bluuebunny/crossref_metadata_2025 huggingface dataset:
Community persistence in Broadstone Stream (U.K.) over three decades
Authors: WOODWARD GUY , JONES JOHN I. , HILDREW ALAN G.
Published: March 2003

1. Few detailed long‐term data sets exist for fresh waters with which to examine large‐scale temporal changes in community composition. Consequently, insight into community persistence has been restricted to a few, contingent case studies. We collated and analysed data for the aquatic macroinvertebrate community of Broadstone Stream in south‐east England, spanning three decades. The pH of this naturally acid stream has risen progressively since the 1970s, and we sought to examine the potential effects of this environmental change upon the community.

2. Persistence within Broadstone was high when compared with other systems that have been analysed using similar methods. The stream was characterised by a `core' community of eight taxa that were always present, and contributed 75–97% of total invertebrate abundance, with a trailing limb of progressively rarer and more acid‐sensitive taxa. There was little species turnover, although the time‐series exceeded 20 generations for most species.

3. Despite this high persistence, a long‐term response to rising pH was detected: species indicating profound acidity (identified apriorifrom independent studies) have declined since the 1970s, whereas indicators of moderate acidity increased. The structure of the community food web has also changed since the 1970s, with increased predator diversity and abundance, and a lengthening of food chains following the invasion of a new top predator.

4. These changes in the community appeared to be driven by an interaction between pH and climate. The unusually hot, dry summers characteristic of the 1990s may have raised pH during the more sensitive (i.e. early) stages of the life‐cycle, and thus provided a window of opportunity for less acid‐tolerant taxa to colonise and become established. Changes in pH appeared to set the boundaries of the available local species pool, within which biotic interactions ultimately shaped the community.
Restoration strategies for river floodplains along large lowland rivers in Europe
Authors: BUIJSE A. D. , COOPS H. , STARAS M. , JANS L. H. , VAN GEEST G. J. , GRIFT R. E. , IBELINGS B. W. , OOSTERBERG W. , ROOZEN F. C. J. M.
Published: March 2003

1. Most temperate rivers are heavily regulated and characterised by incised channels, aggradated floodplains and modified hydroperiods. As a consequence, former extensive aquatic/terrestrial transition zones lack most of their basic ecological functions.

2. Along large rivers in Europe and North America, various floodplain restoration or rehabilitation projects have been planned or realised in recent years. However, restoration ecology is still in its infancy and the literature pertinent to river restoration is rather fragmented. (Semi‐) aquatic components of floodplains, including secondary channels, disconnected and temporary waters as well as marshes, have received little attention, despite their significant contribution to biological diversity.

3. Many rehabilitation projects were planned or realised without prior knowledge of their potential for success or failure, although, these projects greatly contributed to our present understanding of river–floodplain systems.

4. River rehabilitation benefits from a consideration of river ecosystem concepts in quantitative terms, comparison with reference conditions, historical or others, and the establishment of interdisciplinary partnerships.

5. We present examples from two large European rivers, the Danube and the Rhine, in which the role of aquatic connectivity has been extensively studied. The Danube delta with its diversity of floodplain lakes across an immense transversal gradient (up to 10 km) serves as a reference system for restoration projects along lowland sections of large rivers such as the Rhine in the Netherlands.
Using diatoms to assess the biological condition of large rivers in Idaho (U.S.A.)
Authors: Fore Leska S. , Grafe Cynthia
Published: March 2003

SUMMARY 1. Diatoms were collected from 49 sites located on 23 rivers and identified to species. We defined 26 attributes of the diatom assemblage on the basis of tolerance and intolerance, autecological guild, community structure, morphological guild and individual condition.

2. We grouped sites into three geographical regions on the basis of altitude, land cover and use. Within each region, we tested for an association between diatom attributes and human disturbance.

3. We selected nine attributes for inclusion in a multimetric index, the river diatom index (RDI): percentage of valves belonging to species sensitive to disturbance, percentage of valves belonging to species very tolerant of disturbance, eutrophic species richness, percentage of valves belonging to nitrogen heterotrophic species, percentage of valves belonging to polysaprobic species, alkaliphilic species richness, percentage of valves belonging to species that require high oxygen, percentage of valves belonging to very motile genera and percentage of deformed valves.

4. The RDI was significantly correlated with measures of human disturbance made at the site (conductivity, percentage of fine sediments and number of human activities) and at the catchment level (percentage of urbanisation and agriculture in the upstream catchment).

