bluuebunny/crossref_metadata_2025 huggingface dataset:
Pseudodominant inheritance of spondylocostal dysostosis type 1 caused by two familial delta‐like 3 mutations
Authors: Whittock NV , Ellard S , Duncan J , De Die‐Smulders CEM , Vles JSH , Turnpenny PD
Published: June 2004

Spondylocostal dysostoses (SCD) are a heterogeneous group of disorders of axial skeletal malformation characterized by multiple vertebral segmentation defects and rib anomalies. Sporadic cases with diverse phenotypes, sometimes including multiple organ abnormalities, are relatively common, and monogenic forms demonstrating autosomal recessive (AR) and, more rarely, autosomal dominant (AD) inheritance have been reported. We previously showed that mutations in delta‐like 3 (DLL3), a somitogenesis gene that encodes a ligand for the notch signaling pathway, cause AR SCD with a consistent pattern of abnormal segmentation. We studied an SCD family previously reported to show AD inheritance, in which the phenotype is similar to that in AR cases. Direct DLL3 sequencing of individuals in two generations identified the affected father as homozygous for a novel frameshift mutation, 1440delG. His two affected children were compound heterozygotes for this mutation and a novel missense mutation, G504D, the first putative missense mutation reported in the transmembrane domain of DLL3. Their two unaffected siblings were heterozygotes for the 1440delG mutation. Pseudodominant inheritance has been confirmed, and the findings raise potential consequences for genetic counseling in relation to the SCD disorders.
Localization of a novel locus for hereditary nail dysplasia to chromosome 17q25.1‐17q25.3
Authors: Rafiq MA , Ansar M , Pham T , Amin‐ud‐din M , Anwar M , Haque S , Chahrour MH , Yan K , Leal SM , Ahmad W
Published: June 2004

We report on a six‐generation Pakistani consanguineous family with autosomal recessive transmission of a form of hereditary nail dysplasia. Affected individuals presented with onycholysis of fingernails and anonychia of toenails. Associated abnormalities of ectodermal appendages were not observed in any of the affected individuals. Linkage has been established to chromosome 17q. A maximum multipoint analysis logarithm of the odds ratio score of 4.85 was obtained at marker D17S1301. Due to the consanguineous nature of this kindred, the gene for nail dysplasia is probably contained within a 5.0‐cM (3 MB on the sequence‐based physical map) region of homozygosity flanked by markers D17S1807 and D17S937.
Molecular cytogenetic characterization of multiple intrachromosomal rearrangements of chromosome 2q in a patient with Waardenburg's syndrome and other congenital defects
Authors: Shim SH , Wyandt HE , McDonald‐McGinn DM , Zackai EZ , Milunsky A
Published: June 2004

At 6 years of age, a boy with bilateral sensorineural deafness, lateral displacement of inner canthi, a bulbous nasal tip, synophrys, and cryptorchidism was clinically diagnosed as having Waardenburg's syndrome type I (WS‐1). In addition, he had a lumbar spina bifida with hydrocephalus shunted on the second day of life and severe mental retardation with a head circumference at the fifth percentile. Neither parent showed signs of WS‐1, and the family history was negative. Because of the WS‐1 features, attention was focused on the PAX3 location in 2q, at which time a de novo paracentric inversion of 2q23–q37.1 was noted. Subsequent high‐resolution chromosome analysis 8 years later indicated a complex rearrangement involving regions 2q31–q35 and 2q13–q21. Whole chromosome painting and high‐resolution comparative genomic hybridization yielded negative results for any translocation, duplication, or deletion of any chromosome segments. Sequencing of the PAX3 gene yielded no detectable mutation. Fluorescent in situ hybridization (FISH) studies with human BAC clones revealed five breakpoints in chromosome 2q resulting in two paracentric inversions and one insertion, the karyotype being interpreted as 46,XY,der(2)inv(2)(q13q21)inv(2)(q21q24.2)ins(2)(q24.2q33q35). In this extremely rare chromosomal rearrangement, the FISH result showed a breakpoint at 2q35 being proximal to and without involvement of the PAX3 gene. While further studies continue, possible interpretations include involvement of a regulatory gene(s) for PAX 3 and other genes at the other breakpoints related causally to the spina bifida and mental retardation.
Resolving the departures of observed results from the Ideal Free Distribution with simple random movements
Authors: Jackson A. L. , Humphries S. , Ruxton G. D.
Published: June 2004

The Ideal Free Distribution (IFD) is one of the most widely applied theoretical concepts in ecology. Many experimental tests of the IFD incorporating unequal competitors have revealed three consistent departures of observed results from those predicted by the theory. Specifically these are: (1) the full range of predicted equilibria are rarely realized; (2) under‐matching of individuals to resource inputs; and (3) continued movement of individuals after equilibrium is reached.

It has been suggested previously that a model including simple random movements can explain simultaneously all three of these departures. The acceptance of this theory has been hindered by arguments about model construction relating to the timing of events and whether an analytical or individual‐based model is more appropriate.

