bluuebunny/crossref_metadata_2025 huggingface dataset:
Polyunsaturated fatty acids in zooplankton: variation due to taxonomy and trophic position
Authors: PERSSON JONAS , VREDE TOBIAS
Published: March 2006

1. Food quality has major effects on the transfer of energy and matter in food webs, and essential long‐chained polyunsaturated fatty acids (PUFAs) can affect the quality of phytoplankton as food. In a study of oligotrophic lakes in north‐western Sweden, we investigated the fatty acid composition of four planktonic cladocerans and two calanoid copepods, representing herbivorous and carnivorous species. We also collected seston samples.

2. The proportions of long‐chain PUFAs in the organisms increased with their increasing trophic position. Thus, both their quality as food for other organisms, as well as their requirement for fatty acids (FAs), differed among taxa and depended on their trophic position.

3. We found taxon‐specific differences in the FA composition of zooplankton that were not related to sestonic FA composition. This implies that the variation in zooplankton FA composition is constrained by phylogenetic origin, life history characteristics, or both.

4. The cladoceran taxa contained 12–23% eicosapentaenoic acid (EPA) but only 0.9–2.1% docosahexaenoic acid (DHA) of the total FA content. In contrast, the calanoid copepods contained 7–11% EPA and 14–21% DHA. Thus, our results show that differences in the PUFA content among zooplankton species could have repercussions for both food web structure and function.
Prey switching inRhyacophila dorsalis(Trichoptera) alters with larval instar
Authors: ELLIOTT J.M.
Published: March 2006

1. Ontogenetic shifts in predator behaviour can affect the assessment of food‐web structure and the development of predator–prey models. Previous studies have shown that the diel activity pattern and functional response differed between larval instars of the carnivorous caddis,Rhyacophila dorsalis. The present study examines switching by larvae ofR. dorsalispresented with different proportions of two prey types; either small (length 2–4 mm) and large (5–8 mm)Chironomuslarvae for second, third, fourth and fifth instars ofR. dorsalis; orBaetis rhodani(9–12 mm) and largeChironomuslarvae for fourth and fifth instars. Experiments were performed in stream tanks with oneRhyacophilalarva per tank and 200 prey arranged in nine different combinations of the two prey types (20 : 180, 40 : 160, 60 : 140, 80 : 120, 100 : 100, 120 : 80, 140 : 60, 160 : 40 and 180 : 20). Prey were replaced as they were eaten. A model predicted the functional response in the absence of switching and provided a null hypothesis against which any tendency to switch could be tested.

2. There was no prey switching in the second and third instars, with both instars always showing a preference for small over largeChironomuslarvae. Prey switching occurred in the fourth and fifth instars. As the relative abundance of one prey type increased in relation to the alternative, the proportion eaten of the former prey changed from less to more than expected from its availability, the relationship being described by an S‐shaped curve. In the experiments with small and largeChironomus, the two instars switched to large larvae when their percentage of the total available prey exceeded 29% and 37% for fourth and fifth instars, respectively. In the experiments withBaetisand largeChironomus, both instars switched toBaetislarvae when their percentage of the total available prey exceeded 36%.

3. Non‐switching in second and third instars was related to their feeding strategies, both instars preferring smaller prey items. When the fourth and fifth instars foraged actively at night, they preferred larger over smallChironomuslarvae, but when they behaved as ambush predators at dusk, they captured the more activeBaetislarvae in preference to the more sedentary largeChironomuslarvae and only switched to the latter when they were >64% of the available prey.
Annual cycle and inter‐annual variability of gross primary production and ecosystem respiration in a floodprone river during a 15‐year period
Authors: UEHLINGER URS
Published: March 2006

1. Temporal variation in ecosystem metabolism over a 15‐year period (1986–2000) was evaluated in a seventh order channelised gravel bed river (mean annual discharge 48.7 m3 s−1) of the Swiss Plateau. The river is subject to frequent disturbance by bed‐moving spates. Daily integrals of gross primary production (GPP) and ecosystem respiration (ER) were calculated based on single‐station diel oxygen curves.

2. Seasonal decomposition of the time series of monthly metabolism rates showed that approximately 50% of the variation of GPP and ER can be attributed to season. Annual GPP averaged 5.0 ± 0.6 g O2 m−2 day−1 and showed no long‐term trend.

3. Ecosystem respiration, averaging 6.2 ± 1.4 g O2 m−2 day−1, declined from 8.8 to 4.1 g O2 m−2 day−1 during the 15‐year period. This significant trend paralleled a decline in nitrate and soluble reactive phosphorus concentrations, and the biochemical oxygen demand discharged by sewage treatment facilities upstream of the study reach. The ratio of GPP to ER (P/R) increased from 0.53 to about 1 as consequence of ER reduction.

4. Bed moving spates reduced GPP by 49% and ER by 19%. Postspate recovery of GPP was rapid between spring and autumn and slow during winter. Recovery of ER lacked any seasonal pattern. Annual patterns of daily GPP and to a minor extent of daily ER can be described as a sequence of recovery periods frequently truncated by spates.

