bluuebunny/crossref_metadata_2025_split huggingface dataset:
Egg size, offspring quality and food level in planktonic rotifers
Authors: KIRK KEVIN 
Published: November 2003

1. For two species of planktonic rotifers, Brachionus calyciflorus and Synchaeta pectinata, neonates from larger eggs were more resistant to starvation than neonates from smaller eggs, so egg size was positively correlated with offspring quality.2. Theories of optimal offspring size in zooplankton predict either a decrease in offspring size with increasing food level, or maximum offspring size at intermediate food levels. In experiments using acclimated, even‐aged individuals, neither rotifer species changed its egg size as predicted by theory. B. calyciflorus egg size increased with increasing food concentration, while S. pectinata egg size did not change.3. The lack of fit to theory may have occurred because of constraints on minimum or maximum egg size, constraints on total reproductive effort, or because offspring fitness is influenced by traits in addition to neonate starvation time.
Assessing conservation value of stream communities: a comparison of approaches based on centres of density and species richness
Authors: ANGERMEIER PAUL , WINSTON MATTHEW 
Published: November 2003

1. We used a recently developed Index of Centres of Density (ICD) to assess conservation value of thirty‐nine sites in the upper Clinch River drainage of Virginia and Tennessee, U.S.A. The ICD incorporates information on the population density of each species at a site relative to sites throughout the region.2. Value assessments based on the ICD were compared to those based on species richness. Species richness at sites was not related to ICD scores, but collective species lists from high‐ranking sites were similar for both approaches. All sites with rare species had either a high ICD score or high species richness.3. Four community types (defined by physiography and stream size) were better represented in sites with high‐ranking ICDs than in sites with high‐ranking species richness. Sites with high ICD scores were distributed uniformly throughout the region.4. The ICD is a more powerful tool than species richness for assessing conservation value because the ICD identifies areas with regionally rare species, especially viable populations, or distinctive communities, all of which are key components of a region’s biodiversity.
Genetic and behavioural divergence among desert spring amphipod populations
Authors: THOMAS PERRY , BLINN DEAN , KEIM PAUL 
Published: November 2003

1. Random amplification of polymorphic DNA (RAPD) analyses and behavioural trials were conducted on eleven Hyalella azteca populations and one population of H. montezuma from lakes and springs across northern Arizona, U.S.A. Genetic distances among populations were calculated based on fifty‐five RAPD markers.2. A cluster analysis indicated two genetic lineages among the Hyalella populations. One group consisted of populations inhabiting lakes with submerged vegetation, while a second group consisted of populations that clung to roots of emergent vegetation. Behaviour also diverged between these two groups in laboratory trials: amphipods from the submerged vegetation lineage spent significantly more time swimming than did those from the emergent vegetation lineage.3. Based on patterns in genetic distance data, it is suggested that a xeric landscape may promote diversity among passively dispersed invertebrates.
Wave‐induced shear stresses, plant nutrients and chlorophyll in seven shallow lakes
Authors: HAMILTON DAVID , MITCHELL STUART 
Published: November 2003

1. Sediment resuspension dynamics were investigated in relation to changes in water column nutrients (TP, TN, PO4‐P, NO3‐N and NH4‐N), chlorophyll a and phaeopigment in seven shallow (Zm < 1.5 m) lakes in South Island, New Zealand, ranging in area from 0.1 to 180 km2.2. Benthic shear stress, calculated from wind speed, effective fetch and depth, was a considerably better predictor of nutrient and pigment concentrations than wind speed.3. For TP, TN, chlorophyll a and phaeopigment, sixteen of the possible twenty‐eight linear correlations with benthic shear stress were significant at P < 0.05, with 16–87% of the variation being explained by shear stress.4. Wind decreased the ratios of TN : TP, with ratios exponentially approaching those of the sediments as shear stress increased in four of the lakes.5. Relationships of dissolved inorganic nutrients to shear stress were considerably weaker than those for total nutrients and showed no consistent trend over the seven lakes.6. Estimated annual mean TP inclusive of resuspension was over four times higher than that derived from measured calm samples in two lakes.7. The number of nutrient and pigment parameters that were significantly correlated with shear stress and the strengths of the relationships varied widely from lake to lake. We could establish no simple relationships between these effects and any single characteristic of the lake, sediment, or water.8. A function is developed to predict the rate of entrainment of TN and TP in response to an applied shear stress, where the independent variables are sediment nutrient content and particle size, and the macrophyte density in the lake.
Calanoid–cyclopoid interactions: evidence from an 11‐year field study in a eutrophic lake
Authors: ADRIAN RITA 
Published: November 2003

