersal suggested that house mice responded to their environment as consisting of aggregated patches of suitable habitat.

In comparison, non‐commensal house mice have lower mortality, seasonal breeding, and individuals move more frequently and further than commensal house mice.

These differences illustrate the responses of house mice to the specific opportunities and demands of commensal habitats and demonstrate the importance of a flexible life‐history strategy for animals exploiting these habitats.
Habitat structure mediates the non‐lethal effects of predation on enclosed populations of house mice
Authors: ARTHUR ANTHONY D. , PECH ROGER P. , DICKMAN CHRIS R.
Published: August 2004

Prey behavioural changes in response to predation risk can result in significant effects on prey body growth rates and reduced reproductive output, with resultant impacts on prey population dynamics. This paper examines the influence of habitat structure on these non‐lethal impacts of predation using a model, field‐based experimental system, with house mice as prey.

Three treatments were employed in eight 50 × 50 m pens that contained mice, but allowed access to a suite of free‐living vertebrate predators, which included feral foxes, feral cats and native raptors: a treatment where the natural grassland vegetation in the pens was maintained at a height < 10 cm; a treatment where small, felled cypress pine trees covered with wire netting were added to low grassland vegetation to create refuge areas covering 10–15% of the area in a pen; and a treatment where predators were excluded from a 25 × 25 m section of some pens with an underlying grassland structure. A 5 × 5 grid of felled trees was added to grassland and predator‐exclusion pens to allow assessment of mouse behaviour.

Mice in grassland pens avoided open areas, had lower body growth rates, and began breeding later in spring than mice in both predator‐exclusion areas, where they foraged more readily in the open, and in refuge pens, where mice avoided open areas but had safe access to supplementary food located within the refuge. These results occurred despite mouse population densities being much lower in grassland pens, and presumably competition for food being much less, compared with under the other treatments.

The results indicate predators can have significant non‐lethal impacts on prey, and these effects can be mediated by habitat structure.
Individual diet specialization, niche width and population dynamics: implications for trophic polymorphisms
Authors: SVANBÄCK RICHARD , PERSSON LENNART
Published: August 2004

We studied a perchPerca fluviatilisL. population that during a 9‐year period switched between a phase of dominance of adult perch and a phase dominated by juvenile perch driven by cannibalism and intercohort competition. We investigated the effects of these population fluctuations on individual diet specialization and the mechanisms behind this specialization.

Due to cannibalism, the survival of young‐of‐the‐year (YOY) perch was much lower when adult perch density was high than when adult perch density was low.

Both the individual niche breadth (if weighed for resource encounter) and the population niche breadth were highest when adult population density was high and, consequently, individual specialization was highest at high adult perch densities.

When adult perch density was low, the abundances of benthic invertebrate and YOY perch were high and dominated the diet of adult perch, whereas the density of zooplankton was low due to predation from YOY perch. At high perch densities, benthic invertebrate abundance was lower and zooplankton level was higher and some perch switched to feed on zooplankton.

Our results show that individual specialization may fluctuate with population density through feedback mechanisms via resource levels. Such fluctuations may have profound implications on the evolution of resource polymorphisms.
Time to extinction in relation to mating system and type of density regulation in populations with two sexes
Authors: SÆTHER BERNT‐ERIK , ENGEN STEINAR , LANDE RUSSELL , MØLLER ANDERS PAPE , BENSCH STAFFAN , HASSELQUIST DENNIS , BEIER JOSEF , LEISLER BERND
Published: August 2004

Population viability models usually consider only the female segment of the population. However, random variation in sex ratio as well as the mating system may also affect variation in fitness among females. Here we develop population models incorporating demographic stochasticity in both sexes. Furthermore, we consider the effects on the estimated time to extinction and whether density regulation acts only on females or on total population size.

We applied these models to two populations of polygynous great reed warblers Acrocephalus arundinaceus L. with differences in population trends to investigate the importance of considering sex in population viability models.

Demographic stochasticity was larger in a polygynous than in a monogamous mating system.

The estimated time to extinction was considerably shorter for a monogamous than for a polygynous mating system, particularly if density regulation acted only on females than rather on the total population.

This study demonstrates that structure of mating system must be included when making population viability analysis based on counts of total population sizes. It is especially important to model the specific effects of density regulation on the two sexes.
How coccidian parasites affect health and appearance of greenfinches
Authors: HÕRAK PEETER , SAKS LAURI , KARU ULVI , OTS INDREK , SURAI PETER F. , McGRAW KEVIN J.
Published: August 2004

The aim of this study was to examine the mechanisms by which parasites can affect the expression of ornamental traits.