Here we present the first internally consistent and biologically realistic model of the IFD incorporating random non‐IFD movements (movements made at a rate independent of intake rates). We use this model to confirm that random movements alone can explain all three of the observed departures from the IFD. Furthermore, it is not necessary to have any detailed a priori knowledge about the motivation behind the non‐IFD movements, in order to predict their consequences. We expect non‐IFD movements to be widespread in animal systems, and so warrant further experimental consideration and investigation.
Lifetime reproductive success in relation to morphology in the house sparrowPasser domesticus
Authors: Jensen Henrik , SÆther Bernt‐Erik , Ringsby Thor Harald , Tufto Jarle , Griffith Simon C. , Ellegren Hans
Published: June 2004

In this study we relate variation in lifetime reproductive success (LRS) of male and female house sparrowsPasser domesticusto morphological characteristics.

Our analyses demonstrated no sex‐specific difference in the distribution ofLRS. The variance inLRSwas influenced mainly by variation in individual annual reproductive success, and to a lesser extent by variation in individual lifespan.

Phenotypic traits explained a significant proportion of the variation inLRSin males, but not in females. The effect of male morphology onLRSoperated mainly through an effect on the number of recruiting daughters.

The size of the patch of black feathers on the chest of males (badge size) and male bill length were both positively associated withLRS. Lifespan and bill length were positively related and reproductive success increased with badge size. In females, number of recruiting daughters was positively related to bill length, body mass and body condition index due to the positive effect of these traits on annual production of daughters.

These results indicate that identifying factors causing the large individual variation inLRS, which is likely to be closely related to fitness, will be important to understand microevolutionary processes in this metapopulation, and hence their demographic feedbacks.
Lack of homeward orientation and increased mobility result in high emigration rates from low‐quality fragments in a dune wolf spider
Authors: Bonte Dries , Lens Luc , Maelfait Jean‐Pierre
Published: June 2004

Mobility and emigration were investigated for the wolf spider Pardosa monticola in grey dune fragments from two high‐density and one low‐density population, where population density was related to patch quality. Pitfall trapping was applied in combination with absolute density estimates by means of quadrat sampling. Orientation behaviour was additionally observed in the high‐ and low‐density patches during two periods in the adult life‐phase (mating and reproduction period). Dune grassland is the core habitat; moss dominated vegetation is the matrix in which dispersal occurs.

Our field experiments confirm the hypothesis that increased activities of a dune wolf spider in a low‐density habitat result in higher emigration rates.

The diffusive emigration rates, which are higher close to the patch border, and mobility within the patch are higher in the low‐density population. In the low‐density patch, females are even more active than males and emigrate in the same proportions as males.

Both males and females were not able to orientate and perform homeward movements during the spring period, in which vegetation height is more or less equal in the core habitat (grassland) and the matrix (moss dune). In June, no homeward orientation was observed in the habitat patch with low quality and low densities (low vegetation height). In the high‐density patch, females but not males were able to perform homeward orientation behaviour at distances close to the pronounced border between grassland and moss dune. At distances of 3 m, females also orientated randomly.

The pattern of differentiated homeward orientation behaviour indicates that it results from visual perception of high contrast borders by the females but not by the males or by sex‐differentiated motivation to return to the core habitat.

Increased emigration rates as a result of higher spider mobility together with the absence of visual orientation towards the patch border suggest the presence of an Allee effect in low‐density patches.
Fish abundance with no fishing: predictions based on macroecological theory
Authors: Jennings Simon , Blanchard Julia L.
Published: June 2004

Fishing changes the structure of fish communities and the relative impacts of fishing are assessed usefully against a baseline. A comparable baseline in all regions is fish community structure in the absence of fishing.

The structure of unexploited communities cannot always be predicted from historical data because fisheries exploitation usually precedes scientific investigation and non‐fisheries impacts, such as climate change, modify ecosystems over time.

We propose a method, based on macroecological theory, to predict the abundance and size‐structure of an unexploited fish community from a theoretical abundance–body mass relationship (size spectrum).

We apply the method in the intensively fished North Sea and compare the predicted structure of the unexploited fish community with contemporary community data.

We suggest that the current biomass of large fishes weighing 4–16 kg and 16–66 kg, respectively, is 97·4% and 99·2% lower than in the absence of fisheries exploitation. The results suggest that depletion of large fishes due to fisheries exploitation exceeds that described in many short‐term studies.

Biomass of the contemporary North Sea fish community (defined as all fishes with body mass 64 g−66 kg) is 38% lower than predicted in the absence of exploitation, while the mean turnover time is almost twice as fast (falls from 3·5 to 1·9 years) and 70% less primary production is required to sustain it.

The increased turnover time of the fish community will lead to greater interannual instability in biomass and production, complicating management action and increasing the sensitivity of populations to environmental change.

