bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geomorphic thresholds in riverine landscapes
Authors: CHURCH MICHAEL 
Published: March 2003

1. Rivers are subject to thresholds of several types that define significant changes in processes and morphology and delimit distinctive riverine landscapes and habitats. Thresholds are set by the conditions that govern river channel process and form, amongst which the most important are the flow regime, the quantity and calibre of sediment delivered to the channel, and the topographic setting (which determines the gradient of the channel). These factors determine the sediment transport regime and the character of alluvial deposits along the channel.2. Changes occur systematically along the drainage system as flow, gradient and sediment character change, so a characteristic sequence of morphological and habitat types – hence of riverine landscapes – can be described from uplands to distal channels. The sequence is closely associated with stream competence to move sediment and with bank stability.3. The paper proposes a first order classification of river channel and landscape types based on these factors. The riverine landscape is affected seasonally by flow thresholds, and further seasonal thresholds in northern rivers are conditioned by the ice regime.4. It is important to understand geomorphic thresholds in rivers not only for the way they determine morphology and habitat, but because human activity can precipitate threshold crossings which change these features significantly, through either planned or inadvertent actions. Hence, human actions frequently dictate the character of the riverine landscape.
Calcium content of crustacean zooplankton and its potential role in species distribution
Authors: Wærvågen Svein B. , A. Rukke Nina , Hessen Dag O. 
Published: March 2003

SUMMARY 1. The occurrence and species composition of crustacean zooplankton in Norwegian lakes was related to ambient Ca concentrations, pH, total phosphorus and chlorophyll a, and to the presence/absence of other zooplankters and a planktivorous fish (roach: Rutilus rutilus).2. Ambient Ca concentrations appeared to influence the distribution of Daphnia species: Daphnia longispina often occurred in Ca‐rich lakes with low fish‐predation pressure while the smaller Daphnia cristata often occurred in opposite conditions.3. Body Ca contents were measured in zooplankters from a wide range of localities, to examine Ca requirements and thus the potential for Ca‐limitation of common species.4. All Daphnia species had relatively high specific Ca contents [ranging from 0.8 to 4.4% Ca dry weight (DW)−1] compared with other cladocerans and also copepods (ranging from 0.1 to 0.4% Ca DW−1). Within the Daphnia genus, the specific Ca content increased with increasing body size of the species, and thus the large‐bodied species had especially high Ca demands.5. Because of their high Ca demands, species of Daphnia could be competitively disadvantaged in softwater lakes relative to less Ca‐demanding species.
Predation on exotic zebra mussels by native fishes: effects on predator and prey
Authors: Magoulick Daniel D. , Lewis Lindsey C. 
Published: March 2003

SUMMARY 1. Exotic zebra mussels, Dreissena polymorpha, occur in southern U.S. waterways in high densities, but little is known about the interaction between native fish predators and zebra mussels. Previous studies have suggested that exotic zebra mussels are low profitability prey items and native vertebrate predators are unlikely to reduce zebra mussel densities. We tested these hypotheses by observing prey use of fishes, determining energy content of primary prey species of fishes, and conducting predator exclusion experiments in Lake Dardanelle, Arkansas.2. Zebra mussels were the primary prey eaten by 52.9% of blue catfish, Ictalurus furcatus; 48.2% of freshwater drum, Aplodinotus grunniens; and 100% of adult redear sunfish, Lepomis microlophus. Blue catfish showed distinct seasonal prey shifts, feeding on zebra mussels in summer and shad, Dorosoma spp., during winter. Energy content (joules g−1) of blue catfish prey (threadfin shad, Dorosoma petenense; gizzard shad, D. cepedianum; zebra mussels; and asiatic clams, Corbicula fluminea) showed a significant species by season interaction, but shad were always significantly greater in energy content than bivalves examined as either ash‐free dry mass or whole organism dry mass. Fish predators significantly reduced densities of large zebra mussels (>5 mm length) colonising clay tiles in the summers of 1997 and 1998, but predation effects on small zebra mussels (≤5 mm length) were less clear.3. Freshwater drum and redear sunfish process bivalve prey by crushing shells and obtain low amounts of higher‐energy food (only the flesh), whereas blue catfish lack a shell‐crushing apparatus and ingest large amounts of low‐energy food per unit time (bivalves with their shells). Blue catfish appeared to select the abundant zebra mussel over the more energetically rich shad during summer, then shifted to shad during winter when shad experienced temperature‐dependent stress and mortality. Native fish predators can suppress adult zebra mussel colonisation, but are ultimately unlikely to limit population density because of zebra mussel reproductive potential.
Growth and survival of Daphnia in epilimnetic and metalimnetic water from oligotrophic lakes: the effects of food and temperature
Authors: Cole Peter C. , Luecke Chris , Wurtsbaugh Wayne A. , Burkart Greta 
Published: March 2003