5. The percentage of the total variance of RDI related to transect location was very small (1%) compared with among‐site differences (73%) and time of sampling (26%). The RDI could reliably detect approximately three categories of biological condition based on annual monitoring and potentially more if sampling were restricted to the same month each year.
The balance between photosynthesis and grazing in Antarctic mixotrophic cryptophytes during summer
Authors: Marshall William , Laybourn‐Parry Johanna
Published: March 2003

SUMMARY 1. Grazing and photosynthetic contributions to the carbon balance of planktonic, mixotrophic cryptophytes in Lakes Fryxell and Hoare in the Taylor Valley, Antarctica were measured during November and December 2000.

2. The cryptophytes never became entirely photosynthetic, although carbon derived from grazing decreased in December. Individual grazing rates ranged between 5.28 and 10.08 bacteria cell−1 day−1 in Lake Fryxell and 0.36–11.76 bacteria cell−1 day−1 in Lake Hoare. Grazing rates varied temporally and with depth in the water column. In Lake Fryxell, which is a meromictic lake, highest grazing occurred just above the chemocline. Individual photosynthetic rates ranged from 0.23 to 1.35 pg C cell−1 h−1 in Lake Fryxell and 0.074 to 1.08 pg C cell−1 h−1 in Lake Hoare.

3. Carbon acquisition by the cryptophyte community gained through grazing ranged between 8 and 31% during November in Lake Fryxell, dropping to between 2 and 24% in December. In Lake Hoare grazing contributed 12–21% of the community carbon budget in November and 1–28% in December. Around 4% of the carbon acquired from grazing and photosynthesis was remineralised through respiration.

4. Mixotrophy is probably a major survival strategy for cryptophytes in the extreme lakes of the Dry Valleys, because perennial ice‐cover severely limits light penetration to the water column, whereas these phytoflagellates are not normally mixotrophic in lower latitude lakes. The evidence suggests that mixotrophy may be a mechanism for supplementing the carbon budget, as well as a means of acquiring nutrients for growth.
Preparation of phosphorus and carbohydrate microcapsules for manipulating dietary C : P ratio for aquatic suspension‐feeders
Authors: Kreeger Daniel A. , Kilham Susan S. , Lanka Sujani , Linder Alison
Published: March 2003

SUMMARY 1. Dietary phosphorus can be limiting for aquatic animals such as suspension‐feeders. However, our understanding has been limited by the difficulty of manipulating dietary P without altering other aspects of food quality. We microencapsulated various forms of bioavailable P with carbohydrate to manipulate dietary C : P ratio for suspension‐feeders.

2. Calcium phosphate, sodium hexametaphosphate, sodium tripolyphosphate and tetrasodium pyrophosphate were each mixed with a concentrated solution of a carbohydrate base (either maltodextrin or potato starch) and microencapsulated using an interfacial polymerisation technique. Each of the 10 types of capsules produced had a particle size ideal for suspension‐feeders (3–10 μm).

3. Leakage rates were low (<12% of capsule weight per day). Relative enzymatic breakdown in vitro by carbohydrases (amylase or cellulase) was similar among the 10 capsule types and was always at least 15 times the comparable leakage rate.

4. Release of dissolved P from enzyme‐treated capsules varied depending on capsule P content. Liberation of P from capsules prepared from 20% w/w sodium hexametaphosphate in maltodextrin (molar C : P = 1.8) was three times greater than all other types, and this combination appears most suitable as a dietary supplement for zooplankton.

5. Although P content and capsule integrity were greatly influenced by choice of carbohydrate, choice of P compound, and the mixing ratio of the two, P‐rich artificial microparticles can be produced that have low leakiness, high digestibility, and a physical size suitable for aquatic suspension‐feeders. Therefore, microcapsules represent promising tools for manipulating dietary C : P for suspension feeders.
Modelling the impact of benthic filter‐feeders on the composition and biomass of river plankton
Authors: Descy J.‐P. , Everbecq E. , Gosselain V. , Viroux L. , Smitz J. S.
Published: March 2003

SUMMARY 1. The POTAMON model [Everbecq E. et al. (2001) Water Research, 35, 901] has been used to simulate the effect of benthic bivalves (mainly Dreissena polymorpha) on the phytoplankton and zooplankton in a lowland Western European river (the Moselle). Here we use a modified version of the POTAMON model with five categories of phytoplankton (Stephanodiscus, Cyclotella‐like, large diatoms, Skeletonema and non‐siliceous algae) to model filter‐feeding effects of benthic bivalves in the Moselle. Zooplankton has been represented in the model by two categories, Brachionus‐like and Keratella‐like rotifers.

