bluuebunny/crossref_metadata_2025 huggingface dataset:
The relationship between land use and physicochemistry, food resources and macroinvertebrate communities in tributaries of the Taieri River, New Zealand: a hierarchically scaled approach
Authors: TOWNSEND COLIN , ARBUCKLE CHRIS , CROWL TODD , SCARSBROOK MIKE
Published: November 2003

1. The relationship between land use and stream conditions was investigated, including physicochemistry, the availability of primary food resources and species richness, species composition and trophic structure of stream macroinvertebrate communities. The survey involved eight subcatchments of the Taieri River (New Zealand) encompassing reasonably homogeneous examples of four major land uses: native forest, native tussock grassland, plantations of introduced pine and agricultural pasture.

2. Each land use was represented by two subcatchments, each subcatchment by two to four tributaries, and each tributary by two to three sampling sites. These three sampling scales each represent typical designs for stream community studies. By recording responses at all scales, it can be determined explicitly whether the scale of sampling influences interpretation of community structure.

3. Elevation, riffle length, proportion of large substrata in the bed, total phosphorus and alkalinity were significantly related to land use, as were canopy cover and the relative abundance of leaves and wood in the streams. Principal components analysis of invertebrate density data identified nine orthogonal community types, the distributions of two of which were significantly related to land use. The role played by browsers and shredders in the stream community depended on land use.

4. Primary analysis was at the level of the tributary. When it focused on sites within tributaries, more variables were related to land use and at a higher level of significance. This was largely a result of enhanced statistical power due to increased replication. When whole subcatchments were the focus of attention, statistical power was so low, even with six to eleven subsamples to generate overall means, that few significant patterns could be identified. However, the community patterns that were revealed were similar whatever the scale of sampling.
Reconciling landscape and local views of aquatic communities: lessons from Michigan trout streams
Authors: WILEY MICHAEL , KOHLER STEVEN , SEELBACH PAUL
Published: November 2003

1. Rapidly advancing geographical information systems (GIS) technologies are forcing a careful evaluation of the roles and biases of landscape and traditional site‐based perspectives on assessments of aquatic communities. Viewing the world at very different scales can lead to seeming contradictions about the nature of specific ecological systems. In the case of Michigan trout streams, landscape analyses suggest a predictable community shaped by large‐scale patterns in hydrology and geology. Most site‐based studies, however, suggest these communities are highly variable in structure over time, and are strongly shaped by site‐specific physical and biological dynamics. As the real world is comprised of processes operating both at local and landscape scales, an analytical framework for integrating these paradigms is desirable.

2. Decomposition of variances by factorial ANOVA into time, space and time–space interaction terms can provide a conceptual and analytical model for integrating processes operating at landscape and local scales. Using this approach, long‐term data sets were examined for three insects and two fishes common in Michigan trout streams. Each taxon had a unique variance structure, and the observed variance structure was highly dependent upon sample size.

3. Both spatially extensive designs with little sampling over time (typical of many GIS studies) and temporally extensive designs with little or no spatial sampling (typical of population and community studies), are biased in terms of their view of the relative importance of local and landscape factors. The necessary, but in many cases costly, solution is to develop and analyse data sets that are both spatially and temporally extensive.
Seasonal variation in vertical and horizontal movement of the freshwater bivalve Elliptio complanata (Mollusca: Unionidae)
Authors: AMYOT JEAN‐PIERRE , DOWNING JOHN
Published: November 2003

1. Vertical and horizontal movement were studied in the freshwater bivalve Elliptio complanata at a sandy site in an oligotrophic lake over 3 years. Mussel movement did not vary significantly between day and night. On average, between 2 and 8% of 527 mussels moved each month during the ice‐free season and the distance travelled by moving mussels averaged 0.6 cm day–1.

2. Mussels were endobenthic during the winter, emerged from the sandy substrate in mid‐May, peaked in sediment surface abundance in July, and descended into the sediments for the winter in September–October. Vertical displacement of mussels was closely correlated with water temperature although daylength may play a role. Mussels apparently move very little beneath the sediment during the winter.

