bluuebunny/crossref_metadata_2025 huggingface dataset:
Population size and the risk of local extinction: empirical evidence from rare plants
Authors: Matthies Diethart , Bräuer Ingo , Maibom Wiebke , Tscharntke Teja
Published: May 2004

Due to habitat fragmentation many plant species today occur mainly in small and isolated populations. Modeling studies predict that small populations will be threatened more strongly by stochastic processes than large populations, but there is little empirical evidence to support this prediction for plants. We studied the relationship between size of local populations (number of flowering plants) and survival over ten years for 359 populations of eight short‐lived, threatened plants in northern Germany (Lepidiumcampestre,Thlaspiperfoliatum,Rhinanthusminor,R.serotinus,Melampyrumarvense,M.nemorosum,GentianellaciliataandG.germanica). Overall, 27% of the populations became extinct during the study period. Probability of survival of a local population increased significantly with its size in all but one species (R. minor). However, estimated population sizes required for 90% probability of survival over 10 years varied widely among species. Survival probability increased with decreasing distance to the nearest conspecific population inR.serotinus, but not in the other species. The mean annual growth rate of surviving populations differed greatly between species, but was only forG.germanicasignificantly lower than 1, suggesting that there was no general deterministic decline in the number of plants due to deteriorating habitat conditions. We conclude that the extinction of populations was at least partly due to stochastic processes. This is supported by the fact that in all species a considerable proportion of small populations survived and developed into large populations.
Asymmetric competition between Rana clamitans and Hyla versicolor tadpoles
Authors: Smith Geoffrey R. , Dingfelder Haley A. , Vaala David A.
Published: May 2004

When two organisms interact over a potentially limiting resource, several outcomes are possible (e.g. neither affected, both equally affected, one affected more than the other). The outcome depends on a variety of factors, both internal and external to the organism. We performed a laboratory experiment to investigate the outcome of potential competitive interactions between tadpoles of the green frog (Rana clamitans) and the gray treefrog (Hyla versicolor), and to examine the factors that may explain the outcome of the interaction. We found that competition between these two species was asymmetric. Hylaversicolor tadpoles were more affected by intraspecific competition than interspecific competition (i.e. grew faster when grown with heterospecifics than conspecifics); whereas, R. clamitans tadpoles were more affected by interspecific competition than intraspecific competition (i.e. grew faster when grown with conspecifics than heterospecifics). Based on behavioral observations, this result could not be explained on the basis of activity levels, a trait previously linked to competitive ability in tadpoles. However, differences in initial body size may help explain the observed results; the gray treefrog tadpoles were larger than the green frog tadpoles.
Intraclonal variation in defence substances and palatability: a study on Carex and lemmings
Authors: Anne Bråthen Kari , Agrell Jep , Berteaux Dominique , Jónsdóttir Ingibjörg S.
Published: May 2004

Clonal sedges consist of integrated ramets at different development stages. Many of these sedges are important food for herbivores, yet differences in herbivore preferences and defence allocation between ramet development stages have not previously been evaluated. In this study we investigated intraclonal ramet variation in level of plant defence and nutrient compounds and intraclonal ramet preferences by lemmings (Lemmus trimucronatus) in field samples of a rhizomatous sedge (Carex stans). Plant defence was measured as the level of proteinase inhibitor activity (PIA) and the ratio of PIA to soluble plant proteins (SPP), whereas plant nutrients were measured as the level of soluble plant sugars (SPS) and SPP. Flowering ramets generally had a higher content of defence compared to vegetative ramets, which is consistent with the optimal defence theory predicting that defence compounds are allocated to the ramet stage of the highest fitness value. Compared to vegetative ramets, the flowering ramets had a lower content of SPP and a higher content of SPS. The lemmings showed preference differences between the ramet development stages, and to a large extent the ramet content of defence compounds and nutrient compounds covaried with these preferences in the predicted way. This study shows that defence allocation between ramet development stages of the clonal sedge Carex conforms to predictions of the optimal defence theory.
Inducible defences and the paradox of enrichment
Authors: Vos Matthijs , Kooi Bob W. , DeAngelis Donald L. , Mooij Wolf M.
Published: May 2004

In order to evaluate the effects of inducible defences on community stability and persistence, we analyzed models of bitrophic and tritrophic food chains that incorporate consumer‐induced polymorphisms. These models predict that intra‐specific heterogeneity in defence levels resolves the paradox of enrichment for a range of top‐down effects that affect consumer death rates and for all possible levels of primary productivity. We show analytically that this stability can be understood in terms of differences in handling times on the different prey types. Our predictions still hold when defences also affect consumer attack rates. The predicted stability occurs in both bitrophic and tritrophic food chains.