Levels of an intestinal coccidian parasite, Isospora lacazei, were manipulated in captive male greenfinches (Carduelis chloris) by suppressing the natural infections with a coccidiostatic sulphonamide drug. Subsequently, half the birds were experimentally infected, while another half continued receiving medication.

Over the course of the experiment the effect of our treatments upon 14 mainly haemato‐serological condition indices was recorded. Additionally, changes in colour and carotenoid content of yellow tail and breast feathers, which serve as sexually dimorphic ornamental traits, were measured.

Eighty‐nine per cent of birds hosted chronic isosporan infection before the experiment, yet experimental inoculation with mixed parasite strains resulted in drastic but transient decreases in serum carotenoid, vitamin E, triglyceride and albumin concentrations, and reduced body mass, indicating serious pathology and probable nutrient malabsorption due to damaged intestinal epithelium.

Laboratory‐grown tail feathers of infected birds contained 52% less carotenoids and also had smaller values of chroma and hue than those of medicated birds.

These results suggest that coccidian infection reduced the expression of plumage coloration by creating a deficiency of carotenoids available for deposition in ornamental feathers.
The importance of ice cover for energy turnover in juvenile Atlantic salmon
Authors: FINSTAD ANDERS G. , FORSETH TORBJØRN , NÆSJE TOR F. , UGEDAL OLA
Published: August 2004

Under benign laboratory tank conditions we compared food consumption and metabolism of Atlantic salmon (Salmo salar) juveniles exposed to simulated ice cover (darkness) with fish in natural short, 6 h light, day length (without ice). Three different populations along an ice‐cover gradient were tested (59°N−70°N).

Resting metabolism was on average 30% lower under simulated ice cover (6·6 J g−1 day−1) than under natural day length (9·4 J g−1 day−1), and the response was similar for all populations. Northern salmon grew equally well in dark and light conditions, whereas the southern grew significantly poorer in the dark. Fish from all populations fed more under natural day length than in the dark and the northern population had higher consumption than the southern. The relative high growth of fish from the northern population in the dark compared to the southern populations was due partly to higher consumption and partly to higher growth efficiency. Fish from the southern populations had negative growth efficiency in the dark.

We also studied the importance of ice cover under more hostile conditions in stream channels using the northern population only. Juveniles held in channels with simulated ice cover lost less energy (20 J g−1 day−1) than those held in channels with transparent cover (26 J g−1 day−1). This difference in energy loss was due partly (50%) to higher food consumption under simulated ice (4·5 and 1·6 J g−1, respectively) and partly (30%) to light‐induced differences in resting metabolic rate.

In conclusion, both experiments showed lower metabolic costs in darkness under simulated ice cover than without ice. Under benign laboratory conditions the response to light (ice cover) varied among populations and only the northern population were able to attain positive growth in the dark. Under semi‐natural conditions the lack of ice cover induced strong negative effects on the energy budget. Because energetic deficiencies are assumed to be an important cause of winter mortality, our study indicates that ice break‐ups or removal following climatic change may affect winter survival significantly, particularly in northern populations.
Stage‐structured harvesting and its effects: an empirical investigation using soil mites
Authors: CAMERON T. C. , BENTON T. G.
Published: August 2004

Population dynamics results from an interplay between the environmental state and population density. With many organisms there is structure to the life history, and this structure has important consequences for the population's density dependence and its interaction with environmental noise, and therefore its population dynamics. Perturbing population structure, such as through harvesting, may therefore affect the way that the populations respond to stochastic environmental variation.

We conducted three experiments on populations of soil mites kept under controlled conditions and harvested a constant proportion of eggs, juveniles or adults. The experiments (a) minimized environmental variability, (b) created environmental variability by randomizing food supplies, and (c) provided excess food and repeatedly subdivided the populations to maintain them below carrying capacity.

We find that harvesting different stages has marked effects on stage structure, which differ between constant and variable environments. For example, harvesting adults decreases the number of adults, harvesting eggs increases the number of adults and harvesting juveniles has no effect under near constant conditions, whereas in a variable environment harvesting adults and juveniles reduces adult numbers, but harvesting eggs has no effect.