1. The interactions between calanoid and cyclopoid copepods were examined in an 11‐year field study of a eutrophic lake (Heiligensee, Berlin, Germany).2. A diminishing ratio of calanoids to cyclopoids was observed. The responses, however, were species specific. While two cyclopoid species responded with increased populations (Cyclops vicinus, Thermocyclops oithonoides), one species exhibited marked declines (C. kolensis). Other species extended the duration of their pelagic phase (Mesocyclops leuckarti, Diacyclops bicuspidatus, T. oithonoides, C. vicinus), leading to higher population overlaps. Eudiaptomus graciloides and E. gracilis, which used to be present throughout the year, were more frequently absent.3. These changes coincided with a series of mild winters during which prey availability (algae and rotifers) was high.4. Enhanced prey availability, in conjunction with a flexible diapausing strategy, are hypothesized to underly the increased success of C. vicinus. Predatory losses due to early occurrence and enhanced abundances of C. vicinus, rather than competition for the same food resources, are hypothesized to be responsible for the declines of C. kolensis and Eudiaptomus.5. Summer species tended to develop higher abundances early in the season, which led to enhanced seasonal means during spring. These changes cannot be explained by the interaction between calanoids and cyclopoids alone, but were probably a result of changes in fish predation.
Factors influencing stream chemistry in catchments on Prince of Wales Island, Alaska
Authors: WISSMAR ROBERT , SWANSTON DOUGLAS , BRYANT MASON , McGEE KATHERINE 
Published: November 2003

1. Factors influencing the water chemistry of streams were evaluated for remote catchments on Prince of Wales Island, Alaska, a high‐latitude geologically diverse landscape.2. We evaluated the hypothesis that weathering rates of dominant geological formations of catchments would be the major factor influencing the water chemistry of streams.3. Catchments were compared by synoptic sampling of stream and cave waters, mapping to define the distribution of geological formations, and laboratory studies of rock weathering.4. Carbonation was identified as the major mechanism influencing the weathering of rocks. High Pco2 levels of cave and upwelling waters in streams suggested CO2, supplied by soil respiratory processes, was the major factor controlling the concentration of dissolved CO2, carbonic acid dissociation, and H+ replacement of cations on rock surfaces.5. Additional evidence of carbonation included the relationship between HCO31– and Ca2+ + Mg2+ (r2 = 0.95) for low‐ and high‐alkalinity waters. The relationship suggested that the high‐alkalinity waters were associated with the weathering of calcareous rocks. Waters with high alkalinities (> 1254 μeq l–1), pH (> 7.0), Ca : Mg ratios (> 6.0.) and saturation values for Ca2+ (SIc = –0.59–0.06) indicated that karst (limestone) formations with calcite minerals were the major sources of calcium (> 1266 μeq l–1). Waters with the lowest alkalinity, pH, HCO31– and cation concentrations were associated with granodiorite (igneous) rocks. Laboratory studies substantiated these findings, with weathering being highest when waters contacted Heceta and Bay of Pillars limestone formations and lowest with igneous rocks.6. Weathering of rocks, and possibly soils, appeared to be facilitated by surface and subsurface movements of CO2 and water through fractured karst formations, and water availability in rain‐dominated forests. The proximity of the sea and sulphur in marine aerosols and rainfall, and sulphate reacting with water, may also supply hydrogen ions to weathering reactions.7. This study provides a basis for developing a better understanding of the influences of surface–subsurface geological and hydrological factors, and climatic conditions, on stream chemistry and biota in high‐latitude ecosystems.
Predicting development, metabolism and secondary production for the invertebrate predator Bythotrephes
Authors: LEHMAN JOHN , BILKOVIC DONNA MARIE , SULLIVAN CHRIS 
Published: November 2003