This size‐based method based on macroecological theory may provide a powerful new tool for setting ecosystem indicator reference levels, comparing fishing impacts in different ecosystems and for assessing the relative impacts of fishing and climate change.
Mycoplasma gallisepticuminfection dynamics in a house finch population: seasonal variation in survival, encounter and transmission rate
Authors: Faustino Cristina R. , Jennelle Christopher S. , Connolly Véronique , Davis Andrew K. , Swarthout Elliott C. , Dhondt André A. , Cooch Evan G.
Published: June 2004

We considered the impact of an emerging pathogen (Mycoplasma gallisepticumEdward and Kanarek) on apparent survival, encounter and transition rates in a population of a novel host (the house finch,Carpodacus mexicanusMüller). We used a multistate analysis of mark–encounter data from individually marked birds. Individual birds were categorized to a particular disease ‘state’; transition rates among states, conditional on apparent survival, were analogous to rates of new infection and recovery from infection. We hypothesized thatM. gallisepticuminfection would reduce the apparent survival of infected individuals, and that the magnitude of this reduction would vary as a function of the physiological condition of the host (which was characterized in our analyses by including a demographic and an environmental surrogate as covariates).

We found consistent support for the hypothesis thatM. gallisepticuminfection resulted in lower apparent survival among infected individuals, and that recovery rates (from infected to non‐infected) were greater than infection rates in this population. We also found strong evidence indicating that infected individuals were less likely to be encountered than were non‐infected individuals. Although we predicted that both sex and temperature (proxies for physiological condition) would explain a significant proportion of the variation in our data, only marginal influences of both factors on apparent survival, encounter and state transition rates were detected.

Our analyses identified several factors that may be important to studies of disease in the wild. First, disease state assignment may be uncertain, which can complicate parameter estimation. Secondly, encounter rate for infected individuals in our study was low relative to that for non‐infected individuals, reflecting possible behavioural changes in infected individuals. Low encounter rates reduces precision of estimated parameters, especially for multistate models. Finally, our results (and mark–recapture models in general) assume independence among individual birds. However, we are aware that there is a social structuring in house finches (and in general for many bird species). Accounting for such non‐independence may be especially important for situations where the state transitions are directly related to the pattern of social contact.
Demographic mechanisms of the population decline of the song thrush Turdus philomelos in Britain
Authors: Robinson Robert A. , Green Rhys E. , Baillie Stephen R. , Peach Will J. , Thomson David L.
Published: June 2004

In Britain, the song thrush Turdus philomelos is categorized as a species of high national conservation concern because of a large population decline during the last three decades. We calculated a series of annual national population estimates for woodland and farmland habitats combined for the period 1964–2000. We then used turning points analysis to identify seven blocks of years within the period of decline (1968–2000) with uniform rates of population change in the smoothed trend.

We used recoveries of song thrushes ringed as nestlings, juveniles and adults during April–September to estimate survival rates separately for the post‐fledging period, the remainder of the first year and for adults. Daily survival probability was lower during the post‐fledging period than during the remainder of the first year or for older birds.

There was evidence for variation in survival rates among blocks of years with different rates of population change, particularly for first‐year survival. There were significant positive correlations across blocks between mean population multiplication rate (PMR) and both post‐fledging and first‐year survival.

Survival of first‐year birds was correlated negatively with the duration of the longest run of frost days and the survival of adults was correlated negatively with the duration of the longest summer drought. Variation among blocks in mean PMR was correlated with block means of the duration of runs of frost days and drought days, but significant correlations between PMR and both post‐fledging and first‐year survival remained after allowing for the influence of weather on survival.

Changes in survival in the first winter, and perhaps also the post‐fledging period, are sufficient to have caused the song thrush population decline. The environmental causes of these changes are not known, but changes in farming practices, land drainage, pesticides and predators are all candidates. Adverse weather conditions contributed to the decline, but were not the primary driver.
Spatial synchrony in population dynamics of West African fishes: a demonstration of an intraspecific and interspecific Moran effect
Authors: Tedesco Pablo A. , Hugueny Bernard , Paugy Didier , Fermon Yves
Published: June 2004

Synchronous fluctuations of the abundance of several populations at a regional scale can be a sign of a climatic effect on their dynamics (Moran effect). However, the interpretation of spatial synchrony is often complicated by the interaction between climatic disturbances and migrations between the studied populations.

We addressed this question by studying 24‐year time‐series of abundance estimates for four populations of four fish species in three different catchment basins in Côte d’Ivoire (West Africa). As localities from two different basins cannot exchange individuals, dispersal cannot be considered a synchronizing factor in this system.

A sign test performed on the four site × site correlation matrices rejected the null hypothesis of no spatial synchrony. No relation was detected in relating the level of synchrony in species dynamics (r = 0·58 on average) to the geographical distances between the four sites (176–367 km). A more detailed analysis taking account of sampling error was carried out between two sites, and confirmed the above results. When corrected for sampling noise, high values of spatial synchrony were obtained (r = 0·88 on average).