5. The study showed that disturbance by frequent bed‐moving spates resulted in major stochastic variation in GPP and ER but annual patterns were still characterised by a distinct seasonal cycle. It also became evident that stream metabolism is a suitable method to assess effects of gradual changes in water quality.
High efficiency site‐specific genetic engineering of the mosquito genome
Authors: Nimmo D. D. , Alphey L. , Meredith J. M. , Eggleston P.
Published: March 2006

Current techniques for the genetic engineering of insect genomes utilize transposable genetic elements, which are inefficient, have limited carrying capacity and give rise to position effects and insertional mutagenesis. As an alternative, we investigated two site‐specific integration mechanisms in the yellow fever mosquito, Aedes aegypti. One was a modified CRE/lox system from phage P1 and the other a viral integrase system from Streptomyces phage phi C31. The modified CRE/lox system consistently failed to produce stable germline transformants but the phi C31 system was highly successful, increasing integration efficiency by up to 7.9‐fold. The ability to efficiently target transgenes to specific chromosomal locations and the potential to integrate very large transgenes has broad applicability to research on many medically and economically important species.
Evidence for a putative antennal clock in Mamestra brassicae: Molecular cloning and characterization of two clock genes –period and cryptochrome– in antennae
Authors: Merlin C. , François M.‐C. , Queguiner I. , Maïbèche‐Coisné M. , Jacquin‐Joly E.
Published: March 2006

Circadian rhythms are generated by endogenous circadian clocks, organized in central and peripheral clocks. An antennal peripheral clock has been demonstrated to be necessary and sufficient to generate Drosophila olfactory rhythms in response to food odours. As moth pheromonal communication has been demonstrated to follow daily rhythms, we thus investigated the occurence of a putative antennal clock in the noctuid Mamestra brassicae. From moth antennae, we isolated two full‐length cDNAs encoding clock genes, period and cryptochrome, which appeared to be expressed throughout the body. In the antennae, expression of both transcripts was restricted to cells that likely represent olfactory sensory neurones. Our results suggest the occurence of a putative antennal clock that could participate in the pheromonal communication rhythms observed in vivo.
Reversible introduction of transgenes in natural populations of insects
Authors: Le Rouzic A. , Capy P.
Published: March 2006

The most serious challenge concerning genetically modified insects remains their invasion ability. Indeed, transgenic insects often show lower fitness than wild individuals, and the transgene does not seem able to spread through a natural population without a driving system. The use of remobilizable vectors, based on the invading properties of transposable elements, has been frequently suggested. Simulations show that this strategy can be efficient. Moreover, if the transgene is designed to use transposition machinery already present in the genome, the transgene invasion appears to be potentially reversible after a few hundred generations, leading to new experimental perspectives.
The mitochondrial genome of the bristletail Petrobius brevistylis (Archaeognatha: Machilidae)
Authors: Podsiadlowski L.
Published: March 2006

The complete mitochondrial genome of the bristletail Petrobius brevistylis has been determined. The genome is 15 698 bp long and bears the standard set of genes common to all arthropods as well as a major non‐coding A + T‐rich region, the putative mitochondrial control region. A unique gene order was revealed as it differs from other hexapod and crustacean mitochondrial genomes in the position of tRNA‐Tyr. Genome features like nucleotide composition and codon usage are compared with that of other insect taxa. A + T content is similar in species of Archaeognatha and Zygentoma, but obviously lower than in Collembola and Pterygota. This A + T bias significantly affects also amino acid frequencies and may be a problem for phylogenetic analyses.
Genomic organization and functional characterization of the alcohol dehydrogenase locus of Ceratitis capitata (Medfly)
Authors: Brogna Saverio , Bourtzis Kostas , Gomulski Ludvik M. , Denaxa Myrto , Babaratsas Alekos , Gasperi Giuliano , Savakis Charalambos
Published: March 2006

Approximately 30 kb of genomic DNA enclosing the Adh locus from the medfly, Ceratitis capitata have been cloned and about 15 kb has been structurally and functionally characterized. The locus consists of two genes, Adh‐1 and Adh‐2, separated by an intergenic region, which is polymorphic in size ranging from ≈ 6.4 kb to 8.1 kb. Both genes consist of three exons and two introns. The introns are below 200 bp in size, except the 1st intron of Adh‐1, which is unexpectedly long, variable in size and contains a deleted mariner‐like element (postdoc). The two genes are transcribed in different orientations. The Adh‐2 gene shows the typical pattern of transcription seen in the homologous genes of Drosophilidae presenting high levels of expression in the fat body, gut and ovaries. The Adh‐1 gene is only expressed in the body muscle tissues of embryos, larvae and adult flies, raising the question of what its biological function may be. A DNA fragment containing bases −102 to −1666 relative to the first base of the initiating ATG of Adh‐1 is sufficient to drive the expression of a reporter gene in body muscles of Drosophila melanogaster embryos, larvae and adult flies. The study provides further insights into the evolution of the Adh genes of higher diptera.
Rain forest promotes trophic interactions and diversity of trap‐nesting Hymenoptera in adjacent agroforestry
Authors: KLEIN ALEXANDRA‐MARIA , STEFFAN‐DEWENTER INGOLF , TSCHARNTKE TEJA
Published: March 2006

Human alteration of natural ecosystems to agroecosystems continues to accelerate in tropical countries. The resulting world‐wide decline of rain forest causes a mosaic landscape, comprising simple and complex agroecosystems and patchily distributed rain forest fragments of different quality. Landscape context and agricultural management can be expected to affect both species diversity and ecosystem services by trophic interactions.

