bluuebunny/crossref_metadata_2025_split huggingface dataset:
A combined radiographic and computerized scanning method to evaluate remaining dentine thickness in mandibular incisors after various intracanal procedures
Authors: Katz A. , Tamse A. 
Published: September 2003

AbstractAim  To develop a computerized model to evaluate remaining dentine thickness after various intracanal procedures.Methodology  A three‐step model was developed, in which injection of radiopaque solution into the root‐canal space of 20 extracted mandibular incisors, exposure of periapical radiographs from two directions, and computerized scanning and printing of the image were combined. Following root‐canal preparation and preparation of post space, evaluation of remaining dentine thickness was completed using appropriate software.Results  Remaining dentine thickness was significantly affected (P < 0.01) by place (mesial–distal more than buccal–lingual), stage (root‐canal preparation more than post space) and location (coronal more than middle and apical).Conclusions  This in vitro study confirmed that in an oval root‐canal space, the mesial and distal aspects are mainly affected by intraradicular procedures. The three‐step method is a useful tool to evaluate root‐canal instrumentation as the root or tooth can remain intact during the procedure.
Factors influencing the removal of posts
Authors: Hauman C. H. J. , Chandler N. P. , Purton D. G. 
Published: September 2003

AbstractAim  To determine whether metal type, cement type and the use of ultrasonic vibration influence the amount of tensile force required to remove parallel‐sided, prefabricated, metal posts from tooth roots.Methodology  Ninety extracted canine teeth were sectioned horizontally 1‐mm coronal to the labial cemento–enamel junction and embedded in acrylic blocks. Standardized post spaces were prepared with a ParaPost no. 5 (1.25 mm) drill to 10 mm and ParaPost XP no. 5 stainless steel and titanium posts were cemented using zinc phosphate, glass ionomer or composite resin cement. Sixty posts were subjected to 16 min of ultrasonic vibration whilst 30 stainless steel posts received no vibration. The force required for post removal was determined using a universal testing machine. Results were analysed using univariate anova.Results  The univariate anova revealed no statistically significant differences between the groups at the P = 0.05 level.Conclusions  In this in vitro experiment, metal type, cement type and ultrasonic vibration did not influence the force required to remove posts.
How important is climate? Effects of warming, nutrient addition and fish on phytoplankton in shallow lake microcosms
Authors: Moss Brian , Mckee D. , Atkinson D. , Collings S. E. , Eaton J. W. , Gill A. B. , Harvey I. , Hatton K. , Heyes T. , Wilson D. 
Published: September 2003

Summary

Climate is changing. Predictions are for at least a 3 °C rise in mean temperature in northern Europe over the next century. Existing severe impacts of nutrients and inappropriate fish stocking in freshwater systems remain.
Effects of warming by 3 °C above ambient, nutrient addition and the presence or absence of sticklebacks Gasterosteus aculeatus were studied in experimental microcosms dominated by submerged plants, mimicking shallow lake ecosystems.
Warming had considerably smaller effects on the phytoplankton community than did fish and nutrients. It had very minor effects on chlorophyll a and total phytoplankton biovolume. However, it significantly decreased the biovolumes of Cryptophyceae (a major component in the controls) and Dinophyceae. Contrary to expectation, warming did not increase the abundance of blue‐green algae (cyanophytes). Warming decreased the abundances of Cryptomonas erosa (Cryptophyceae) and Oocystis pusilla (Chlorophycota) and increased those of two other green algae, Tetraedron minimum and Micractinium pusillum. It had no effect on a further 17 species that were predominant in a community of about 90 species.
Fish and nutrients, either together or separately, generally increased the crops of most of the 21 abundant species and of the algal groups. Exceptions were for diatoms and chrysophytes, which were very minor components of the communities. Fish, but neither nutrients nor warming, increased the number of species of phytoplankton detected. This was probably through removal of zooplankton grazers, and parallels terrestrial studies where the presence of top predators, by controlling herbivores, leads to increased plant diversity.
There was no particular pattern in the taxonomy or biological characteristics of those species affected by the treatments. In particular, there was no link between organism size (a surrogate for many important biological features of phytoplankton species) and the effects of warming, nutrient addition or presence or absence of fish. However, all species were relatively small and potentially vulnerable to grazing.
Synthesis and applications. The results suggest that fears of an increasing abundance of cyanophytes with current projections of global warming may be unrealized, at least in shallow unstratified lakes still dominated by macrophytes. However, they emphasize that eutrophication and fish manipulations remain very important impact factors that determine the abundance of phytoplankton and subsequent problems caused by large growths.
Demographic models and the management of endangered species: a case study of the critically endangered Seychelles magpie robin
Authors: Norris Ken , Mcculloch Neil 
Published: September 2003