1. Rates of embryonic and post‐embryonic development for Bythotrephes cederstroemi from Lakes Erie, Huron and Michigan are represented almost equally well by three empirical models across water temperatures ranging from about 12–22 °C, but at lower temperatures two of the competing models fail and an exponential development rate model proves most robust.2. Clutch masses of parthenogenic females can greatly exceed the tissue mass of the mother. Clutch size is strongly correlated with the mass of reproductive adults, accounting for over 90% of the variation among individuals. Hence, the mass gain from neonate to reproductive adult can be estimated directly from clutch size.3. Tissue stoichiometries, respiration quotients and stoichiometries of C and N metabolism were determined experimentally, extending the predictions of existing respiration and growth models.4. A predictive model for growth and production by the invertebrate predator has advantages over previous model formulations owing to our expanded calibration data base. The model is presented in a modular design that is easily upgraded as additional calibration data become available.
Algal species composition and phosphorus recycling at contrasting grazing pressure: an experimental study in sub‐Antarctic lakes with two trophic levels
Authors: HANSSON LARS‐ANDERS , TRANVIK LARS 
Published: November 2003

1. To test the response of algal communities to altered grazer abundance in lakes lacking efficient predators on herbivores, we performed field and experimental studies in two sub‐Antarctic lakes (South Georgia).2. The number of algal species in these high latitude lakes is low, and all dominant species have grazer‐resistant adaptations, including spines in three dimensions (Staurastrum sp.), large size (Tribonema sp.), a mucus sheet allowing viable passage through the gut (Chlamydocapsa sp., Elakatothrix sp.) or ability to recruit individuals from the sediment surface (Mallomonas sp.).3. Algal community composition was only slightly changed by experimentally altered grazer abundance, indicating that it was already adapted for a high grazing pressure. Hence, the diets of herbivores were restricted to vulnerable food organisms such as Mallomonas sp. and heterotrophic flagellates in the water column, and to benthic food sources.4. At high grazer abundance, the concentration of available phosphorus (PO4‐P) in the water was lower than at low grazer abundances, due to inefficient nutrient regeneration by the copepod herbivores. Hence, in lakes where copepods are dominant grazers, algae suffer both directly from grazing and indirectly from reduced nutrient availability.
The affect of temperature on the metabolism and behaviour of an endemic amphipod, Hyalella montezuma, from Montezuma Well, Arizona, U.S.A.
Authors: OBERLIN GAYE , BLINN DEAN 
Published: November 2003

1. Hyalellamontezuma is endemic to Montezuma Well, Arizona, and is exposed to minimal diel and seasonal temperature fluctuations in the pelagic zone (21 ± 4 °C). Juvenile H. montezuma feed in the pelagic zone during the day and migrate into the littoral vegetation at night, while adults remain primarily in the littoral vegetation.2. Oxygen consumption (VO2) of adult and juvenile H. montezuma was measured at 20, 25 and 30 °C. The VO2 of both adult and juvenile H. montezuma increased with temperature. However, the VO2 of juveniles was significantly greater than that of adults at all temperatures, with greatest divergence at 30 °C where mean juvenile VO2 (6.31 μl mg–1 dry weight (DW) h–1) was almost twice that of adults (3.60 μl mg–1 DW h–1).3. Survivorship of juveniles was significantly lower (54%) at 30 °C than at 27.5 °C (95%) after 4 h, whereas adults showed at least a 93% survivorship at both temperatures.4. Our data suggest that temperature may have been the proximate cue that elicited the diel horizontal migration of juvenile H. montezuma in Montezuma Well, with the behaviour maintained and enhanced by intensive invertebrate predation in the pelagic and littoral zones.
Production of benthic macroinvertebrate communities along a southern Appalachian river continuum
Authors: GRUBAUGH JACK , WALLACE BRUCE , HOUSTON ELIZABETH 
Published: November 2003