Interspecific spatial synchronies (r = 0·57 on average) were almost as high as intraspecific values, suggesting that the four species are reacting in the same way to the same Moran effect.

A good correlation (r = 0·54) between a regional river discharge index and the total catch of the four species 1 year later was observed, suggesting that hydrological variability is one of the main synchronizing factors. Moreover, as expected on theoretical grounds, spatial synchrony in river discharge (r = 0·84 and 0·88 on a log scale) is similar to spatial synchrony in population dynamics (r = 0·88 on average and corrected for sampling error).
Parasitoids flip a coin before deciding to superparasitize
Authors: Plantegenest Manuel , Outreman Yannick , Goubault Marlene , Wajnberg Eric
Published: June 2004

Host acceptance decision in parasitic wasps depends strongly on the parasitism status of the encountered host. In solitary species, a host allows the development of only a single parasitic larva, and then any oviposition in an already parasitized host leads to larval competition and to potential loss of offspring. The ability of parasitoids to discriminate between parasitized and healthy hosts is well documented. Despite this, parasitized hosts are still accepted by the foraging wasps, an occurrence termed superparasitism.

In the last decades, theoretical studies have suggested that under certain circumstances superparasitism can be optimal. Generally, the superparasitism theory predicts that the optimal host acceptance decision should follow a zero‐one rule: in response to both environmental and physiological state characteristics, a given female should switch from acceptance to rejection of parasitized hosts.

However, some experiments have shown that parasitoids may decide to accept parasitized hosts with an intermediate probability.

A model was developed in order to explain this partial preference in parasitoids.

More generally, the present study demonstrates that when the consequences of one decision cannot be predicted perfectly, the optimal decision rules could be stochastic rather than deterministic. Accordingly, behavioural stochasticity need not necessarily result from errors in decision‐making or from an incapacity to assess the actual environmental state but could instead have evolved as the optimal response to the uncertainty of future environmental state.
Migration supports uneven consumer control in a sewage‐enriched river food web
Authors: DeBruyn Adrian M. H. , McCann Kevin S. , Rasmussen Joseph B.
Published: June 2004

We studied the response of the St Lawrence River food web to enrichment by primary‐treated sewage from the city of Montreal, Canada.

Despite the richness and complexity of this food web, the openness of the system and the limited production possible in this temperate river's short growing season, we found that biomass densities of consumers responded to enrichment according to the qualitative predictions of a simple bioenergetic model.

All consumer trophic levels responded to sewage enrichment, but not all members of each trophic level: top piscivores seemed to control small, benthivorous fish but were unable to control larger fish, so the intermediate consumer level became dominated by Catastomidae (suckers). Consequently, the epiphytic prey of small fish were free to respond to sewage enrichment, but the benthic prey of suckers were not.

The important elements of complexity seemed to be the factors that determine the realized pattern of feeding linkages: heterogeneity in prey vulnerability (predator–prey size ratios) and predator efficiency (vegetation cover for ambush predators, inaccessibility of epiphytic prey to bottom‐feeding suckers).

Because of the openness of the system, the community was able to respond to enrichment by a combination of demographic (production) and behavioural (migration) mechanisms. We argue that the food web model described an energetically favourable state, and that migration provided a ‘shortcut’ for the system to approach this state within a short growing season.
Stage‐structured competition and the cyclic dynamics of host–parasitoid populations
Authors: Wearing Helen J. , Sait Steven M. , Cameron Tom C. , Rohani Pejman
Published: June 2004

Cyclic dynamics of various periods are pervasive in many insect populations where interactions with natural enemies are known to be important. How stage‐structured processes within the host population, such as competition and cannibalism, affect these interactions has received little attention so far.

Using the well‐studied laboratory host–parasitoid system ofPlodia interpunctellaandVenturia canescens, we explore a series of host–parasitoid models of increasing complexity. Specifically, we identify the circumstances under which stage‐structured processes both within the host and parasitoid populations generate dynamical behaviour ranging from generation to true consumer–resource (multi‐generation) cycles.

We find that both within‐host interactions (strong competition and egg cannibalism by late instar larvae) and parasitoid recruitment structure (a developmental lag in the parasitism of larvae) can suppress long period cycles and promote host generation cycles. In short, we show that simple stage‐structured processes in both host and parasitoid can modulate the strength of the consumer–resource interaction.

For some parameters we find more than one stable cyclic attractor. The presence of multiple attractors means that the same mechanism can give rise to cycles of different periods depending on initial population numbers. Because the host‐alone system may exhibit transient dynamics for a substantial period, the timing of a parasitoid invasion can be crucial to the dynamical outcome.

We discuss the consequences of using a single descriptor of an ecological time series, the cycle period, to infer properties about the underlying system and its food web interactions.
Food patch use by parent birds: to gather food for themselves or for their chicks?
Authors: Markman Shai , Pinshow Berry , Wright Jonathan , Kotler Burt P.
Published: June 2004

Despite its importance in the evolution of central‐place foraging strategies, few studies have distinguished between patch use by parent birds for their own consumption vs. patch use for the purpose of provisioning young in the nest.

