bluuebunny/crossref_metadata_2025 huggingface dataset:
Tundra Plant Uptake of Amino Acid and NH4+ Nitrogen in Situ: Plants Complete Well for Amino Acid N
Authors: Schimel Joshua P. , Chapin F. Stuart
Published: May 2006

Traditional models of nutrient cycling assume that soil microorganisms must decompose organic matter, releasing inorganic N, to make N available to plants. Several lines of evidence have raised doubts about this assumption in arctic tundra, but no firm evidence existed. Here we demonstrate that Eriophorum vaginatum and Carex aquatilis, two tundra sedges, compete well for glycine and aspartate N relative to NH$_4+$ in situ. At relatively high concentrations (25 $\mu$g N/g soil), during the peak of the season, E. vaginatum took up amino acid N more rapidly than NH$_4+$, while later in the season and at lower concentrations (2—4 $\mu$g N/g soil) both E. vaginatum and C. aquatilis took up glycine N and NH$_4+$ at similar rates. These results are incompatible with a simple mechanism of amino acid mineralization followed by plant uptake of the released N. These results indicate that these tundra plants have active mechanisms for enhancing their access to amino acid N in situ.
The Role of Fire During Climate Change in an Eastern Deciduous Forest at Devil's Bathtub, New York
Authors: Clark James S. , Royall P. Daniel , Chumbley Craig
Published: May 2006

Annual records of charcoal and sedimentation rate were compared with fossil pollen to investigate the role of fire in eastern deciduous forest around Devil's Bathtub, New York, USA. Changes in peak and background charcoal suggest that changes in fire regime have accompanied the principal vegetation and climatic changes of the last 10 400 yr. A distribution of return times (50—200—yr intervals) similar to parts of modern boreal Canada prevailed when late—Glacial spruce woodland dominated the site. Expansion of Pinus banksiana appears to have altered the fire regime to one of crown fires with high particulate emissions, but return intervals similar to those of the preceding Picea forest. Expansion of Pinus strobus might be linked to change in fire occurrence, but the broad dispersal of Pinus pollen makes interpretation difficult. If Pinus strobus expansion around the site is reflected in its pollen curve, then that expansion coincides with a time of frequent fire. Alternatively, if increasing pollen abundance precedes the local expansion of trees, as has been observed elsewhere, then local expansion might correspond to an abrupt decline in fire frequency and in regional importance of fire. An abrupt decline in background charcoal follows a fire and coincides $(\pm 100 yr)$ with the expansion of hardwood taxa such as Fagus. The decline in background charcoal occurs over several years, suggesting that it may be linked to effects of hardwood expansion on fuels. Fires do not appear to have occurred during the time of hardwood dominance, suggesting that fire may not be an explanation for maintenance of species diversity in this deciduous forest. However, frequent occurrence of thick varves during the latter half of the Holocene suggests that the frequency of other types of disturbance may have increased.
Thermal Effects of Radiation and Wind on a Small Bird and Implications for Microsite Selection
Authors: Wolf Blair O. , Walsberg Glenn E.
Published: May 2006

The physical environmental factors (air temperature, solar radiation, wind speed) that define specific microclimates and their effects on water and energy budgets of small birds are of major importance to our understanding of avian thermal biology. We examined the effects of solar radiation, wind speed, and their interaction on metabolic rates in the Verdin, Auriparus flaviceps. Daytime resting metabolic rates and evaporative water loss rates as a function of air temperature, as well as basal metabolic rate, were also measured to allow estimation of water and energy flux rates in diverse microclimates. In the absence of solar radiation, as wind speed was increased from 0.4 to 3.0 m/s, metabolic rate increased 14%. Exposure to simulated solar radiation significantly reduced metabolic heat production at all wind speeds measured except 3.0 m/s. Solar heat gain (SHG) was estimated for an irradiance of 1000 W/m$2$, similar to that commonly observed in nature. At 0.4 m/s wind speed and 1000 W/m$2$ irradiance, SHG may reduce metabolic rate by 46%. SHG declines precipitously as wind speed is increased, and at 3.0 m/s, metabolic rate is only reduced by 3%. Analyses of changes in thermostatic costs associated with microclimate selection in winter suggest that Verdins may reduce metabolic rate by as much as 50% by shifting from a shaded, windy site to one protected from the wind and exposed to 1000 W/m$2$ solar radiation. Similar analyses for Verdins during the summer suggest that microsite selection can result in significant water savings. By remaining out of the sun and wind, Verdins can reduce their rate of evaporative water loss by at least a factor of four. This analysis clearly demonstrates the potential importance of daytime microclimate selection to balancing water and energy budgets in small birds.
Patch Utilization by Three Species of Chilean Rodents Differing in Body Size and Mode of Locomotion
Authors: Vasquez Rodrigo A.
Published: May 2006

