bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of magnetic resonance cholangiography in the management of children and young adults after liver transplantation
Authors: Norton Karen I. , Lee Jacob S. , Kogan Debora , Glass Ronald B. , Shneider Benjamin L. , Rodriguez‐Laiz Gonzalo P. , Emre Sukru
Published: November 2004

Abstract: We reviewed the results of 50 magnetic resonance (MR) cholangiograms to evaluate their usefulness in directing clinical management in young patients after liver transplantation (LTx). Thirty‐two patients underwent 50 MR cholangiograms on a 1.5‐T unit. Studies were performed from 1 week to 16 yr after LTx. Indications included biochemical abnormalities with (n = 19) or without (n = 16) biopsy evidence for chronic rejection, sepsis (n = 14), and intractable ascites (n = 1). Original interpretations were compared to laboratory and ultrasound findings, and clinical outcome. Of 19 studies performed on 14 patients with biopsy evidence of chronic rejection, 16 were abnormal on MR (but only one was abnormal on ultrasound), resulting in corrective surgery (n = 1), re‐Tx (n = 1), and endoscopic dilatation (n = 1). Of 16 studies on 16 patients with biochemical abnormalities without evidence of chronic rejection on biopsy, 14 were abnormal on MR (but only five of 13 on ultrasound), leading to corrective surgery (n = 3) and re‐listing for Tx (n = 3). Thirteen of 14 studies on six patients with sepsis were abnormal on MR (five of nine were abnormal on ultrasound), identifying surgically correctable strictures (n = 2), and leading to re‐Tx (n = 1) and percutaneous biliary drainage procedures (n = 2). The one patient with ascites had a normal study. We advocate usage of MR cholangiography for the detection of biliary complications after LTx, particularly in those patients who present with biochemical abnormalities that are not easily explained by acute cellular rejection or viral infection and in those with biliary sepsis.
Macrophage depletion improves survival of porcine neonatal pancreatic cell clusters contained in alginate macrocapsules transplanted into rats
Authors: Omer Abdulkadir , Keegan Mitchell , Czismadia Eva , De Vos Paul , Van Rooijen Nico , Bonner‐Weir Susan , Weir Gordon C.
Published: November 2004

Omer A, Keegan M, Czismadia E, De Vos P, Van Rooijen N, Bonner‐Weir S and Weir GC. Macrophage depletion improves survival of porcine neonatal pancreatic cell clusters contained in alginate macrocapsules transplanted into rats. Xenotransplantation 2003; 10: 240–251. © Blackwell Munksgaard 2003

Background: Macrophages can accumulate on the surface of empty and islet‐containing alginate capsules, leading to loss of functional tissue. In this study, the effect of peritoneal macrophage depletion on the biocompatibility of alginate macrocapsules and function of macroencapsulated porcine neonatal pancreatic cell clusters (NPCCs) was investigated. Methods: Clodronate liposomes were injected into the peritoneal cavities of normoglycemic Lewis rats 5 and 2 days before the transplantation. Empty or NPCC‐containing Ca‐alginate poly L‐lysine (PLL)‐coated macrocapsules were transplanted into the peritoneal cavities of rats injected with either clodronate liposomes or saline. On days 7, 14 and 21, samples were evaluated by immunohistochemistry for cellular immune responses on the surface of the macrocapsules and for macrophage populations in omental tissue. To assess the function of macroencapsulated NPCCs, insulin secretory responses to glucose and theophylline were measured after capsule retrieval. Results: In saline‐injected control groups, all of the empty and NPCC‐containing macrocapsules were overgrown with macrophages, this being especially severe on NPCC‐containing macrocapsules. In the clodronate liposomes‐injected group, the majority of the empty macrocapsules were free of macrophage accumulation and the NPCC‐containing macrocapsules were less overgrown than in control animals. Higher insulin responses to glucose and theophylline were observed in NPCCs retrieved from rats injected with clodronate liposomes. Conclusion: We conclude that depletion of peritoneal macrophages with clodronate liposomes improve the survival of macroencapsulated NPCCs.
Conspecific brood parasitism and egg rejection in Great‐tailed Grackles
Authors: Peer Brian D. , Sealy Spencer G.
Published: November 2004

In this study, we tested whether conspecific brood parasitism (CBP) has selected for egg rejection behavior in the colonial Great‐tailed Grackle Quiscalus mexicanus. No evidence of CBP was recorded at 797 Great‐tailed Grackle nests, and we did not induce CBP by experimentally removing nests while grackles were laying. We determined experimentally that Great‐tailed Grackles are determinate layers, an attribute opposite to that sometimes associated with CBP. Despite the absence of CBP, Great‐tailed Grackles rejected 8% of experimentally introduced conspecific eggs, rarely rejecting or damaging their own eggs. Conspecific eggs added to nests during incubation tended to be rejected more frequently than eggs switched between nests, and eggs that differed the most from the host's eggs tended to be rejected sooner. There was no relationship between rejection and the stage of the nest cycle when experimental parasitism occurred; however, eggs were rejected faster when added during the prelaying and incubation stages than during laying. Evidence suggests, therefore, that egg rejection behavior in Great‐tailed Grackles has not evolved in response to CBP.
Quantifying habitat use in satellite‐tracked pelagic seabirds: application of kernel estimation to albatross locations
Authors: Wood A. G. , Naef‐Daenzer B. , Prince P. A. , Croxall J. P.
Published: November 2004

