bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observational and simulated evidence of ecological shifts within the soil nematode community of agroecosystems under conventional and organic farming
Authors: Mulder CH. , Zwart D. DE , Van Wijnen H. J. , Schouten A. J. , Breure A. M. 
Published: August 2003

SummarySoil sustainability implies a sufficient diversity and abundance of organisms to perform soil functions and to resist environmental stress. Previous studies have shown the importance of functional biodiversity for soil organisms.Soil samples have been collected within the framework of a long‐term monitoring programme in the Netherlands. Nematological and microbiological techniques were combined to facilitate a more comprehensive understanding of possible below‐ground effects of land management.A possible bias due to stochastic circumstances was investigated. The Mantel test showed that the diversity at species level is largely related to air temperature, but at genus level the effect of temperature disappears. No direct influence of rainfall on the soil biodiversity was found in our model.To extrapolate our data to a national level, habitat–response relationships for soil organisms have been derived. Generalized linear models (GLMs) and Monte Carlo simulation allowed the estimation of the probability of occurrence at a given abundance for 95 nematode genera.Our study describes the influence of abiotic conditions and land use intensity on the composition of nematode communities in grasslands on sand. The results obtained reveal a major influence of pH and livestock density on the diversity of the nematode community at both taxonomic levels as well as at different trophic levels (feeding habits). The presence and abundance of soil nematodes decrease with cattle pressure.Functional diversity decreases with increasing management intensity. It is shown that the Shannon diversities of bacterial feeding nematodes and fungal feeding nematodes are strictly related to cattle pressure, whereas the bacterial biomass occurring under organic farming scores higher than in other farming systems.
Locomotor speeds of gravid lizards: placing ‘costs of reproduction’ within an ecological context
Authors: Shine R. 
Published: August 2003

Summary

Mathematical models suggest that ‘costs of reproduction’ (decrements in an organism's probable future reproductive output due to investing in current reproduction) are major determinants of life‐history evolution.
Pregnancy decreases locomotor performance in many taxa, and could render reproducing females more vulnerable to predators. To evaluate the importance of this ‘cost of reproduction’, however, we need to know the magnitude of performance decrement induced by reproduction relative to that induced by other factors in the animal's biology.
Studies on adult female skinks (Lampropholis guichenoti) confirm that pregnancy significantly impairs maternal locomotion, but also show that factors such as a moderate decrease in body temperature, a large meal or loss of the tail reduced locomotor speeds even more than did pregnancy. Thus, reproductive state probably causes only a minor proportion of the total temporal variation in a female skink's locomotor ability.
In such a system, even a large effect of pregnancy on running speeds may not impose a significant selective pressure on reproductive investment.
Climate and foraging modes may affect the degree to which locomotor speeds are influenced by pregnancy vs. other factors, offering a potential explanation for the lower overall reproductive investment per clutch in tropical vs. temperate‐zone reptiles, and in lizards vs. snakes.
Nutrient resorption from senescing leaves of the clonal plant Linnaea borealis in relation to reproductive state and resource availability
Authors: Niva M. , Svensson B. M. , Karlsson P. S. 
Published: August 2003

Summary

We tested the hypotheses that (i) reproductive ramets of Linnaea borealis L. (Caprifoliaceae) compensate for reproductive investments by enhanced resorption of nitrogen (N) and phosphorus (P) from leaves before abscission, and that (ii) resorption is decreased by increased soil nutrient availability. We also investigated (iii) the significance of resorption for ramet growth and nutrient pool sizes.
Leaves from reproductive, post‐reproductive and non‐reproductive ramets were used to investigate compensatory resorption of N and P. To study resorption responses to increased nutrient availability, slow‐release fertilizer was applied and differences between defoliated and shaded ramets were noted.
No compensation for reproductive investments via resorption from senescing leaves was detected. Resorption efficiency increased with increased nutrient availability for N, but showed no response for P. No effect of experimentally denied resorption was seen.
We propose that extensive physiological integration within clonal fragments of L. borealis buffers resource alterations in ramets associated with reproduction, fertilization and prevented resorption.
Our results show that the performance of a ramet of a physiologically well integrated plant is not governed by local conditions – ramets can exceed patch nutrient availability without reduced growth and nutrient status.
The effects of spatially heterogeneous nutrient supply on yield, intensity of competition and root placement patterns in Briza media and Festuca ovina
Authors: Day Kieron J. , John Elizabeth A. , Hutchings Michael J. 
Published: August 2003