Predation risk influences differentially the foraging decisions of rodent species with different morphologies (body size and locomotion type). Explanations for different foraging patterns have been derived largely from the behavior of heteromyid rodents, and there is a lack of information regarding the behavior of other rodent groups with different morphologies. Nevertheless, the explanations are thought to be applicable to other groups. In order to study the generality of hypotheses about the effect of morphology on foraging ecology, I investigated the foraging decisions of Chilean sigmodontine rodents (Muridae) in the laboratory, experimentally manipulating nocturnal illumination (a surrogate of predation risk) and food distribution. Three coexisting rodent species from the Chilean matorral were compared: two quadrupeds, one with large body size (Phyllotis darwini) and another with small body size (Abrothrix olivaceus), and one small species with bipedal escape behavior (Oligoryzomys longicaudatus). The species did not differ in patch utilization and food consumption in response to different food distributions. However, there was an overall significant effect of illumination on food consumption. When illumination was higher, A. olivaceus and P. darwini increased food transportation to the refuge and decreased patch consumption and total food consumption. They also increased significantly the number of trips between food patch and refuge. P. darwini showed the most cautious foraging behavior. O. longicaudatus was insensitive to different conditions of illumination. It is argued that a large body size and quadrupedal locomotion seem to confer higher sensitivity to nocturnal illumination. Bipedality may confer less vulnerability to predation, and quadrupedal species show facultative central—place foraging, diminishing a possible greater vulnerability to potential risk. Former explanations for different foraging behaviors under the risk of predation may not be as general as previously assumed. This study emphasizes the need to consider the particular features of the system under investigation.
Coexistence of Specialist and Generalist Rodents Via Habitat Selection
Authors: Morris Douglas W.
Published: May 2006

Habitat specialization is an effective mechanism of coexistence among competing species. But many communities also include generalized species whose habitat use overlaps that of the specialists. Two hypotheses seem most likely to account for the pattern: (1) Habitat generalists may coexist in competitively structured communities by exploiting habitats unused, or underused, by habitat specialist. (2) Population densities of the specialized species may be limited (e.g., by predation) below levels where the specialists can competitively exclude habitat generalists. I evaluated these ideas in a community of small mammals occupying mesic and xeric habitats at nine different locations in the Rocky Mountains of southern Alberta, Canada. A chipmunk generalist coexists with two specialists, one with a distinct preference for xeric habitat (deer mouse), and another with a similar preference for mesic habitat (red—backed vole). Habitat selection appeared to depend primarily on the density of conspecifics. The generalist coexisted by responding to habitat at a larger scale than did the specialists. Shared predators, whose habitat selection operates on a larger scale than that of their prey, may augment coexistence of all species by reinforcing habitat selection by the specialists.
Spatial and Temporal Patterns of Small‐Rodent Population Dynamics at a Regional Scale
Authors: Steen Harald , Ims Rolf A. , Sonerud Geir A.
Published: May 2006

Many species exhibit regional synchrony in population dynamics, and different influential biotic and abiotic factors can be indicated by the observed scale of spatial synchrony. Here, we present analyses of spatial patterns of bank vole Clethrionomys glareolus population fluctuations, based on a 5—yr (1990—1994) trapping series obtained from 31 trap stations regularly spaced along a 256—km transect in the boreal forest in southeastern Norway. The bank vole was known to exhibit typically cyclic population dynamics in this region prior to this study. Bank vole fall densities exhibited fluctuations with little year—to—year variation; all $s$—indices (a measure of temporal variability) were below 0.5. There was a large scale trend in the temporal variability of the populations, with highest variability at the south end and lowest in the middle of the transect. Analysis (Mantel correlogram) of the year—to—year rate of change of local populations showed that the opposite ends of the transect appeared to be most out of phase. At a smaller spatial scale (up to 30—40 km), local populations exhibited statistically significant synchrony in growth patterns. Spatiotemporal patterns in the dynamics of local populations were not related to habitat quality. We suggest that the scale domain of population synchrony is related to intrinsic population scaling properties such as dispersal capacity.
Founding, Foraging, and Fighting: Colony Size and the Spatial Distribution of Harvester Ant Nests
Authors: Gordon Deborah M. , Kulig Alan W.
Published: May 2006

This study examines how the spatial distribution of nests is related to the behavioral interactions of conspecific neighbors in a population of the seed—eating ant, Pogonomyrmex barbatus. Colonies live for 15—20 yr, reaching reproductive age and a stable size at $\approx$5 yr. Spatial distributions were measured for 6 yr (1988—1993) in a population of $\approx$250 colonies of known age. The probability that a 1—yr—old colony occurs in a given location is related to the distance to, and ages of, its five nearest conspecific neighbors. One—year—old colonies are most likely to occur near small, 2— and 3—yr—old colonies. Neighboring colonies encounter each other when foragers of both colonies search the same area on the same day. The probability of an encounter between two colonies decreases with the distance between their nests. For colonies of all ages, encounters are most likely with their larger neighbors, $\geq 5$ yr old. Encounters are more likely if there was an encounter the previous day, and this effect can overwhelm the effect of distance. Two—yr—old colonies are more likely than colonies of other ages to lose ground in repeated encounters with a particular neighbor. Though encounters are frequent, their costs are low: few of the foragers on a trail that meets a neighbor's actually encounter an ant of the neighboring colony, and interaction with a neighboring colony does not increase the typical duration of a foraging trip. If foragers of two colonies do meet, most fights are brief, with few resulting in injury or death. These results suggest that the cost of conspecific neighbors searching the same ground for seeds may be greater than the cost of behavioral interaction itself. Exploitative competition may have more important effects than interference competition on founding colony survival and thus on the spatial distribution of nests.
Differentiating Climatic and Successional Influences on Long‐Term Development of a Marsh
Authors: Singer Darren K. , Jackson Stephen T. , Madsen Barbara J. , Wilcox Douglas A.
Published: May 2006