Inducible defences may promote population persistence in tritrophic food chains. Here the minimum densities of cycling populations remain bound away from zero, thus decreasing the risk of population extinctions. However, the reverse can be true for the equivalent bitrophic predator–prey model. This shows that theoretical extrapolations from simple to complex communities should be made with caution. Our results show that inducible defences are among the ecological factors that promote stability in multitrophic communities.
Environmental determinants of recruitment and their influence on the population dynamics of stream‐living brown troutSalmo trutta
Authors: Lobón‐Cerviá Javier , Rincón Pedro A.
Published: May 2004

The relative importance of endogenous feedback mechanism vs environmental factors in the dynamics of animal populations is a long‐standing, but not fully resolved yet, issue in ecology. We have addressed this subject by examining the dynamics of a stream‐resident population ofSalmo truttain a northwestern Spain stream. Recruitment was the major determinant of population size and the abundance of recruits resulted from a combination of regional and local environmental factors. Stream discharge in March determined the amount of stream area suitable for newly emerged trout (r2=0.59–0.79%), that in turn determined the abundance of recruits at each site (r2=0.51–0.77%). Stream discharge determines the overall strength of annual recruitment. Discharge, however, combines with stream morphology at the site scale to result in a site‐specific area suitable for juveniles and, hence, site‐specific recruitment. Thus, our study exemplifies how an environmentally driven animal population may persist on time with little or no operation of endogenous regulatory mechanisms.
Escaping the Bonferroni iron claw in ecological studies
Authors: García Luis V.
Published: May 2004

I analyze some criticisms made about the application of alpha‐inflation correction procedures to repeated‐test tables in ecological studies. Common pitfalls during application, the statistical properties of many ecological datasets, and the strong control of the tablewise error rate made by the widely used sequential Bonferroni procedures, seem to be responsible for some ‘illogical’ results when such corrections are applied. Sharpened Bonferroni‐type procedures may alleviate the decrease in power associated to standard methods as the number of tests increases.

More powerful methods, based on controlling the false discovery rate (FDR), deserve a more frequent use in ecological studies, especially in those involving large repeated‐test tables in which several or many individual null hypotheses have been rejected, and the most significant p‐value is relatively large.

I conclude that some reasonable control of alpha inflation is required of authors as a safeguard against striking, but spurious findings, which may strongly affect the credibility of ecological research.
Senescence and hyperspectral reflectance of cotton leaves exposed to ultraviolet‐B radiation and carbon dioxide
Authors: Kakani Vijaya Gopal , Reddy Kambham Raja , Zhao Duli , Gao Wei
Published: May 2004

The objectives of this study were to determine the effects of UV‐B radiation and atmospheric carbon dioxide concentrations ([CO2]) on leaf senescence of cotton by measuring leaf photosynthesis and chlorophyll content and to identify changes in leaf hyperspectral reflectance occurring due to senescence and UV‐B radiation. Plants were grown in controlled‐environment growth chambers at two [CO2] (360 and 720 µmol mol−1) and three levels of UV‐B radiation (0, 7.7 and 15.1 kJ m−2 day−1). Photosynthesis, chlorophyll, carotenoids and phenolic compounds along with leaf hyperspectral reflectance were measured on three leaves aged 12, 21 and 30 days in each of the treatments. No interaction was detected between [CO2] and UV‐B for any of the measured parameters. Significant interactions were observed between UV‐B and leaf age for photosynthesis and stomatal conductance. Elevated [CO2] enhanced leaf photosynthesis by 32%. On exposure to 0, 7.7 and 15.1 kJ of UV‐B, the photosynthetic rates of 30‐day‐old leaves compared with 12‐day‐old leaves were reduced by 52, 76 and 86%, respectively. Chlorophyll pigments were not affected by leaf age at UV‐B radiation of 0 and 7.7 kJ, but UV‐B of 15.1 kJ reduced the chlorophylls by 20, 60 and 80% in 12, 21 and 30‐day‐old leaves, respectively. The hyperspectral reflectance between 726 and 1142 nm showed interaction for UV‐B radiation and leaf age. In cotton, leaf photosynthesis can be used as an indicator of leaf senescence, as it is more sensitive than photosynthetic pigments on exposure to UV‐B radiation. This study revealed that, cotton leaves senesced early on exposure to UV‐B radiation as indicated by leaf photosynthesis, and leaf hyperspectral reflectance can be used to detect changes caused by UV‐B and leaf ageing.
The constant proportion of grana and stroma lamellae in plant chloroplasts
Authors: Albertsson Per‐Åke , Andreasson Eva
Published: May 2004

The relative proportion of stroma lamellae and grana end membranes was determined from electron micrographs of 58 chloroplasts from 21 different plant species. The percentage of grana end membranes varied between 1 and 21% of the total thylakoid membrane indicating a large variation in the size of grana stacks. By contrast the stroma lamellae account for 20.3 ± 2.5 (sd)% of the total thylakoid membrane. A plot of percentage stroma lamellae against percentage of grana end membranes fits a straight line with a slope of zero showing that the proportion of stroma lamellae is independent of the size of the grana stacks. That stroma lamellae account for about 20% of the thylakoid membrane is in agreement with fragmentation and separation analysis (Gadjieva et al.Biochim. Biophys. Acta 144: 92–100, 1999). Chloroplasts from spinach, grown under high or low light, were fragmented by sonication and separated by countercurrent distribution into two vesicle populations originating from grana and stroma lamellae plus end membranes, respectively. The separation diagrams were very similar lending independent support for the notion that the proportion of stroma lamellae is constant. The results are discussed in relation to the composition and function of the chloroplast in plants grown under different environmental conditions, and in relation to a recent quantitative model for the thylakoid (Albertsson, Trends Plant Sci. 6: 349–354, 2001).
Promotion of 5‐aminolevulinic acid on photosynthesis of melon (Cucumis melo) seedlings under low light and chilling stress conditions
Authors: Wang Liang Ju , Jiang Wei Bing , Huang Bao Jian
Published: May 2004