We develop a new approach to quantifying habitat use within the foraging ranges of satellite‐tracked seabirds. We applied kernel estimation techniques to 167 days (3738 locations) of data from Black‐browed and Grey‐headed albatrosses Diomedea melanophris and
D. chrysostoma during the chick‐rearing period of the breeding
cycle at South Georgia. At this time the activity range of these two
species covers an estimated 440 000 and 640 000
km2, respectively, with very substantial overlap. In contrast,
kernel estimation reveals that the main foraging areas of these two
sympatric, congeneric species are very distinct. Based on location
density categories accounting for 50% of locations, the foraging areas
cover c. 81 500 and c. 119 700 km2, respectively, with 42% and 50% of the range of one species overlapping with that of the other.
Does the foraging strategy of adult Short‐tailed Shearwaters cause obesity in their chicks?
Authors: Schultz Mark A. , Klomp Nicholas I.
Published: November 2004

The chick provisioning behaviour of Short‐tailed Shearwaters Puffinus tenuirostris breeding at the northern edge of their distribution on Montague Island, New South Wales, was examined in February and March 1997. The duration of individual foraging trips of parents, weight changes of adults and chicks, and meal sizes delivered to chicks were determined. It was found that individual parents mixed a long foraging trip to Antarctic waters (14.4±2.0 days) with one to three short foraging trips (1.36±0.7 days, mode=1 day). Adults gained body mass on long trips and lost weight on short trips. The size of meals fed to the chicks was significantly greater after a long trip (161±21 g) than after a short trip (135±28 g), although short trips increased the overall chick feeding frequency. The variable number of short trips made by adult Short‐tailed Shearwaters and the relationship between short trips and adult body condition were consistent with current life‐history theory: adults do not sacrifice their own body condition to increase food delivered to their chicks.  Modelling revealed that this dual foraging strategy inevitable leads to chicks enduring long intervals between meals. These long intervals may have led to the evolution of an over‐feeding strategy by parents and the nestling obesity reported in this shearwater. The durations of the long trips from Montague Island were significantly greater than those for Short‐tailed Shearwaters breeding at the centre of their distribution in Tasmania, although there was no significant difference in the length of short trips. A commitment to feed regularly in Antarctic waters may explain why the breeding distribution of this species does not extend much further north.
Body size and determinants of laying date variation in the Snow Petrel Pagodroma nivea
Authors: Barbraud Christophe , Lormée Hervé , LeNevé Arnaud
Published: November 2004

We studied several determinants of laying date variation and the relationship between laying date and reproductive success in the Snow Petrel Pagodroma nivea. The effects of female body size and condition, year, individual laying period, colony size, mate fidelity, previous reproductive success, and duration of the pre‐laying exodus on laying date, were investigated during a 3‐year study. The average laying date was 4 December. The laying period was compressed into 10–16 days and was very constant from year to year, both for the population as a whole and for individual females. The laying period of individual females varied from year to year on average by less than one day. Body size explained 24% of the variation in laying dates, with large females laying their egg later than small ones. Laying in large colonies occurred c. 2 days later than in small colonies, mainly because a higher proportion of large females bred in large colonies. There was no effect of mate fidelity, age, body condition and previous reproductive success on laying date, but the duration of the pre‐laying exodus was strongly correlated with laying date. Smaller females had shorter pre‐laying exodus (c. 17.7 days) than larger ones (c. 20.4 days). During the three years of the study reproductive success either increased, decreased or did not vary with laying date. Although body size is not maintained by selection on laying date alone, the genetic body size component of this species suggests that balancing selection on body size may act through laying date.
Advances in imaging: impact on studying craniofacial bone structure
Authors: Majumdar S
Published: November 2004

Author– Majumdar S

Methods for measuring the structure of craniofacial bones are discussed in this paper. In addition to the three‐dimensional macro‐structure of the craniofacial skeleton, there is considerable interest in imaging the bone at a microscopic resolution in order to depict the micro‐architecture of the trabecular bone itself. In addition to the density of the bone, the micro‐ architecture reflects bone quality. An understanding of bone quality and density changes has implications for a number of craniofacial pathologies, as well as for implant design and understanding the biomechanical function and loading of the jaw. Trabecular bone micro‐architecture has been recently imaged using imaging methods such as micro‐computed tomography, magnetic resonance imaging, and the images have been used in finite element models to assess bone mechanical properties. In this paper, some of the recent advances in micro‐computed tomography and magnetic resonance imaging are reviewed, and their potential for imaging the trabecular bone in mandibular bones is presented. Examples of in vitro and in vivo images are presented.
Using three‐dimensional imaging to assess treatment outcomes in orthodontics: a progress report from the University of the Pacific
Authors: Baumrind S , Carlson S , Beers A , Curry S , Norris K , Boyd RL
Published: November 2004