In Central Sulawesi, Indonesia, 24 agroforestry systems, differing in the distance to the nearest natural forest (0–1415 m), light intensity (37·5–899·6 W/m−2) and number of vascular plant species (7–40 species) were studied. Ten standardized trap nests for bees and wasps, made from reed and knotweed internodes, were exposed in each study site. Occupied nests were collected every month, over a period totalling 15 months.

A total of 13 617 brood cells were reared to produce adults of 14 trap‐nesting species and 25 natural enemy species, which were mostly parasitoids. The total number of species was affected negatively by increasing distance from forest and increased with light intensity of agroforestry systems. The parasitoids in particular appeared to benefit from nearby forests. Over a 500‐m distance, the number of parasitoid species decreased from eight to five, and parasitism rates from 12% to 4%.

The results show that diversity and parasitism, as a higher trophic interaction and ecosystem service, are enhanced by (i) improved connectivity of agroecosystems with natural habitats such as agroforestry adjacent to rain forest and (ii) management practices to increase light availability in agroforestry, which also enhances richness of flowering plants in the understorey.
Breeding birds on small islands: island biogeography or optimal foraging?
Authors: RUSSELL GARETH J. , DIAMOND JARED M. , REED TIMOTHY M. , PIMM STUART L.
Published: March 2006

We test MacArthur and Wilson's theory about the biogeography of communities on isolated habitat patches using bird breeding records from 16 small islands off the coasts of Britain and Ireland.

A traditional examination of patterns of species richness on these islands suggests that area and habitat diversity are important predictors, but that isolation and latitude have a negligible impact in this system.

Unlike traditional studies, we directly examine the fundamental processes of colonization and local extinction (cessation of breeding), rather than higher‐order phenomena such as species richness.

We find that many of MacArthur and Wilson's predictions hold: colonization probability is lower on more isolated islands, and extinction probability is lower on larger islands and those with a greater diversity of habitats.

We also find an unexpected pattern: extinction probability is much lower on more isolated islands. This is the strongest relationship in these data, and isolation is the best single predictor of colonization and extinction.

Our results show that examination of species richness alone is misleading. Isolation has a strong effect on both of the dynamic processes that underlie richness, and in this system, the reductions in both colonization and extinction probability seen on more distant islands have opposing influences on species richness, and largely cancel each other out.

We suggest that an appropriate model for this system might be optimal foraging theory, which predicts that organisms will stay longer in a resource patch if the distance to a neighbouring patch is large. If nest sites and food are the resources in this system, then optimal foraging theory predicts the pattern we observe.

We advance the hypothesis that there is a class of spatial systems, defined by their scale and by the taxon under consideration, at which decision‐making processes are a key driver of the spatiotemporal dynamics. The appropriate theory for such systems will be a hybrid of concepts from biogeography/metapopulation theory and behavioural ecology.
Recruitment pulses induce cannibalistic giants in Arctic char
Authors: BYSTRÖM PÄR
Published: March 2006

Recent theoretical studies on the population dynamic consequences of cannibalism have focused on mechanisms behind the emergence of large cannibals (giants) in size‐structured populations. Theoretically, giants emerge when a strong recruiting cohort imposes competition induced mortality on stunted adults, but also provides a profitable resource for a few adults that accelerate in growth and reach giant sizes.

Here the effects of a recruitment pulse on the individual and population level in an allopatric Arctic char population have been studied over a 5‐year period and these results were contrasted with theoretical model predictions for the conditions necessary for the emergence of cannibalistic giants.

The recruitment pulse had negative effects on invertebrate resource abundance, and the decrease in body condition and increase in mortality of adult char suggested that strong intercohort competition took place.

The frequency of cannibalism increased and a few char accelerated in growth and reached ‘giant’ sizes.

The main discrepancy between model predictions and field data was the apparently small effect the recruited cohort had on resources and adult char performance during their first summer. Instead, the effects became pronounced when the cohort was 1 year old. This mismatch between model predictions and field observations was suggested to be due to the low per capita fecundity in char and the restricted nearshore habitat use in young‐of‐the‐year (YOY) char.

This study provides empirical evidence that the emergence of giants is associated with the breakthrough of a strong recruiting cohort and also suggests that the claimed stable char populations with large cannibals may instead be populations with dynamic size structure that results in intermittent breakthroughs of recruitment pulses, providing the conditions necessary for char to enter the cannibalistic niche.

The data suggest that increased recruit survival through restricted habitat use may destabilize dynamics and cause the emergence of giants. However, they also suggest that this does not necessarily develop into populations with bi‐modal size structure in populations with low per capita fecundity and size‐ and density‐dependent habitat use of recruiting cohorts.
Spatio‐temporal dynamics of alternative male phenotypes in coho salmon populations in response to ocean environment
Authors: KOSEKI YUSUKE , FLEMING IAN A.
Published: March 2006

The coexistence of alternative reproductive phenotypes will probably be shaped by spatial and temporal variability in the environment. However, the effects of such variability on coexistence and the scale at which it operates are seldom understood.

