bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reflections on Citizens' Juries: the case of the Citizens' Jury on genetic testing for common disorders
Authors: Iredale Rachel , Longley Marcus 
Published: March 2003

IntroductionCitizens' Juries are a relatively innovative way of involving ordinary members of the public in decision‐making processes. Participants in Wales' first Citizen Jury reflect on their experiences, and some observers give their view about Citizens' Juries as a method of involving the public in policy making.
Assessment of the effects of environmental change on the performance and density ofBistorta vivipara: the use of multivariate analysis and experimental manipulation
Authors: Totland Ø. , Nyléhn J. 
Published: March 2003

1 Studies of plant performance in relation to local variability in environmental conditions can be used to predict the responses of species to environmental change.2We used redundancy analysis to study how interpopulation variation in average plant weight, flower and bulbil number, bulbil weight and population density among 28 populations ofBistorta viviparawas related to variation in 15 environmental factors. We also examined the responses of plants to a 4‐year experimental increase in temperature.3Significant differences in average plant performance were found between populations. Variance partitioning of the response data showed that environmental factors explained 45% of the variation in plant performance and density between populations, whereas variation due to transect position was small (10.8%). Soil pH, altitude and season length were the most influential of the environmental variables, and explained 23%, 21% and 14%, respectively, of the variation. Plant performance was in general negatively correlated with these variables, whereas plant density increased along the pH and altitude gradients, suggesting that environmental factors associated with elevation (temperature and vegetation cover) and pH (soil fertility) had opposing effects on individual performance and density. Season length was highly important for average bulbil weight.4Plants growing in open top chambers had significantly enhanced growth and produced significantly heavier bulbils than those in control plots, whereas flower and bulbil number were unaffected by experimentally increased temperatures. Plant density was equal for warmed and control plots.5Although warming may increase bulbil weight and plant size inB. vivipara, the response to climate change is complicated by the fact that population densities may decrease due to intensified competition for light caused by a denser vegetation cover.
Separating the effects of number of individuals sampled and competition on species diversity: an experimental and analytic approach
Authors: Goldberg Deborah E. , Estabrook George F. 
Published: March 2003

1 Species richness typically increases with the number of individuals sampled, although many ecological processes that influence species richness are also well known to depend on density of individuals. We separated the effects of density on species richness that are due to sampling, from those due to density‐dependent ecological processes such as competition or predation, by manipulating the density of an entire community. 2 A seed bank from a community of desert annual plants that occur on semi‐stabilized sand dunes in Israel was collected from the field and sown in an experimental garden at a range of densities from 1/16 to eight times the natural density. The species pool observed in the lowest density plots was used as the null community, which was repeatedly sampled to calculate the species richness (and other diversity indices) in higher density plots that would be expected from sampling considerations alone. The significance of deviations of observed diversity from this expected diversity was then evaluated. 3 Both observed and expected number of species increased substantially with the experimental increase in density. However, observed species richness, the Shannon–Wiener diversity index and Simpson's diversity index were often significantly lower than that expected based on sampling considerations. The magnitude of the deviation from expected increased significantly with increasing density for richness and the Shannon–Wiener index. This provides some of the first direct experimental evidence from diverse natural assemblages that increasing competition among all the individuals in a community can lead to competitive exclusion.
The ecology of pollen limitation in buzz‐pollinated Rhexia virginica (Melastomataceae)
Authors: Larson Brendon M. H. , Barrett Spencer C. H. 
Published: March 2003

1 Pollen limitation of female fertility has often been documented in animal‐pollinated plants, but seldom have the ecological mechanisms responsible been investigated. We examined factors influencing pollen limitation in Rhexia virginica (Melastomataceae), a species in which pollen transfer depends on bumblebees capable of buzz pollination. Experimental studies were conducted in two populations at Lake Matchedash, southern Ontario, Canada, where the species occurs at the edge of its familial range. 2 Supplemental hand pollination of flowers increased their probability of fruit set compared with open‐pollinated control flowers by an average of 57.6%. Pollen limitation was assessed on a per flower basis because the median floral display size at Lake Matchedash was one flower. Pollen limitation was prevalent throughout the 3–4‐week blooming period in one population, whereas in the other it was only evident at the beginning of flowering, despite their close proximity. 3 Bumblebee visits (primarily Bombus impatiens) to R. virginica flowers were infrequent and variable in their occurrence. Visitation was recorded on 14 days during flowering. The median number of visits was 0.65 bees per hour; on 6 days there was virtually no bee activity, but on 2 days visitation rates were high. Variation in pollinator activity was apparently unrelated to local weather conditions. 4 Field experiments demonstrated that the poricidal anthers of R. virginica dispense pollen gradually, with only 10.2% of pollen removed from flowers during a single bumblebee visit. This level of pollen removal is lower than reported in other flowering plants. On average, 47.3% of pollen remained in anthers at the end of anthesis. 5 Investigation of the relation between pollen dispersal and pollen limitation demonstrated a significant negative correlation between the proportion of pollen removed from anthers on a given day and the intensity of pollen limitation. It appears that the pollen‐dispensing mechanism of R. virginica and infrequent visitation by bumblebees compromise pollen dispersal, causing pollen limitation in Ontario populations.
Intraclonal regulation in a perennial caespitose grass: a field evaluation of above‐ and below‐ground resource availability
Authors: Derner J. D. , Briske D. D. 
Published: March 2003