Authors– Baumrind S, Carlson S, Beers A, Curry S, Norris K, Boyd RL

Past research in integrated three‐dimensional (3D) craniofacial mapping at the Craniofacial Research Instrumentation Laboratory (CRIL) of the University of the Pacific is summarized in narrative form. The advantages and limitations of recent commercial developments in the application of cone beam geometry volumetric X‐ray scanners in dentistry and surface digital mapping of study casts are discussed. The rationale for methods currently in development at CRIL for merging longitudinal information from existing 3D study casts and two‐dimensional lateral X‐ray cephalograms in studies of orthodontic treatment outcome is presented.
Measurement of mechanical strain on mandibular surface with mastication robot: influence of muscle loading direction and magnitude
Authors: Usui T , Maki K , Toki Y , Shibasaki Y , Takanobu H , Takanishi A , Hatcher D , Miller A
Published: November 2004

Structured Abstract

Authors– Usui T, Maki K, Toki Y, Shibasaki Y, Takanobu H, Takanishi A, Hatcher D, Miller A

Objectives –
To investigate the mechanical effects of mastication on the mandible, we developed computational controlled mastication robot system with human dry skull and analyzed the strain distribution on the mandibular bone surface.

Design –
In the mastication robot, the mandible was suspended by eight wires, which simulated masticatory muscles. A non‐linear spring damper generated viscoelastic properties, and tension sensors for simulation of jaw reflection to avoid unusual biting force were applied as a biological feedback mechanism. By using this robot system, various patterns of muscle loading (change of wire direction and magnitude) were performed.

Results –
From the results, significant differences in the amount of principal strain and its distribution were demonstrated in each condition (ANOVA, post hoc test, and p < 0.05). The value of maximum principal strain ranged from 79.66 × 10−6 [at anterior border of ramus (Buccal side), 128 N] to −1.42 × 10−6 [at foramen mentale (Buccal side), 32 N].

Conclusion –
These results suggested that the muscle loading generated the mechanical strain on the mandibular bone surface and it was affected by the changes in loading direction and magnitude.
Designing multimedia instruction in dentistry: need for sequencing model
Authors: Aly M. , Willems G. , Carels C. , Elen J.
Published: November 2004

When designing any piece of instruction, multimedia or other, the designer must answer two important issues: (i) how the instructional events should be sequenced over time (sequencing); (ii) how the interrelationships among these ideas should be taught to the students (synthesis). Two fundamental levels of instructional design strategies have been identified to provide sequence and synthesis: ‘macro’ and ‘micro’ strategies. Instructional designers use macro strategies to structure a number of different content ideas. Macro strategies are concerned with the organisation of memory. Many of the prescriptions about sequencing are at the macro level. Some of the well‐known sequencing strategies are: spiral curriculum; progressive differentiation; hierarchical sequencing; shortest path sequencing and elaboration sequencing.

When using the multimedia environment as a learning tool, are these four basic macro strategies effective in providing sequence and synthesis of theoretical as well as clinical knowledge for dental students? Or is there a need to create a new clinical macro‐sequencing model for instructional multimedia programs in dentistry?

We concluded that further research is needed on the methods, strategies and models that induce a cognitive process when adopting a computer‐assisted learning approach. A possible approach will be discussed.
Human cobalamin deficiency: alterations in serum tumour necrosis factor‐α and epidermal growth factor
Authors: Peracchi M. , Bamonti Catena F. , Pomati M. , De Franceschi M. , Scalabrino G.
Published: November 2004

Abstract: Objectives:We have previously demonstrated that vitamin B12 (cobalamin)‐deficient central neuropathy in the rat is associated with local overexpression of neurotoxic tumour necrosis factor (TNF)‐α combined with locally decreased synthesis of neurotrophic epidermal growth factor (EGF). The aims of this study were to investigate whether a similar imbalance also occurs in the serum of adult patients with clinically confirmed cobalamin deficiency and whether it can be corrected by vitamin B12 replacement therapy. Patients and methods: We studied 34 adult patients with severe cobalamin deficiency, 12 patients with pure iron deficiency anaemia and 34 control subjects. Haematological markers of cobalamin deficiency and serum TNF‐α and EGF levels were measured using commercial kits. Thirteen cobalamin‐deficient patients were re‐evaluated after 3 and 6 months of parenteral vitamin B12 treatment. Results: TNF‐α was significantly higher (p < 0.01) and EGF significantly lower (p < 0.01) in the patients with cobalamin deficiency, but both were unchanged in patients with pure iron deficiency anaemia. In cobalamin‐deficient patients the serum TNF‐α levels correlated significantly with plasma total homocysteine levels (r = 0.425; p < 0.02). In the treated patients TNF‐α and EGF levels normalised concomitantly with clinical and haematological disease remission. Conclusions: In humans, as in rats, cobalamin concentration appears to be correlated with the synthesis and release of TNF‐α and EGF in a reciprocal manner, because cobalamin deficiency is accompanied by overproduction of TNF‐α and underproduction of EGF.
Reduced hepatic glycogen stores in patients with liver cirrhosis
Authors: Krähenbühl Lukas , Lang Corinne , Lüdes Saskia , Seiler Christian , Schäfer Markus , Zimmermann Arthur , Krähenbühl Stephan
Published: November 2004

Abstract: Background: Patients with alcoholic liver cirrhosis have reduced hepatic glycogen stores but the mechanisms leading to this finding are not clear.