Summary

An experiment was carried out to determine whether the spatial pattern of soil nutrient distribution influences plant growth and root placement, and the intensity of competition between plants. Our hypotheses were that (i) growth would be greater for plants in heterogeneous than homogeneous conditions (ii) competitive intensity would be greater when nutrients were confined to a small proportion of the substrate volume than when uniformly distributed, and (iii) plants would selectively place roots in nutrient‐rich patches in heterogeneous conditions.
We grew plants of Briza media and Festuca ovina alone, or with an intra or interspecific competitor, in pots in which the same total supply of nutrients was distributed either homogeneously or heterogeneously. Nutrients in the heterogeneous treatment were confined to three soil cores occupying only 6·5% of the substrate volume.
Pattern of nutrient supply did not affect yield of plants grown alone. However, the reduction in target plant yield caused by competition was much greater in heterogeneous than homogeneous conditions (i.e. competitive intensity was greater in heterogeneous conditions).
Plants growing in heterogeneous conditions placed roots preferentially in the nutrient‐rich substrate patches. This may have been the cause of greater competitive intensity in heterogeneous conditions. It is speculated that soil‐based heterogeneity might exert an important influence on community structure and composition through its effects on competition.
Allocation of above‐ground growth is related to light in temperate deciduous saplings
Authors: King D. A. 
Published: August 2003

SummaryAllocational shifts in response to light may be an important factor in allowing plants to survive in shade, while increasing their extension rates and competitive ability in sun. To investigate this response, the allocation of above‐ground growth between leaves, branches and stems was studied in saplings ofAcer pensylvanicumL. andCastenea dentata(Marsh.) Borkh. in the Appalachian mountains of western Virginia, USA. Measurements of current leaf biomass, current and past year leaf numbers and the growth ring widths of branches and stem were used to estimate biomass partitioning for saplings growing in locations ranging from forest understorey to large openings.Both species showed higher leaf area per unit leaf biomass (SLA) and higher allocation of above‐ground growth to leaves in shade than in sun.There were no differences between species in the slopes of the relationships of allocation and SLAvsestimated irradiance, but SLA was significantly greater inA. pensylvanicumthan inC. dentataat a given light level. Hence, somewhat lower production per unit leaf area is required to maintain the canopy inA. pensylvanicum, consistent with foresters’ ratings of greater shade tolerance for this species.Greater foliar allocation in shade than sun has also been observed in broad‐leaved evergreen saplings, but generally not in seedlings. This difference is probably related to differences in size and age between seedlings and saplings. Young seedlings typically show exponential growth with no immediate foliar losses, while shaded saplings lie closer to the steady state where new leaves replace old ones with little additional stem growth.Thus trees shift their allocation patterns in an acclimatory fashion, depending on their size and light environment, with the costs of replacing senesced leaves becoming of consequence as juveniles age.
Leaf attributes in the seasonally dry tropics: a comparison of four habitats in northern Australia
Authors: Prior L. D. , Eamus D. , Bowman D. M. J. S. 
Published: August 2003