Summary 1
Intraclonal regulation of the C4 caespitose perennial grass Schizachyrium scoparium was evaluated in response to various levels of above‐ground (radiation intensity) and below‐ground (soil volume) resource availability in the field for three successive growing seasons. We reasoned that the relative plasticity of clonal growth in response to various levels of resource availability may provide insight into the mechanism of intraclonal regulation. 2  Six naturally occurring clones were randomly assigned to each of five treatments: (i) unrestricted soil volume (control); (ii) large soil volume in which roots were confined to a cylinder of soil with a radius four times that of the clone; (iii) small soil volume, twice the clone radius; (iv) large soil volume with radiation intensity reduced to 55% of ambient; and (v) small soil volume with reduced radiation intensity. 3  Ramet recruitment increased within the first season following root confinement in large soil volumes, while ramet and leaf growth exhibited less plasticity. The effects of a reduction in radiation intensity were smaller, and, in contrast, increased ramet and leaf growth, but did not modify ramet recruitment. 4  The pattern and magnitude of ramet mortality in clones confined to the large soil volume were similar to those of clones in unrestricted soil volume, indicating that intraclonal regulation was sufficient to reduce ramet recruitment and thus density to within the carrying capacity established by resource availability. 5  Similar growth and ramet demography of clones in the unrestricted and small soil volumes suggest that unrestricted clones normally access resources from a soil volume similar to that of the small soil volumes. 6  Rapid clonal growth in response to root confinement to large soil volumes, resource acquisition from a relatively small soil volume that contains the zone of resource accumulation, and the capacity for rapid expression of ramet plasticity provide circumstantial evidence that individual caespitose clones may respond to resource accumulation in soils beneath them.
Variability in the dynamics of northern peripheral versus southern populations of two clonal plant species, Helianthus divaricatus and Rhus aromatica
Authors: Nantel Patrick , Gagnon Daniel 
Published: March 2003

Summary 1
The clonal perennial herb Helianthus divaricatus and the clonal shrub Rhus aromatica reach the northern limit of their distribution in southern Québec (Canada), where both are rare, but they are more common southwards in the adjacent province of Ontario. We tested whether peripheral populations of these species maintain themselves by having highly variable individual growth and survival rates. Their annual rates of population growth, λ, would then vary more, from year to year, than those of more southern populations in neighbouring Ontario, where the species are common. 2  Demographic analyses compared, over two transition intervals, size‐based transition matrices for two northern (Gatineau Park, southern Québec) and two southern populations (Pinery Park, southern Ontario) of each species. Comparisons used log‐linear analyses, bias‐corrected λ‐values with 95% confidence intervals, and elasticity values. 3
For both species, the northern populations showed a larger variation between transition intervals and local populations in some of their vital rates and in λ‐values. For H. divaricatus, elasticity values combined with log‐linear analyses indicated that differences in the growth and survival of medium‐sized ramets contributed most to the differences in λ‐values between northern and southern populations. For R. aromatica, they indicated that differences in the fate of both medium and large ramets contributed to variation in λ. 4
Most of our data indicated a greater demographic variability in the northern populations of H. divaricatus and R. aromatica. At the northern periphery, these species grow in very few of the numerous habitat patches that appear to be suitable for them, whereas the two species together present a near continuous cover in all suitable habitats further south. High demographic variability therefore appears to contribute to determining the distribution of plant species, by increasing the extinction probabilities of local populations at the distribution limit.
Can plasticity compensate for architectural constraints on reproduction? Patterns of seed production and carbohydrate translocation in Perilla frutescens
Authors: Preston Katherine A. 
Published: March 2003