3. The number of mussels moving horizontally at any given time was linearly correlated with daylength, but the distance travelled during a sampling period was related to daylength in a non‐linear fashion. Greatest horizontal displacement of epibenthic mussels was found during spring and early summer, coincident with spawning in E. complanata
Internal shell annuli yield inaccurate growth estimates in the freshwater mussels Elliptio complanata and Lampsilis radiata
Authors: KESLER DAVID , DOWNING JOHN
Published: November 2003

1. The objective of this study was to compare, in freshwater bivalves, growth rates inferred from the spacing of internal annuli to those obtained directly by measuring annual changes in shell length.

2. The unionid mussels studied were Elliptio complanata and Lampsilis radiata from a pond in the north‐eastern U.S.A. Age was inferred from internal lines of 157 E. complanata and twenty‐five L. radiata. Actual length change was determined from comparisons of annual remeasurements of marked E. complanata (n = 520) in 1992–95 and L. radiata (n = 81) in 1993–95.

3. High retrieval rates of painted mussels demonstrated the efficacy of the marking method.

4. Annual length changes determined by remeasurement were significantly lower than annual length changes predicted by length‐at‐age data from internal annuli. Should this be a common occurrence, past estimates of annual growth based on annuli are probably too large, and unionid mussels may be much older than previously assumed.
Seasonal, discharge‐driven patterns of mayfly assemblages in an intermittent Neotropical stream
Authors: NOLTE ULRIKE , DE OLIVEIRA MARIA JOSÉ , STUR ELISABETH
Published: November 2003

1. Streams in the seasonal wet and dry tropics have highly dynamic discharge regimes. Our study stream, located in mid‐western Brazil, drains into the Pantanal, South America’s largest wetlands, and is characterized by frequent spates in the rainy season and several weeks of interrupted flow in the dry season.

2. In order to understand how these seasonal flow patterns influence the aquatic fauna, floating litter was studied because: (i) this habitat is exposed to the current, and thus is likely to be most affected abiotically and biotically by changes in flow; and (ii) this habitat is abundant in unaltered tropical streams. Studies were conducted in a third‐ and a fourth‐order reach. Mayflies were chosen as study organisms because they were frequent and species‐rich on floating litter, and because they should to be responsive to changes in current velocity.

3. In the course of 15 months, covering one rainy and two dry seasons, mayflies showed pronounced seasonal patterns at family and genus level, which were evidently driven by discharge. Two periods of high mayfly densities were observed in the course of one year. One maximum coincided with the peak of the rainy season, the other with the peak of the dry season, and both were distinct in faunistic composition. At high current velocities the leptophlebiid Farrodes sp. was dominant and Leptohyphes sp., Acerpenna sp. and Paracloeodes sp. were frequent. In the dry season, when the river was reduced to isolated standing waters, 86–93% of all mayflies were Caenis sp.

4. Altogether sixteen mayfly genera from the families Baetidae, Caenidae, Leptohyphidae, Leptophlebiidae and Oligoneuriidae were recorded. Two genera are new to science, the baetid Aturbina was recently described (among others, from material from our study river), Acerpenna and Paracloeodes are new records for South America, and Miroculis and Terpides are recorded for the first time south of the Amazon.
The role of carbon dioxide in the initiation and maintenance of blue‐green dominance in lakes
Authors: SHAPIRO JOSEPH
Published: November 2003

1. In 1993 the south basin of Squaw Lake, Wisconsin, U.S.A., was artificially circulated and injected with CO2 in an attempt to eliminate the massive quantities of blue‐greens normally present during summer. The unmixed, uninjected north basin was the control. Despite a great difference in CO2 concentration and in pH between the two basins, their blue‐green maxima began simultaneously and eventually reached the same size. The predominant algae in both basins were Aphanizomenon flos‐aquae and Anabaena flos‐aquae.

2. From 13 May to 9 September, experiments were done to determine the responses of photosynthesis (oxygen production) of the phytoplankton communities in both basins to changes in pH over the range 7–9. Both the north and south basins underwent two distinct shifts in the slopes of their photosynthetic responses to pH. These shifts paralleled changes in the proportion of blue‐greens in their phytoplankton.