Summary

Patterns of leaf attributes were compared at regional and global scales in relation to the seasonal availability of water.
Light‐saturated assimilation rate (Amass), leaf mass per area (LMA), leaf density, thickness, life span, saturated water content, chlorophyll, nitrogen and phosphorus content were determined during the wet season for 21 tree species in four contrasting habitats in northern Australia. Rainfall in this area is extremely seasonal.
A
mass and foliar chlorophyll, N and P contents were positively correlated with each other, and were all negatively correlated with LMA, leaf thickness, density and life span.
Deciduous species had smaller LMA and leaf life span, and larger foliar N and P contents than did evergreen species.
The eight Myrtaceous species had smaller Amass, foliar chlorophyll, N and P contents, and larger LMA, leaf thickness and leaf life span than did the non‐Myrtaceous species.
Leaves from the closed canopy dry monsoon forest had significantly larger Amass, chlorophyll and P contents than did leaves from the three open canopy habitats (eucalypt open forest, mixed woodland and Melaleuca swamp). This reflected the relatively low proportions of evergreen and Myrtaceous species in the dry monsoon forest. There were also significant intraspecific differences among habitats.
Leaf thickness, density and LMA were lower than predicted from globally derived relationships with temperature and precipitation. Tropical seasonally dry biomes are under‐represented in such global analyses.
Condition dependence of pheromones and immune function in the grain beetle Tenebrio molitor
Authors: Rantala Markus J. , Kortet Raine , Kotiaho Janne S. , Vainikka Anssi , Suhonen Jukka 
Published: August 2003

Summary

Pheromones are chemical signals that function not only as mate attractors, but may also relay important information to prospective mates. In order for the information to be reliable, the signal must be costly to produce and this is likely to result in condition dependent expression of the signal.
We present results from two experiments on the grain beetle Tenebrio molitor examining phenotypic condition dependence of pheromones and patterns of female preference for pheromones. We also analysed condition dependence of two measures of immunocompetence: encapsulation response and phenoloxidase activity.
By manipulating the nutritional condition of the males we found that the attractiveness of the male pheromones to virgin females was condition‐dependent, indicating that the production of the pheromones is affected by the condition of the male. We also found that the phenoloxidase activity of the males was affected by the nutritional condition of the male but that encapsulation rate was not.
Our results show that pheromones are condition‐dependent signals, the quantity of which females use in their mate choice.
How feather colour reflects its carotenoid content
Authors: Saks Lauri , McGraw Kevin , Hõrak Peeter 
Published: August 2003

Summary

Many birds sequester carotenoid pigments in colourful patches of feathers to advertise or compete for mates. Because carotenoids can be scarce in nature and serve valuable physiological functions, only the highest‐quality individuals are thought to acquire or allocate more pigments for use in sexual displays.
A critical but rarely tested assumption of carotenoid‐based signals is that the colour of pigmented feather patches directly reveals the total amount of carotenoids contained within them.
We studied the relationship between carotenoid‐based coloration (hue, chroma and brightness) and the pigment content of tail feathers in wild‐caught and captive male greenfinches (Carduelis chloris[Linnaeus]). Greenfinches incorporate two main carotenoids − canary xanthophylls A and B − into feathers to develop yellow patches of colour in their tail.
Variation in feather carotenoid content explained 32–51% of variation in chroma and hue of the yellow parts of tail feathers, while feather brightness was not significantly related to carotenoid concentration. Hence, chroma and hue appear good candidates to indicate feather carotenoid content.
Birds with the most colourful feathers deposited significantly more of both canary xanthophylls into plumage. Thus, there does not appear to be a specific biochemical strategy for becoming colourful in greenfinches; males instead follow the general decision rule to deposit as many xanthophylls as possible into feathers to become yellow.
Leaf life span differs from retention time of biomass and nutrients in the crowns of evergreen species
Authors: Mediavilla S. , Escudero A. 
Published: August 2003