When melon seedlings (Cucumis melo L. Ximiya No. 1) were cultured in a growth chamber with about 150 µmol m−2 s−1 photon flux density, the leaf photosynthetic ability reduced dramatically as leaf position decreased from the top. The application of 5‐aminolevulinic acid (ALA) solutions significantly increased the net photosynthetic rate (Pn) as well as apparent quantum yield (AQY), carboxylation efficiency (CE) and stomata conductance (Gs). After irrigation with 10 ml of ALA solution (10 mg l−1 or 100 mg l−1) per container filled with approximately 250 g clean sand for 3 days, the leaf Pn was about 40–200% higher than that of controls, and AQY, CE and Gs increased 21–271%, 55–210% and 60–335%, respectively. Furthermore, ALA treatments increased leaf chlorophyll content and soluble sugar levels, as well as the rate of dark respiration, but decreased the rate of respiration under light. On the other hand, after melon seedlings that had been cultured in the chamber suffered chilling at 8°C for 4 h and then recovered at 25–30°C for 2 and 20 h, the Pn of the water‐irrigated plants was only 12–18% and 37–47%, respectively, compared with the initial Pn before chilling treatment. If the seedlings underwent the same treatment but with ALA (10 mg l−1), the respective Pn was 22–38% and 76–101%, compared with that of the control before chilling stress. If chilling was prolonged for 6 h, the ALA‐pre‐treated plants only showed a few symptoms in the leaf margins whereas all water‐irrigated plants died, which suggested that ALA presumably promoted chilling tolerance of the plants under low light.
Bud endophytes of Scots pine produce adenine derivatives and other compounds that affect morphology and mitigate browning of callus cultures
Authors: Pirttilä Anna Maria , Joensuu Päivi , Pospiech Helmut , Jalonen Jorma , Hohtola Anja
Published: May 2004

Endophytes are found in meristematic bud tissues of Scots pine (Pinus sylvestris L.) especially prior to growth, which would suggest their involvement in growth of the bud. To test this hypothesis, production of phytohormones by two bacterial (Methylobacterium extorquens, Pseudomonas synxantha) and one fungal endophyte (Rhodotorula minuta) was studied by mass spectrometry. The most common gibberellins, auxins, or cytokinins were not detected in the fractions studied. Instead, M. extorquens and R. minuta produced adenine derivatives that may be used as precursors in cytokinin biosynthesis. A plant tissue culture medium was conditioned with the endophytes, and pine tissue cultures were started on the media. Tetracycline inhibited callus production, which was restored on the endophyte‐conditioned media. In addition, conditioning mitigated browning of the Scots pine explants. However, a decrease in tissue size was observed on the endophyte‐conditioned media. Addition of adenosine monophosphate in the plant culture medium restored callus production and increased growth of the tissues, but had no effect on browning. Therefore, production of adenine ribosides by endophytes may play some role in the morphological effect observed in the pine tissues.
Role of abscisic acid in perianth senescence of daffodil (Narcissus pseudonarcissus“Dutch Master”)
Authors: Hunter Donald Alexander , Ferrante Antonio , Vernieri Paolo , Reid Michael Stuart
Published: May 2004

Daffodil (Narcissus pseudonarcissus L. ‘Dutch Master’) flowers detached at the base of their ovaries and held with their cut ends in 10–100 μM abscisic acid (ABA) senesced prematurely. Symptoms of the ABA treatment included water‐soaking of the tepals and early collapse of the corona. No water‐soaking was seen in tepals of flowers held in water. Instead, the tepals of these flowers dried. The ABA content increased in tepals of the potted flowers as they senesced. The rise in tepal ABA content coincided with the appearance of visual signs of senescence. When the flowers were cut and placed in water, a treatment that accelerated their senescence, the increase in ABA occurred earlier. Exogenously applied ABA enhanced the premature accumulation of senescence‐associated transcripts in the tepals. Their ABA‐mediated induction was not prevented when the flowers were pre‐treated with 1‐methylcyclopropene, an inhibitor of ethylene action, indicating that ABA induced the transcripts independently of ethylene. The transcripts accumulated in opened control flowers before the rise in endogenous ABA. Attempts to extend floral longevity by using putative inhibitors of ABA biosynthesis [tungstate, fluridone (applied as Sonar®) and 1,1‐dimethyl‐4‐(phenylsulphonyl)semicarbazide (DPSS)] were unsuccessful. However, inclusion of 100 μM gibberellic acid (GA3) in the vase solution reduced the senescence‐inducing effects of 50 μM ABA suggesting a possible mechanism for in‐vivo control of senescence.
What causes the decrease in haematocrit during egg production?
Authors: WILLIAMS T. D. , CHALLENGER W. O. , CHRISTIANS J. K. , EVANSON M. , LOVE O. , VEZINA F.
Published: May 2004

Anaemia has been reported in wild animals, typically associated with traumatic events or ill health. However, female birds routinely become ‘anaemic’ during egg‐laying; we sought to determine the causes of this reduction in haematocrit.