2. According to density estimates from field surveys (Bachmann V. et al. (1995) Hydroécologie Appliquée, 7, 185, Bachmann V. & Usseglio‐Polatera P. (1999) Hydrobiologia, 410, 39), zebra mussel density varied among river stretches, and increased through the year to a maximum in summer. Dreissena filtration rates from the literature were used, and mussels have been assumed to feed on different phytoplankton categories (but less on large and filamentous diatoms) as well as on rotifers.

3. The simulations suggest a significant impact of benthic filter‐feeders on potamoplankton and water quality in those stretches where the mussels are abundant, their impact being maximal in summer. Consequently, different plankton groups were not affected to the same extent, depending on their period of development and on indirect effects, such as predation by mussels on herbivorous zooplankton.

4. A daily carbon balance for a typical summer shows the effect of benthic filter‐feeders on planktonic and benthic processes: the flux of organic matter to the bottom is greatly enhanced at high mussel density; conversely, production and breakdown of organic carbon in the water column are reduced. Mussel removal would drive the carbon balance of the river toward autotrophy only in the downstream stretches.
Behavioural fitness component effects of the alba polymorphism of Colias (Lepidoptera, Pieridae): resource and time budget analysis
Authors: Nielsen M. G. , Watt W. B.
Published: March 2003

1. Alba, a white wing colour morph of butterflies of the genus Colias, makes fitness‐related changes at several levels of phenotypic organization: physiology, development and behaviour. Two sympatric species of Colias are studied, which differ greatly in their frequency of alba vs its sister yellow/orange morph. How resource and time constraints on Colias interact with the morphs’ different patterns of pupal resource allocation to alter the balance of the morphs’ fitness components in the two species is discussed.

2. These species, C. alexandra and C. scudderi, differ in melanin‐based solar energy absorption, in larval dietary richness and in local adult nectar resources. The two female morphs determine alternate thermal balance, internal resource allocation and behavioural effects in each species, thus changing the morphs’ time budgets and fitness‐component impacts between the species. In particular, female egg output differences between the morphs appears to reverse between species: alba fecundity is greater than yellow fecundity in C. scudderi, but alba is less than yellow in C. alexandra.

3. These differences are consistent with the large observed differences in alba frequency between the species. Some important questions about the selective regime maintaining a polymorphism here, rather than an alternation of monomorphisms, remain.
Effect of water‐borne zinc on osmoregulation in the freshwater amphipod Gammarus pulex (L.) from populations that differ in their sensitivity to metal stress
Authors: Spicer J. I. , Morritt D. , Maltby L.
Published: March 2003

1. Although there is some evidence that exposure to heavy metals can disrupt osmoregulation in crustaceans, most studies have been carried out on relatively pollution‐tolerant, marine or estuarine species. Consequently the effects of water‐borne zinc (Zn) on osmoregulation by the freshwater amphipod, Gammarus pulex (L.), from two populations that differ in their heavy metal sensitivity, have been compared.

2.‘Clean’ site animals (Clowne, Derbyshire) exhibited a marked haemoconcentration (after 4 days at 37·0 μmol Zn l–1, 5 days at 18·2 μmol Zn l–1) shown by an increase in haemolymph osmotic pressure (OPh) and [Na+] and [K+]. However, after 5 days at 37·0 μmol Zn l–1, haemolymph of survivors exhibited an OPh significantly less than controls. ‘Contaminated’ site animals showed a reduction in OPh (but not ions) only after 5 days at 76·2 μmol Zn l–1.

3. There were differences in the threshold and nature of osmoregulatory response to Zn between animals from ‘clean’ and ‘contaminated’ sites, but only at concentrations in excess of those (a) known to affect growth and reproduction in ‘clean’ site animals and (b) occurring at the ‘contaminated’ site. Clearly population differences in physiological capacity and tolerance do exist but their ecological significance is unclear.
The establishment of fucoid zonation on algal‐dominated rocky shores: hypotheses derived from a simulation model
Authors: Johnson M. P. , Hawkins S. J. , Hartnoll R. G. , Norton T. A.
Published: March 2003

1. A model was developed for the growth of intertidal algae with photosynthesis simulated both in air and in a tidal water column. Morphological data on dry mass per unit area and length–area relationships were used to separate the growth of different fucoid species. The relative growth rate of fronds at any height on the shore depended on a trade‐off between net photosynthetic performance and tolerance to desiccation.