Summary

A long leaf life span has been interpreted as an adaptation to low nutrient availability. It is commonly assumed that a long leaf life span permits a longer utilization of nutrients in the leaf biomass and that this contributes to improving nutrient use efficiency. However, a long leaf life span is also associated with other leaf traits that reduce instantaneous productivity, which might reduce the growth rate of the leaf biomass and shorten the functional life of the leaf.
We studied the relationships between leaf life span and the retention time of biomass and nutrient pools in several woody species with different leaf life spans. We measured the monthly variations in the total number of leaves per annual shoot, mass per leaf, and N and P contents per leaf. With these data, the leaf life span and the mean residence time (MRT) of leaf biomass and nutrient pools were estimated.
The increase in the total number of leaves was fast in all species studied at the start of the growth season. In contrast, in evergreen species mass per leaf and total N and P contents per leaf increased gradually after the first year of life of the leaves, and the maximum mass and nutrient contents per leaf were attained only towards the end of the lifetime of the leaves.
Owing to the delay in the development of mass and nutrient pools with respect to leaf number dynamics, in evergreen species leaf life span was longer than the MRT of leaf biomass and nutrient pools because part of the leaf biomass and nutrient pool remained in the crown for a shorter time than the mean duration of the individual leaves.
The differences between leaf life span and the MRT of the biomass and nutrients increased with leaf life span. The slow growth of evergreen leaves therefore contributes to reduce the adaptive value of a long leaf life span as a mechanism to increase the duration of the photosynthetic machinery.
Exogenous jasmonic acid mimics herbivore‐induced systemic increase in cell wall bound peroxidase activity and reduction in leaf expansion
Authors: Moore Jason P. , Paul Nigel D. , Whittaker John B. , Taylor Jane E. 
Published: August 2003

Summary

Jasmonic acid (JA), a ubiquitous regulator of the wound response in plants, is part of a long distance defence signalling pathway and when applied exogenously induces several defence related responses in many species including the activation of proteinase inhibitor (PIN) proteins and defence‐related metabolites.
There is evidence for an induced systemic resistance mechanism linking increased cell wall peroxidase activity with reductions in leaf expansion rates in Rumex obtusifolius, following limited grazing by the chrysomelid beetle Gastrophysa viridula. We hypothesised that herbivory induces strengthening of cell walls in distal, non‐damaged tissue through increases in peroxidase activity and that this mechanism was mediated systemically by JA.
JA was applied to the fully expanded fourth leaf of R. obtusifolius and expansion of leaf 8 was measured over 19 days. Treatment with exogenous JA induced a temporary reduction in the expansion rate of leaf 8 beginning 6 days after treatment. This reduction continued until day 7 and reduced final leaf areas in treated plants by approximately 20%.
Final epidermal cell areas in leaf 8 were reduced by approximately 25%, while epidermal cell numbers remained unchanged.
Cell wall bound peroxidase activity was measured in leaf 8 over a 6‐day period following application of JA to leaf 4. Activity increased approximately 9‐fold 2 days after treatment, before returning to control activities on day 3.
Treatment of leaf 4 with JA reduced the gregariousness of G. viridula larvae on the fully expanded leaf 8.
We postulate that JA acts as a signalling molecule in a long‐distance pathway responsible for inducing resistance to future attack through increases in cell wall bound peroxidase activity leading to cell wall toughening, while incurring a potential ecological cost in the form of reductions in subsequent leaf expansion.
Interpretation of tests for nut allergy in one thousand patients, in relation to allergy or tolerance
Authors: Clark A. T. , Ewan P. W. 
Published: August 2003