To quantify such effects, we examined spatial and temporal dynamics in the abundance and frequency of alternative phenotypes of male coho salmon, Oncorhynchus kisutch Walbaum, which mature as either large fighters (age‐3 ‘hooknoses’) or small sneakers (age‐2 ‘jacks’). Using over 20 years of data on coded‐wire tagged fish released from nine Oregon hatcheries, we tested for the effects of ocean environment independent of those due to freshwater rearing.

Annual fluctuations of the abundance of jack and hooknose males within populations were correlated strongly by brood year (cohort) but not by return year (breeding group). This occurred independently of significant effects of release practice (i.e. the number of fish released, body size at release and date of release), indicating that a synchronized fluctuation in mortality during the first year at sea was the predominant cause. As a result, the annual frequency of the alternative phenotypes at breeding varied considerably within populations.

Spatial patterns in the annual fluctuations of the two phenotypes were similar (i.e. synchronous among populations), except that jacks showed local spatial structure (decreased synchrony with distance) not evident among hooknoses. This suggests that oceanic processes affecting the two phenotypes operate at different spatial scales. Despite effects on salmon abundance, the ocean environment had little influence through its effects on salmon growth on the relative frequencies of the alternative phenotypes within and among populations.

The results provide insight into the evolutionary dynamics of alternative phenotypes, including an intragenerational time lag that increases annual variability in phenotype frequencies at breeding (return years) and the significance of local freshwater processes, rather than oceanic processes, on phenotype expression. Freshwater processes, such as juvenile growth, timing of migration and breeding competition, operating at evolutionary and intragenerational time‐scales, are probably the predominant forces affecting phenotype frequency.
Quantitative analysis of bottlenose dolphin movement patterns and their relationship with foraging
Authors: BAILEY HELEN , THOMPSON PAUL
Published: March 2006

Broad‐scale telemetry studies have greatly improved our understanding of the ranging patterns and habitat‐use of many large vertebrates. However, there often remains considerable uncertainty over the function of different areas or the factors influencing habitat selection. Further insights into these processes can be obtained through analyses of finer scale movement patterns. For example, search behaviour may be modified in response to prey distribution and abundance.

In this study, quantitative analysis techniques are applied to the movements of bottlenose dolphins, recorded from land using a theodolite, to increase our understanding of their foraging strategies. Movements were modelled as a correlated random walk (CRW) and a biased random walk (BRW) to identify movement types and using a first‐passage time (FPT) approach, which quantifies the time allocated to different areas and identifies the location and spatial scale of intensive search effort.

Only a quarter of the tracks were classed as CRW movement. Turning angle and directionality appeared to be key factors in determining the type of movement adopted. A high degree of overlap in search effort between separate movement paths indicated that there were small key sites (0·3 km radius) within the study area (4 km2). Foraging behaviour occurred mainly within these intensive search areas, indicating that they were feeding sites.

This approach provides a quantitative method of identifying important foraging areas and their spatial scale. Such techniques could be applied to movement paths for a variety of species derived from telemetry studies and increase our understanding of their foraging strategies.
Delayed population explosion of an introduced butterfly
Authors: BOGGS CAROL L. , HOLDREN CHERYL E. , KULAHCI IPEK G. , BONEBRAKE TIMOTHY C. , INOUYE BRIAN D. , FAY JOHN P. , MCMILLAN ANN , WILLIAMS ERNEST H. , EHRLICH PAUL R.
Published: March 2006

The causes of lagged population and geographical range expansions after species introductions are poorly understood, and there are relatively few detailed case studies.

We document the 29‐year history of population dynamics and structure for a population ofEuphydryas gillettiiBarnes that was introduced to the Colorado Rocky Mountains, USA in 1977.

The population size remained low (< 200 individuals) and confined to a single habitat patch (∼2·25 ha) to 1998. These values are similar to those of many other populations within the natural geographical range of the species.

However, by 2002 the population increased dramatically to > 3000 individuals and covered ∼70 ha, nearly all to the south of the original site. The direction of population expansion was the same as that of predominant winds.

By 2004, the butterfly's local distribution had retracted mainly to three habitat patches. It thus exhibited a ‘surge/contraction’ form of population growth. Searches within 15 km of the original site yielded no other new populations.

In 2005, butterfly numbers crashed, but all three habitat patches remained occupied. The populations within each patch did not decrease in the same proportions, suggesting independent dynamics that are characteristic of metapopulations.

We postulate that this behaviour results, in this species, in establishment of satellite populations and, given appropriate habitat structure, may result in lagged or punctuated expansions of introduced populations.
Habitat type and density influence vocal signal design in satin bowerbirds
Authors: NICHOLLS JAMES A. , GOLDIZEN ANNE W.
Published: March 2006

This study provided a thorough test of the acoustic adaptation hypothesis using a within‐species comparison of call structure involving a wide range of habitat types, an objective measure of habitat density and direct measures of habitat‐related attenuation.