As well as changing the mean age structure, harvesting can change the variance of the different stages. For example, in a constant environment harvesting juveniles does not change the variability in juvenile numbers or population size, but in a variable environment harvesting juveniles increases the variability in the size of the juvenile class and hence the total population variability.

For populations that are kept at one‐third to one‐half carrying capacity (approximately where the maximum sustainable yield should result) harvesting of the different age classes has marked positive effects on the population growth rates. Harvesting different age classes causes changes in the density dependence, which explains the way in which the population parameters respond.

In conclusion, the population response to harvesting depends on the stage/age structure and the way it changes with harvesting and environmental conditions. Managing economically important populations, subject to harvesting, should consider structured life histories.
Culture and Language in the Emergence of Autobiographical Memory
Authors: Fivush Robyn , Nelson Katherine
Published: August 2004

Current conceptualizations of childhood amnesia assume that there is a “barrier” to remembering early experiences that must be overcome in order for one to begin to accumulate autobiographical memories. In contrast, we present a social-cultural-developmental perspective on the emergence of autobiographical memory. We first demonstrate the gradual emergence of autobiographical memories across the preschool years and then relate this developmental process to specific developments in language, narrative, and understanding of self and other that vary among individuals, as well as by culture and gender.
When Strangers Pass
Authors: Pelphrey Kevin A. , Viola Ronald J. , McCarthy Gregory
Published: August 2004

Using functional magnetic resonance imaging (fMRI), we investigated brain activity evoked by mutual and averted gaze in a compelling and commonly experienced social encounter. Through virtual-reality goggles, subjects viewed a man who walked toward them and shifted his neutral gaze either toward (mutual gaze) or away (averted gaze) from them. Robust activity was evoked in the superior temporal sulcus (STS) and fusiform gyrus (FFG). For both conditions, STS activity was strongly right lateralized. Mutual gaze evoked greater activity in the STS than did averted gaze, whereas the FFG responded equivalently to mutual and averted gaze. Thus, we show that the STS is involved in processing social information conveyed by shifts in gaze within an overtly social context. This study extends understanding of the role of the STS in social cognition and social perception by demonstrating that it is highly sensitive to the context in which a human action occurs.
Perceiving Action Identity
Authors: Repp Bruno H. , Knoblich Günther
Published: August 2004

Can skilled performers, such as artists or athletes, recognize the products of their own actions? We recorded 12 pianists playing 12 mostly unfamiliar musical excerpts, half of them on a silent keyboard. Several months later, we played these performances back and asked the pianists to use a 5-point scale to rate whether they thought they were the person playing each excerpt (1 = no, 5 = yes). They gave their own performances significantly higher ratings than any other pianist's performances. In two later follow-up tests, we presented edited performances from which differences in tempo, overall dynamic (i.e., intensity) level, and dynamic nuances had been removed. The pianists' ratings did not change significantly, which suggests that the remaining information (expressive timing and articulation) was sufficient for self-recognition. Absence of sound during recording had no significant effect. These results are best explained by the hypothesis that an observer's action system is most strongly activated during perception of self-produced actions.
The Cost of a Voluntary Task Switch
Authors: Arrington Catherine M. , Logan Gordon D.
Published: August 2004

Task-switching paradigms are widely used to study executive control. However, standard paradigms may not require active control to switch tasks. We examined voluntary task switching by having subjects choose which task to perform on a series of bivalent stimuli. Subjects performed parity or magnitude judgments on single digits. Instructions were to perform the two tasks equally often and in a random order. The response-to-stimulus interval (RSI) was either 100 or 1,000 ms, manipulated between blocks. Task alternations were slower than task repetitions, and this switch cost was greater at the short RSI than at the long RSI (310 and 94 ms, respectively). Additionally, subjects produced more task repetitions than expected if the tasks were performed in a random sequence. These results show costs associated with a voluntary task switch, when subjects must actively control the choice of the task to be performed.
Advance Preparation in Task Switching
Authors: Altmann Erik M.
Published: August 2004

The preparation effect in task switching is usually interpreted to mean that a switching process makes use of the interval between task-cue onset and trial-stimulus onset (the cue-stimulus interval, or CSI) to accomplish some of its work ahead of time. This study undermines the empirical basis for this interpretation and suggests that task activation, not task switching, is the functional process in cognitive control. Experiments 1 and 2 used an explicit cuing paradigm, and Experiments 3 and 4 used a variation in which the trial after a task cue was followed by several cueless trials, requiring retention of the cue in memory. Experiments 1 and 3 replicated the preparation effect on switch cost, and Experiments 2 and 4 showed that this effect vanishes when CSI is manipulated between subjects, leaving only a main effect of CSI when the task cue is a memory load.
Constant Capacity in an Immediate Serial-Recall Task
Authors: Cowan Nelson , Chen Zhijian , Rouder Jeffrey N.
Published: August 2004