SUMMARY 1. In oligotrophic lakes, phytoplankton and bacteria growing in the deep chlorophyll maximum in the cool metalimnion of lakes often dominate biomass and production, but the importance of this source of food for zooplankton is unknown.2. During much of the day, Daphnia rosea in two mountain lakes inhabited deep chlorophyll layers where food availability was at least equal to that in the epilimnion.3. To determine the importance of the two strata (epilimnion and metalimnion) for Daphnia, we used a cross‐classified factorial experiment to measure how epilimnetic and metalimnetic food and temperature (10 and 16 °C) influenced survival, growth and reproduction.4. Daphnia survived and grew better when fed seston from the epilimnion of one lake, although chlorophyll, particulate nitrogen and particulate carbon were 2–2.5 times greater in the metalimnion.5. Temperature had no significant influence on Daphnia survival or growth. Similar results were obtained with food from the second lake, with Daphnia surviving and reproducing better when provided with epilimnetic, rather than metalimnetic food, although the quantities of chlorophyll and carbon in the two strata were similar.6. Food quality, rather than quantity or temperature, appeared to be the most important determinant influencing survival, growth and reproduction, and the greater food quantity in the metalimnia was not used effectively by the Daphnia.
Top‐down control of phytoplankton: the role of time scale, lake depth and trophic state
Authors: Benndorf JÜrgen , Böing Wiebke , Koop Jochen , Neubauer Ivonne 
Published: March 2003

SUMMARY 1. One of the most controversial issues in biomanipulation research relates to the conditions required for top‐down control to cascade down from piscivorous fish to phytoplankton. Numerous experiments have demonstrated that Phytoplankton biomass Top‐Down Control (PTDC) occurs under the following conditions: (i) in short‐term experiments, (ii) shallow lakes with macrophytes, and (iii) deep lakes of slightly eutrophic or mesotrophic state. Other experiments indicate that PTDC is unlikely in (iv) eutrophic or hypertrophic deep lakes unless severe light limitation occurs, and (v) all lakes characterised by extreme nutrient limitation (oligo to ultraoligotrophic lakes).2. Key factors responsible for PTDC under conditions (i) to (iii) are time scales preventing the development of slow‐growing inedible phytoplankton (i), shallow depth allowing macrophytes to become dominant primary producers (ii), and biomanipulation‐induced reduction of phosphorus (P) availability for phytoplankton (iii).3. Under conditions (iv) and (v), biomanipulation‐induced reduction of P‐availability might also occur but is insufficient to alter the epilimnetic P‐content enough to initiate effective bottom‐up control (P‐limitation) of phytoplankton. In these cases, P‐loading is much too high (iv) or P‐content in the lake much too low (v) to initiate or enhance P‐limitation of phytoplankton by a biomanipulation‐induced reduction of P‐availability. However, PTDC may exceptionally result under condition (iv) if high mixing depth and/or light attenuation cause severe light limitation of phytoplankton.4. Recognition of the five different conditions reconciles previous seemingly contradictory results from biomanipulation experiments and provides a sound basis for successful application of biomanipulation as a tool for water management.
Thermal patterns in the surface waters of a glacial river corridor (Val Roseg, Switzerland)
Authors: Uehlinger U. , Malard F. , Ward J. V. 
Published: March 2003