The structure of the bower advertisement call of the satin bowerbird was measured in 16 populations from throughout the species’ range and related to the habitat type and density at each site. Transmission of white noise, pure tones and different bowerbird dialects was measured in five of six habitat types inhabited by satin bowerbirds.

Bowerbird advertisement call structure converged in similar habitats but diverged among different habitats; this pattern was apparent at both continent‐wide and local geographical scales. Bowerbirds’ call structures differed with changes in habitat density, consistent with the acoustic adaptation hypothesis. Lower frequencies and less frequency modulation were utilized in denser habitats such as rainforest and higher frequencies and more frequency modulation were used in the more open eucalypt‐dominated habitats.

The white noise and pure tone transmission measurements indicated that different habitats varied in their sound transmission properties in a manner consistent with the observed variation in satin bowerbird vocalizations.

There was no effect of geographical proximity of recording locations, nor was there the predicted inverse relationship between frequency and body size.

These findings indicate that the transmission qualities of different habitats have had a major influence on variation in vocal phenotypes in this species. In addition, previously published molecular data for this species suggest that there is no effect of genetic relatedness on call similarity among satin bowerbird populations.
Hybridization increases measures of innate and cell‐mediated immunity in an endangered bird species
Authors: TOMPKINS DANIEL M. , MITCHELL ROBIN A. , BRYANT DAVID M.
Published: March 2006

Given the increasing threat of ‘emerging infectious diseases’ (EIDs), and the vulnerability of small inbred populations to such novel challenges (at least partly through compromised immunity), a degree of interspecific hybridization may improve the viability of endangered species by enriching depauperate gene pools.

To investigate this hypothesis, we quantified indicators of the strength of both innate and cell‐mediated immunity in wild populations of hybridizing parakeets on the Chatham Islands, New Zealand.

We show that both measures of immune function are markedly higher in the cosmopolitan red‐crowned parakeet Cyanoramphus novaezelandiae than in the island endemic Forbes’ parakeet C. forbesi, as is to be expected when comparing relatively outbred vs. relatively inbred species.

In addition, we show that both measures of immune function are higher in Forbes’× red‐crowned parakeet hybrids than in the Forbes’ parakeet. Even those individuals with few red‐crowned characteristics, suggesting they are the products of matings between hybrids and Forbes’ parakeets, have significantly higher measures of immune function.

As at least one of the immune indicators measured correlates directly with both survivorship and the viability of small bird populations, this study reveals a potential management option for hybridizing species of conservation concern, where an increase in resilience to novel disease challenges could outweigh some loss of genetic integrity.
A silver spoon for a golden future: long‐term effects of natal origin on fitness prospects of oystercatchers (Haematopus ostralegus)
Authors: VAN DE POL MARTIJN , BRUINZEEL LEO W. , HEG DIK , VAN DER JEUGD HENK P. , VERHULST SIMON
Published: March 2006

Long‐term effects of conditions during early development on fitness are important for life history evolution and population ecology. Using multistrata mark–recapture models on 20 years of data, we quantified the relation between rearing conditions and lifetime fitness in a long‐lived shorebird, the oystercatcher (Haematopus ostralegus). We addressed specifically the relative contribution of short‐ and long‐term effects of rearing conditions to overall fitness consequences.

Rearing conditions were defined by differences in natal habitat quality, in which there is a clear dichotomy in our study population. In the first year of life, fledglings from high‐quality natal origin had a 1·3 times higher juvenile survival. Later in life (age 3–11), individuals of high‐quality natal origin had a 1·6 times higher adult prebreeder survival. The most striking effect of natal habitat quality was that birds that were reared on high‐quality territories had a higher probability of settling in high‐quality habitat (44% vs. 6%). Lifetime reproductive success of individuals born in high‐quality habitat was 2·2 times higher than that of individuals born in low‐quality habitat. This difference increased further when fitness was calculated over several generations, due to a correlation between the quality of rearing conditions of parents and their offspring.

Long‐term effects of early conditions contributed more to overall fitness differences as short‐term consequences, contrary to common conceptions on this issue.

This study illustrates that investigating only short‐term effects of early conditions can lead to the large underestimation of fitness consequences. We discuss how long‐term consequences of early conditions may affect settlement decisions and source–sink population interactions.
Towards a population ecology of stressed environments: the effects of zinc on the springtailFolsomia candida
Authors: NOËL HELEN L. , HOPKIN STEVE P. , HUTCHINSON THOMAS H. , WILLIAMS TIM D. , SIBLY RICHARD M.
Published: March 2006

To understand population dynamics in stressed environments it is necessary to join together two classical lines of research. Population responses to environmental stress have been studied at low density in life table response experiments. These show how the population's growth rate (pgr) at low density varies in relation to levels of stress. Population responses to density, on the other hand, are based on examination of the relationship betweenpgrand population density.

The joint effects of stress and density onpgrcan be pictured as a contour map in whichpgrvaries with stress and density in the same way that the height of land above sea level varies with latitude and longitude. Here a microcosm experiment is reported that compared the joint effects of zinc and population density on thepgrof the springtailFolsomia candida(Collembola).