2. The simulated zonation patterns and growth rates were consistent with those observed previously for Fucus spp. and Pelvetia canaliculata.

3. The simulated growth of Ascophyllum nodosum was always slower than for the other species. This species did not form its characteristic distribution zones in simulations without including further processes in the model. However, Ascophyllum collected from the field could be separated into upper and lower shore morphologies which formed separate zones when they were simulated in competition with each other.

4. Several hypotheses were proposed concerning the relative locations and sharpness of interspecies boundaries on the shore. Zonation patterns were relatively insensitive to changes in most model parameters except the desiccation rate.
Life span and dynamics of leaves of herbaceous perennials in high‐elevation environments: ‘news from the elephant’s leg’
Authors: Diemer M.
Published: March 2003

1. Leaf life spans, determined as half‐lives, of 16 herbaceous perennial plant species from the aseasonal, tropical Andes at altitudes between 4000 and 4600 m were on average 193±19 days and thus two to three times greater than those of herbaceous perennials from the seasonal northern hemisphere. The duration of lamina expansion was positively correlated with life span. Growth was continuous all year round, but rates of leaf initiation in the high‐elevation tropics were lower than in the temperate zone.

2. Significant positive inter‐relationships were found between leaf life span and mass‐based foliar nitrogen concentration of Andean taxa. The correlation between life span and leaf mass per area (LMA) was marginally significant, while life span and area‐based foliar N content were unrelated.

3. Leaf traits of 46 Andean herbaceous perennials (forbs and graminoids), spanning an altitudinal range of 1500 m, indicated that the 16 taxa utilized for growth and leaf life span determinations were representative. For graminoids no altitudinal changes in LMA or foliar N were observed across species. However, in forbs LMA and area‐based foliar N increased significantly with altitude. No differences in leaf traits were observed between herbaceous rosette and cushion growth forms.

4. The Andean data set was used in conjunction with data from the temperate, subarctic and arctic zones to evaluate the significance of leaf life spans in herbaceous plants from a biogeographical perspective. Leaf life span declined significantly with increasing seasonality, expressed as latitude and duration of the annual growth period. Because temperature regimes are similar along this gradient during the respective growth periods (Diemer 1996), observed differences should be the result of variation in the day length and/or duration of the growing season.

5. Data on leaf life spans and leaf traits of herbaceous plants from contrasting latitudes were used to evaluate the validity of general inter‐relationships proposed by Reich (1993). The high correlation between LMA and life span observed in both data sets indicates that this relationship holds for various growth forms. On the other hand, the apportionment of mass‐based foliar N concentration in relation to life span appears to differ between herbaceous and woody growth forms.
Confirmation of soil‐feeding termites (Isoptera; Termitidae; Termitinae) in Australia using stable isotope ratios
Authors: Tayasu I. , Inoue T. , Miller L. R. , Sugimoto A. , Takeichi S. , Abe T.
Published: March 2003

1. Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of termites (Isoptera) were examined in Darwin, northern Australia. It is suggested that the stable isotope technique, together with phylogenetics, is a useful tool to understand the evolution of functional groups in detritivores.

2. A high δ15N value was observed in the Termes‐Capritermes branch of the subfamily Termitinae and the genus Amitermes, two distinct taxonomic groups that evolved from wood‐feeding to soil‐feeding in Australia. Among eight Termes‐Capritermes branch species, only two species (Xylochomitermes melvillensis and Ephelotermes melachoma) were discernible as wood/soil interface feeders, the remaining six species analysed were soil‐feeders, where the diet preference was identified by using δ15N of workers.

3. The Termes‐Capritermes group in Australia contains both wood/soil interface feeders and soil‐feeders, whereas wood/soil interface feeders in Cameroon are from the Termes‐Capritermes branch while soil‐feeders are from Cubitermes group. The result confirmed that soil‐feeding forms evolved both in Australia and Africa, but from different phylogenetic groups.
Interaction between temperature and cadmium toxicity in the isopod Porcellio scaber
Authors: Abdel‐Lateif H. M. , Donker M. H. , Van Straalen N. M.
Published: March 2003

1. Temperature has an important effect on all physiological processes in animals that rely on external sources of heat (ectotherms). In an attempt to elucidate the interaction between temperature and the response of ectotherms to heavy metals, a study was made of growth (increase of body mass) of the isopod Porcellio scaber under four constant temperature regimes (12, 16, 20, 24 °C), and four different exposures to cadmium (0·016, 0·071, 0·14 and 0·31 μmol g–1 in the diet), in a factorial experiment.