Comparison of long—term records of local wetland vegetation dynamics with regional, climate—forced terrestrial vegetation changes can be used to differentiate the rates and effects of autogenic successional processes and allogenic environmental change on wetland vegetation dynamics. We studied Holocene plant macrofossil and pollen sequences from Portage Marsh, a shallow, 18—ha marsh in northeastern Indiana. Between 10 000 and 5700 yr BP the basin was occupied by a shallow, open lake, while upland vegetation consisted of mesic forests of Pinus, Quercus, Ulmus, and Carya. At 5700 yr BP the open lake was replaced rapidly by a shallow marsh, while simultaneously Quercus savanna developed on the surrounding uplands. The marsh was characterized by periodic drawdowns, and the uplands by periodic fires. Species composition of the marsh underwent further changes between 3000 and 2000 yr BP. Upland pollen spectra at Portage Marsh and other sites in the region shifted towards more mesic vegetation during that period. The consistency and temporal correspondence between the changes in upland vegetation and marsh vegetation indicate that the major vegetational changes in the marsh during the Holocene resulted from hydrologic changes forced by regional climate change. Progressive shallowing of the basin by autogenic accumulation of organic sediment constrained vegetational responses to climate change but did not serve as the direct mechanism of change.
Phenotypic Plasticity for Offspring Traits in Polygonum Persicaria
Authors: Sultan S. E.
Published: May 2006

This paper investigates the effects of parental environment and genotype on offspring provisioning, structure, and growth traits in the annual plant Polygonum persicaria. Replicate offspring were studied from cloned individuals of five parental genotypes grown in high vs. low light, soil moisture, and soil nutrients. Genotypic norms of reaction were determined for ecologically important offspring traits. The effects on those traits of parental genotype, parental environment, and their interaction were tested by analysis of variance. The results showed that parental genotypes altered offspring traits in response to particular resource limits, such that offspring quality was maintained or enhanced despite parental resource deprivation. By maximizing the probability of offspring success, resource—deprived parental plants may partly offset the reduction in their fitness due to lower offspring number. Although overall patterns of plasticity were common to all parents, even this small sample revealed differences among parental genotypes in their response to environment. This may reflect the degree to which variation in fitness—related offspring traits occurs within parents and hence is unavailable to selection.
Thermoregulation in a Lacertid Lizard: The Relative Contributions of Distinct Behavioral Mechanisms
Authors: Bauwens Dirk , Hertz Paul E. , Castilla Aurora M.
Published: May 2006

The lacertid lizard Podarcis hispanica atrata maintained remarkably constant body temperatures (Tb) throughout its daily activity period in early autumn, despite significant variability in available operative temperatures (Te). Lizard Tbs were substantially closer to the species' selected temperature range (the target Tbs for thermoregulation, estimated by the central 80% of the temperatures selected in a laboratory photothermal gradient) than were a random sample of Tes, indicating that this population thermoregulates both accurately and effectively. We compared observed behaviors and Tbs to the predictions of two hypotheses. The no thermoregulation null hypothesis predicted that lizard activity and microsite use would be unaffected by thermal constraints. The only thermoregulation" hypothesis predicted that lizards would be active only at those times and in those places where Tes fell within the selected temperature range. To evaluate the contributions of various behavioral adjustments (activity times, use of microhabitats and sun—shade patches, basking, and shuttling) to temperature regulation, we combined results from direct behavioral observations with information on the Tes available at different times of day and in different microsites (combinations of structural microhabitats and sun—shade patches). Lizard activity patterns did not match the predictions of either hypothesis, but the observed pattern of activity produced Tbs that were, on average, 1.0°C closer to the selected temperature range than were Tbs predicted by the no thermoregulation" hypothesis. The lizards' use of microsites (combinations of structural microhabitats and sun—shade patches) was more similar to predictions of the no thermoregulation hypothesis than to those of the only thermoregulation hypothesis. Nevertheless, the lizards' use of specific microsites produced Tbs that were, on average, 1.9°C closer to the selected temperature range than were randomly available Tes. The relative contributions of different behavioral mechanisms varied with time of day. In the early morning, low movement rates, selection of sunny microsites, and most notably, adoption of a basking posture contributed to temperature regulation. In the late morning and early afternoon, no thermoregulatory behaviors were necessary, as indicated by randomly positioned models that achieved mean Tes within the selected temperature range. At midday, frequent movements between sunny and shaded microsites probably reduced heat loads on lizards, preventing Tbs from exceeding the selected temperature range. In the late afternoon, nonrandom use of microsites and basking behavior appeared to contribute equally to the elevation of Tbs above randomly sampled Tes.
Environmental Influence on Life‐History Traits: Growth, Survival, and Fecundity in Black Brant (Branta Bernicla)
Authors: Sedinger James S. , Flint Paul L. , Lindberg Mark S.
Published: May 2006