Our experiments allowed the plotting of a complete map of the effects of density and a stressor onpgr. Particularly important was the position of thepgr= 0 contour, which suggested that carrying capacity varied little with zinc concentration until toxic levels were reached.

This prediction accords well with observations of population abundance in the field. The method also allowed us to demonstrate, simultaneously, hormesis, toxicity, an Allee effect and density dependence.

The mechanisms responsible for these phenomena are discussed. As zinc is an essential trace element the initial increase inpgris probably a consequence of dietary zinc deficiency. The Allee effect may be attributed to productivity of the environment increasing with density at low density. Density dependence is a result of food limitation.

Synthesis and applications.We illustrate a novel solution based on mapping a population's growth rate in relation to stress and population density. Our method allows us to demonstrate, simultaneously, hormesis, toxicity, an Allee effect and density dependence in an important ecological indicator species. We hope that the approach followed here will prove to have general applicability enabling predictions of field abundance to be made from estimates of the joint effects of the stressors and density on population growth rate.
Point transect sampling with traps or lures
Authors: BUCKLAND STEPHEN T. , SUMMERS RON W. , BORCHERS DAVID L. , THOMAS LEN
Published: March 2006

The ability to monitor abundance of animal populations is becoming increasingly important, in light of growing concerns over the loss of biodiversity through anthropogenic changes. A widely used tool for such monitoring is distance sampling, in which distances of detected animals from a line or point are modelled, to estimate detectability and hence abundance. Nevertheless, many species still prove problematic to survey. We have developed two extensions to point transect sampling that potentially allow abundance to be estimated for a number of species from diverse taxa for which good survey methods have not previously been available.

For each method, the primary survey comprises a random sample of points, or more usually a systematic grid of points, through the region of interest. Animals are lured to a point, or trapped at a point, and the number of animals observed at each point is recorded. A separate study is conducted on a subset of animals, to record whether they respond to the lure or enter the trap, for a range of known distances from the point. These data are used to estimate the probability that an animal will respond to the lure or enter the trap, as a function of its initial distance from the point. This allows the counts to be converted to an estimate of abundance in the survey region.

We illustrated the methods using a lure survey of crossbillsLoxiaspp. in coniferous woodland in Scotland.

Synthesis and applications.Two extensions of point transect sampling that use the same statistical methodology, lure point transects and trapping point transects, have been developed. Lure point transects extend the applicability of distance sampling to species that can be lured to a point, while trapping point transects potentially allow abundance estimation of species that can be trapped, with fewer resources needed than trapping webs and conventional mark–recapture methods.
Light and thermal environments as modified by a wheat crop: effects on weed seed germination
Authors: KRUK BETINA , INSAUSTI PEDRO , RAZUL ANDREA , BENECH‐ARNOLD ROBERTO
Published: March 2006

Knowledge of the regulatory effects of the crop canopy on weed seed germination is necessary to understand fully the behaviour of weed seed banks during a crop cycle. It is well known that canopy presence interferes with seed germination through modifications to the light and thermal environment, but the changing effect of a growing canopy has not been assessed, thus precluding the identification of shading‐intensity thresholds for triggering the different types of canopy‐detection mechanisms in different seed populations.

Field experiments were performed with artificially modified thermal and light environments, using two types of seed banks (seeds buried or located at the soil surface). Conditions below a wheat canopy were modified to match light and thermal conditions prevailing on bare soil (i.e. soil without vegetation).

Most weed emergence patterns during the early stages of crop establishment were not modified by the thermal regime produced by the incipient canopy compared with a bare soil control. However, the reduction of the red : far‐red ratio from the bare soil value of 1·2–0·9 below the wheat canopy reduced germination of some weed species located at the soil surface, and the effect could by reversed by far‐red filters.

The weed Galinsoga parviflora developed two generations during the crop cycle. The modified light and thermal environments beneath an establishing wheat canopy was not sufficient to inhibit the germination of Galinsoga parviflora, even if seeds were located at the soil surface. Only for seeds of the second generation, dispersed from seeds of the first plant generation, was there sufficient modification of the photothermal environment below the wheat canopy to interfere with dormancy termination.

Synthesis and applications. Understanding seed responses to modifications in the photothermal environment below a crop canopy (e.g. wheat crop) should allow us to improve weed management strategies by manipulating crop canopy attributes. This could be achieved by modification of sowing date, crop density, spatial arrangement and genotype. For example, increasing the crop plant density would diminish the number of weeds emerging during the first phase of crop establishment. This strategy would be appropriate where weed seeds are predominantly located at the soil surface, typically found in a no‐till cropping system.
Long‐term demographic fluctuations in an orchid species driven by weather: implications for conservation planning
Authors: PFEIFER MARION , WIEGAND KERSTIN , HEINRICH WOLFGANG , JETSCHKE GOTTFRIED
Published: March 2006

Management decisions are increasingly based on matrix models intended to predict the long‐term fate of endangered species. However, certain elements of these models, such as life‐state transition probabilities (vital rates), are difficult to parameterize and their values may vary depending on external conditions such as weather. Details of how weather might influence population performance are rare, yet necessary to assess the effects of global climate change on a species’ distribution.