3. Experiments with additions of KHCO3 or NaHCO3 showed that the responses to pH were really responses to CO2 concentration. Therefore, the data obtained in the photosynthesis experiments were used to calculate the kinetic parameters Ks* and Vmax*. The Ks* values varied in relation to the proportion of blue‐greens, with lower values during the period when blue‐greens predominated. The Vmax*values showed no such systematic changes.

4. CO2 compensation and zero photosynthesis concentrations confirm that when the blue‐greens dominated, CO2 was taken up much more efficiently than when the phytoplankton comprised mostly non‐blue‐greens. No evidence appeared suggesting direct use of bicarbonate even at pH values of 10.0.

5. Experiments with water collected seasonally from four other lakes show that Squaw Lake is not unique. In each case the response slopes (and therefore Ks* values) were high during spring when non‐blue‐greens were dominant, but decreased when the blue‐green maximum began.

6. Experiments with individual species of algae confirm that blue‐greens generally have better CO2 kinetics than do greens.

7. It is concluded that initiation of the blue‐green maximum does not depend upon conditions of low CO2 concentration or high pH. However, once the blue‐greens become abundant they ensure their dominance by reducing concentrations of CO2 to levels available only to themselves.
Response of littoral invertebrates to reduction of fish density: simultaneous experiments in ponds with different fish assemblages
Authors: PIERCE CLAY , HINRICHS BRUCE
Published: November 2003

1. We experimentally reduced densities of predatory fish in replicated 2 m2 areas of the littoral zone in two ponds to test whether density and biomass of invertebrates would respond to release from fish predation. The ponds are of similar size and in close proximity, but support different fish assemblages: bluegills (Lepomis macrochirus Rafinesque) and largemouth bass (Micropterus salmoides (Lacepede)) in one pond, and bluespotted sunfish (Enneacanthus gloriosus (Holbrook)) and chain pickerel (Esox niger Lesueur) in the other. Fish densities were reduced to less than 15% of ambient levels in both experiments.

2. In the bluegill–bass pond, density and biomass of most invertebrate taxa and size classes were unaffected by the fish manipulation. Total invertebrate densities did not differ significantly between fish treatments, but total invertebrate biomass was significantly greater where fish density was reduced, averaging 30% higher over the course of the study. Likewise, manipulation of fish in the bluespotted sunfish–pickerel pond had few significant effects on individual taxa and size classes. There were no significant effects on total invertebrate abundance in the bluespotted sunfish–pickerel pond.

3. Our results provide direct experimental evidence consistent with the collective evidence from previous work, suggesting that the impact of fish predation on density and biomass of invertebrate prey in littoral habitats is variable, but generally weak. Invertebrates that coexist successfully with fish in littoral systems probably are adept at taking advantage of refugia offered by the structurally complex physical environment.
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.
A biomechanical hypothesis explaining upstream movements by the freshwater snail Elimia
Authors: HURYN A. D. , DENNY M. W.
Published: November 2003

1. Many taxa of freshwater invertebrates show active upstream movements, particularly the snails. Hypotheses explaining this behaviour invoke the search for food or space, compensation for drift, avoidance of predation and hydrodynamic effects. The pervasiveness of upstream movements among remote lineages of snails (two subclasses, three orders, 10 families), however, suggests that snails may move upstream for mechanical rather than adaptive reasons.

2. It is proposed that upstream movements by snails are a function of torque on the snail’s foot generated by hydrodynamic drag on the shell. When subject to high broadside drag‐forces on their shells, snails are able to reduce torque and stabilize orientation only by directing their anterior aspect upstream.

3. Movements of the freshwater pleurocerid snail Elimia were studied by following marked free‐ranging individuals in six streams in Alabama, USA (four species, eight populations).

4. Populations showed either no net movement (two streams) or significant upstream movements ranging to a mean of ≈40 m over a 3‐month period (four streams). Movement patterns were stream specific rather than species or population specific. Within populations showing significant upstream movements, snails with shell lengths ≤10 mm showed little net movement. Larger snails showed movements from 0 to >200 m upstream.