1. Annual production was estimated for macroinvertebrate communities of principle habitats along a first‐ to seventh‐order river continuum in the southern Appalachian Mountains (U.S.A.). Annual production was relatively low in depositional habitats, pebble/gravel substrata, and on cobble devoid of plant biomass (mosses and hydrophytes). Production was greater in bedrock habitats and greatest on hydrophyte‐covered cobble, with estimates reaching 364 g AFDM (ash‐free dry mass)m–2 yr–1 in a sixth‐order river reach. Annual production in depositional habitats was correlated to standing crops of benthic organic material (BOM) in low‐order stream reaches but not in higher‐order reaches, indicating differences in BOM availability with stream size. In cobble, pebble/gravel and bedrock habitats production was significantly correlated to standing crops of aquatic plants, which can stabilize substrata and enhance access of collector‐filtering invertebrates to entrained food resources.2. By accounting for proportional availability of habitats along the continuum, estimates of total production ranged from 5 to 154 g AFDM m–2 yr–1, and increased significantly with stream size. Annual production estimated for sixth‐ and seventh‐order reaches of the continuum were amongst the highest reported thus far for lotic systems. Organization of the benthic community along the continuum, based on production estimates for individual functional feeding‐groups, generally supported predictions of the River Continuum Concept (RCC): shredder contributions were greatest in low‐order reaches and declined downstream; scraper percentages were greatest in the middle of the continuum; collector‐filterer contributions increased with increasing stream size. Longitudinal trends for collector‐gatherers and predators did not support RCC predictions; these groups appeared to be influenced by localized changes in habitat availability and occurrence of vertebrate predators along the continuum.
A new apparatus to measure the rate of fall of seeds
Authors: ASKEW A. P. , CORKER D. , HODKINSON D. J. , THOMPSON K. 
Published: November 2003

1. Seed dispersal is widely recognized to be of crucial importance in the ecology of plant communities, yet characterization of dispersal capacity rarely goes beyond two categories: ‘good’ and ‘poor’ dispersers, defined on the basis of dispersule morphology. 2. We describe a new apparatus which determines the rate of fall of seeds in air by detecting their passage through two fans of laser light. 3. This apparatus is able to measure rate of fall in smaller seeds than previously published methods and reveals that there is no justification for the arbitrary division of species into two wind dispersal categories.
Resprouters vs reseeders in South African forest trees; a model based on forest canopy height
Authors: KRUGER L. M. , MIDGLEY J. J. , COWLING R. M. 
Published: November 2003

1. We expect tree species that regenerate primarily by sprouting to produce fewer seedlings than co‐occurring species that regenerate mainly from seedlings, because of the trade‐off between allocating resources either to ensuring vegetative reproduction (e.g. protective bark/latent buds) or to sexual reproduction (e.g. seeds). 2. Furthermore, resprouting species, because of their multi‐stemmed nature, should be at a relative disadvantage, and therefore relatively infrequent, in tall forests. This is because a resprouting individual allocates resources to a number of basal branches/stems and buds rather than maximizing vertical extension of a single leader, as is the case in a seeder. Also, many tall stems arising from the same multi‐stemmed base, as is the case in resprouters, will be relatively poorly supported in comparison to the single stem of a reseeder. 3. To test these two ideas we surveyed a number of plots in a range of South African forests and thicket communities. We noted the numbers of seedlings and resprouts for each species and determined a mean for each site. 4. Short forests and thickets were dominated by multi‐stemmed species and there was an almost total absence of seedlings. In contrast, tall forests were dominated by single‐stemmed reseeding species and were accompanied by seedlings.
Nutrient dynamics of the highly productive C4 macrophyte Echinochloa polystachya on the Amazon floodplain
Authors: PIEDADE M. T. F. , JUNK W. J. , LONG S. P. 
Published: November 2003