Based on a 26‐year data set of a population of Himantoglossum hircinum in a nature reserve in Germany, variations of life‐history traits and vital rates were studied. Matrix analysis was used to identify the most important life‐state transitions for population growth. Multiple linear regression was used to quantify the response of population traits and vital rates to changing weather conditions.

Population size increased exponentially and density effects could not be observed. Flowering plants and large plants had the highest and second highest reproductive value, respectively. The population's finite rate of increase fluctuated strongly among years; life‐history traits varied strongly and were interlinked, thereby violating the assumptions of matrix modelling in a population viability analysis.

Some vital rates and the population growth rate showed a trend over the total period. A certain and sometimes large amount of that variability could be attributed to variability of weather conditions, with warmer winter conditions favouring population performance. Prediction of population size was fairly accurate within a time frame of 10 years, but size class structure was not.

Synthesis and applications. Matrix modelling proved to be unreliable for predicting long‐term population dynamics, despite the long‐term data set used for matrix construction. This can be explained by weather‐dependent variability of vital rates driving population dynamics. A minimum study period of 4 years is necessary to produce relevant information for model development. Our study emphasizes the need for critical evaluation of management decisions based only on single short‐term studies and for studies covering longer time intervals than 2–3 years.
Effect of forest clearing on the abundance of Ixodes ricinus ticks and the prevalence of Borrelia burgdorferi s.l.
Authors: Hubálek Z. , Halouzka J. , Juřicová Z. , Šikutová S. , Rudolf I.
Published: March 2006

Abstract.  Questing Ixodes ricinus L. (Acari: Ixodidae) ticks were collected on a forest trail that had been completely cleared of shrubs and ground vegetation in winter 2002 and on a nearby control uncleared forest transect in South Moravia (Czech Republic). Samples were collected each May in 2003, 2004 and 2005. Nymphal ticks were 3.4 times, 1.9 times and 1.2 times less frequent on cleared forest than on uncleared forest trails in the three respective years, whereas adult tick abundance was 27.2 times, 4.0 times and 2.2 times lower, respectively. The ticks were examined for borreliae by dark‐field microscopy: prevalence of nymphal ticks infected with Borrelia burgdorferi sensu lato (12.6% to 20.0%) did not differ significantly between the cleared and uncleared trail during the 3 years. In conclusion, the habitat modification appeared to result in a decreased abundance of I. ricinus as well as a reduced frequency of infected ticks (and thus indirectly a lower potential risk of Lyme borreliosis), which lasted, however, for only 2 years. Eight cultures of borreliae isolated from the ticks were all identified as the ‘ornithophilic’ genomic species Borrelia garinii, possibly indicating a greater role of forest birds than that of forest rodents as the hosts of immature I. ricinus in the tick (and borrelial) colonization of the cleared part of the forest.
Influence of glutamine on pancreatic blood flow and apoptosis of pancreatic acinar in rats with severe acute pancreatitis
Authors: XU Xue Feng , LOU Wen Hui , WANG Dan Song , JIN Da Yong , NI Xiao Lin , WU Zhao Han
Published: March 2006

OBJECTIVE:  To investigate the role of glutamine on splanchnic blood flow, apoptosis of pancreatic acinar and the underlying mechanism in rats with severe acute pancreatitis.

METHODS:  Forty‐eight rats were randomized into two groups: the glutamine group (n = 24) and the severe acute pancreatitis group (n = 24). Jejunotomy was performed in all rats: the glutamine group also received glutamine, and the severe acute pancreatitis group received normal saline. Each group was then subdivided into three subgroups of eight rats each, with the rats be killed at 12, 24 and 36 h after the operation, respectively. A control group underwent sham operation (n = 8). The regional pancreatic microvascular blood flow was measured by Doppler ultrasound. The blood flow of the portal vein, splenic artery and superior mesenteric artery were also recorded. Apoptosis of pancreatic acinar cells was evaluated by TUNEL method.

RESULTS:  The regional pancreatic microvascular blood flow (KHz) decreased significantly in the severe acute pancreatitis group (P < 0.01), and continued to decrease after 24 h (vs. 12 h, P < 0.01). The blood flow of the portal vein, splenic artery and superior mesenteric artery also decreased in the severe acute pancreatitis group. The glutamine group showed increased regional pancreatic microvascular blood flows, as well as increased blood flow of the portal vein, splenic artery and superior mesenteric artery (vs. the severe acute pancreatitis group, P < 0.01). The apoptotic index of pancreatic acinar in the glutamine group was higher than in the severe acute pancreatitis group (P < 0.01), and both were much higher than that in the control group (P < 0.01).