SummaryDemographic models are assuming an important role in management decisions for endangered species. Elasticity analysis and scope for management analysis are two such applications. Elasticity analysis determines the vital rates that have the greatest impact on population growth. Scope for management analysis examines the effects that feasible management might have on vital rates and population growth. Both methods target management in an attempt to maximize population growth.The Seychelles magpie robinCopsychus sechellarumis a critically endangered island endemic, the population of which underwent significant growth in the early 1990s following the implementation of a recovery programme. We examined how the formal use of elasticity and scope for management analyses might have shaped management in the recovery programme, and assessed their effectiveness by comparison with the actual population growth achieved.The magpie robin population doubled from about 25 birds in 1990 to more than 50 by 1995. A simple two‐stage demographic model showed that this growth was driven primarily by a significant increase in the annual survival probability of first‐year birds and an increase in the birth rate. Neither the annual survival probability of adults nor the probability of a female breeding at age 1 changed significantly over time.Elasticity analysis showed that the annual survival probability of adults had the greatest impact on population growth. There was some scope to use management to increase survival, but because survival rates were already high (> 0·9) this had a negligible effect on population growth. Scope for management analysis showed that significant population growth could have been achieved by targeting management measures at the birth rate and survival probability of first‐year birds, although predicted growth rates were lower than those achieved by the recovery programme when all management measures were in place (i.e. 1992–95).Synthesis and applications.We argue that scope for management analysis can provide a useful basis for management but will inevitably be limited to some extent by a lack of data, as our study shows. This means that identifying perceived ecological problems and designing management to alleviate them must be an important component of endangered species management. The corollary of this is that it will not be possible or wise to consider only management options for which there is a demonstrable ecological benefit. Given these constraints, we see little role for elasticity analysis because, when data are available, a scope for management analysis will always be of greater practical value and, when data are lacking, precautionary management demands that as many perceived ecological problems as possible are tackled.
Monitoring salt stress in grapevines: are measures of plant trait variability useful?
Authors: Sinclair Chantelle , Hoffmann Ary A. 
Published: September 2003

Summary

Measures of trait variability, in particular fluctuating asymmetry (FA), have been proposed as biological tools for monitoring environmental quality, but relevant data are often collected under artificial conditions and it can be difficult to separate genetic and environmental factors. We considered a number of trait variability measures for potential use as indicators in field grapevines exposed to salt stress.
Vine responses to a salt gradient were compared using two measures of developmental stability (DS). DS quantifies an organisms’ ability to buffer developmental noise. The two measures of DS tested were leaf FA, representing random deviations from perfect bilateral symmetry, and translational asymmetry (TA), representing deviations in allometric relationships, in this case the relationship between internode distance and node order. Leaf size (measured as centroid size), leaf shape (calculated using the Procrustes method) and maximum internode length were also tested for sensitivity to salinity.
We found that both measures of DS, FA and TA, failed to identify salinity stress in grapevines. Other measures, such as maximum internode length, leaf shape and leaf size, were sensitive to salt stress.
Synthesis and applications. Often, salinity stress is detected only when the impact is harmful enough to cause severe biological effects. Alternative, more sensitive monitoring techniques would allow earlier intervention and management of the problem. We evaluated a number of techniques and showed that indices of bilateral and TA were not useful in detecting salt stress in grapevines. However, changes in internode length, leaf size and leaf shape proved to be sensitive and are potential tools for monitoring salinity in vineyards.
Aerial activity of linyphiid spiders: modelling dispersal distances from meteorology and behaviour
Authors: Thomas C. F. G. , Brain P. , Jepson P. C. 
Published: September 2003