5. A torque‐constrained random walk model was used to perform a post hoc test of the hypothesis that upstream movements were a function of torque on the snail’s foot generated by hydrodynamic drag on the shell. The model predicted upstream and size‐dependent movement patterns that approximated those observed for snails in the field.
Influence of pregnancy on the thermal biology of the lizard, Sceloporus jarrovi: why do pregnant females exhibit low body temperatures?
Authors: MATHIES T. , ANDREWS R. M.
Published: November 2003

1. Selected body temperatures of female lizards, Sceloporus jarrovi, were measured on a photothermal gradient during late pregnancy and again when postpartum, and pregnant females were subjected to one of three fluctuating temperature regimes that simulated body temperatures of (1) pregnant females, (2) postpartum females or (3) allowed normal thermoregulation.

2. Overall, females selected lower body temperatures when pregnant (mean = 32·0°C) than when postpartum (mean = 33·5°C).

3. Females regulated body temperature more precisely when pregnant than when postpartum as judged by their smaller variances in body temperature throughout the day.

4. When pregnant, females selected a lower mean maximum body temperature (mean: pregnant = 32·8°C; postpartum = 34·5°C) than when postpartum, but selected mean minimum body temperatures did not differ.

5. None of the experimental temperature treatments was detrimental to pregnant females. Female body length increased during pregnancy but the rate of increase did not differ among treatments. Moreover, length‐adjusted body mass of postpartum females did not differ among treatments.

6. Pregnant females that experienced postpartum body temperatures produced neonates that were smaller in body mass and length than pregnant females that experienced pregnant body temperatures and females that were allowed to thermoregulate.

7. For neonates resulting from the postpartum body temperature treatment, the disparity in the body length, but not mass, was still observed at 9 days of age, although survival and growth of neonates was high and did not differ among treatments.

8. The results demonstrate that pregnant females could maintain higher postpartum body temperatures without compromising their physical condition, but select relatively low body temperatures, presumably to avoid decrements in offspring fitness.
The effect of nitrogen fertilization and rust fungus infection, singly and combined, on the leaf chemical composition of Rumex obtusifolius
Authors: HATCHER P. E. , PAUL N. D. , AYRES P. G. , WHITTAKER J. B.
Published: November 2003

1. The chrysomelid beetle Gastrophysa viridula occurs on Rumex obtusifolius growing in a range of nutrient conditions and also on plants infected with the foliar fungus Uromyces rumicis. In a controlled environment, we investigated the effect of fertilizing plants with eight nitrate and four ammonium concentrations, with or without infection, on leaf nutritional quality.

2. Increasing nitrate fertilization increased leaf oxalate, total nitrogen and nitrate concentrations and water content, and decreased total non‐structural carbohydrate (NSC) concentrations. Increasing ammonium fertilization increased leaf nitrogen concentration and water content, decreased nitrate and NSC concentrations, and had no effect on oxalate concentrations.

3. Infection produced a mainly additive effect to fertilization, increasing NSC and oxalate, and decreasing nitrate and nitrogen concentration in whole plants fed nitrate, and increasing nitrate and NSC in whole plants fed ammonium.

4. Young leaves on infected plants remained uninfected and had greater nitrogen and NSC concentrations, and lower oxalate and nitrate concentrations, than infected leaves on the same plant.

5. These results are discussed in relation to changes in C:N and NSC:organic nitrogen ratios, the effect of nitrate and oxalate, and the known feeding and oviposition preferences of the beetle. The results suggest that there is an optimum nitrogen fertilization level for G. viridula development.
The influence of preformed defences on the dynamic wound response in Spruce bark
Authors: WAINHOUSE D. , ROSE D. R. , PEACE A. J.
Published: November 2003

1. Two of the principal defences in conifer bark against attack by bark beetles and associated fungi, the flow of preformed resin and the dynamic wound response (DWR), are commonly regarded as separate, sequential responses to attack. In this paper the concentration of three preformed defences (resin, total polyphenols and lignified stone cell masses) was measured at different heights on the stem of Norway and Sitka Spruce to determine their effect on the size of lesions formed during the DWR to inoculation with three facultatively pathogenic fungi (Phacidium coniferarum, Ophiostoma piceae and Cryptosporiopsis sp.) inoculated during the dormant season.

2. There was considerable within‐tree variation in concentration of lignin and there was a dose‐dependent negative effect of lignin on lesion size. The form of the relationship, however, was influenced by fungal and tree species and for some fungi, also by an individual tree effect.