Summary 1 The architecture of Perilla frutescens was manipulated by growing plants in a greenhouse under two photoperiodic regimes, representing conditions near the northern and southern ends of the species’ range, to investigate its effect on patterns of seed production. Within each photoperiodic regime, plants were labelled with 14C at one of three developmental stages at one of three leaf positions to assess the effects of architecture on carbohydrate translocation. 2 Perilla flowers in response to short days, i.e. southern‐treatment plants flowered earlier and were smaller and more sparsely branched than northern‐treatment plants. Branch number limits inflorescence number in Perilla, and southern‐treatment plants therefore made fewer inflorescences. Inflorescences are, however, indeterminate, and the southern‐treatment plants made more flowers per inflorescence than the northern‐treatment plants, such that architecture did not constrain flower number. 3 As a result, plants in both treatments made a similar number of seeds and did not differ in total seed mass. 4 Increased seed production per inflorescence was associated with reduced carbohydrate movement between branches and more 14C‐labelled assimilate per seed at the labelled node. 5 In summary, plasticity at the level of the inflorescence largely compensated for architectural constraints on inflorescence number, and was associated with differences in carbon translocation patterns between the photoperiod treatments.
Seasonal occurrence of fire and availability of germinable seeds in Hakea sericea and Petrophile sessilis
Authors: Brown Claire L. , Whelan Robert J. 
Published: March 2003

Summary 1 Although the season of fire occurrence is known to affect recruitment to plant populations, it has received little attention. This study investigated the dynamics of the canopy‐stored seed banks of two Australian obligate seeder shrubs, Petrophile sessilis and Hakea sericea (Proteaceae), with the objective of determining the changes in viable seed supply over a year. 2 The total number of germinable seeds in the canopy, each month for 12 months during 1996–97, was estimated from separate measures of (i) pre‐dispersal predation of fruits; (ii) seed predation of insect parasitoids; (iii) viability of intact seeds; and (iv) loss of seed viability following experimental heating. 3 The two species had very different seed bank dynamics throughout the year. The seed store of P. sessilis appeared to be being replaced annually, as seeds in the older fruits rapidly lost germinability and new fruits matured to replace them. For H. sericea, the seed store appeared to be accumulating each year, because older fruits retained a high level of germinability. 4 The study indicates that no one fire season will maximize the germinable seed release after fire for all species. Management strategies should therefore include varied seasons of prescribed burning to avoid compositional change and a decrease in diversity that may result from a single‐season approach.
Linking forest edge structure to edge function: mediation of herbivore damage
Authors: Cadenasso M. L. , Pickett S. T. A. 
Published: March 2003

Summary 1 Forest edges, which are prominent features in the north‐eastern United States landscape, may control the flux of organisms between forest and non‐forest habitats. Previous studies have described edge structure rather than function, as determined by interaction with such fluxes. 2 The function of the forest edge may be linked to the structure of its vegetation. We tested this hypothesis by experimentally altering the structure of the vegetation at two deciduous forest edges in Millbrook, New York, USA. Intact and thinned plots were established at each edge and we determined whether the structure of the edges influenced the flux of herbivores, as measured by herbivore damage to transplanted tree seedlings. 3 Herbivore damage to seedlings at site 1 was affected by edge vegetation structure and by distance from the edge. The edge structure effect was due to herbivory by voles, which was significantly greater in the intact than in the thinned treatment. Regardless of treatment, voles damaged seedlings only on the edge and 30–40 m from the edge and did no damage in the forest interior (90–100 m), whereas deer damaged significantly more seedlings in the forest interior than on the edge. At site 2, where vole damage was concentrated on the edge, damage to seedlings was affected only by distance from the edge, not edge structure. 4 The two dominant herbivores, white‐tailed deer and meadow voles, preferentially damaged different seedling species. In addition, tree seedlings browsed by deer resprouted more frequently than those clipped by voles. Our results suggest that both edge structure and distance from the edge influence herbivore activity and, as a result, influence the spatial arrangement, density and composition of populations of tree seedlings during regeneration in forest fragments.
Designs for greenhouse studies of interactions between plants: an analytical perspective
Authors: Freckleton R. P. , Watkinson A. R. 
Published: March 2003

Summary 1 Experiments on competition between plant species are frequently designed without considering the analysis stage of the study. We argue that this omission may lead to over‐complication of the issue of designing experiments. 2 An overwhelming number of studies have shown that the effects on performance of competition in plant mixtures may be described by simple (hyperbolic) regression models. The most natural view of the problem of measuring plant competition is therefore as a problem in regression. 3 Only with experiments designed explicitly to apply regression analyses can phenomena such as frequency dependence and the size dependence of measures of competition be identified. In contrast to previous assertions, this means that designs that are based around, or allow, regression analysis are the most robust as such effects may be tested for using appropriate statistics. 4 Experiments are probably most easily designed to measure competition as a function of the density of interacting species, rather than biomass. This is because the per unit biomass effect of competition on performance is a function of density. Competition measures based on biomass will hence be dependent on the density at which the experiment is performed. Furthermore, the most effective way to manipulate biomass is through changing species’ densities. 5 In terms of economy of design, we would recommend simple additive series. Whilst this does not allow the role of frequency dependence to be analysed, this phenomenon appears to be rare in any case.
Soil seed banks in Mediterranean Aleppo pine forests: the effect of heat, cover and ash on seedling emergence
Authors: Izhaki Ido , Henig‐Sever Nava , Ne'Eman Gidi 
Published: March 2003