We assessed a hypothesis that working memory capacity should include a constant number of separate mental units, or chunks (cf. Miller, 1956). Because of the practical difficulty of measuring chunks, this hypothesis has not been tested previously, despite wide attention to Miller's article. We used a training procedure to manipulate the strength of associations between pairs of words to be included in an immediate serial-recall task. Although the amount of training on associations clearly increased the availability of two-item chunks and therefore the number of items correct in list recall, the number of total chunks recalled (singletons plus two-word chunks) appeared to remain approximately constant across association strengths, supporting a hypothesis of constant capacity.
Federal tax arrears in Russia Liquidity problems, federal redistribution or regional resistance?*
Authors: Ponomareva Maria , Zhuravskaya Ekaterina
Published: August 2004

Three hypotheses about the nature of federal tax arrears in Russia in the second half of the 1990s are tested empirically. Tax arrears can be a result of: 1) liquidity problems in firms, 2) redistributive subsidies of the federal government, or 3) regional political resistance to federal tax collectors. Liquidity problems in firms explain a large part of the variation in tax arrears. Regional political resistance to federal tax collectors was also an important factor: For a given level of liquidity, federal arrears accumulated faster in regions where governors had a larger popular base, in regions with a better bargaining position vis‐à‐vis the centre, and in regions with governors in political opposition to the centre. We find that patterns of federal arrears are inconsistent with the redistributive politics premise that redistribution favours jurisdictions with ‘closer races’ for the incumbent in the national elections. Variation in authorized tax deferrals can be explained in part by federal redistributive politics.
The curse of natural resources in the transition economies*
Authors: Kronenberg Tobias
Published: August 2004

The curse of natural resources is a well‐documented phenomenon for developing countries. Economies that are richly endowed with natural resources tend to grow slowly. Among the transition economies of the former ‘Eastern Bloc’, a similar pattern can be observed. This paper shows that a large part of the variation in growth rates among the transition economies can be attributed to the curse of natural resources. After controlling for numerous other factors, there is still a strong negative correlation between natural resource abundance and economic growth.

 Among the transition economies the prime reasons for the curse of natural resources were corruption and a neglect of basic education. In order to overcome the curse of natural resources and move to a sustainable path of development, the resource abundant transition countries should fight corruption and ensure that their resource revenues are invested in human capital or the preservation of natural capital.
The sequencing of reform policies in China's agricultural transition*
Authors: De Brauw Alan , Huang Jikun , Rozelle Scott
Published: August 2004

This paper provides evidence regarding gains due to agricultural market liberalization in China. We empirically identify the different effects that incentive and farm restructuring reforms and gradual market liberalization have on China's agricultural economy during its transition period. We find that average gains within the agricultural sector due to reforms that improved incentives and increased decision‐making authority of producers exceed gains due to market liberalization by a large margin. Our method of analyzing the effects of transition policies on economic performance can be generalized to other reform paths in other transition economies.
Relative price shifts, economies of scale and poverty during economic transition1
Authors: Lanjouw Jean O. , Lanjouw Peter , Milanovic Branko , Paternostro Stefano
Published: August 2004

Economic transition is associated with significant shifts in relative prices between private and public goods. If, as a result, public goods claim a larger share of total expenditures, economies of scale in consumption increase. We show how relative price changes might alter the welfare of different‐sized households in the short run and over time. We illustrate, for a selection of transition economies, that conventional poverty profiles are quite sensitive to assumptions made about economies of scale in consumption. In particular, the common view that large households with many children are poor relative to small households (such as those comprising the elderly) is shown to be highly non‐robust.
Capital flows and speculative attacks in prospective EU member states1
Authors: Gibson Heather D. , Tsakalotos Euclid
Published: August 2004