Methods: We therefore determined the hepatic glycogen content in patients with alcoholic (n = 9) or biliary cirrhosis (n = 8), and in control patients undergoing liver surgery (n = 14). All patients were in the postabsorptive state. In addition, we performed a morphometric analysis of the livers, and measured activities and mRNA expression of several enzymes involved in glycogen metabolism. Cirrhotic and control patients were similar regarding age and body weight.

Results: Cirrhotic patients had a reduced glycogen content per gram liver wet weight (17 ± 11 versus 45 ± 17 mg/g, P < 0.05), per milliliter hepatocytes (28 ± 16 versus 52 ± 21 mg/ml, P < 0.05) and per liver (28 ± 17 versus 64 ± 22 g, P < 0.05), the reduction being observed in both patients with alcoholic or biliary cirrhosis. Liver histology confirmed these findings and revealed that the decrease in liver glycogen in cirrhotic patients was not homogenous across cirrhotic lobules. Activities of glycogen synthase and phosphorylase (total activity and active form) were not different between cirrhotic and control patients, whereas hepatic mRNA expression was decreased in cirrhotics by approximately 50%. The activity of glucokinase was decreased in cirrhotic as compared in control patients (0.06 ± 0.30 versus 0.42 ± 0.21 U/ml hepatocytes, P < 0.05), the reduction being observed in both patients with alcoholic or biliary cirrhosis.

Conclusions: We conclude that patients with alcoholic or biliary cirrhosis have decreased hepatic glycogen stores per volume of hepatocytes and per liver. Decreased activity of glucokinase may represent an important mechanism leading to this finding.
Accumulating CD57 + CD3 +  natural killer T cells are related to intrahepatic bile duct lesions in primary biliary cirrhosis
Authors: Harada Kenichi , Isse Kumiko , Tsuneyama Koichi , Ohta Hajime , Nakanuma Yasuni
Published: November 2004

Abstract: Background: Some populations of extrathymic T cells including natural killer T (NKT) cells are involved in autoimmune diseases. In particular, a deficiency of NKT cells has been implicated in human systemic sclerosis. Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by the selective destruction of intrahepatic small bile ducts and the formation of granulomas. It is generally believed that cellular immune mechanisms, particularly T cells, cause the bile duct damage in PBC.

Methods: In this study, to investigate the unique population of extrathymic T cells in PBC, we examined the T cell receptor (TCR) Vα24‐JαQ gene and CD57 + CD3 +  cells corresponding to the major genotype and one of the phenotypes of NKT cells, respectively.

Results: By reverse transcription‐polymerase chain reaction (RT‐PCR), amplicons of the Vα24‐JαQ gene fragment in liver tissues of PBC were found to be similar to those of control diseased livers, demonstrating that there was no distinct deficiency of Vα24‐JαQ +  NKT cells in PBC. Immunohistochemistry for CD57 and CD3 revealed the CD57 + CD3 +  cells to be distributed in portal tracts and hepatic parenchyma in all cases studied, but the numbers of these cells were increased within portal tracts in PBC, in particular around injured interlobular bile ducts, compared to other diseased and normal livers.

Conclusion: This indicates that an immune disturbance induced by a selective reduction of Vα24‐JαQ +  NKT cells is unlikely to occur in PBC. Inversely, it can be postulated that auto aggressive CD57 + CD3 +  NKT cells are recruited to regulate the altered immunity of the periductal microenvironment in PBC.
The molecular physiology of liver regeneration following partial hepatectomy
Authors: Mangnall David , Bird Nigel C , Majeed Ali W.
Published: November 2004

Abstract: The ability of the liver to regenerate after resection has been known for many years. Two reports from Germany in the late 1800s probably mark the introduction of the phenomenon into the scientific literature, but in the early 1900s the first reviews of this subject had appeared in the English literature. Predating these early scientific reports the legends from the Greek mythology described the fate of Prometheus. As punishment for defying Zeus and revealing the secret of fire to man, Prometheus was chained to a rock and each day had part of his liver ripped out by an eagle which, returning the following day, repeated the torture because his liver regenerated itself overnight. Although the speed of regeneration in the Greek legend is somewhat greater than that observed either clinically or in the laboratory, the myth does serve to emphasise the remarkable ability of the liver to repeatedly regenerate following repeated resections. This review aims to summarise the more recent literature concerning the early molecular events accompanying liver regeneration and to integrate this with the existing knowledge of this subject.
Gastrin reverses established cholangiocyte proliferation and enhanced secretin‐stimulated ductal secretion of BDL rats by activation of apoptosis through increased expression of Ca2+‐dependent PKC isoforms
Authors: Glaser Shannon , Alvaro Domenico , Ueno Yoshiyuki , Francis Heather , Marzioni Marco , Phinizy Jo Lynne , Baumann Brandy , Mancino Maria Grazia , Venter Julie , LeSage Gene , Alpini Gianfranco
Published: November 2004

Abstract: We posed these questions: (i) Does administration of gastrin to 1‐week bile duct ligation (BDL) rats inhibits established cholangiocyte proliferation and ductal secretion? (ii) Is gastrin inhibition of cholangiocyte proliferation and secretion of BDL rats associated with enhanced apoptosis? (iii) Are gastrin's effects on cholangiocyte function associated with increased expression of protein kinase C (PKC) isoforms; and (iv) Is gastrin stimulation of cholangiocyte apoptosis regulated by the Ca2+‐dependent PKC pathway?