We studied relationships between body size of female Black Brant goslings (Branta bernicla nigricans) late in their growth period and first year survival, eventual adult body size, breeding propensity, and size and volume of clutches they eventually produced to examine the relationship between growth and fitness in this population. We indexed body size by calculating PC1 scores based on either culmen and tarsus, or culmen, tarsus, and mass. Gosling (PC scores based on culmen and tarsus) size was positively correlated with resighting rate (P = 0.005), indicating that larger goslings survived at a higher rate than did smaller goslings. Gosling size was correlated with adult size of the same individuals (P = 0.0004). Larger goslings were more likely to breed as 2— or 3—yr—olds than were medium or small goslings (P = 0.008). Larger adult brant laid more eggs (P = 0.03) and produced clutches with greater total volume (P = 0.03) than did smaller brant. Given the important role of foraging environment in growth of goslings, these data suggest an important role of early environment in determining life—history traits.
Holocene Tree‐Limit and Climate History from the Scandes Mountains, Sweden
Authors: Kullman Leif
Published: May 2006

Elevational tree—limit change of Pinus sylvestris, Betula pubescens ssp. tortuosa, and Alnus incana during the Holocene was studied from subfossil wood remains in the Scandes Mountains, Sweden. From 8250 yr BP to the present, the Pinus—limit descended at an average rate of 20 m per millennium (after adjustment for glacioisostatic land upheaval). In contrast, Betula and Alnus ascended until ≈ 3000 yr BP, whereafter an altitudinal decline is apparent. The relative abundance of Pinus in the tree—limit ecotone has decreased, while that of Betula increased throughout much of the Holocene. The present—day subalpine belt of Betula developed after 7000 yr BP in response to long—term cooling interacting with short—term climatic disturbance of pine stands. The inferred tree—limit histories are consistent with climatic model simulations of solar radiation and the atmospheric circulation for the Holocene (the Milankovitch theory). Based on the current climate requirements of the tree—limit species, an early Holocene summer thermal optimum ≈ 1.0°C higher than present is inferred. Subsequently, tree—limit vegetation changed gradually, in dynamic equilibrium with progressive summer cooling and increasing humidity and snow cover, i.e., a decreasingly seasonal climate. Accelerated recession of Pinus, indicative of abrupt cooling, is recorded for a short period around 7200 yr BP. A short—term advance of the Pinus tree—limit, presumably a consequence of climatic warming, occurred ≈ 4300 yr BP. Rapid and persistent reductions in the quantitative record of subfossils of all tree species, after 5500—5000 yr BP, may result from fragmentation of the tree—limit ecotone. This response is inferred as the combined effect of long— and short—term cooling passing a threshold, which initiated periglaciation, podzolization, and paludification
Edaphic and Human Effects on Landscape‐Scale Distributions of Tropical Rain Forest Palms
Authors: Clark Deborah A. , Clark David B. , Sandoval Rosa M. , Castro Marco Vinicio C.
Published: May 2006

We studied the landscape—level spatial variation in distribution and abundance of seven species of canopy and subcanopy palms in a neotropical rain forest. Within 568 ha of nonswamp old—growth lowland forest at the La Selva Biological Station, Costa Rica, we sampled at 516 intersections of a reserve—wide grid to systematically assess the species' distributions across the major edaphic gradients. We found mosaics of community structure related to marked within—forest variability in both soil and topography. Total stem density of this guild varied with both edaphic factors. Steep sites had twice as many large palms (>10 m tall) per hectare than those on gentler topography or at lower slope positions. The combined density of subcanopy and canopy palms also varied significantly among soil types in the smallest size class (1—5 m tall), but not for larger individuals. Local (point) species richness of the subcanopy and canopy palms varied among soil types. Of the seven species, two (Astrocaryum alatum and A. confertum) were rare. All others showed significant edaphic variation in their distribution and/or estimated density. Two closely related species had strong and opposite edaphic associations. Euterpe macrospadix was biased toward steep topography and less fertile sites. Prestoea decurrens was nearly ommipresent on soil types with gentle topography while absent from half the points on soils with steep slopes. Two other closely related species, Iriartea deltoidea and Socratea exorrhiza, while virtually omnipresent across soil types and topographic positions, showed marked reciprocal variation in density between related soils. Iriartea's spatial distribution further indicates local removal of this species from one sector of the old growth by human harvesting (with subsequent apparent release of Socratea in this site). The most abundant species, Welfia georgii, while present at all sample points, showed significant among—soil variation in density. This substructuring of the arborescent palm guild results from the interplay of edaphic variation and past human activity. These findings and evidence from other sites suggest that marked spatial heterogeneity in community structure, at small to large scales (0.5—103 ha), may be general among tropical wet forests. Study of the spatial scales and causes of this variability will produce a more robust understanding of these complex ecosystems.
Life History Correlates of Taxonomic Diversity
Authors: Marzluff John M. , Dial Kenneth P.
Published: May 2006

One of the most pervasive, nonrandom evolutionary patterns is extreme domination of a taxon by one subtaxon or only a few subtaxa. Domination refers to taxonomic diversity and the fraction of the taxon that is classified in the most diverse subtaxon. We attempt to explain how subtaxa come to dominate their phyletic counterparts by examining correlations between taxonomic diversity and life history traits such as age of first reproduction, longevity, fecundity and partitioning of reproduction, and resource availability in a variety of vertebrate, invertebrate, and plant groups. Regardless of taxonomic group or rank, the number of taxa within an assemblage, or the school of taxonomy employed, diverse taxa were characterized by short generation time (early age of first reproduction and short life—span) and the ability to contact many resources (high mobility and high resource availability). We suggest that the intrinsic character of short generation time increases diversity because it promotes speciation and reduces extinction. Extrinsic factors such as resource availability and environmental complexity and variability may have a secondary influence on diversity by constraining or enhancing speciation for taxa with short generation times.
Estimates of Movement and Site Fidelity Using Mark‐Resight Data of Wintering Canada Geese
Authors: Hestbeck Jay B. , Nichols James D. , Malecki Richard A.
Published: May 2006