3. Results suggest that resistance of conifer bark to pests and pathogens depends on an interaction between preformed and induced defences.
Latitudinal compensation in oyster ciliary activity
Authors: DITTMAN D. E.
Published: November 2003

1. Theories of latitudinal compensation predict that individuals living in colder temperature regimes should physiologically compensate for the slowing of standard physiological rates, owing to the relatively low temperature of their local environments, by increasing their metabolic rate in colder water temperatures relative to individuals living in warmer water temperature regimes.

2. This hypothesis was tested with oyster strains originally from geographically separated populations that were raised in a common environment for seven generations. The physiological parameter measured was ciliary activity across a temperature gradient.

3. Support for the latitudinal compensation hypothesis was found: the strain originally from the colder temperature regime had more active cilia at lower experimental temperatures than individuals originally from the warmer temperature regime. Ciliary activity of the more northern Long Island Sound oysters was significantly greater than activity in the more southern Delaware Bay oysters at temperatures of –1, 2 and 6 °C.

4. These results suggest that there is genetically based physiological differentiation between these populations of oysters consistent with the latitudinal compensation for local temperature regime.
Periodic arousals in hibernating mammals: is evaporative water loss involved?
Authors: THOMAS D. W. , GEISER F.
Published: November 2003

1. Using existing data on the rate of cutaneous and pulmonary evaporative water loss (EWL) for hibernating Little Brown Bats (Myotis lucifugus) and on the duration of torpor bouts, body temperature (Tb) and oxygen uptake (VO2) of Golden‐mantled Ground Squirrels (Spermophilus saturatus), the rate of EWL was modelled for ground squirrels hibernating at ambient temperatures (Ta) of –2, 2, 4 and 8 °C.

2. Total EWL showed a curvilinear response to Ta, being lowest at 2 °C and increasing with both increasing and decreasing Ta. EWL at –2 °C was about equal to that at 4 °C. The duration of torpor bouts showed the same curvilinear response to Ta and torpor bout duration at –2 °C was similar to that at 4 °C (8·5 vs 8·3 days, respectively).

3. At Ta≥ 2 °C, where Tb of torpid S. saturatus is not metabolically defended, torpor bout duration is significantly related to Tb, VO2 and EWL, with the three variables having similar r2 values.

4. Using the regression equations generated at Ta≥ 2 °C to predict torpor bout durations at –2 °C, where Tb is metabolically defended, shows that the three variables do not have equivalent predictive abilities. Tb and VO2 predicted torpor bout durations of 15·2 and –40·4 days, respectively, compared with observed durations of 8·5 days at –2 °C. EWL predicted torpor bout durations of 8·4 days or only 0·1 days less than that observed at –2 °C.

5. The relation between torpor bout duration and total EWL was insensitive to major variations in cutaneous EWL. Over Ta ranging from –2 °C to 8 °C, a stepwise multiple regression including Tb, VO2 and EWL as independent variables identified EWL as the only variable significantly correlated with torpor bout duration.

6. Our analyses suggest that torpor bout duration may be influenced by EWL, indicating that animals may need to obtain free water when they arouse. An analysis of the structural and temperature characteristics of ground squirrel hibernacula suggests that they may function as a biological condensing tower. Throughout winter, water should evaporate from the warm lower levels and condense in the colder upper regions and so free water may be available to animals when they arouse.
Reduced tail regeneration in the Common Lizard, Lacerta vivipara, parasitized by blood parasites
Authors: OPPLIGER A. , CLOBERT J.
Published: November 2003

1. Many lizards will lose their tail through autotomy as an antipredator device even though there must be significant costs during tail regeneration.

2. Parasites are energetically costly to the host, and may reduce the rate of cell regeneration. The relation between the presence of haemogregarines (phylum Sporozoa) and the rate of tail regeneration in the Common Lizard Lacerta vivipara (Jacquin) was examined.

3. Experimentally induced autotomy in parasitized lizards resulted in a significantly reduced rate of tail regeneration compared with non‐parasitized lizards. On the other hand, tail loss was not associated with an abnormal increase of parasite load, suggesting that the physiological stress (induced by tail loss) did not cause a decrease in parasite defence.