SummaryBackground Peanut and tree nut allergy are common, increasing in prevalence and the commonest food cause of anaphylaxis. In the USA, 7.8% are sensitized (have nut‐specific IgE), but not all those sensitized are allergic. Lack of data makes interpretation of tests for nut‐specific IgE difficult.Objectives This is the first study to investigate the clinical significance of test results for peanut and tree nut allergy in allergic or tolerant patients. Findings are related to the severity of the allergy.Method An observational study of 1000 children and adults allergic to at least one nut. History of reactions (severity graded) or tolerance to up to five nuts was obtained and skin prick test (SPT)/serum‐specific IgE (CAP) performed.Results There was no correlation between SPT size and graded severity of worst reaction for all nuts combined or for peanut, hazelnut, almond and walnut. For CAP, there was no correlation for all nuts. Where patients tolerated a nut, 43% had positive SPT of 3–7 mm and 3% ≥ 8 mm. For CAP, 35% were positive (0.35–14.99 kU/L) and 5% ≥ 15 kU/L. In SPT range 3–7 mm, 54% were allergic and 46% were tolerant. There was poor concordance between SPT and CAP (66%). Of patients with a clear nut‐allergic history, only 0.5% had negative SPT, but 22% negative CAP.Conclusions Magnitude of SPT or CAP does not predict clinical severity, with no difference between minor urticaria and anaphylaxis. SPT is more reliable than CAP in confirming allergy. Forty‐six per cent of those tolerant to a nut have positive tests ≥ 3 mm (sensitized but not allergic). One cannot predict clinical reactivity from results in a wide ‘grey area’ of SPT 3–7 mm; 22% of negative CAPs are falsely reassuring and 40% of positive CAPs are misleading. This emphasizes the importance of the history. Understanding this is essential for accurate diagnosis. Patients with SPT ≥ 8 mm and CAP ≥ 15 kU/L were rarely tolerant so these levels are almost always (in ≥ 95%) diagnostic.
Sleep Loss Reduces Diurnal Rhythm Amplitude of Leptin in Healthy Men
Authors: Mullington J. M. , Chan J. L. , Van Dongen H. P. A. , Szuba M. P. , Samaras J. , Price N. J. , Meier‐Ewert H. K. , Dinges D. F. , Mantzoros C. S. 
Published: August 2003

AbstractThe aim of the current study was to investigate the effects of sleep loss on the diurnal rhythm of circulating leptin levels. An indwelling forearm catheter was used to sample blood at 90‐min intervals for a total of 120 h, which included 88 h of sustained sleeplessness, in 10 healthy men. The diurnal amplitude of leptin was reduced during total sleep deprivation and returned toward normal during the period of recovery sleep. This finding provides evidence that sleep influences the nocturnal leptin profile, and may have implications for the understanding of the role of sleep in metabolic regulation and the aetiologies of obesity and the night eating syndrome.
Immunocytochemical Detection of Progesterone Receptor in the Female Rabbit Forebrain: Distribution and Regulation By Oestradiol and Progesterone
Authors: Caba M. , Rovirosa M. J. , Beyer C. , González‐Mariscal G. 
Published: August 2003

AbstractThere is no information on the neuroanatomical distribution of the progesterone receptor (PR) in the rabbit. Therefore, we mapped the distribution of PR‐immunoreactive cells in the forebrain of ovariectomized female rabbits. Vehicle‐injected ovariectomized rabbits showed PR‐immunoreactive cells only in the infundibular nucleus (IN) and nucleus X (lateral to the ventromedial hypothalamic nucleus). The injection of oestradiol benzoate (EB; 5 µg/day for 5 days) increased the number of PR‐immunoreactive cells in the IN and in three nuclei of the preoptic region (periventricular, medial, and principal). Abundant PR were also found in the paraventricular nucleus and nucleus X. Administration of progesterone (10 mg/day) for 3 days to EB‐treated rabbits (a treatment that induces digging behaviour for the maternal nest and suppresses sexual receptivity and scent‐marking) eliminated PR‐immunoreactivity from all brain areas analysed except the IN. Thus, one‐third of the number of cells seen in the ovariectomized + EB condition persisted in this region despite progesterone injections. Withdrawal of progesterone (and continuation of EB) for 5 (but not for 2) days (in a schedule similar to the one that induces straw‐carrying and hair‐pulling for the maternal nest) increased the number of PR‐immunoreactive cells in all regions analysed. These results show that restricted regions of the female rabbit forebrain express abundant PR which are either: (i) up‐regulated by oestradiol and down‐regulated by progesterone; (ii) oestradiol‐insensitive and down‐regulated by progesterone; or (iii) insensitive to both oestradiol and progesterone.