Population ecologists have devoted disproportionate attention to the esti— mation and study of birth and death rates and far less effort to rates of movement. Movement and fidelity to wintering areas have important ecological and evolutionary implications for avian populations. Previous inferences about movement among and fidelity to wintering areas have been restricted by limitations of data and methodology. We use multiple observation data from a large—scale capture—resighting study of Canada Geese in the Atlantic flyway to estimate probabilities of returning to previous wintering locations and moving to new locations. Mark—resight data from 28,849 Canada Geese (Branta canadensis) banded woth individually coded neck bands in the mid—Atlantic (New York, Pennsylvania, New Jersey), Chesapeake (Delaware, Maryland, Virginia), and Carolinas (North and South Carolina) were used to estimate movement and site—fidelity. Two three—sample mark—resight models were developed and programmed using SURVIV to estimate the probability of moving among or remaining within these three wintering regions. The model (MV2) that incorporated tradition" or memory of previous wintering regions fit the data better than the model (MV1) that assumes that a first—order Markov chain described movement among regions. Considerable levels of movement occured among regions of the Atlantic flyway. The annual probability of remaining in the same region for two successive winters, used as a measure of site fidelity, was 0.710 plus or minus 0.016 (estimated mean plus or minus SE, 0.889 plus or minus 0.006, and 0.562 plus or minus 0.025, for the mid—Atlantic, Chesapeake, and Carolinas, respectively. The estimated probability of moving between years corresponded to changes in winter harshness. In warm years, geese moved north and in cold years, they moved south. Geese had a high probability of moving to and remaining in the Chesapeake. Annual changes in the movement probabilities did not correspond to annual changes in the United States Fish and Wildlife midwinter survey. Considerable numbers of geese from the Carolinas appeared to be wintering in more northerly locations (short—stopped) in subsequent winters.
Reduced Postfire Tree Regeneration Along A Boreal Forest‐Forest‐Tundra Transect in Northern Quebec
Authors: Sirois Luc , Payette Serge
Published: May 2006

The large 1950s fires that burned >5500 km2 of land across a south—to—north climatic gradient in northern Quebec provide an opportunity to evaluate the role of fire in forest—tundra development on a demographic basis. The tree population density before and ° 30 yr after fire was estimated by censusing trees in plots of 400 m2 located in upland and lowland within four representative ecoregions of northern Quebec. The analysis of tree recruitment before and after fire, in 410 randomly selected sites along a transect crossing the upper boreal forest and forest—tundra zones, indicated that wild fires induced substantial depletion of tree populations. Taken as a whole, fires have significantly reduced the density of black spruce populations in forest—tundra uplands, but not in the lowlands. A reduction in tree population density of °75% was observed in 22% of upper boreal forest sites, and 45% and 93% of sites located in the forest and shrub subzones, respectively, of the forest—tundra zone. Complete exclusion of tree populations by fire was observed in 43% of upland sites in the northern part of the transect, while complete removal was a rare event in the southern part. Sustained reduction of tree population density after several destructive fires appears as one of the main deforestation processes in the subarctic zone. This leads to the patchy distribution of forest stands and scattered tree populations typical of the forest—tundra biome. Comparisons with paleoecological data suggest that the impact of the 1950s fires contribution to the expansion of the forest tundra into the upper boreal forest. The ecological impact of these fires was probably similar to those fires responsible for development of the forest tundra during the Holocene. It is suggested that the fire—climate interaction should be considered in order to predict the ecological impact of warming climate on high—altitude forest ecosystems.
Importance of Spatial and Temporal Dynamics in Species Regional Abundance and Distribution
Authors: Collins Scott L. , Glenn Susan M.
Published: May 2006

Several recent models have been proposed to explain the pattern of species distribution within a region. Brown's niche—based model, Levins' stochastic immigration—extinction model, and Hanski's core—satellite hypothesis (a modification of Levins' model) differ in relative spatial scales, and degree of stochastic variation in species distribution over time. To test the predictions of these models, we analyzed the regional distribution and temporal dynamics of plant species across 19 sites in tallgrass prairie over an 8—yr period. Spatial patterns of species regional distribution were bimodal each year, a pattern in accord with the core—satellite hypothesis. In addition, temporal patterns of species distribution within a site were also bimodal. The dynamics of the core—satellite hypothesis are driven by patterns of immigration and extinction. Extinction was positively related to richness, however, in contrast to the theory of island biogeography, immigration was not related to species richness. In addition, the variances in the differences in species frequencies from one year to the next were greater than three times the mean, a condition necessary for bimodality in the core—satellite model, for 88 of 135 (65.1%) species. These results provide strong support in favor of the core—satellite hypothesis and imply that stochastic factors may be the primary determinant of plant species dynamics and plant community structure in grasslands at the scale of several kilometres. Evidence from prairie communities at much larger spatial scales supported the patterns predicted by Brown's niche—based model. Thus, these apparently competing models are, in fact, compatible when viewed at the appropriate spatial scale.
Soil Fauna Increase Betula Pendula Growth: Laboratory Experiments With Coniferous Forest Floor
Authors: Setala Heikki , Huhta Veikko
Published: May 2006