Methods: Seven days after BDL, rats were treated with gastrin by minipumps for 14 days. Cholangiocyte proliferation was assessed by measurement of the number of PCNA and CK‐19 positive cholangiocytes in sections, and PCNA expression in cholangiocytes. Ductal secretion was determined by measurement of secretin‐induced cAMP levels and choleresis. Apoptosis was evaluated by TUNEL analysis in sections and annexin‐V staining in cholangiocytes. The expression of PKC isoforms was determined by immunoblots.

Results: Gastrin inhibits established cholangiocyte proliferation and enhanced secretin‐stimulated ductal secretion of BDL rats. Gastrin's effects on cholangiocyte function were associated with enhanced apoptosis and increased expression of PKC alpha, and beta I and II. Gastrin increases in cholangiocyte apoptosis were blocked by BAPTA/AM and H7.

Summary/conclusion: Gastrin inhibits cholangiocyte proliferation and secretin‐induced ductal secretion in BDL rats by increasing apoptosis through a PKC‐mediated mechanism.
Predator‐induced life‐history changes and the coexistence of five taxa in a Daphnia species complex
Authors: Spaak Piet , Vanoverbeke Joost , Boersma Maarten
Published: November 2004

Interspecific hybridization is common in water fleas of the Daphnia
galeata species complex (e.g. D. galeata, D. cucullata,
D. hyalina and their interspecific hybrids). We studied the effect
of fish on the life histories of five taxa of this species complex
originating from the Plußsee, northern Germany. Using four clones
per taxon, we found that fish kairomones reduce size at birth and size at
maturity significantly. For size at maturity larger taxa showed a
significantly stronger reaction to fish kairomones than the smaller taxa.
With respect to the intrinsic rate of increase, r, we compared two
predation regimes (positive size selective and not selective). We found
that under the fish predation regime most clones had a higher r
when cultured with fish kairomones, leading to a higher r, and a
stronger reaction for the smaller taxa. We conclude that fish predation
might be an important factor influencing the co‐occurrence of
Daphnia parental taxa with their hybrids.
Flood disturbance, algal productivity, and interannual variation in food chain length
Authors: Marks Jane C. , Power Mary E. , Parker Michael S.
Published: November 2004

The length of a river food chain changed from year to year, shifting with the hydrologic regime. During drought years, grazers suppressed algae across a nutrient gradient, while predators were functionally unimportant. Following flood disturbance, predators suppressed grazers, releasing algae. These results suggest that hydrologic regime, rather than productivity, determines the functional length of this river food chain. Within years, algae and grazer biomass responded to an experimental productivity gradient in patterns predicted by simple trophic models that assume efficient energy transfer. Understanding differences among species within trophic levels, however, was crucial in delineating the controlling interactions.
The route to extinction in variable environments
Authors: Ripa Jörgen , Lundberg Per
Published: November 2004

Estimating the extinction risk of natural populations is not only an urgent problem in conservation biology but also involves some profound aspects of population dynamics. Apart from the obvious case of a continuous decrease in a population's carrying capacity, understanding the extinction process necessarily includes environmental and demographic stochasticity. Here, we build from first principles two stochastic, single‐population models that can account for various routes to extinction via demographic and environmental variability.  The Ricker model of population dynamics generates extinctions from either low or high (around or above carrying capacity) population densities, primarily depending on the growth parameter r. Since extinctions from high densities seem ‘unnatural’, there is either something wrong with the model or with our intuition. Suitable data are scarce.  Environmental variability has its strongest influence on extinction risk via per capita birth rates and is only marginally influencing that risk via per capita death rates if the growth parameter is high. The distribution of the environmental noise and the stochastic structure of the model have quantitative, but not qualitative effects on the estimates of extinction risks.  We conclude that to determine the route to extinction and to estimate the extinction risk require a careful choice of both the deterministic component of the population model (e.g., under‐ or over‐compensation) and the structure of the demographic and environmental variabilities.
Sequence effects of disturbance on community structure
Authors: Fukami Tadashi
Published: November 2004