Haematocrit in female European Starlings (Sturnus vulgaris Linnaeus) decreased between pre‐breeding and egg‐laying in 3 out of 4 years (the decrease was marginally non‐significant in the fourth year). This was independent of changes in ambient temperature altering the metabolic requirements for thermoregulation.

There was a positive relationship between haematocrit and plasma levels of the yolk precursor vitellogenin among egg‐laying birds, supporting the hypothesis that the initial reduction in haematocrit is caused by increased blood volume associated with osmoregulatory adjustments to elevated levels of yolk precursors.

However, haematocrit did not always recover upon cessation of egg production, remaining low at clutch completion (2 of 4 years), incubation (1 of 2 years) and chick rearing (1 of 4 years), suggesting an additional cause of the prolonged reduction in haematocrit.

Given the magnitude and prolonged nature of the changes in haematocrit we report, and the interannual variation in haematocrit even during chick‐rearing (47–54%), we suggest that ‘anaemia’ associated with egg production might have implications for aerobic performance during later stages of breeding.
Morphological plasticity of shade‐tolerant tropical rainforest tree seedlings exposed to light changes
Authors: BLOOR J. M. G. , GRUBB P. J.
Published: May 2004

Previous studies on tropical rainforest seedlings have demonstrated low physiological plasticity in shade‐tolerant species in response to light, but little is known about the morphological plasticity of such species. We examined morphological traits in seedlings of 10 shade‐tolerant tropical rainforest tree species grown in four combinations of high and low light (10 and 0·8% full daylight, respectively). Plasticity of each trait was quantified using coefficients of variation.

Plant traits varied in their plasticity, and could broadly be ranked as follows: stem form > crown traits > root form > leaf form > biomass allocation. Acclimation to an increase in light was generally greater than acclimation to a decrease in light, but crown traits showed significant changes in the high–low treatment.

The ranking of species according to plasticity varied depending on the trait examined. Mean plasticity across all light treatments showed no relationship with either dry mass or relative growth rate of dry mass (RGRM) across species. However, plasticity in stem mass fraction (fraction of stem to total dry mass) was negatively correlated with low‐light RGRM across species.

Principal components analysis indicated clustering of species depending on trait plasticity. These results suggest different strategies of light response among shade‐tolerant tropical tree seedlings.
An ecological evaluation of Eagleson's optimality hypotheses
Authors: KERKHOFF A. J. , MARTENS S. N. , MILNE B. T.
Published: May 2004

The pioneering work of Peter Eagleson has been proposed as a theoretical basis for ecohydrology. Central to the theory are three ‘ecological optimality hypotheses’ which represent ecologically important aspects of atmosphere–soil–vegetation interactions.

The model and its underlying assumptions have never been evaluated in an explicitly ecological context. We examine each of the three optimality hypotheses in turn and test the ability of the model to make ecologically relevant predictions using climate, soil and vegetation data from a semi‐arid woodland site in central New Mexico, USA.

We find that all three of the optimality hypotheses are ecologically flawed. While we could qualitatively reproduce previously published results, model behaviour under novel conditions was highly variable and frequently unrealistic.

The poor performance of the model was probably due to the inadequate treatment of water‐limited transpiration in its original derivation. The theory thus requires redevelopment for ecological application, and we suggest several strands of research that could contribute to its improvement.
Plant palatability can be inferred from a single‐date feeding trial
Authors: ELGER A. , BARRAT‐SEGRETAIN M. H.
Published: May 2004

Most studies of plant palatability do not consider its seasonal variability, and infer general life‐history patterns from single‐date feeding experiments. This paper investigates whether different seasonal patterns in the palatability of perennial plant species in one community can alter their relative susceptibility to grazing.

The palatability of eight freshwater macrophyte species growing at the same site was monitored during 1 year through nine consecutive feeding experiments using a generalist consumer, the pond snail Lymnaea stagnalis.

Plant palatability varied significantly throughout the year, and reached its maximum in autumn. Beyond this general trend, seasonal patterns in palatability differed markedly between species, and two (Callitriche platycarpa and Nuphar lutea) showed no significant seasonal variations.

Despite the interspecific differences in seasonal patterns of palatability, species’ palatability rankings remained stable throughout the year. Therefore feeding experiments performed at a single sampling date are suitable to assess the relative palatability of a set of species.
Spatial interactions between the hemiparasitic angiosperm Rhinanthus minor and its host are species‐specific
Authors: KEITH A. M. , CAMERON D. D. , SEEL W. E.
Published: May 2004

Effects of organisms that obtain resources from others (e.g. herbivores) can depend on the location of resource removal with respect to their ‘prey’. We investigated whether such an effect can be seen in hemiparasitic plant–host plant interactions.

We conducted rhizotron studies of the interactions between Rhinanthus minor and individuals of two common host species, Festuca rubra and Festuca ovina. Parasites were grown at two distances from the host, and growth characteristics of hosts and parasites measured over time.