The effects of soil fauna on the growth and nutrient contents of birch seedlings were studied in laboratory microcosms simulating the complexity of a coniferous forest floor. In one set of microcosms partially sterilized soil was reinoculated with soil microorganisms only; another set was reinoculated with microorganisms and a diverse soil fauna. A birch seedling (Betula pendula) was planted in each microcosm, all of which were incubated in a climate chamber with various temperature and illumination regimes. During two growing periods birch—leaf, stem, and root biomasses were 70%, 53%, and 38% greater, respectively, in the presence of fauna. The N and P contents of leaves were °3— and 1.5—times higher, respectively, in the refaunted microcosmms than in the controls with microorganisms only. The amount of K, Ca. and Mg in leaf tissue were almost the same in both treatments. Despite the greater leaf biomass, and therefore more effective transpiration, the water content of the soil remained significantly higher in the refaunted microcosms. The results clearly indicate that soil fauna, via enhanced nutrient mobilization and favorable changes in the structural soil properties, expert a positive influence on plant growth.
Nutritional Controls Over Nitrogen and Phosphorus Resorption From Alaskan Birch Leaves
Authors: Chapin F. Stuart , Moilanen Lori
Published: May 2006

Little is known about factors that control nutrient loss from plants. We measured N (nitrogen) and P (phosphorus) resorption from leaves of Alaskan birch (Betula papyrifera) trees that differed strongly in their tissue nutrient status. We then experimentally manipulated those factors that we thought were most likely to control nutrient resorption. Trees of high nutrient status had larger maximum leaf N and P pools, translocated more N and P out of leaves, and left larger N and P pools in abscised leaves than did trees on infertile soils. However, plant nutrient status had no effect on the efficiency of N or P resorption (i.e., the proportion of the maximum nutrient pool resorbed from leaves during autumn senescence) except for low efficiency of P resorption in the highly fertile lawn. Prolonging the time that a leaf remained attached to the tree had no effect on N and P resorption efficiency. Leaching by autumn rains accounted for 25% of the N disappearance and 55% of the P disappearance from senescing leaves in a high—fertility field. Weakening of source—sink interactions by shading senescing leaves in a high—fertility field. Weakening of source—sink interactions by shading senescing leaves or by removing catkins (a sink for carbohydrates and nutrients) significantly reduced resorption efficiency. On the basis of our results and previous work, we conclude that nutrient resorption efficiency is influenced more strongly by carbohydrate flux from leaves (i.e., source—sink interactions) than by factors governing hydrolysis of nutrient—containing fractions in leaves.
pH‐sensitive flocculation: Settling rates and sediment densities
Authors: Franks George V. , Sepulveda Carola V. , Jameson Graeme J.
Published: May 2006

The polyelectrolytes chitosan and polyacrylic acid have been used to flocculate alumina, silica, and zircon suspensions. The flocculant concentrations and pH were such as to cause attractive interaction forces between particles, resulting in rapid sedimentation. Initial settling rates were typically on the order of 0.1 to 5 m/hr. After the formation of a sediment bed, the pH was changed to establish repulsive forces between the particles; additional sediment consolidation was seen to occur. By creating repulsion between the particles in the sediment, the volume of sediments could be reduced by between 10 to 50% compared to attractive flocculation only. For each case, increasing the molecular weight of the flocculant increased the settling rate and improved the supernatant clarity, but decreased the density of sediments. © 2006 American Institute of Chemical Engineers AIChE J, 2006
Visualizing linguistic and cultural differences using Web co‐link data
Authors: Vaughan Liwen
Published: May 2006

The study examined Web co‐links to Canadian university Web sites. Multidimensional scaling (MDS) was used to analyze and visualize co‐link data as was done in co‐citation analysis. Co‐link data were collected in ways that would reflect three different views, the global view, the French Canada view, and the English Canada view. Mapping results of the three data sets accurately reflected the ways Canadians see the universities and clearly showed the linguistic and cultural differences within Canadian society. This shows that Web co‐linking is not a random phenomenon and that co‐link data contain useful information for Web data mining. It is proposed that the method developed in the study can be applied to other contexts such as analyzing relationships of different organizations or countries. This kind of research is promising because of the dynamics and the diversity of the Web.
N1‐allyl‐3‐substituted‐6,7‐dimethyl‐1,2‐dihydro‐2‐quinoxalinone as key intermediate for new acyclonucleosides and their regioisomer O‐analogues
Authors: Ali Ibrahim A. I. , Fathalla Walid
Published: May 2006

The key intermediates allyloxyquinoxaline 2a–c and N‐allylquinoxaline 3a–c were used to synthesize a number of acyclonucleosides whose chemical modifications include quinoxaline ring and the acyclic part is either N1‐propanediol or 3‐hydroxy‐ propyl substituents and their O‐analogues. These compounds were characterized by elemental analysis, MALDI MS, and NMR data. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:280–288, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20203
Spatial learning induces presynaptic structural remodeling in the hippocampal mossy fiber system of two rat strains
Authors: Holahan Matthew R. , Rekart Jerome L. , Sandoval Jimena , Routtenberg Aryeh
Published: May 2006