Summary

Dispersal parameters are critical for modelling spatially dynamic populations yet remain among the most difficult to quantify. Linyphiid spider aerial dispersal by ‘ballooning’ on silk threads is dependent on meteorological factors and amenable to analysis and quantification.
Spider aerial activity was measured during consecutive 10‐min periods for up to 11 h a day. Aerial density was measured at four heights using sticky traps. The time intervals between successive flights were measured by observing spiders landing and taking‐off.
Meteorological measurements (wind speeds and temperatures) were taken simultaneously with the collection of airborne spiders, and used to calculate Richardson numbers to estimate atmospheric turbulence.
Numbers of airborne spiders on any given day, and their vertical density profile on different days, were significantly correlated with Richardson numbers.
Single flight distances were modelled using estimates of ascent and descent rates, the vertical density profile of airborne spiders and the wind speeds they experience aloft. The distributions of single flight distances and the time spent between successive flights were combined in an alternating renewal process to model the number of flights and the total daily dispersal distances of ballooning spiders as a function of available dispersal time.
On a day with, for example, 6 h of suitable weather, linyphiid spiders can potentially disperse a mean distance of approximately 30 km downwind.
Synthesis and applications. We have developed a dispersal model of linyphiid spiders that is central to the further development of spatially dynamic population models of these spiders in agricultural landscapes. It could also be adapted for application to other wind‐borne organisms. Such models have a key role in the future management of sustainable agricultural systems where natural predators are seen as major components of pest control.
Soil ammonium accumulation after sod cutting hampers the restoration of degraded wet heathlands
Authors: Dorland E. , Bobbink R. , Messelink J. H. , Verhoeven J. T. A. 
Published: September 2003

Summary

Restoration of formerly species‐rich wet heaths and matgrass swards has not always been successful. The constraints on this restoration process are not yet fully understood and need further investigation, particularly the accumulation of ammonium in the soil after sod cutting, i.e. the removal of the vegetation and topsoil layer. This accumulation is known from sod cutting experiments in dry heaths, but had not previously been studied in wet heaths and matgrass ecosystems.
In 2000, sods were cut from two degraded Dutch wet heaths. Soil chemistry and germination in the sod‐cut plots were measured at irregular intervals between April 2000 and August 2001. To test the influence of ammonium on germination and survival, a glasshouse dose–response experiment was conducted with two endangered wet heath plant species.
In both wet heaths, an accumulation of KCl‐extractable ammonium up to 600 µmol kg−1 dry soil was found in the upper 10 cm of the soil within the first year after sod cutting. These high ammonium concentrations lasted for about 10 months. Germination was very low in the sod‐cut plots in 2000 and 2001, and few target species were found, although they were present in the vicinity.
The dose–response experiment indicated a significant, negative correlation of both germination and survival with increasing ammonium addition for both plant species. Mean soil ammonium concentrations of the control, 100 and 250 µm ammonium treatments were significantly lower than those of the 500 and 1000 µm ammonium treatments (47, 45, 70, 144 and 252 µmol kg−1 dry soil, respectively).
Maximum concentrations of KCl‐extractable ammonium in the field corresponded to water‐extractable concentrations that were higher than those found to be limiting germination and growth in the glasshouse experiments. The low germination in the field is likely to have been adversely affected by high concentrations of ammonium as a result of sod cutting.
Synthesis and applications. High ammonium concentrations occur in wet heaths following sod cutting. Low rates of germination of restoration target plant species occur under such conditions. To increase the success of wet heath restoration, the accumulation of ammonium after sod cutting should be prevented by additional measures, such as liming. Because sod cutting is also applied as a restoration measure in the restoration of other ecosystems, such as fens, the effects on increased soil ammonium concentrations need further attention.
Indirect effects of grazing and nutrient addition on the hemipteran community of heather moorlands
Authors: Hartley S. E. , Gardner S. M. , Mitchell R. J. 
Published: September 2003