SUMMARY 1. We examined the thermal patterns of the surface waters in the catchment of the Roseg River, which is fed by the meltwaters of two valley glaciers. One of the glaciers has a lake at its terminus. The river corridor comprised a proglacial stream reach below one glacier, the glacier lake outlet stream, a 2.5‐km long complex floodplain and a constrained reach extending to the end of the catchment.2. Temperatures were continuously measured with temperature loggers at 27 sites between 1997 and 1998. Moreover, from 1997 to 1999, spot measurements were taken at 33–165 floodplain sites (depending on water level) at monthly intervals.3. The temperature regime of glacial streams, including the glacier lake outlet, was characterised by rapidly increasing temperatures in April and May, a moderate decline from June to September (period of glacial melt) and a subsequent fast decline in autumn. During summer, the lake increased temperatures in the outlet stream by 2–4 °C, compared with the adjacent proglacial stream reach.4. In the main channel (thalweg) of the Roseg River, annual degree‐days (DD) ranged from 176 DD in the upper proglacial reach to 1227 DD at the end of the catchment.5. Thermal variation among different channels within the floodplain was higher than the variation along the entire main channel. Floodplain channels lacking surface connection to the main channel accumulated up to 1661 annual DDs.6. Thermal heterogeneity within the floodplain was linked to the glacial flow pulse. With the onset of ice melt, temperatures in the main channel and in channels surface‐connected to the main channel began to decline, whereas in surface‐disconnected channels temperatures continued to increase; as a consequence, thermal heterogeneity at the floodplain scale rose slightly until September.7. High thermal heterogeneity was not anticipated in the harsh environment of a largely glacierised alpine catchment. The relatively wide range of thermal environments may contribute to the highly diverse zoobenthic community.
Critical thermal limits in Mediterranean ant species: trade‐off between mortality risk and foraging performance
Authors: Cerdá X. , Retana J. , Cros S. 
Published: March 2003

1.In Mediterranean ant communities, a close relationship has been found between activity rhythm in the period of maximum activity and position in the dominance hierarchy: subordinate species are active during the day, when conditions are more severe, while dominants are active during the afternoon and the night.2.Results obtained in this study confirmed that the species foraging at higher temperatures were closer to their critical thermal limits than the species foraging at lower temperatures.3.This enabled two extreme strategies of foraging in relation to temperature to be distinguished: (1) heat‐intolerant ant species behaved as risk‐averse species, foraging at temperatures very far from their critical thermal limits; and (2) heat‐tolerant ant species behaved as risk‐prone species, foraging very near their critical thermal limits and running a high heat mortality risk.4.Heat‐tolerant species benefited from this strategy by having better foraging performance at high temperatures.5.This wide range of thermal niches may be one reason why Mediterranean ant faunas are so diverse in the face of limited diversity in vegetation and habitat structure: the daily range of temperature may be sufficiently great to meet the requirement both of heat‐adapted and cold‐adapted species as well as a spectrum of intermediate forms.
Multiple breeding in the Great Tit, II. The costs of rearing a second clutch
Authors: Verhulst S. 
Published: March 2003

1. Multiple breeding (raising more than one batch of young per breeding season) is a common life‐history tactic, but little is known as yet of the accompanying costs and benefits. Second clutches of Great Tits, a facultative multiple breeder, were removed over three years to investigate the costs of rearing a second clutch. 2. Female parents, but not males, survived significantly better than unmanipulated control birds when the second clutch was removed. The difference between the sexes indicates a potential sexual conflict over the decision to start a second clutch. In neither sex were effects found on egg production in the next year. However, birds of both sexes produced more fledglings from first clutches in the following year when the second clutch had been removed. 3. In males, the experimental effect on fledgling production in the next year could be attributed to their mates, because this effect was restricted to males that bred with the same female as in the previous year. In females, this effect was also found among birds that bred with a new mate, which suggests that rearing a second clutch had a long‐term effect. Females, but not males, found roosting in the following winter had lower mass when the second clutch had been removed, which supports the conclusion that rearing a second clutch has long‐term effects. 4. The experimental effect on female survival was found in two winters with low food availability, but not in a winter with high food availability. This is in agreement with the results of a non‐experimental analysis of data collected in the same population. The effect on fledgling production in the next year was also restricted to years with low food availability in the intervening winter. This suggests that the costs of rearing a second clutch depend on food availability in winter. The possibility that the costs of reproduction generally depend on environmental quality and possible mechanisms are discussed. 5. Food availability in winter is probably unpredictable at the time second clutches are started, and therefore Great Tits should ‘bet‐hedge’ with regard to the decision to start a second clutch.
The contribution of fungus to the diets of three mycophagous marsupials in Eucalyptus forests, revealed by stable isotope analysis
Authors: Mcilwee A. P. , Johnson C. N. 
Published: March 2003