Hebb (1949) proposed that after learning both presynaptic and postsynaptic structural changes form the neural substrate oflong‐lasting memory. Despite this, there are few instances linking presynaptic remodeling with learning. Here the authors demonstrate in two different rat strains that learning the location of a hidden platform induces expansion of the presynaptic hippocampal mossy fiber terminal field (MFTF) from the stratum lucidum to the distal stratum oriens (dSO). Prior to any training, Long Evans rats (LER) showed an extensive endogenous MFTF innervation of DSO, in contrast to Wistar rats (WR) that showed minimal innervation. LER showed better recall than WR on the hidden platform water maze task and a visible reversal water maze task. In both strains, significant MFTF expansion to dSO, spanning approximately 200 μm, was detected 7 days after training on the hidden platform task, but only LER showed significant MFTF expansion 24 h after training. It is attractive to think that the MFTF expansion to dSO contributes both to long‐lasting memory formation and to facilitating spatial navigation strategies. The present results establish learning‐induced axonal remodeling of the hippocampal MF system in adult rats as an especially useful system for exploring presynaptic morphological adjustments consequent to learning. © 2006 Wiley‐Liss, Inc.
Comparison between polyaniline‐phosphate and polypyrrole‐phosphate composite coatings for mild steel corrosion protection
Authors: Hosseini M. G. , Sabouri M. , Shahrabi T.
Published: May 2006

Polyaniline, polypyrrole and their composites have been deposited on mild steel electrode from aqueous oxalic acid solution by using cyclic voltammetry (CV) technique. The resulting coatings were characterized by scanning electron microscopy and EDX analysis. The protective performance against corrosion of these coatings is evaluated by using electrochemical impedance spectroscopy (EIS) technique in corrosive solution (3.5% NaCl). Impedance data indicates a noticeable enhancement of protection against corrosion processes. Also, comparison of polyaniline‐phosphate and polypyrrole‐phosphate coatings indicates better corrosion protection with polyaniline‐phosphate coatings.
Complete 1H‐ and 13C NMR assignments of saponins from roots of Gypsophila trichotoma Wend.
Authors: Gevrenova Reneta , Voutquenne‐Nazabadioko Laurence , Harakat Dominique , Prost Elise , Henry Max
Published: May 2006

The assignments of 1H and 13C NMR spectra of two new aminoacyl triterpene saponins from roots of Gypsophila trichotoma Wend. are reported. In addition to 1D NMR methods, 2D NMR techniques (COSY, TOCSY, ROESY, HSQC, HMBC, and HSQC–TOCSY) were used for the assignments. The structures were completed by analysis of HR‐ESI‐MS and ESI‐MSn. Copyright © 2006 John Wiley & Sons, Ltd.
Quantitative analysis of prostate metabolites using 1H HR‐MAS spectroscopy
Authors: Swanson Mark G. , Zektzer Andrew S. , Tabatabai Z. Laura , Simko Jeffry , Jarso Samson , Keshari Kayvan R. , Schmitt Lars , Carroll Peter R. , Shinohara Katsuto , Vigneron Daniel B. , Kurhanewicz John
Published: May 2006

A method was developed to quantify prostate metabolite concentrations using 1H high‐resolution magic angle spinning (HR‐MAS) spectroscopy. T1 and T2 relaxation times (in milliseconds) were determined for the major prostate metabolites and an internal TSP standard, and used to optimize the acquisition and repetition times (TRs) at 11.7 T. At 1°C, polyamines (PAs; T1mean = 100 ± 13, T2mean = 30.8 ± 7.4) and citrate (Cit; T1mean = 237 ± 39, T2mean = 68.1 ± 8.2) demonstrated the shortest relaxation times, while taurine (Tau; T1mean = 636 ± 78, T2mean = 331 ± 71) and choline (Cho; T1mean = 608 ± 60, T2mean = 393 ± 81) demonstrated the longest relaxation times. Millimolal metabolite concentrations were calculated for 60 postsurgical tissues using metabolite and TSP peak areas, and the mass of tissue and TSP. Phosphocholine plus glycerophosphocholine (PC+GPC), total choline (tCho), lactate (Lac), and alanine (Ala) concentrations were higher in prostate cancer ([PC+GPC]mean = 9.34 ± 6.43, [tCho]mean = 13.8 ± 7.4, [Lac]mean = 69.8 ± 27.1, [Ala]mean = 12.6 ± 6.8) than in healthy glandular ([PC+GPC]mean = 3.55 ± 1.53, P < 0.01; [tCho]mean = 7.06 ± 2.36, P < 0.01; [Lac]mean = 46.5 ± 17.4, P < 0.01; [Ala]mean = 8.63 ± 4.91, P = 0.051) and healthy stromal tissues ([PC+GPC]mean = 4.34 ± 2.46, P < 0.01; [tCho]mean = 7.04 ± 3.10, P < 0.01; [Lac]mean = 45.1 ± 18.6, P < 0.01; [Ala]mean = 6.80 ± 2.95, P < 0.01), while Cit and PA concentrations were significantly higher in healthy glandular tissues ([Cit]mean = 43.1 ± 21.2, [PAs]mean = 18.5 ± 15.6) than in healthy stromal ([Cit]mean = 16.1 ± 5.6, P < 0.01; [PAs]mean = 3.15 ± 1.81, P < 0.01) and prostate cancer tissues ([Cit]mean = 19.6 ± 12.7, P < 0.01; [PAs]mean = 5.28 ± 5.44, P < 0.01). Serial spectra acquired over 12 hr indicated that the degradation of Cho‐containing metabolites was minimized by acquiring HR‐MAS data at 1°C compared to 20°C. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Time use and daily activities in people with persistent mental illness
Authors: Leufstadius Christel , Erlandsson Lena‐Karin , Eklund Mona
Published: May 2006