Adult Palestine sunbirds (Nectarinia osea) consume nectar and arthropods, but feed only arthropods to their nestlings. This partial separation of food types allowed us to experimentally test sex‐specific trade‐offs in parental foraging effort between two patches.

A ‘variable’ patch on one side of a pair's territory contained only artificial nectar for parental self‐feeding (in varying sucrose concentrations between 0·25 and 0·75 mol kg−1 H2O). A ‘constant’ patch on the other side of the territory contained artificial nectar for parental self‐feeding (sucrose concentration = 0·25 mol kg−1 H2O), plus a dish of flightless houseflies for provisioning young.

Experimental increases in sucrose concentration in the variable patch led the parents to: (a) consume greater amounts of sucrose solution from this patch; (b) collect more flies from the constant patch to feed their young; and (c) persistently use the 0·25 mol kg−1 H2O feeder near the dish of flies. By titration (gradually changing the sucrose concentration in the variable patch), we demonstrate that at concentrations of 0·47 mol kg−1 H2O for males and 0·55 mol kg−1 H2O for females, the birds spent an equal amount of time foraging in both patches. Therefore, sucrose concentration in the variable patch (for self‐feeding only), had to be higher for the females than for the males, in order to balance the additional value females placed upon the flies provided for chick‐feeding in the constant patch.

These results reflect previously described sex‐specific parental roles in this species, with females provisioning young mainly in the nest and males patrolling more and guarding against nest predators. Furthermore, we demonstrate for the first time the fine details of alternative adaptive trade‐offs in foraging effort by parent birds when using patches for self‐feeding or for delivery of food to the young.
Assessment of hypotheses about dispersal in a long‐lived seabird using multistate capture–recapture models
Authors: Cam Emmanuelle , Oro Daniel , Pradel Roger , Jimenez Juan
Published: June 2004

Dispersal contributes to spatio‐temporal variation in population size and is a key process in studies of life history evolution and studies with conservation implications. However, dispersal is still one of the major gaps in our knowledge of ecological dynamics. The very large literature on metapopulation dynamics lacks empirical bases on dispersal and relevant behavioural parameters. We used multistate capture–recapture models (data from 1988 to 2001) to address hypotheses about movement probability and habitat selection within a system of two breeding colonies in Audouin's gulls (Larus audouinii), an endemic species breeding in the Mediterranean and considered as threatened.

Movement probability varied over time, and differed greatly between the colonies.

We did not find evidence of an influence of colony size or density of predators on movement probability.

In dispersers, our results did not support the hypotheses that movement probability between yeartandt+ 1 was influenced by mean breeding success in the colony of origin (i.e. an indicator of habitat quality) or the destination colony in yeartort+ 1, or by the ratio of breeding success in these colonies in yeartort +1 (i.e. quality gradient).

Overall, movement probability was higher from the smaller colony to the larger, and from the colony with lower breeding success in yeartto the more productive one. This provides slight support for two nonexclusive hypotheses about habitat selection (conspecific attraction and conspecific success attraction).

Movement probability from the smaller, less productive colony was very high in some years, suggesting that the dynamics of both colonies were strongly influenced by adult dispersal. However, in absolute numbers, more individuals moved from the larger, more productive colony to the smaller one. This suggests that the system may function as a source–sink system.

Use of multistate models to re‐assess local survival showed that survival was lower in the less productive colony with higher emigration probability. This may reflect genuine differences in mortality between colonies, or more probably differences in permanent emigration from the study area.
Detritus processing, ecosystem engineering and benthic diversity: a test of predator–omnivore interference
Authors: Zhang Yixin , Richardson John S. , Negishi Junjiro N.
Published: June 2004

Interference between species from different functional groups may influence ecosystem functioning and biological diversity. This study tested whether interactions between predacious cutthroat trout and an omnivorous signal crayfish modified the crayfish's trophic and engineering effects within a detrital‐based, stream benthic community.

We show in a trough experiment that omnivorous crayfish through their trophic and engineering roles enhance detritus decomposition, reduce particulate organic matter (POM) accumulation, and diminish diversity in leaf packs.

In crayfish troughs by day 30, leaf dry weight loss was 1·8‐fold greater, whereas POM trapped in leaf packs was 80% less, than of those in controls, and the abundance, biomass and taxon richness of benthos in leaf packs were lower than those in controls. Predatory cutthroat trout did not affect those variables and did not interfere with the crayfish.

Crayfish and cutthroat trout both decreased fine material sedimentation in the troughs.