1. Many field studies have shown that small herbivorous mammals include fungus (usually hypogeous sporocarps of ectomycorrhizal fungi) in their diets. However, the dietary importance of fungus relative to other foods is generally unclear because of limitations on the power of conventional techniques of diet analysis. Stable isotope analysis in conjunction with faecal analysis was used in an attempt to overcome these limitations. 2. Two foregut‐fermenting marsupials (the Northern Bettong Bettongia tropica and Rufous Bettong Aepyprymnus rufescens) and a hindgut fermenter (the Northern Brown Bandicoot Isoodon macrourus) were studied. The Northern Bettong and Northern Brown Bandicoot are of similar body size (around 1 kg); the Rufous Bettong is significantly larger at 3 kg. Faecal analysis showed that the two bettongs ate a variety of grasses, lilies and fungi; the bandicoot ate these foods and also invertebrates. 3. Ratios of 15N/14N and 13C/12C differed in major food types collected in the field (fungus, grass, lily and invertebrates). Grass was clearly separated from the other food types by its low 13C/12C ratio, while fungus was separated from the other types by its high 15N/14N ratio. Invertebrates and lilies differed slightly in 13C/12C ratios. 4. Isotope ratios in body tissue (sampled in hair) of the three mammals were also discrete, showing that the species differed in the predominant sources of their C and N. Estimates of the proportion of C assimilated in body tissue that was derived from grass were 80% for the Rufous Bettong, 40% for the Northern Bettong and 45% for the Northern Brown Bandicoot. Analysis of 15N/14N ratios suggested that the Northern Bettong derived almost all its N from fungus, the Northern Brown Bandicoot derived practically no N from fungus, and the Rufous Bettong was intermediate. 5. The results confirm that for the Northern Bettong, fungus is a predominant source of N and C assimilated into body tissue. Differences between the use of fungi by the Northern Bettong and the Northern Brown Bandicoot strengthen conclusions from other studies that foregut fermentation confers on small mammals a greater ability to utilize fungus than does hindgut fermentation. It is hypothesized that the limited use of fungus by the Rufous Bettong is due to the patchy distribution of hypogeous sporocarps, which would result in a high energy cost of foraging for this larger‐bodied species with a higher absolute food requirement.
A simple graphical technique for displaying individual fertility data and cohort survival: case study of 1000 Mediterranean Fruit Fly females
Authors: Carey J. R. , Liedo P. , MÜller H.‐G. , Wang J.‐L. , Vaupel J. W. 
Published: March 2003

1.A graphic technique is presented in which data on age‐specific reproduction of individuals are portrayed using: (i) a horizontal life line, the length of which is proportional to individual longevity; (ii) colour‐coded segments depicting the level of reproduction at each age; and (iii) a cohort survival schedule created by rank‐ordering individual life lines from shortest‐ to longest‐lived.2.The resulting graphic, referred to as an event history diagram, portrays data at the individual level and thus allows visual comparisons of detailed life‐history patterns such as age of first reproduction, longevity, ages of high, medium, low and zero reproduction, and post‐reproductive period.3.Example graphs are shown for reproductive and longevity data gathered on 1000 medfly females. The average female lived 35·6 days and laid 759·3 eggs and therefore the graphs display information for 35 600 fly days and the age‐distribution of laying for 759 300 eggs.4.Because the graphics provide a means for visualizing large amounts of data precisely and efficiently, they reveal details and nuances in the data that are not apparent from conventional graphic methods.5.The advantages of longitudinal data gathered on individuals and reasons why visualizing individual‐level data is important are discussed.
Echolocation, olfaction and fruit display: how bats find fruit of flagellichorous cucurbits
Authors: Kalko E. K. V. , Condon M. A. 
Published: March 2003