The sequence in which disturbance events occur has the potential to affect the structure of ecological communities, but its role has been generally overlooked. Most disturbance studies have focused on the frequency or intensity of disturbance, probably reflecting the influence of the intermediate disturbance hypothesis. To investigate the effects of disturbance sequence on community structure, I created laboratory microcosms of protists and small metazoans analogous to communities found in water‐filled bamboo stumps. Using drought (disturbance D) and larval mosquito addition (disturbance M), I examined the following five treatments of disturbance sequence: D‐M‐D‐M, D‐D‐M‐M, M‐D‐M‐D, M‐M‐D‐D, and no disturbance as a control. The response of species to disturbance varied between disturbance types (D or M) as well as among species, and disturbance effects depended on previous disturbance events. As a result, disturbance sequence drove the microcosms onto different successional trajectories, sometimes leading to divergence in final community states in terms of species richness or species composition and relative abundance. This divergence occurred even under the same frequency and intensity of disturbance. These results suggest that historical information on disturbance sequence can be essential for explaining variation in community structure. The interaction of sequence with frequency and intensity likely enhances the role played by disturbance in ecological communities.
Downward adjustment of carbon fluxes at the biochemical, leaf, and ecosystem scale in beech‐spruce model communities exposed to long‐term atmospheric CO2 enrichment
Authors: Egli Philipp , Maurer Stefan , Spinnler Dieter , Landolt Werner , Günthardt‐Goerg Madeleine S. , Körner Christian
Published: November 2004

Young beech (Fagus sylvatica) and spruce (Picea abies) trees from different provenances or genotypes were grown in competition in large model ecosystems and were exposed to two concentrations of atmospheric CO2 (370 vs 570 μmol mol−1), two levels of wet nitrogen deposition (7 vs 70 kg N ha−1 yr−1), and two native forest soils (acidic vs calcareous) for four years in open‐top chambers. The 2×2×2 factorial experimental design was fully replicated (n=4) with each CO2×N combination applied to each soil type. Exposure to atmospheric CO2 enrichment stimulated daytime net ecosystem CO2 flux (NEC) as measured during sunny days in the middle of the third growing season. Nevertheless, we observed substantial down‐regulation of NEC, with larger adjustments on acidic than on calcareous soil. NEC adjustment was associated with slightly reduced leaf area index (LAI) on the acidic soil (no response on calcareous soil), enhanced soil CO2 efflux from both substrate types, and, most importantly, with down‐regulation of CO2 uptake at the leaf scale. Downward adjustment of light‐saturated single‐leaf photosynthesis (A) and of Rubisco was more pronounced in beech than in spruce and these species‐specific differences increased over time. By year four, A adjustment (except in one specific treatment combination in each species) had become complete in beech but had disappeared in spruce. At no time did we observe a genotype or provenance effect on the downward adjustment of carbon fluxes, and nitrogen deposition rate generally had little effect as well. Overall, our results suggest that tree species and soil quality will have profound effects on ecosystem CO2 fluxes under continued atmospheric CO2 enrichment.
Productivity and complementarity in grassland microcosms of varying diversity
Authors: Dukes Jeffrey S.
Published: November 2004

Several researchers have hypothesized that, through various mechanisms, loss of species and functional group richness from a plant community will affect the magnitude and interannual variability of productivity. To test this hypothesis, I conducted a microcosm study of California grassland communities that differed in species richness. I grew cohorts of microcosms that simulated undisturbed grassland (in one year) and gopher‐disturbed grassland (in two consecutive years). As the number of species per functional group decreased from 4 to 1, biomass production remained constant in all three cohorts. As species richness decreased from 16 to 1 (or 8 to 1, in either case including a drop in functional group richness), productivity declined in one of the cohorts. In this cohort, productivity of one polyculture marginally exceeded that of the most productive monoculture. Resource complementarity and a type of selection effect may have each contributed to the observed diversity‐productivity relationships. Results suggest the existence of a selection effect that involves species that are highly productive in mixtures, rather than in monoculture. Over two seasons, species and functional group richness did not affect the interannual variability of biomass production. Comparisons of interannual changes in the productivity of monocultures and polycultures suggested that, in some polycultures, increased water availability might have relieved interspecific competition more than intraspecific competition. Based on results from this experiment and other manipulative experiments, I develop a framework to explain the relationship between species richness and productivity in terrestrial plant communities. The framework highlights the importance of environmental variation in shaping the diversity/productivity relationship.
Plants as resource mosaics: a functional model for predicting patterns of within‐plant resource heterogeneity to consumers based on vascular architecture and local environmental variability
Authors: Orians Colin M. , Jones Clive G.
Published: November 2004

Plant characteristics that determine food quantity and quality to consumers exhibit extensive within‐plant heterogeneity, and this heterogeneity is an important influence on the interactions between plants and consumers (herbivores, pathogens, mutualists, soil‐dwelling microorganisms). Here we present a functional model – based on plant vascular architecture and local environmental variability – that can be used to predict the patterns of within‐plant resource heterogeneity. We argue that heterogeneity is generated largely by sectoriality, the restricted movement of resources along vascular traces within a plant. In essence, the combination of sectoriality and spatial variation in previous damage, nutrient, water, and light availability generates predictable patterns of within‐plant heterogeneity in tissue quality. We point out that vascular architecture differs across taxa, growth habit and plant developmental stage, and suggest that certain attributes of the environment maximize the extent of heterogeneity.
Of mice and mallards: positive indirect effects of coexisting prey on waterfowl nest success
Authors: Ackerman Joshua T.
Published: November 2004