Thus, with no interference from cutthroat trout, the signal crayfish acted as ecosystem processors and engineers, and strongly influenced detrital processing, benthic diversity, and the accumulation of POM and fine sediments.
High trophic overlap within the seabird community of Argentinean Patagonia: a multiscale approach
Authors: Forero Manuela G. , Bortolotti Gary R. , Hobson Keith A. , Donazar Jose A. , Bertelloti Marcelo , Blanco Guillermo
Published: June 2004

Food web interactions in animal communities can be investigated through the measurement of stable isotopes (e.g. δ15N, δ13C). We used this approach in a community of 14 species of seabirds breeding on the Argentinean Patagonian coast. Tissue samples were collected from nestling and adult seabirds, as well as prey, during three consecutive breeding seasons in 28 breeding colonies.

Relative to those in other temperate and polar regions, this seabird community showed a high degree of overlap in trophic level (TL) among species (93% of species within a TL range of 0·7) and also a comparatively high mean trophic level (4·1).

Relative positions of seabirds in relation to prey suggest that most species feed on pelagic fish and to a lesser extent on invertebrates. Stable isotope values of specialist feeders, Olrolg's (Larus atlanticus) and dolphin gulls (Leucophaeus scoresbii), which were previously assumed to feed mainly on crabs and sea lion excrement, respectively, suggested a broader diet than expected.

Based on stable isotope values of individuals, groups of phylogenetically related species generally showed a high degree of overlap within each group.

Given the degree of isotope overlap in this species‐rich community, coexistence could be interpreted as a consequence of superabundance of food or species diversification in morphology and foraging strategies. The short range of trophic level makes these seabirds vulnerable to the reduction of fish stocks due either to commercial fishing or stochastic fluctuations.
The shape of red grouse cycles
Authors: Shaw Darren J. , Haydon Daniel T. , Cattadori Isabella M. , Hudson Peter J. , Thirgood Simon J.
Published: June 2004

We examined 223 time‐series of red grouse (Lagopus lagopus scoticus) numbers compiled from shooting bag‐records from grouse moors located across England, Scotland and Wales for evidence of non‐time‐reversibility, asymmetry in cycle shape and non‐linearity.

We found 44% of time‐series to be non‐time‐reversible. Over 80% of time‐series spent more time increasing than decreasing (but only 32% did so significantly).

Non‐linearity was detected in 44% of time‐series examined, and these non‐linear time‐series were 1·7 times more likely to be non‐time‐reversible compared to the linear time‐series.

The occurrence of non‐linear and non‐time‐reversible series was not related to location, number of days with rain, temperature, moor area or population growth rate. The predominance of symmetrical peaks increased with easting but was not related to number of days with rain, temperature, northing or moor area.

There were no significant relationships between time‐reversibility or non‐linearity status and either tendency to cycle or cycle periodicity. However, populations that cycled with longer periods exhibited slower rates of increase and more equal lengths of time increasing and decreasing in numbers.

Our results provide little evidence that grouse cycles observed in different parts of the species range in the United Kingdom arise from fundamentally different processes.
Identifying the demographic determinants of population growth rate: a case study of red‐billed choughs Pyrrhocorax pyrrhocorax
Authors: Reid J. M. , Bignal E. M. , Bignal S. , McCracken D. I. , Monaghan P.
Published: June 2004

Identifying which age‐specific demographic rates underlie variation in a population's growth rate (λ) is an important step towards understanding the population's dynamics. Using data from a 20‐year study of marked individuals, we describe patterns of demographic variation and covariation in the Scottish red‐billed chough population (Pyrrhocorax pyrrhocorax), and investigate which demographic rates have the greatest projected and realized influence on λ.

Survival, the probability of breeding and breeding success varied with age in this population. Data were sufficient to estimate year‐specific probabilities of first‐year, second‐year and adult (all ages over 2) survival and mean breeding success. A population trajectory modelled using these parameter estimates closely matched census data, suggesting that estimates and simplifying assumptions were sufficient to accurately describe important demographic processes.

Elasticity analyses based on stage‐classes for which year‐specific survival was estimable suggested that λ was more elastic to variation in adult survival than first‐ or second‐year survival or breeding success. These ranks were consistent across all 15 years for which λ could be estimated directly, although the elasticity of adult survival declined with population growth.

Survival and breeding success were positively correlated across years. λ remained most sensitive to adult survival when this demographic covariation was incorporated into elasticity analyses.

However, elasticities calculated from a fully age‐structured model suggested that λ was more elastic to variation in first‐ and second‐year survival than to survival at any individual older age class. These ranks were robust to realistic demographic variation, but sensitive to postulated patterns of demographic covariation. We emphasize that covariation should be measured and incorporated into elasticity analyses, and that estimated elasticities must be interpreted in the context of the way in which stage‐classes are defined.