The aim of this study was to investigate time use in work/education, self‐care/self‐maintenance, play/leisure, rest/relaxation, and sleep in people with persistent mental illness. A further aim was to investigate how time use in the daily activities was associated with health‐related variables and social interaction. The study comprised 103 participants with a diagnosis of persistent mental illness who completed self‐ratings and interviews in order to assess (1) time use of activities during one 24‐hour day, (2) social interaction and (3) health‐related factors. The major results indicated that the total time in activity (TTA) and the time spent on work/education and sleep seemed to be related to the majority of the target variables. Four groups of daily rhythm were identified and the daily rhythm groups differed concerning perceived mastery and social interaction. Although the results of this study were statistically significant they did not indicate clinical significance. Therefore, the assumption that there is a relationship between occupation and well‐being could not be clearly verified. This study had a cross‐sectional design based on a one‐time measure, which is an important limitation for the validity of the study. Furthermore, no Bonferroni corrections were made for mass significance and some of the findings would have disappeared if such corrections had been made. More studies concerning time use in daily activities, and daily rhythm in relation to health and well‐being are needed. Copyright © 2006 John Wiley & Sons, Ltd.
Desmoplastic small round cell tumor in childhood: The St. Jude Children's Research Hospital experience
Authors: Saab Raya , Khoury Joseph D. , Krasin Matthew , Davidoff Andrew M. , Navid Fariba
Published: May 2006

Background

Desmoplastic small round cell tumor (DSRCT) is a rare, primarily intra‐abdominal tumor that has a poor outcome with current therapies.

Procedure

We retrospectively reviewed patient characteristics, presenting symptoms, tumor pathology, treatment, and outcome of 11 pediatric patients with DSRCT at our institution.

Results

The cohort included 1 female and 10 male patients. Median age at diagnosis was 14 years (range 5–21 years). In eight (73%) patients, the primary tumor was abdominal or pelvic, and in one patient each, it was submental, mediastinal, and paratesticular. Nine (82%) patients had metastatic disease. All tumors showed polyphenotypic differentiation by immunohistochemistry. The EWS‐WT1 transcript was detected in six of seven tumors tested. One tumor showed rhabdomyoblastic differentiation after therapy. All patients received chemotherapy; eight underwent surgical resection, seven received primary site radiation, and four received myeloablative chemotherapy with stem‐cell support. Three (27%) patients are alive 23 months, 8 years, and 10 years from diagnosis. Two died of treatment‐related toxicity, six died of disease. None of the patients in whom surgery and initial chemotherapy failed to induce complete remission survived.

Conclusions

DSRCT is an aggressive malignancy that does not respond well to contemporary treatments, and patients who do not enter complete remission after initial chemotherapy and surgery appear to have a particularly dismal outcome. Patients with localized extra‐abdominal disease have a better prognosis, most likely due to increased feasibility of resection. Better understanding of molecular and genetic mechanisms of tumorigenesis and treatment‐related changes may contribute to development of more effective therapy for DSRCT. Pediatr Blood Cancer 2007;49:274–279. © 2006 Wiley‐Liss, Inc.
Synthesis and characterization of new polymeric ionic liquid microgels
Authors: Marcilla Rebeca , Sanchez‐Paniagua Marta , Lopez‐Ruiz Beatriz , Lopez‐Cabarcos Enrique , Ochoteco Estibalitz , Grande Hans , Mecerreyes David
Published: May 2006

A new two‐step route toward the synthesis of polymeric ionic liquid microgel particles is presented. In the first step, hydrophilic microparticles were prepared by the concentrated emulsion polymerization of the ionic liquid 1‐vinyl‐3‐ethylimidazolium bromide in the presence of small amounts ofN,N‐dimethylenebisacrylamide as a crosslinking agent. In the second step, the bromide anion was exchanged in water with different anions such as BF, CF3SO, (CF3SO2)2N−, (CF3CF2SO2)2N−, and dodecylbenzenesulfonate, and this resulted in the coagulation of the microparticles, which were easily recovered by filtration. The obtained polymeric ionic liquid microparticles could be swollen in a very broad range of organic solvents, including apolar organic solvents. As an application, glucose oxidase was encapsulated inside polymeric ionic liquid microparticles, which were used in an amperometric biosensor. The response of the biosensor showed excellent values that strongly depended on the nature of the polymeric ionic liquid counteranion in the order of Br−> BF> (CF3SO2)2N−. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3958–3965, 2006