2. There were significant effects on growth rate for both cadmium and temperature, and the interaction between cadmium and temperature was also significant. The average growth rate per week increased with increasing temperature, but the results showed that when cadmium was present at concentrations higher than 0·071 μmol g–1, it disturbed the temperature‐induced growth enhancement.

3. There was a tendency for cadmium to be least toxic at intermediate temperature (16 °C), but the 50% and 10% effect concentrations in the diet, estimated by loglogistic curve fitting, did not significantly vary with temperature. The average values were EC50 = 0·330 μmol g–1 and EC10 = 0·041 μmol g–1.

4. The Arrhenius model was used to describe the temperature–growth rate relationship, and activation energies were estimated for each cadmium exposure. At the highest cadmium concentration the Arrhenius model did not describe the data very well. The lowest activation energy was observed at 0·14 μmol g–1.

5. Cadmium accumulation in isopods was linearly related to the cadmium concentration in food, for all temperature levels. The significant increase in cadmium concentration with temperature indicates that the effect of temperature on cadmium accumulation is stronger than its effect on body growth. As a whole the data illustrate the importance of taking temperature into account when conducting ecotoxicological studies with soil invertebrates.
Lineage‐dependent rates of evolutionary diversification: analysis of bivariate ellipses
Authors: Ricklefs R. E. , Nealen P.
Published: March 2003

1.A method based on the calculation of major and minor axes of bivariate ellipses to estimate relative rates of evolutionary diversification of two traits is presented. The advantage of ellipse analysis over the more common allometric or regression approaches to variation in comparative data is that diversification of each trait is estimated relative to that of the other. This can reveal differences in the relative rates of diversification of two traits among sister groups or, through hierarchical analysis, over the history of a lineage.

2.Equations are provided for calculating the size, shape and orientation of bivariate ellipses based on the variance–covariance matrix of the original data. Standard errors and biases of these parameters are also quantified.

3.Applications of ellipse analysis to the relationship between egg size and incubation period in birds illustrate differences in the diversification of two traits between independent lineages. Nested analysis of covariance based on taxonomic levels further illustrates how relative rates of evolutionary diversification may vary through the history of a monophyletic group.

4.A simple model incorporating both independent (special) and correlated (general) change in two traits shows how different shapes and orientations of bivariate ellipses can be produced by different rates of evolutionary diversification in special and general genetic factors.

5.Ellipse analysis is a descriptive tool that can clarify patterns of diversification. It cannot distinguish differences in evolutionary responsiveness (phylogenetic constraint) from differences in the selective environment affecting the shape and orientation of the bivariate ellipse. It can, however, provide a more detailed characterization of trait evolution than other comparative methods, taking advantage of the additional information provided by the shape and, in some cases, the dimensions of the bivariate ellipse.
Effects of Free‐Air CO2 Enrichment (FACE) on experimental grassland communities
Authors: Norton L. R. , Firbank L. G. , Blum H.
Published: March 2003

1. Experimental grassland communities (turves) were exposed to elevated (60 Pa) and ambient (35 Pa) CO2 partial pressures (pCO2) in a Free‐Air Carbon Dioxide Enrichment (FACE) experiment between 30 March 1995 and 4 July 1996. The vegetation was cut once during the experiment prior to the final harvest (harvest 2).

2. No significant treatment effects on total plant biomass at the whole turf level were detected, although biomass was typically about 25% higher under fumigation in year 1 and about 15% higher in year 2.

3. Biomass for two of the six sown species was significantly higher at harvest 2 than at harvest 1. There were no significant differences between individual species’ biomass under the two CO2 treatments at either harvest 1 or 2 or in terms of overall cumulative biomass. However, in four of the five sown species in both years biomass tended to be higher in the fumigated than in the control rings (Cerastium holosteiodes, Phleum pratense, Plantago lanceolata and Poa trivialis). In contrast, Lolium perenne showed increased biomass under the control treatment relative to the fumigated treatment in both years. Owing to the high variance both within and between rings for each of the two treatments the statistical power of most, but not all, of the analyses carried out was poor.