Of the demographic rates in which we quantified between‐year variation, first‐year survival varied most, followed by second‐year survival, breeding success and adult survival. These rates consequently contributed more equally to variation in λ than elasticities predicted. Overall, variation in λ was caused primarily by variation in survival rather than breeding success, and variation in prebreeding survival accounted for 56% of the total variation in λ.
How Dogs Navigate to Catch Frisbees
Authors: Shaffer Dennis M. , Krauchunas Scott M. , Eddy Marianna , McBeath Michael K.
Published: June 2004

Using micro-video cameras attached to the heads of 2 dogs, we examined their optical behavior while catching Frisbees. Our findings reveal that dogs use the same viewer-based navigational heuristics previously found with baseball players (i.e., maintaining the target along a linear optical trajectory, LOT, with optical speed constancy). On trials in which the Frisbee dramatically changed direction, the dog maintained an LOT with speed constancy until it apparently could no longer do so and then simply established a new LOT and optical speed until interception. This work demonstrates the use of simple control mechanisms that utilize invariant geometric properties to accomplish interceptive tasks. It confirms a common interception strategy that extends both across species and to complex target trajectories.
The Effects of Speed on Skilled Chess Performance
Authors: Burns Bruce D.
Published: June 2004

Two types of mechanisms may underlie chess skill: fast mechanisms, such as recognition, and slow mechanisms, such as search through the space of possible moves and responses. Speed distinguishes these mechanisms, so I examined archival data on blitz chess (5 min for the whole game), in which the opportunities for search are greatly reduced. If variation in fast processes accounts for substantial variation in chess skill, performance in blitz chess should correlate highly with a player's overall skill. In addition, restricting search processes should tend to equalize skill difference between players, but this effect should decrease as overall skill level increases. Analyses of three samples of blitz chess tournaments supported both hypotheses. Search is undoubtedly important, but up to 81% of variance in chess skill (measured by rating) was accounted for by how players performed with less than 5% of the normal time available.
The Role of Inhibitory Control in Forgetting Semantic Knowledge
Authors: Johnson Sarah K. , Anderson Michael C.
Published: June 2004

Previous research has shown that episodic retrieval recruits inhibitory processes that impair memory for related events. We report two experiments examining whether inhibitory processes may also be involved in causing semantic memory lapses. In a semantic retrieval-practice paradigm, subjects were given trials presenting a cue (a homograph in Experiment 1, a category in Experiment 2) linked to many different items in semantic memory. For each cue, subjects used general knowledge to generate no (baseline), one, four, or eight different items of semantic knowledge. Afterward, we determined through an apparently unrelated free-association test whether a critical nonpracticed concept associated to the cue had been inhibited. Both experiments found that generating items from semantic memory suppressed competing concepts, and that this impairment was cue independent. These findings show that inhibitory control processes overcome interference during semantic retrieval and that recruitment of these processes may contribute to semantic forgetting.
Role of Attention and Perceptual Grouping in Visual Statistical Learning
Authors: Baker Chris I. , Olson Carl R. , Behrmann Marlene
Published: June 2004

Statistical learning has been widely proposed as a mechanism by which observers learn to decompose complex sensory scenes. To determine how robust statistical learning is, we investigated the impact of attention and perceptual grouping on statistical learning of visual shapes. Observers were presented with stimuli containing two shapes that were either connected by a bar or unconnected. When observers were required to attend to both locations at which shapes were presented, the degree of statistical learning was unaffected by whether the shapes were connected or not. However, when observers were required to attend to just one of the shapes' locations, statistical learning was observed only when the shapes were connected. These results demonstrate that visual statistical learning is not just a passive process. It can be modulated by both attention and connectedness, and in natural scenes these factors may constrain the role of stimulus statistics in learning.
Suppressing Where but Not What:
Authors: Irwin David E. , Brockmole James R.
Published: June 2004

Some cognitive processes are suppressed during saccadic eye movements, whereas others are not. In two experiments, we investigated the locus of this interference effect. In one experiment, subjects decided whether pictured items were objects or nonobjects while making saccades of different lengths. Saccade distance had no effect on response time, indicating that saccades do not interfere with object recognition. However, in a second experiment, in which subjects decided whether pictured items faced to the left or to the right, response time increased with saccade distance, indicating that processing was suppressed during the saccade. These results (along with others) suggest that dorsal-stream (where) processes are suppressed during saccades, whereas ventral-stream (what) processes are not. Because the dorsal stream is instrumental in generating saccades, we propose that cognitive saccadic suppression results from dual-task interference within this visual subsystem.
Integrating Temporal Biases
Authors: Sanna Lawrence J. , Schwarz Norbert
Published: June 2004

We provide an integrative account of temporal biases (confidence changes, planning fallacy, impact bias, and hindsight bias). Students listed either 3 or 12 thoughts about success or failure before an upcoming real-life exam or immediately after learning their grades. Previous explanations had focused on how thought content alone (what comes to mind) influences temporal biases. We found, however, an interaction between thought content and accessibility experiences (how easily or difficultly thoughts come to mind). Thinking about 3 ways to succeed (success was easy to bring to mind) was equivalent to thinking about 12 ways to fail (failure was difficult to bring to mind), and conversely, thinking about 3 ways to fail was equivalent to thinking about 12 ways to succeed. In no case was thought content alone sufficient to predict the biases. These results have implications for debiasing strategies and other judgments over time.
Forgetting Trauma Stimuli
Authors: DePrince Anne P. , Freyd Jennifer J.
Published: June 2004