CONCLUSIONS:  Enteral administration of glutamine increased the splanchnic blood flow in severe acute pancreatitis rats. The apoptotic index of pancreatic acinar was negatively correlated with the severity of the disease. The interrelation between glutamine and apoptosis in severe acute pancreatitis is worthy of further investigation.
Clinical aspects of ulcerative colitis in mainland China
Authors: ZHENG Jia Ju
Published: March 2006

Inflammatory bowel disease (IBD), including Crohn's disease (CD) and ulcerative colitis (UC), is reported to be increasing in incidence and prevalence in provinces and cities in mainland China. This article specifically reviews clinical features, extra‐intestinal manifestations, complications, diagnosis and differential diagnosis, and medical treatment of UC. Compared to patients in Western countries, more mild to moderate and left‐sided colitis cases were observed in a nation‐wide study in China. Complications included anal fistula, anal abscess, anal fissure, severe bleeding, intestinal perforation, intestinal obstruction and colonic carcinoma. The extra‐intestinal manifestations were arthritis/arthralgia, eye and skin disorders and oral ulcers. The high specificity of antineutrophil cytoplasmic antibody may useful for distinguishing UC from infectious colitis; in addition, serum levels of antisaccharomyces cerevisia antibody may helpful for distinguishing between UC and CD. Oral sulfasalazine and 5‐aminosalicylic acid (ASA) remain the mainstays for the management of mild to moderate UC in China. Corticosteroids and immunosuppressive agents are also widely used in severe or refractory UC.
Treatment of surgically induced acute liver failure by transplantation of HNF4‐overexpressing embryonic stem cells
Authors: KUAI Xiao Ling , CONG Xiao Qian , DU Zhong Wei , BIAN Yu Hai , XIAO Shu Dong
Published: March 2006

OBJECTIVE:  Tissue‐specific stem cells from differentiating embryonic stem (ES) cells are both pluripotent and genetically flexible. Recent observations indicate that ES cells can differentiate into hepatocytes. Therefore, cell‐based therapy can potentially be a therapeutic alternative to liver transplantation. In this study the treatment of acute liver failure in rats by transplantation of hepatocyte nuclear factor 4 (HNF4)‐overexpressing ES cells was investigated.

METHODS:  The HNF4 was transfected into ES cells and ES cell clones overexpressing HNF4 were selected. The levels of markers of hepatocyte differentiation, including albumin, transthyretin, glucose‐6‐phosphates (G‐6‐P) and SAPK/ERK kinase‐1 (SEK1) mRNA, were tested in spontaneously differentiated HNF4‐overexpressing ES cells by reverse transcription‐polymerase chain reaction (RT‐PCR). The ultrastructure of the spontaneously differentiated HNF4‐overexpressing ES cells was examined by electron microscopy. To induce acute liver failure, Sprague–Dawley rats were subjected to 90% hepatectomy and given 5% oral dextrose. The rats were divided into three groups. The rats in the treatment group (n = 12) received intraliver injection of 2 × 107 undifferentiated HNF4‐overexpressing ES cells from the same clone, the rats in control group 1 (n = 12) received 2 × 107 undifferentiated ES cells, and the rats in control group 2 (n = 12) received the same volume of media without any cells.

RESULTS:  All rats in control group 1 and control group 2 died within 72 h, while 33% of rats that received undifferentiated HNF4‐overexpressing ES cells transplantation survived more than 1 month. Spontaneously differentiated HNF4‐overexpressing ES cells only expressed transthyretin mRNA. The cells were rich in mitochondrion and catalase‐containing peroxisomes in ultrastructure.

CONCLUSIONS:  Transplantation of ES cells could be a potential treatment in supporting life during acute liver insufficiency and could be a bridge to orthotopic liver transplantation.
Abdominal pain related to mitochondrial neurogastrointestinal encephalomyopathy syndrome may benefit from splanchnic nerve blockade
Authors: ÇELEBI NALAN , ŞAHIN ALTAN , CANBAY ÖZGÜR , ÜZÜMCÜGIL FILIZ , AYPAR ULKÜ
Published: March 2006

Patients diagnosed with abdominal pain related to mitochondrial neurogastrointestinal encephalopathy (MNGIE) may benefit from splanchnic nerve blockade. MNGIE, varying in age of onset and rate of progression, is caused by loss of function mutation in thymidine phosphorylase gene. Gastrointestinal dysmotility, pseudo‐obstruction and demyelinating sensorimotor peripheral neuropathy (stocking‐glove sensory loss, absent tendon reflexes, distal limb weakness, and wasting) are the most prominent manifestations. Patients usually die in early adulthood (mean 37.6 years; range 26–58 years). We report a case of an 18‐year‐old patient with MNGIE. Our patient's abdominal pain was relieved after splanchnic nerve blockade.
How many freshwater diatoms are pH specialists? A response to Pither & Aarssen (2005)
Authors: Telford Richard J. , Vandvik Vigdis , Birks H. J. B.
Published: March 2006

Pither & Aarssen (2005) propose a null model approach to assess the proportion of niche specialist taxa along ecological gradients. They apply this methodology to a large data set of lacustrine diatom assemblages and conclude that a majority of the taxa are generalists on a pH gradient. This conflicts with previous work, which shows that many diatom taxa have a statistically significant relationship with pH. We demonstrate the methods used by Pither & Aarssen (2005) have a high Type II error for rare taxa, and that this problem is compounded by the non‐uniform sampling of the pH gradient which effectively precludes acid‐lake specialist diatoms from being recognized as such. We re‐analyse the data used by Pither & Aarssen (2005) and show that most of the diatoms have a statistically significant relationship with pH, and we thus refute their conclusions that few diatom species are specialists.