Coexisting prey species interact indirectly via their shared predators when one prey type influences predation rates of the second prey type. In a temperate system where the predominant shared predator is a generalist, I studied the indirect effects of rodent populations on waterfowl nest success, both within the nesting season among sites and among years. Among six to ten upland fields (14 to 27 ha), mallard (Anas platyrhynchos) nest success was positively correlated with rodent abundance in all three years of the study. After removing year effects, mallard nest success remained positively correlated with the relative abundance of rodents. Of the rodent species present, California voles (Microtus californicus) were the most important coexisting prey type influencing nest success. Among years, mallard nest success was positively correlated with vole abundance; the asymptotic relationship suggests a threshold response to vole abundance, beyond which predators become satiated and additional voles do little to affect nest success. I tested and rejected three alternative explanations for the observed positive correlation between mallard nest success and rodent abundance that do not involve an indirect effect of coexisting prey populations. The influences of dense nesting cover, nesting density, and predator activity did not explain the observed patterns of nest success. These results suggest that rodent populations buffer predation on waterfowl nests, both within and among years, via the behavioral responses of shared predators to coexisting prey.
Spatial and temporal dynamics of turtle nest predation: edge effects
Authors: Kolbe Jason J. , Janzen Fredric J.
Published: November 2004

We determined the effect of distance from ecological edges, both wooded and water edges, on nest predation for 862 painted turtle, Chrysemys picta, nests from 1995 to 1999 at an ∼1.5 ha study site. In three of five years and overall, nests closer to the water edge had a higher probability of predation; and in one year nests closer to the wooded edge had a higher probability of predation. Although more turtles nested closer to the water edge as the nesting season progressed in some years and overall, this behavior does not explain the observed patterns of nest predation. We present a novel application of the cubic spline analysis to address the dynamics of predation across continuous distances from an edge and identify threshold values where the predation rate levels off. Threshold values of ∼25–40 m were detected in 1995, 1998, and with all five years combined. However, even though a significant edge effect was detected in 1997, a threshold was not clear. While an edge effect on predation was not detected in each year, this study provides evidence for a strong effect of distance from the water edge on nest predation over significant ecological time. Focusing on turtle nest predation and smaller spatial scales addresses previous taxonomic and spatial bias in edge effects research, and provides further support for the ecological importance of edge effects.
Gene diversity and demographic turnover in central and peripheral populations of the perennial herbGypsophila fastigiata
Authors: Lönn Mikael , Prentice Honor C.
Published: November 2004

Within‐population gene diversity (HS) was estimated (using allozyme markers) for 16 populations of the perennial, outcrossing plant,Gypsophila fastigiata, on the Baltic island of Öland. The populations were characterized by data on extent, density, life‐stages, and habitat diversity. Populations were classed as central or peripheral in relation to the distribution of “alvar” (habitats with shallow, calcareous soils on limestone bedrock) on southern Öland. Three minimal adequate models were used to explain HSand the proportions of juveniles and dead adults. In the first model, HSwas significantly lower in peripheral populations and there were no significant additional effects of other explanatory variables. The lower diversity in peripheral populations can be explained by a combination of genetic drift (in populations that vary in size in response to habitat fragmentation) and lower levels of interpopulation gene flow than in central populations. In the two life‐stage models, peripheral populations had significantly larger proportions of both juveniles and dead adults – indicating a greater demographic turnover than in the central populations. There were also significant effects of HSand species diversity on the proportion of juveniles. The central or peripheral position of populations is the strongest predictor of both within‐population gene diversity and life‐stage dynamics in ÖlandG. fastigiata.
Post‐fledging survival of individual great tits: the effect of hatching date and fledging mass
Authors: Monrós Juan S. , Belda Eduardo J. , Barba Emilio
Published: November 2004

Pre‐breeeding survival is one of the major sources of individual variation in lifetime reproductive success. However, very little is known about the reasons for differences in survival among individuals during this important phase of the life cycle. Some studies, using local return rates as indices of survival, have shown a relationship between post‐fledging survival and fledging date and mass in birds, most of them suggesting directional selection towards heavy masses and early fledging dates. Recent development of capture‐recapture models allows the separate estimate of survival and recapture probabilities, as well as the inclusion of individual covariates into the modelling process. We used here these models to explore the relative effects of fledging date and fledging mass on local recruitment of individual great tit Parus major fledglings. Individual capture‐recapture histories of 2051 fledglings (cohorts 1992–1999), 184 of which were recaptured as breeding birds during 1993–2000, were used in the analyses. Hatching date, offspring mass at day 15, their squared terms, and interactions between mass and date, were included as covariates into the modelling process. Models with age (fledglings and adults) and time (year) dependence were used. The probability of local recruitment increased with fledging mass in each of the years studied. Fledging date also affected recruitment but, against what is commonly thought, fledgling early is not the best option every year. Either early, intermediate or late fledglings were favoured in different years. This between‐year variation in the optimum fledging date offers an alternative explanation to the lack of evolution towards earlier breeding dates, in spite of the advantages of early breeding some years.
The summer decline of the collared lemming,Dicrostonyx groenlandicus,in high arctic Greenland
Authors: Gilg Olivier
Published: November 2004