1. The relationship between plant morphology and the senses used by dispersal agents to find fruit was examined. ‘Flagellichory’ (fruit borne on pendulous structures), a costly morphology associated with dispersal by bats, is focused on. 2. Using Gurania spinulosa, a flagellichorous vine, and its major dispersal agent, Phyllostomus hastatus, the hypothesis was tested that flagellichory increases the conspicuousness of fruit to bats that use echolocation to find fruit. 3. The responses of wild‐caught P. hastatus to various fruiting branch morphologies and fruit odour were recorded. Phyllostomus hastatus used echolocation rather than olfaction to detect fruit, and consistently chose fruit displayed on pendulous leafless branches, ignoring fruit held among leaves on horizontal branches. 4. By comparing echolocation signals with the distance between fruiting branches of G. spinulosa and surrounding vegetation, it was shown that pendulous fruiting branches present clear, clutter‐free targets that can be detected by echolocating bats. This is the first demonstration of neotropical frugivorous bats using echolocation to find fruit.
Growth and physiology of Picea abies populations from elevational transects: common garden evidence for altitudinal ecotypes and cold adaptation
Authors: Oleksyn J. , Modrzýnski J. , Tjoelker M. G. , Z·ytkowiak R. , Reich P. B. , Karolewski P. 
Published: March 2003

1. There are conflicting reports concerning the adaptive features of tree populations originating from cold, high‐altitude environments. We hypothesize that such trees will possess adaptive features that will be demonstrated in a common environment, such as elevated rates of net CO2 exchange, elevated needle nitrogen concentration and high proportional biomass allocation to roots. To test this hypothesis we measured tree and seed properties of 54 populations of Norway spruce [Picea abies (L.) Karst.] located along eight altitudinal transects (from c.600 to 1500m) in southern Poland. We also measured growth, biomass partitioning, net photosynthetic capacity (Amax), needle dark respiration (RS) and carbohydrate, nitrogen (N) and chlorophyll concentration of seedlings originating from these populations grown for 2 to 7 years in a common garden at 150m elevation. Measured in situ along the elevational transects, there were linear declines in seed mass, average d.b.h. and height growth increment of seed trees with increased altitude or lower mean annual temperature. 2. In the common garden, the Norway spruce populations from colder, high‐altitude habitats had higher N concentration in needles than those from low altitudes. Both Amax and needle RS increased with altitude of seed origin and were significantly related to needle N concentration. High‐altitude populations also had higher concentrations of chlorophyll and carotene than those from low elevations. Despite higher photosynthetic rates in high‐altitude populations, seedling height and dry mass in the common garden declined with altitude of seed origin. Proportional dry mass partitioning to roots nearly doubled with increasing altitude of origin, while the length of the shoot‐growth period was reduced. The high respiration rates, high allocation to roots and reduced shoot‐growth period are probably responsible for the low growth rate potential of high‐altitude populations, more than offsetting their higher photosynthetic rates. 3. The results of this study showed that Norway spruce populations from cold mountain environments are characterized by several potentially adaptive features. Because these were similar to conifer population responses along a latitudinal gradient of origin, they are probably driven by climate. These climate‐driven differences were common to all transects: for a given altitude or mean annual temperature, plant traits were independent of mountain range of origin. However, populations originating from cold high‐elevation sites often differed per unit change in altitude or mean annual temperature more than did low elevation populations. The scaling of nitrogen, CO2 exchange and biomass and allocation patterns may be useful in modelling Norway spruce response on montane forest ecosystems under changing environments.