Previous work reported in this journal suggested that the cognitive capacities of high dissociators are impaired under conditions of focused (selective) attention, but not under conditions of divided attention, compared with the cognitive capacities of low dissociators. Using a directed-forgetting paradigm, the current study demonstrated that under divided-attention demands, high dissociators have impaired memory for words associated with trauma (e.g., incest) but not for neutral words, as compared with low dissociators. In addition, high dissociators reported significantly more trauma history and significantly more betrayal trauma (abuse by a caregiver) than low dissociators. These results are consistent with the proposal that dissociation may aid individuals with histories of betrayal traumas to keep threatening information out of awareness.
Psychophysiological Responding During Script-Driven Imagery in People Reporting Abduction by Space Aliens
Authors: McNally Richard J. , Lasko Natasha B. , Clancy Susan A. , Macklin Michael L. , Pitman Roger K. , Orr Scott P.
Published: June 2004

Is recollection of highly improbable traumatic experiences accompanied by psychophysiological responses indicative of intense emotion? To investigate this issue, we measured heart rate, skin conductance, and left lateral frontalis electro-myographic responses in individuals who reported having been abducted by space aliens. Recordings of these participants were made during script-driven imagery of their reported alien encounters and of other stressful, positive, and neutral experiences they reported. We also measured the psychophysiological responses of control participants while they heard the scripts of the abductees. We predicted that if “memories” of alien abduction function like highly stressful memories, then psycho-physiological reactivity to the abduction and stressful scripts would be greater than reactivity to the positive and neutral scripts, and this effect would be more pronounced among abductees than among control participants. Contrast analyses confirmed this prediction for all three physiological measures (ps < .05). Therefore, belief that one has been traumatized may generate emotional responses similar to those provoked by recollection of trauma (e.g., combat).
Increasing Implicit Self-Esteem Through Classical Conditioning
Authors: Baccus Jodene R. , Baldwin Mark W. , Packer Dominic J.
Published: June 2004

Implicit self-esteem is the automatic, nonconscious aspect of self-esteem. This study demonstrated that implicit self-esteem can be increased using a computer game that repeatedly pairs self-relevant information with smiling faces. These findings, which are consistent with principles of classical conditioning, establish the associative and interpersonal nature of implicit self-esteem and demonstrate the potential benefit of applying basic learning principles in this domain.
A Prospective Investigation of the Relationship Between Just-World Beliefs and the Desire for Revenge After September 11, 2001
Authors: Kaiser Cheryl R. , Vick S. Brooke , Major Brenda
Published: June 2004

We prospectively examined the relationship between individuals' belief in a just world and their desire for revenge against the perpetrators of the September 11 terrorist attacks against the United States. Eighty-three undergraduate students who had completed a measure of just-world beliefs prior to the terrorist attacks were assessed approximately 2 months following the attacks. The more strongly they had endorsed just-world beliefs prior to the attacks, the more distressed they felt about the attacks and the more they desired revenge. Furthermore, the relationship between belief in a just world and the desire for revenge was mediated by feelings of distress in response to the terrorist attacks. The results point to the importance of justice beliefs in understanding responses to the terrorist attacks.
Microplankton dynamics in a perennially ice‐covered Antarctic lake – Lake Hoare
Authors: Roberts Emily C. , Priscu John C. , Laybourn‐Parry Johanna
Published: June 2004

1. Temporal and spatial variation in planktonic abundance, biomass and composition were determined in Lake Hoare (McMurdo Dry Valleys, Antarctica) over two summer seasons (1996–97 and 1997–98).

2. Phototrophic nanoflagellates (PNAN) dominated planktonic biomass, with a mean monthly biomass ranging between 27.3 and 40.4 μg C L−1. The deep chlorophyll maximum was mainly composed of cryptophytes (>87% of total PNAN biomass) and varied in depth between 6 and 12 m.

3. Maximum bacterial concentration was 11.8 × 105 cells mL−1. Bacterial abundance showed relatively little temporal variation, with the exception of a drop in numbers that occurred in late November of both years studied.

4. Ciliates were the most successful heterotrophic protozoan group, with a mean monthly biomass (1.2–3.2 μg C L−1) being typically at least double that of heterotrophic nanoflagellate (HNAN) biomass (0.1–0.7 μg C L−1).

5. Microbial processes within this lake appear to be dominated by bottom up control. The relative importance of allochthonous inputs into the lake (from the ice‐cover and stream flow) and autochthonous recycling (by microzooplankton regeneration) are considered.

6. Results from a horizontal transect indicate that the permanence of the main sample hole may have enhanced planktonic biomass over a relatively small spatial scale.