Summary

Moorlands dominated by heather Calluna vulgaris are of international conservation importance, but are declining as a result of increased grazing pressure and deposition of atmospheric pollutants. Grazing and nutrient deposition can alter the composition, structure and nutritional quality of the vegetation, which may affect the diversity of herbivorous insects. However, the drivers of insect community diversity in moorlands remain poorly understood.
Here we quantify the changes in moorland vegetation caused by grazing and nutrient addition, together with the effects of these changes on the community structure of a major group of herbivorous insects on moorlands, the Hemiptera. Fencing and fertilizer treatments were used to test the hypotheses that: (1) hemipteran species richness is related to plant species richness; (2) fertilizer addition increases host plant quality and hence the abundance and diversity of Hemiptera; and (3) a reduction in grazing alters vegetation structure and hence the composition of the hemipteran community.
Sites with more mineral soils had the most plant species and the largest species richness and abundance of Hemiptera, supporting hypothesis 1. Fertilizer increased the nitrogen content of both grasses and Calluna and significantly increased Hemiptera abundance and species richness (hypothesis 2), although the effect of fertilizer on diversity was smaller than that of site‐based factors such as plant species richness.
Grazing altered vegetation structure (hypothesis 3): fenced plots increased Calluna ground cover, height and canopy occupancy but reduced grass cover. Four months after the fencing and fertilizer treatments, the level of grazing on Calluna was the prime factor influencing the composition of the hemipteran community. However, after 2 years of the treatments, soil organic content and prevalence of Nardus and new‐growth Calluna had become the greatest influence on community composition.
Synthesis and applications. Grazing and nitrogen deposition alter the vegetation of moorland landscapes and this study shows that these factors also have significant effects on the abundance, species richness and species composition of moorland invertebrates. However, site‐based factors such as soil organic content and plant species richness had the greatest impact on the hemipteran community because plant diversity appears to be the most important driver of hemipteran diversity. Moorland managers may be able to maximize hemipteran species richness using a grazing regime that maintains a mosaic of dwarf shrub and grass cover. Site‐specific factors such as soil type need to be considered when managing moorlands for conservation.
Microsite availability and establishment of native species on degraded and reclaimed sites
Authors: Elmarsdottir Asrun , Aradottir Asa L. , Trlica M. J. 
Published: September 2003

Summary

Restoration of native plant communities on previously disturbed land requires the identification and modification of environmental factors that impede or restrict ecosystem succession or development. One of the key factors in successful reclamation is to ensure colonization and persistence of native species within an area. Therefore, the identification of microsite types that favour colonization by native species should improve our ability to successfully reclaim degraded areas.
The objectives of this study were to (i) identify and describe microsite types that were conducive to the establishment of five native plant species (Euphrasia frigida, Galium normanii, Thymus praecox, Cerastium spp. and Rumex acetosa) on degraded and reclaimed sites in Iceland; and (ii) to determine the effects of reclamation activities that included the application of manure and inorganic fertilizer on the distribution of microsite types and seedling establishment. Reclamation sites of different ages were examined on an eroded area where the target community was a grass or shrub heath.
The spatial distribution of plant establishment was not random but varied among microsite types and study sites. More seedlings than expected were found in microsite types characterized by small rocks and biological soil crusts. These may have entrapped seed and provided more soil stability and moisture than other microsite types. The cover of these microsite types varied among the study sites but the pattern of seedling establishment among the five native forbs was similar.
Synthesis and applications. Practical reclamation methods are improved by identifying those factors that promote successful seedling establishment by native species. Application of fertilizer without additional seeding proved to be a simple reclamation approach that increased the availability of one favourable microsite type, enhanced the establishment of native species and subsequently allowed vegetation cover to expand. Seed of native plants may be difficult to obtain commercially, but this approach can be used on degraded land where propagules are available but recovery is slowed by soil instability or nutrient limitations.
The effect of density‐dependent catastrophes on population persistence time
Authors: Wilcox Chris , Elderd Bret 
Published: September 2003

Summary

There has been increasing recognition that catastrophes are an important factor in modelling threatened populations. However, density dependence has generally been omitted from models of threatened populations on the assumption that this omission yields conservative predictions. We explore the significance of including density‐dependent catastrophes in models of threatened populations.
Using an analytical model, we show that density‐dependent catastrophes have a significant effect on population persistence, decreasing mean persistence time at large population sizes and causing a relative increase at intermediate sizes.
We illustrate our results with empirical data from a disease outbreak in crabeater seals Lobodon carcinophagus and show that intermediate population sizes have the longest predicted persistence times.
The pattern we found is qualitatively different from previous results on persistence time based on density‐independent models, in which persistence time increases with population size to an asymptote.
Synthesis and applications. This study has important implications for the conservation of species that may experience density‐dependent catastrophes, such as disease outbreaks or starvation. Our results indicate that small and intermediate sized populations may contribute disproportionately to species persistence. Thus populations that have been dismissed as ‘marginal’ may actually be important for conservation. In addition, culling may increase the persistence of populations that experience density‐dependent catastrophes.