4. The relative proportions of each species in the turves under fumigated and control treatments was broadly similar after the first summer, with differences in the second year being mainly owing to the negative response of L. perenne to CO2 fumigation.
Effect of enhanced atmospheric CO2 on mycorrhizal colonization and phosphorus inflow in 10 herbaceous species of contrasting growth strategies
Authors: STADDON P. L. , GRAVES J. D. , FITTER A. H.
Published: March 2003

1. Ten herbaceous species were grown over a 4‐month period under ambient (360 μmol mol–1) and elevated (610 μmol mol–1) atmospheric CO2 conditions. Plants were inoculated with the arbuscular mycorrhizal (AM) fungus Glomus mosseae and given a phosphorus (P) supply which was not immediately available to the plants.

2. Multiple harvests were taken in order to determine whether the effect of elevated CO2 on mycorrhizal colonization and phosphorus inflow was independent of its effect on plant growth.

3. All species grew faster under elevated CO2 and carbon partitioning was altered, generally in favour of the shoots. All species responded similarly to elevated CO2.

4. Elevated CO2 did not affect the percentage of root length colonized by AM fungi, but the total amount of colonized root length was increased, because the plants were bigger.

5. Elevated CO2 increased total P content, but had little or no effect on P concentration. At a given age, P inflow was stimulated by elevated CO2, but when root length was taken into account the CO2 effect disappeared.

6. In these host species there is no evidence for a direct effect of elevated CO2 on mycorrhizal functioning, because both internal mycorrhizal colonization and P inflow are unaffected.

7. Future research should concentrate on the potential for carbon flow to the soil via the external mycelial network.
Competition as an amplifier of short‐term vegetation responses to climate: an experimental test
Authors: Dunnett N. P. , Grime J. P.
Published: March 2003

1. Responses to a spring warming treatment were measured on five common herbaceous species grown in outdoor microcosms in Northern England. Although elevated temperature had a beneficial effect on canopy height and plant cover in monospecific cultures of all species, strongly divergent responses to warming occurred in mixtures.

2. We show that the effect of interspecific competition was to modify and amplify the vegetation response to the warming treatment through effects on phenology and morphological development.

3. The observed responses between the species to warming are consistent with predicted differential responses linked to genome size.

4. We conclude that the mechanism of competitive interaction proposed by Boysen‐Jensen (1929) coupled with the insights related to genome size provide a basis for explaining and predicting the role of interannual variation in temperature in determining year to year fluctuations in the relative abundance of species in productive perennial herbaceous vegetation.
Chemical differentiation between leaves of seedlings and spatially close adult trees from the tropical rain‐forest species Nectandra ambigens (Lauraceae): an alternative test of the Janzen–Connell model
Authors: Sánchez‐Hidalgo M. E. , Martínez‐Ramos M. , Espinosa‐García F. J.
Published: March 2003

1. We tested the hypothesis of Langenheim and Stubblebine that differences in chemical composition between maternal trees and the seedlings under them arise from differential mortality; only seedlings different from the mother survive. Such mortality could explain at least some of the cases where seedlings accumulate under adult conspecifics, contrary to the extreme form of the Janzen–Connell hypothesis.

2. We investigated Nectandra ambigens (Lauraceae), an upper‐canopy tree at Los Tuxtlas tropical rain forest, Mexico, whose seedlings survive under the canopy of conspecific trees. We analysed chromatographic profiles of leaf terpenoids of 15 groups, each formed by an adult tree and its surrounding seedlings.

3. We predicted that seedlings chemically similar to the adult would be absent under the tree canopy and that they would be present outside that canopy. We also predicted that younger seedlings would be more similar to the adult than the older ones.

4. Chemical similarity analyses showed that most seedlings were significantly different from their closest adult and thus supported the Langenheim and Stubblebine hypothesis. However, we did not find chemical differentiation among seedlings regarding their age or their position inside or outside the tree canopy.
Carbon and water fluxes in Beech–Spruce model ecosystems in response to long‐term exposure to atmospheric CO2 enrichment and increased nitrogen deposition
Authors: Maurer S. , Egli P. , Spinnler D. , Körner CH.
Published: March 2003

1. We present data on the gas exchange of 32 Beech–Spruce model ecosystems including understorey species, which were planted on acidic or calcareous soil in 16 (half‐split) open‐top chambers in 1994 and were continuously exposed to the combinations of two CO2 concentrations and two wet nitrogen deposition rates for 3 years.