Parasites close to their host suffered reduced survival as a result of shading. Without shading these parasites attached earlier, produced more haustoria, grew larger and had a greater fecundity than those planted further away. This effect was significant for parasites infecting the fast‐growing F. rubra, but not for parasites infecting the less vigorous F. ovina. Effect of parasite position on host biomass was significant only for F. rubra, which showed a greater reduction when infected by more proximal parasites.

Differences in the response of hosts to infection, and parasite growth, suggest the effect of the position of R. minor is host‐species specific.
The functional significance of synchronous protandry in Alstroemeria aurea
Authors: HARDER L. D. , AIZEN M. A.
Published: May 2004

Synchronous dichogamy, the simultaneous change in sex phases of all flowers in an inflorescence or entire plant, has been proposed to reduce self‐pollination between flowers within a plant (geitonogamy) and so should leave more pollen for export and/or reduce inbreeding. We tested these hypotheses with Alstroemeria aurea Graham, a self‐compatible, clonal herb with synchronous protandrous inflorescences.

We manipulated A. aurea inflorescences to compare pollen export, pollen receipt and pollen‐tube attrition in synchronous and asynchronous inflorescences. We constructed asynchronous inflorescences by tying together female‐ and male‐phase ramets which were collected within 1 m of each other and so had a high probability of being genetically related.

Inflorescences with both male‐ and female‐phase flowers received 27% more pollen than synchronous inflorescences, which was associated with higher pollen‐tube attrition. The selfing suggested by these results would reduce genetic contributions to the next generation as a result of the strong inbreeding depression found in this species.

In contrast, we found no evidence that asynchronous inflorescences exported less pollen to companion female‐phase inflorescences than did synchronous inflorescences.

Our results suggest that synchronous dichogamy evolves primarily as an anti‐selfing mechanism, rather than to promote outcross siring success.
Regulation of development time and hatch synchronization in Black Brant (Branta bernicla nigricans)
Authors: NICOLAI C. A. , S. SEDINGER J. , WEGE M. L.
Published: May 2004

Eggs of precocial bird clutches hatch more synchronously than they are laid. The widely accepted hypothesis to explain hatching synchrony has been that vocalizations from earlier laid embryos accelerate development of later laid embryos. The relationship between position in the laying sequence (hereafter PILS) and time to hatching was investigated in Black Brant (Branta bernicla nigricans L.; hereafter brant). Factors associated with variation in incubation duration were also examined.

Experimental clutches comprising eggs laid on the same day from the same PILS were assembled to eliminate the effects of earlier laid eggs on those laid later. This experiment allowed us to examine developmental time in clutches without the effects of interactions between eggs laid earlier in the sequence and those laid later. In a separate experiment, clutches were manipulated so that the full complement of laying sequences was maintained in each clutch, but each egg originated from a different female. This experiment allowed us to separate the influences of genetic‐maternal effects from the influence of nest environment and incubation behaviour. Developmental time was also monitored in a set of clutches that were unmanipulated.

Metabolic rates of eggs from each PILS were measured at mid‐incubation and the day before hatch for both experimental and control nests. By measuring metabolic rates, it was possible to examine changes in metabolic rates of embryos as hatch approaches, which may be another mechanism to synchronize hatch.

No difference was detected in incubation period between control and manipulated clutches. There was a steady decline in incubation period from first to last laid eggs independent of the clutch type. Fifth laid eggs required >3 days less to hatch than those laid first. These data suggest that sounds produced by brood mates and/or female incubation patterns are not the principal mechanisms for hatching synchrony. Both genetic and host mothers influenced overall developmental time, indicating that genetic‐maternal effects and incubation behaviour and nest environment also influenced developmental time.

Embryonic metabolic rate was negatively correlated with number of days before hatch, but there was not a positive relationship between PILS and metabolic rate. Our findings show that embryonic metabolic rate may affect development more than vocalizations between brood members in synchronizing hatch.
Within‐brood size differences, sex and parasites determine blood stress protein levels in Eurasian Kestrel nestlings
Authors: MARTÍNEZ‐PADILLA J. , MARTÍNEZ J. , DÁVILA J. A. , MERINO S. , MORENO J. , MILLÁN J.
Published: May 2004

Brood hierarchies established through hatching asynchrony are supposed to be costly for small chicks because of impaired growth and survival. An additional cost that has remained unexplored is the stress imposed by competition for resources in the nest.

In the present study of broods of Eurasian kestrels, we have used the level of heat shock proteins such as Hsp60 and Hsp70 in peripheral blood as well as the heterophile/lymphocyte ratio to detect stress in nestlings. The sex of nestlings and theirCaryosporasp. oocyst excretion were included in analyses.

Nestlings showing a large size difference with respect to their largest sibling had higher levels of both stress proteins, and this effect was stronger for female chicks as indicated by a significant interaction sex × size difference, presumably because of their higher food requirements for growth. Nestlings for which the largest sibling was a female had higher levels of Hsp60 than when it was a male. The heterophile/lymphocyte index was a much poorer predictor of competitive stress.