Summary 1
East Mediterranean Aleppo pine (Pinus halepensis) forests are subjected to periodic stand‐replacing fires. We simulated two of the effects of fire on the germinable soil seed bank in four pine stands on Mt. Carmel, Israel, that differed in their post‐fire ages. Soil samples were heated to 100 °C, or covered by pine ash. Vermiculite was used to simulate litter cover. 2  Heat exposure increased overall seedling density, richness and taxon diversity in all stands, but density of annual taxa (e.g. grasses and legumes) were not clearly affected. 3  Ash cover dramatically decreased germination of all taxa and highest germination was achieved with heating and no cover. Vermiculite cover resulted in intermediate germination levels. 4  The combined effect of heat exposure and ash cover, simulating a post‐fire situation under a canopy of pine, reduced the germination level of all taxa in the soil seed bank. However, it also creates conditions that facilitate the establishment of pine seedlings from the canopy stored seed bank.
Fragmentation and changes in hydrologic function of tiger bush landscapes, south‐west Niger
Authors: Wu X. B. , Thurow T. L. , Whisenant S. G. 
Published: March 2003

Summary 1 Fragmentation of tiger bush landscapes in south‐west Niger between 1960 and 1992 is evidenced by a reduction of percentage woody vegetation cover, changes in the spatial attributes of vegetation patches, and an increase in the spatial heterogeneity of the landscapes. The spatial patterns and dynamics of these landscapes were effectively captured using a combination of selected patch‐based landscape metrics that measured specific aspects of the spatial pattern. 2 Derived from the spatial distribution of the alternating bands of vegetation and bare ground, lacunarity curves provide a particularly effective quantitative measure of the spatial pattern and dynamics of tiger bush landscapes in terms of percentage vegetation cover, spatial heterogeneity, and the domain of scale of the landscape. Lacunarity curves can be used to characterize landscapes in areas with different climates and topographic settings, and are an effective and parsimonious indicator of the fragmentation of tiger bush. 3 The dynamics of the vegetation bands during the fragmentation process was anisotropic. A significantly larger proportion of woody vegetation reduction occurred in the downslope than upslope portions of woody patches, while the opposite was true for woody vegetation expansion. These results corroborate the hypothesis that tiger bush bands migrate upslope due to the upslope–downslope resource gradient across the vegetation band. 4 Fragmentation of the tiger bush landscapes reduced retention of water on site, significantly increasing the landscape permeability to surface flow. When vegetation bands were well connected in 1960, no transects were found that allowed surface water percolation. That is, no path travelling through the bare ground areas was found to connect the upslope edge and downslope edge of any of the 200‐m long transects, regardless of their width (50, 100 or 150 m). By 1992, within the same but now severely fragmented landscapes transects of all widths allowed water to percolate across them (44% if 50 m wide to 89% if 150 m wide). This increased landscape permeability to surface flow may have reduced the water available to the remaining fragmented vegetation bands and accelerated their degradation.
Effects of pollution‐induced habitat disturbance on the response of willows to simulated herbivory
Authors: Zvereva E. L. , Kozlov M. V. 
Published: March 2003

Summary Stress may affect compensatory plant growth and plant responses to herbivory may therefore be modified by pollution. We compared the effects of leaf clipping on growth, reproduction and developmental stability of two willow species (Salix borealisandS. caprea) growing at different distances from two copper‐nickel smelters (Monchegorsk, NW Russia and Harjavalta, SE Finland). In unpolluted sites, the defoliation of both willow species adversely affected sexual reproduction and increased the formation of epicormic shoots, but did not change either shoot growth or leaf size. Timing and extent of clipping had little effect on the responses. Compensatory responses to leaf clipping in polluted habitats were reduced, especially inS. borealis, as reflected by decrease in shoot growth and fruit production and an increase in leaf fluctuating asymmetry, a non‐specific indicator of stress. Activation of dormant buds was a common compensatory response to herbivory in unpolluted sites. The lack of an increase in epicormic shoots in polluted sites may be due to already weakened apical dominance. Compensatory abilities may be affected both by direct damage caused by pollutants and pollution‐induced increases in environmental stress. AlthoughS. borealisshows no visible sign of stress in polluted sites, regrowth from dormant buds and enhanced shoot growth were seen under these conditions. Resources were not therefore available for further compensation of damage caused by defoliation. Our results fit the hypothesis that fast growing plants have low compensative abilities. Salix capreashows more pollution‐induced stress thanS. borealis, expressed as increased developmental instability near the weaker and shorter shoots near the stronger pollution source. This may explain the differences in their compensatory responses in polluted sites.