This paper examines the capital flow experience of transition economies which are also prospective EU members with a view to shedding light on the likely problems they might encounter with exchange rate policy in the run up to euro area membership. We show that they have been experiencing fairly sizeable capital flows since the early 1990s. We explain these flows using two separate models. The first explains the level of capital flows using panel data from the prospective EU members. The second concentrates specifically on estimating the probability of a country experiencing downward speculative pressure. In both cases, the contribution of domestic factors and contagion is explored. The results suggest that, while domestic factors have some role to play, it is rather limited. Moreover, there is clear evidence of contagion effects, suggesting that macroeconomic policy in the prospective EU members will be complicated by capital flows in the run up to euro area membership.
Divergence of US and Local Returns in the After‐market for Equity Issuing ADRs
Authors: Kadiyala Padma , Subrahmanyam Avanidhar
Published: August 2004

We study one‐year post‐listing prices and returns to equity issuing ADRs that listed in the US between January 1991 and October 2000. ADRs from countries that impose restrictions on capital flows are priced at a premium to their home market ordinaries. While the mean premium for the full sample is statistically indistinguishable from zero, after an adjustment for asynchronous trading, the magnitude of the premium to ADRs from restricted markets is 11.33% at the 300‐day post listing interval, which is statistically significant. In the short run (30 days) following listing, the magnitude of the premium is larger for ADRs with larger excess demand from US investors. At the longer 300‐day horizon, Nasdaq listed ADRs earn a larger premium than their NYSE/AMEX listed counterparts. Time‐series regressions and two‐stage cross‐sectional regressions establish that the premium to foreign equity issuers is greater if the US listing attracts liquidity and if US returns have a lower correlation with the local country index.
Effects of Market Segmentation and Bank Concentration on Mutual Fund Expenses and Returns: Evidence from Finland
Authors: Korkeamaki Timo P. , Smythe Thomas I.
Published: August 2004

A tremendous amount of research examines US mutual funds, but fund markets also thrive in other countries. However, research about these fast growing markets is lacking. This study addresses Finnish funds. Fast growth of the Finnish fund industry, strong bank dominance in the industry and recent EU membership make it an interesting market to examine. The Finnish fund market is also of particular interest since it had the fastest growth among the EU countries during 1996–2000. We find evidence that bank‐managed and older funds charge higher expenses but investors are not compensated for paying higher expenses with higher risk‐adjusted returns, suggesting a potential agency problem. Overall, Finnish fund expenses have decreased over time, consistent with EU membership reducing market segmentation and generating competition.
The Cost of Capital of Cross‐listed Firms
Authors: Koedijk Kees G. , Van Dijk Mathijs A.
Published: August 2004

This paper analyses the cost of capital of firms with foreign equity listings. Our purpose is to shed light on the question whether international and domestic asset pricing models yield a different estimate of the cost of capital for cross‐listed stocks. We distinguish between (i) the multifactor ICAPM of Solnik (1979) and Sercu (1980) including both the global market portfolio and exchange rate risk premia and (ii) the single factor domestic CAPM. We test for the significance of the cost of capital differential in a sample of 336 cross‐listed stocks from nine countries in the period 1980–99. Our hypothesis is that the cost of capital differential is substantial for firms with international listings, as these are often large multinationals with a strong international orientation. We find that the asset pricing models yield a significantly different estimate of the cost of capital for only 12% of the cross‐listed companies. The size of the cost of capital differential is around 50 basis points for the US, 80 basis points for the UK and 100 basis points for France.
The Effect of Monetary Unification on German Bond Markets
Authors: Dewachter Hans , Lyrio Marco , Maes Konstantijn
Published: August 2004

We develop a benchmark against which the effects of ECB monetary policy on the German bond market can be evaluated. We first estimate an affine term structure model for the pre‐EMU period linking the German yield curve with the Bundesbank monetary policy. The German monetary policy and its implied yield curve are then reprojected onto the EMU period. The reprojected yield curve differs significantly from the observed one. Short‐term interest rates during the EMU period are significantly lower than they would have been in case the Bundesbank were still in charge of monetary policy. Furthermore, yield spreads increased substantially during the EMU period.
Exchange Rates and Capital Flows
Authors: Brooks Robin , Edison Hali , Kumar Manmohan S. , Sløk Torsten
Published: August 2004

This paper explores the ability of portfolio and foreign direct investment flows to track movements in the euro and the yen against the dollar. Net portfolio flows from the euro area into US stocks – possibly reflecting differences in expected productivity growth – track movements in the euro against the dollar closely. Net FDI flows, which capture the recent burst in cross‐border M&A activity, appear less important in tracking movements in the euro‐dollar rate, possibly because many M&A transactions consist of share swaps. Movements in the yen versus the dollar remain more closely tied to conventional variables such as the current account and interest differential.