Stress proteins are effective estimators of competitive, nutritional and parasite‐mediated stress of nestlings in the wild. The cost of sustained stress has to be included in future analyses of the fitness repercussions of dominance hierarchies in avian broods.
Ethical Issues in Dialysis: Institutionalized Racism and End‐Stage Renal Disease: Is Its Impact Real or Illusionary?
Authors: Spital Aaron , Callender Clive O. , Miles Patrice V.
Published: May 2004

Racism is the subjugation of one group (superior) over another (inferior) and may be divided into two categories: overt (gross) and covert. Covert racism (subconscious) is categorized as institutionalized racism. Although institutionalized racism is a more tolerant and restrained practice of this superior/inferior ethnic construct in which African Americans or other people of color are treated as inferiors, it has led to important health disparities between blacks and whites. One area where its mark is most indelible is in the treatment of end‐stage renal disease (ESRD).
Reviews: Residual Renal Function: Considerations on Its Importance and Preservation in Dialysis Patients
Authors: Chandna Shahid M. , Farrington Ken
Published: May 2004

Residual renal function (RRF) remains important even after commencement of dialysis. Its role in the adequacy of peritoneal dialysis (PD) is well recognized and is increasingly utilized in incremental PD regimes, but it is also vitally important in hemodialysis (HD) patients, in whom it, as in PD patients, may improve survival. It may allow for a reduction in the duration of HD sessions. It reduces the need for dietary and fluid restrictions in both PD and HD patients. Other contributions include improved middle molecule clearance, better hemoglobin, phosphate, potassium, and urate levels, enhanced nutritional status and quality of life scores, and better outcomes in pregnancy. On the negative side, hypoalbuminemia may be prolonged in patients with persistent nephrotic‐range proteinuria. Contrary to popular belief, RRF does not necessarily decline rapidly with the initiation of HD. PD may be better than HD in preserving RRF, although this difference may not persist if biocompatible membranes, bicarbonate buffer, and ultrapure water are used. Nocturnal ambulatory peritoneal dialysis (APD) patients may fare worse than continuous ambulatory peritoneal dialysis (CAPD) patients. RRF can be adversely affected by angiotensin‐converting enzyme (ACE) inhibitors, nonsteroidal anti‐inflammatory drugs (NSAIDs), aminoglycosides, and radiocontrast agents. Diuretics can help maintain fluid balance but not RRF.
The Consequences of Uncontrolled Secondary Hyperparathyroidism and Its Treatment in Chronic Kidney Disease
Authors: Goodman William G.
Published: May 2004

Secondary hyperparathyroidism (HPT) is a common complication of chronic kidney disease (CKD) and a frequent cause of clinically significant bone disease. Soft‐tissue and vascular calcification, cardiovascular disease, and calcific uremic arteriolopathy (CUA) are additional serious consequences of the disorder that may contribute directly to cardiovascular morbidity and mortality in patients with CKD. Less widely appreciated manifestations include neurological disturbances, hematological abnormalities, and endocrine dysfunction.

 Secondary HPT arises from alterations in calcium, phosphorus, and vitamin D metabolism that develop early in the course of CKD and become more pronounced as kidney function declines. Treatment is often delayed, however, until the disease is well established. Current therapeutic strategies rely largely on the use of vitamin D sterols to diminish excess parathyroid hormone (PTH) synthesis and to lower serum or plasma PTH levels, but their use is often confounded by increases in serum calcium and phosphorus concentrations, changes that can aggravate soft‐tissue and vascular calcification. As such, there is a need for new therapeutic interventions that can effectively lower serum or plasma PTH levels without producing untoward side effects.

 The current review summarizes the diverse manifestations of secondary HPT in patients with CKD. The consequences of inadequately controlled secondary HPT and the adverse effects of selected therapeutic interventions for the disorder on vascular calcification and cardiovascular disease in those with CKD are discussed.
Seed dispersal and seedling establishment of Rhus trichocarpa promoted by a crow (Corvus macrorhynchos) on a volcano in Japan
Authors: Nishi Hideo , Tsuyuzaki Shiro
Published: May 2004

The interaction between frugivorous birds and trees producing bird‐dispersed seeds in devastated areas has been considered to be weak, owing to the paucity of avifauna and/or food resources for birds. Here, we present evidence that strong interactions between birds and plants may promote the enlargement of tree distribution on harsh environments. The summit of Mount Koma, northern Japan, was denuded by the 1929 volcanic eruption. Vegetation cover gradually decreases from the bottom (secondary forest) to the top (bareground) of the mountain. We recorded 48 bird species in the four seasons of 2001, along a 5‐km line transect on the southwestern slope of the mountain. Birds faeces collected along the transect contained seeds of more than 14 plant taxa. Five of the 14 taxa were bird‐dispersal tree species (Rhus trichocarpa, Sorbus commixta, Prunus ssiori, Prunus maximowiczii and Prunus sargentii) and were established in the summit area. Most faeces were derived from Corvus spp. (mostly C. macrorhynchos) and Turdus naumanni. In particular, the seeds of R. trichocarpa were found mostly from the faeces of Corvus spp. and the seeds of Gaultheria miqueriana, a shrub species, were only from T. naumanni. Rhus trichocarpa retained fruits on the canopy at all times of the year, and crows could feed on them even when food resources were poor in winter. Rhus trichocarpa seedlings established well near rock at higher elevation, while they occurred mostly under the larch canopy of larches at lower elevation. Crows mostly utilized tree canopies and rocks as perches in respective habitats. Therefore, seedlings should be abundant in specific habitats at different elevations. Size‐class distribution of seedlings suggested that seedling mortality was lower at higher elevation where open sites were more abundant. These findings indicate that strong mutual advantages for C. macrorhynchos and R. trichocarpa on denuded areas play an important role on revegetation.
Evaluating alternative data sets for ecological niche models of birds in the Andes
Authors: Parra Juan L. , Graham Catherine C. , Freile Juan F.
Published: May 2004