1.
Echinochloa polystachya forms extensive monotypic stands on the lower levels of the Amazon floodplains. During its annual growth cycle c. 100t (dry mass) ha–1 of biomass is formed as the floodplain is being submerged (December–September) and a phase of death and decomposition occurs when the water has retreated (October–November). This study examines the mineral nutrient dynamics of this plant and its potential significance to the nutrient status of the floodplain. 2.
Echinochloa polystachya was sampled monthly from a study site in the central Amazon. N, P and K contents for different plant organs were determined and net uptake calculated from concurrent measurements of dry matter production and turnover. 3. Leaf N, P and K contents were c. 20, 1·7 and 19gkg–1, values typical of nutrient‐replete stands of C4 plants. Stem concentrations were c. 12% of those of the leaves. Net N and P uptake followed the rise in the river level, whilst K appeared independent of water level. 4. The vegetation accumulated 377, 51 and 1136kgha–2 of N, P and K, respectively, during the growth phase. Over a possible 5000km2 of these stands in the Várzea, this represents a massive sequestration of nutrients in the flood phase and a high release during the following low‐water period. It is suggested that the E. polystachya stands could have a role in maintaining the nutrient status of the Amazon floodplain.
The species–body size distribution: energy, fitness and optimality
Authors: CHOWN S. L. , GASTON K. J. 
Published: November 2003

1. Recently, fresh attempts have been made to understand the mechanisms structuring species–body size distributions. Of these, the model developed by Brown, Marquet & Taper (1993) (BMT), which uses measures of resource acquisition and conversion to determine an optimal body size (M*) for a given assemblage, is potentially the most significant. Here, we examine the novelty of the model and some of its assumptions, and test its empirical predictions. 2. The BMT model is one of a suite of physiological/life‐history models examining size at maturity. Such energetic or ‘physical’ approaches to body size evolution have a considerable modern history and continue to enjoy attention in physiological ecology and life‐history theory. 3. Although mortality significantly influences life‐history evolution and mostly precludes the evolution of a body size that maximizes reproductive power output, it is excluded from the BMT model. Likewise, the model assumes that power and not efficiency is maximized, although there are conditions where this is not likely to be the case. Furthermore, the BMT model assumes that resource acquisition and conversion are physiologically limited, although the importance of physiological limitation in ecology remains unclear. 4. Additional assumptions of the model include coincidence of the optimum body size of an individual and a species, when in many species this is not the case, and coincidence of the most speciose size class in an assemblage and the optimal body size. Similarly, the probable influence of differences in the scaling of various parameters at the intra‐ and interspecific levels are not addressed, nor are the impacts of discrepancies between phenotypic and genotypic optima. 5. The measures of resource acquisition and conversion used in the BMT model are not only problematic, but also limit the utility of the model. If the scaling constants and exponents of field metabolic rate minus basal metabolic are used as a measure of resource acquisition beyond maintenance needs, and those for intrinsic rate of increase (rmax) as a measure of resource conversion, the applicability of the model to other taxa can be extended. 6. Using these measures we show that the model continues to provide a reasonable prediction of M* for the terrestrial mammal assemblages of both North America and Australia. However, when taxonomic inclusiveness is reduced by removing eutherians from the Australian data set and by examining the predictions of the model with regard to diprotodonts only, the model fails to provide reasonable predictions of M*. 7. Given problems with the BMT model, but its clear ability to predict the modal body size of at least two terrestrial mammal assemblages, we suggest that there is considerable scope for exploring the relationships between resource acquisition and conversion at the level of the individual and energy partitioning between individuals in multispecies communities.