I studied the population structure and dynamics of the collared lemming,Dicrostonyx groenlandicusTraill, on Traill Island (NE Greenland) in 1998 to 2000. This is the first comprehensive study of a Greenlandic collared lemming population. During this period, population density continuously declined (>100 fold‐decrease) from more than 10 ind/ha (peak year 1998) to less than 0.1 ind/ha (low year 2000), with the exception of one period of increase in the winter 1998–99. Several population parameters were correlated with these changes in density. Average body mass was greater in the peak year than in the intermediate year (1999) and greater in August than in July in both years. Growth rates were only positive in 1998 and only for young lemmings. Females had unexpectedly larger home ranges than males and were more mobile than males during the decline phase (1999). Poor recruitment and high predation rates (up to 3.4% per day for females in 1998) were the proximate causes of the summer declines in the study area. A simple calculation shows that even with a maximal rate of increase, this lemming population would not have been able to compensate for the high predation rate, and hence it necessarily faced a predation‐induced summer decline during the part of population oscillation studied.
Effect of local and regional processes on plant species richness in tallgrass prairie
Authors: Collins Scott L. , Glenn Susan M. , Briggs John M.
Published: November 2004

Historically, diversity in a community was often believed to result primarily from local processes, but recent evidence suggests that regional diversity may strongly influence local diversity as well. We used experimental and observational vegetation data from Konza Prairie, Kansas, USA, to determine if: (1) there is a relationship between local and regional richness in tallgrass prairie vegetation; (2) local dominance reduces local species richness; and (3) reducing local dominance increases local and regional species richness. We found a positive relationship between regional and local richness; however, this relationship varied with grazing, topography and fire frequency. The decline in variance explained in the grazed vegetation, in particular, suggested that local processes associated with grazing pressure on the dominant grasses strongly influenced local species richness. Experimental removal of one of the dominant grasses,Andropogon scoparius, from replicate plots resulted in a significant increase in local species richness compared to adjacent reference plots. Overall all sites, species richness was higher in grazed (192 spp.) compared to ungrazed (158 spp.) areas. Across the Konza Prairie landscape, however, there were no significant differences in the frequency distribution of species occurrences, or in the relationship between the number of sites occupied and average abundance in grazed compared to ungrazed areas. Thus, local processes strongly influenced local richness in this tallgrass prairie, but local processes did not produce different landscape‐scale patterns in species distribution and abundance. Because richness was enhanced at all spatial scales by reducing the abundance of dominant species, we suggest that species richness in tallgrass prairie results from feedbacks between, and interactions among, processes operating at multiple scales in space and time.
Renal Effects of Supernatant from Macrophages Activated by Crotalus durissus cascavella Venom: The Role of Phospholipase A2 and Cyclooxygenase
Authors: Martins Alice M. C. , Lima Aldo A. M. , Toyama Marcos H. , Marangoni Sergio , Fonteles Manassés C. , Monteiro Helena S. A.
Published: November 2004

Abstract: In Brazil, the genus Crotalus is responsible for approximately 1500 cases of snakebite annually. The most common complication in the lethal cases is acute renal failure, although the mechanisms of the damaging effects are not totally understood. In this work, we have examined the renal effects caused by a supernatant of macrophages stimulated by Crotalus durissus cascavella venom as well as the potential role of phospholipase A2 and cyclo‐oxygenase. Rat peritoneal macrophages were collected and placed in a RPMI medium and stimulated by crude Crotalus durissus cascavella venom (1, 3 or 10 μg/ml) for 1 hr. They were then washed and kept in a culture for 2 hr. The supernatant (1 ml) was tested in an isolated perfused rat kidney. The first 30 min. of each experiment were used as an internal control, and the supernatant was added to the system after this period. All experiments lasted 120 min. A study of toxic effect on perfusion pressure, glomerular filtration rate, urinary flow, percent of sodium tubular transport and percent of proximal tubular sodium transport was made. The lowest concentration of venom (1 μg/ml) was not statistically different from the control values. The most intense effects were seen at 10 μg/ml for all renal parameters. The infusion of the supernatant of macrophages stimulated with crude venom (3 or 10 μg/ml) increased the perfusion pressure, glomerular filtration rate and urinary flow, decreased the percent of sodium tubular transport and percent of proximal tubular sodium transport. Dexamethasone (10 μM) and quinacrine (10 μM) provided protection against the effect of the venom on glomerular filtration rate, urinary flow, percent of sodium tubular transport, percent of proximal tubular sodium transport and perfusion pressure. Indomethacin (10 μM) and nordiidroguaretic acid (1 μM) reversed almost all functional changes, except those of the perfusion pressure. These results suggest that macrophages stimulated with Crotalus durissus cascavella venom release mediators capable of promoting nephrotoxicity in vitro. Moreover, phospholipase A2 and cyclooxygenase products are involved in these biologic effects.