Ecological niche modeling (ENM) is an effective tool for providing innovative insights to questions in evolution, ecology and conservation. As environmental datasets accumulate, modelers need to evaluate the relative merit of different types of data for ENM. We used three alternative environmental data sets: climatic data, remote‐sensing data (Normalized Difference Vegetation Index), and elevation data, to model the distribution of six bird species of the genus Grallaria in the Ecuadorian Andes. We assessed the performance of models created with each environmental data set and all possible combinations by comparing the geographic predictions of our models with detailed maps developed by expert ornithologists. Results varied depending on the specific measure of performance. Models including climate variables performed relatively well across most measures, whereas models using only NDVI performed poorly. Elevation based models were relatively good at predicting most sites of expected occurrence but showed a high over‐prediction error. Combinations of data sets usually increased the performance of the models, but not significantly. Our results highlight the importance of including climatic variables in ENM and the simultaneous use of various data sets when possible. This strategy attenuates the effects of specific variables that decrease model performance. Remote‐sensing data, such as NDVI, should be used with caution in topographically complex regions with heavy cloud‐cover. Nonetheless, remote‐sensing data have the potential to improve ENM. Finally, we suggest a priori designation of modeling purposes to define specific performance measures accordingly.
Potential impact of climatic change on the distribution of forest herbs in Europe
Authors: Skov Flemming , Svenning Jens‐Christian
Published: May 2004

The aim of this study is to evaluate the possible consequences of climate change on a representative sample of forest herbs in Europe. A fuzzy climatic envelope was used to predict the location of suitable climatic conditions under two climatic change scenarios. Expected consequences in terms of lost and gained range size and shift in distribution for 26 forest herbs were estimated. These results were combined in an Index of Predicted Range Change for each species. Finally, the effects of habitat fragmentation for potential dispersal routes were evaluated and options for management on a European scale are discussed.

Generally, a good agreement of the estimated suitability under the present climate and the observed current distribution was observed. However, species vary a lot in the degree to which they occupy the presently climatically suitable areas in Europe. Many species are absent from large areas with suitable climate and thus could be said to have poor range‐filling capacity.

A general change in location (range centroid) of the total suitable area was observed: The total suitable area will on average move strongly northwards and moderately eastwards under the relatively mild B1 scenario and more strongly so under the A2 scenario. The required average minimum migration rate per year to track the potential range shift is 2.1 km under the B1 scenario and 3.9 km under the A2 scenario.

Moderate losses in the total suitable area in Europe are predicted for most species under both scenarios. However, the predicted changes are very variable, with one species (Actaea erythrocarpa) experiencing total range elimination in Europe (A2 scenario) while the total suitable area is predicted to show large increases for other species. The species that are predicted to experience the greatest proportional losses in their climatically suitable area within their presently realised range tend to have northern or eastern range centroids.

The Index of Predicted Range Change roughly divides the species studied in four groups: One species face a high risk of extinction; eight species are expected to experience moderate to severe threat of extinction; 11 species are not considered at risk and, finally, six species may actually benefit from global warming.

An analysis of potential migration routes shows the importance of maintaining and, if possible, improving the network of forest throughout Europe to make migration possible. It is also suggested to closely monitor the status of boreal and subalpine species that are most threatened by global warming. Finally it is recommended that special concern should be given to increased protection and restoration of forest habitats in southern montane areas for their crucial long‐term importance for the maintenance of European plant diversity.
Intersensory Redundancy Guides the Development of Selective Attention, Perception, and Cognition in Infancy
Authors: Bahrick Lorraine E. , Lickliter Robert , Flom Ross
Published: May 2004

That the senses provide overlapping information for objects and events is no extravagance of nature. This overlap facilitates attention to critical aspects of sensory stimulation, those that are redundantly specified, and attenuates attention to nonredundantly specified stimulus properties. This selective attention is most pronounced in infancy and gives initial advantage to the perceptual processing of, learning of, and memory for stimulus properties that are redundant, or amodal (e.g., synchrony, rhythm, and intensity), at the expense of modality-specific properties (e.g., color, pitch, and timbre) that can be perceived through only one sense. We review evidence supporting this hypothesis and discuss its implications for theories of perceptual, cognitive, and social development.
Depression
Authors: Jacobs Barry L.
Published: May 2004

The theory of clinical depression presented here integrates etiological factors, changes in specific structural and cellular substrates, ensuing symptomatology, and treatment and prevention. According to this theory, important etiological factors, such as stress, can suppress the production of new neurons in the adult human brain, thereby precipitating or maintaining a depressive episode. Most current treatments for depression are known to elevate brain serotonin neurotransmission, and such increases in serotonin have been shown to significantly augment the ongoing rate of neurogenesis, providing the neural substrate for new cognitions to be formed, and thereby facilitating recovery from the depressive episode. This theory also points to treatments that augment neurogenesis as new therapeutic opportunities.
Emerging Perspectives on Distinctions Between Romantic Love and Sexual Desire
Authors: Diamond Lisa M.
Published: May 2004

Although sexual desire and romantic love are often experienced in concert, they are fundamentally distinct subjective experiences with distinct neurobiological substrates. The basis for these distinctions is the evolutionary origin of each type of experience. The processes underlying sexual desire evolved in the context of sexual mating, whereas the processes underlying romantic love—or pair bonding—originally evolved in the context of infant-caregiver attachment. Consequently, not only can humans experience these feelings separately, but an individual's sexual predisposition for the same sex, the other sex, or both sexes may not circumscribe his or her capacity to fall in love with partners of either gender. Also, the role of oxytocin in both love and desire may contribute to the widely observed phenomenon that women report experiencing greater interconnections between love and desire than do men. Because most research on the neurobiological substrates of sexual desire and affectional bonding has been conducted with animals, a key priority for future research is systematic investigation of the coordinated biological, behavioral, cognitive, and emotional processes that shape experiences of love and desire in humans.
Siblings' Direct and Indirect Contributions to Child Development
Authors: Brody Gene H.
Published: May 2004

Since the early 1980s, a growing body of research has described the contributions of sibling relationships to child and adolescent development. Interactions with older siblings promote young children's language and cognitive development, their understanding of other people's emotions and perspectives, and, conversely, their development of antisocial behavior. Studies address the ways in which parents' experiences with older children contribute to their rearing of younger children, which in turn contributes to the younger children's development. Finally, by virtue of having a sibling, children may receive differential treatment from their parents. Under some conditions, differential treatment is associated with emotional and behavioral problems in children.
Molecular interactions of fission yeast Skp1 and its role in the DNA damage checkpoint
Authors: Lehmann Anna , Katayama Satoshi , Harrison Clare , Dhut Susheela , Kitamura Kenji , McDonald Neil , Toda Takashi
Published: May 2004

Skp1 is a central component of the E3 ubiquitin ligase SCF (Skp1‐Cullin‐1‐F‐box). It forms an adapter bridge between Cullin‐1 and the substrate‐determining component, the F‐box protein. In order to establish the role of Skp1, a temperature sensitive (ts) screen was carried out using mutagenic PCR (polymerase chain reaction) and 9 independent ts mutants were isolated. Mapping the mutated residues on the 3‐D structure of human Skp1 suggested that the mutants would be compromised in binding to F‐box proteins but not Cullin‐1 (Pcu1). In order to assess the binding properties of ts Skp1, 12 F‐box proteins and Pcu1 were epitope‐tagged, and co‐immunoprecipitation performed. This systematic analysis showed that ts Skp1 retains binding to Pcu1. However, binding to three specific F‐box proteins, essential Pof1, Pof3 involved in maintaining genome integrity, and nonessential Pof10, was reduced. skp1ts cells exhibit a G2 cell cycle delay, which is attributable to activation of the DNA damage checkpoint. Intriguingly, contrary to pof3 mutants, in which this checkpoint is required for survival, checkpoint abrogation in skp1ts suppresses a G2 delay and furthermore almost rescues the ts phenotype. The activation mechanism of the DNA damage checkpoint therefore differs between pof3Δ and skp1ts, implicating a novel role for Skp1 in the checkpoint‐signalling cascade.
A molecular mechanism for autoinhibition of the tandem SH3 domains of p47phox, the regulatory subunit of the phagocyte NADPH oxidase
Authors: Yuzawa Satoru , Suzuki Nobuo N. , Fujioka Yuko , Ogura Kenji , Sumimoto Hideki , Inagaki Fuyuhiko
Published: May 2004

The phagocyte NADPH oxidase is a multisubunit enzyme responsible for the production of reactive oxygen species. p47phox is a cytosolic component of the NADPH oxidase and plays an important role in the assembly of the activated complex. The structural determination of the tandem SH3 domains of p47phox is crucial for elucidation of the molecular mechanism of the activation of p47phox. We determined the X‐ray crystal structure of the tandem SH3 domains with the polybasic/autoinhibitory region (PBR/AIR) of p47phox. The GAPPR sequence involved in PBR/AIR forms a left‐handed polyproline type‐II helix (PPII) and interacts with the conserved SH3 binding surfaces of the SH3 domains simultaneously. These SH3 domains are related by a 2‐fold pseudosymmetry axis at the centre of the binding groove and interact with the single PPII helix formed by the GAPPR sequence with opposite orientation. In addition, a number of intra‐molecular interactions among the SH3 domains, PBR/AIR and the linker tightly hold the architecture of the tandem SH3 domains into the compact structure and stabilize the autoinhibited form synergistically. Phosphorylation of the serine residues in PBR/AIR could destabilize and successively release the intra‐molecular interactions. Thus, the overall structure could be rearranged from the autoinhibitory conformation to the active conformation and the PPII ligand binding surfaces on the SH3 domains are now unmasked, which enables their interaction with the target sequence in p22phox.