2. Instantaneous mid‐season net ecosystem carbon‐exchange rates (NEC) were determined during the day (11.00–16.00 h, NECd) and at night (22.00–02.00 h, NECn) with a mobile chamber in July 1996 and August 1997 for both soil types and, in addition, in August and September 1996 on acidic soil only.

3. Elevated CO2 increased NECd at all sampling dates on both soil types and under both N deposition rates. Increased nitrogen deposition stimulated NECd on acidic soil but not on calcareous soil, irrespective of the CO2 level. NECn was increased in elevated CO2 on both soil types (but more on the calcareous soil), but did not respond to increased nitrogen deposition in both years. The daytime instantaneous ecosystem evapotranspiration (ETd) was not significantly affected by the CO2 and nitrogen treatments at any sampling date. Year to year differences in NECn and ETd were small, but a doubling in NECd occurred throughout the observation period.

4. Elevated CO2 caused a small but significant increase in stem dry mass on calcareous soil only and increased nitrogen deposition stimulated stem biomass production on acidic soil only. Leaf area index was not affected by CO2, but was increased under high nitrogen deposition.

5. Our results suggest that nitrogen deposition and soil type are major co‐determinants of the carbon balance of forests in a future CO2‐rich world.
More on the meanderings of mangabeys: how to test whether bounded walks are random
Authors: Hutchinson J. M. C.
Published: March 2003

1. Barrett & Lowen (1998)andWaser (1976)attempted to explain the net monthly and yearly displacements of Grey‐Cheeked Mangabeys using observed short‐term step lengths and assuming a random walk, with and without boundaries. This paper reanalyses their data.

2. Analytic approaches require the root‐mean‐square step length, not the mean. However, a more flexible approach to making and testing predictions is Monte‐Carlo simulation. With a random walk long‐term displacements have a large variance, so a single observation is unlikely to disprove this null hypothesis.

3. Restricting movement to a square lattice is a reasonable approximation even when rectangular boundaries are incorporated. Describing the boundary configuration accurately is more important.

4. The observed non‐uniformity in turning angles should have been incorporated as it has a large effect on predicted net displacements, unless the arena is tightly constricted. Randomness of movement within a day can be distinguished from that between days. For Waser's population it makes sense to predict long‐term displacements using only long‐distance daily displacements.

5. There are better approaches to establish both whether boundaries exist and whether movements follow a random walk.
The carbon balance of a young Beech forest
Authors: Granier A. , Ceschia E. , Damesin C. , Dufrêne E. , Epron D. , Gross P. , Lebaube S. , Le Dantec V. , Le Goff N. , Lemoine D. , Lucot E. , Ottorini J. M. , Pontailler J. Y. , Saugier B.
Published: March 2003

1. We present measurements of CO2 fluxes over 2 years above and within a young Beech stand in the east of France. This site is part of the Euroflux network set up to monitor fluxes over representative European forests.

2. The net ecosystem carbon (C) exchange was derived from continuous eddy flux measurements. Major components of the total flux (i.e. soil and above‐ground biomass respiration and assimilation of leafy branches) were measured independently using chambers. The main C stocks (i.e. root, stem and branch biomass) were also quantified.

3. Daily minima of CO2 flux were typically around −20 µmol CO2 m−2 s−1 during the period of full leaf expansion, while night‐time ecosystem respiration varied between 5 and 15 µmol CO2 m−2 s−1. The seasonal pattern of net ecosystem assimilation was very close to that of net assimilation at the single branch scale. The seasonal variation of net ecosystem exchange was closely related to leaf expansion and soil water content during the dry year of 1996.

4. Measurements of ecosystem respiration (eddy flux) were corrected for CO2 storage within the stand. This C flux showed a seasonal pattern, the maximum rates (4–7 g C m−2 day−1) occurring in spring and summer, and appeared to be correlated with soil temperature. Temporal variation of soil respiration showed the same pattern, and effects of both temperature and soil drying were found. Annual soil respiration was ≈ 70% of ecosystem respiration. Root respiration was 60% of the total below‐ground respiration.

5. Annual net C exchange was −218 and −257 g C m−2 in 1996 and 1997, respectively, corresponding to net C uptake by the forest. These values are much lower than the annual biomass increment (stems and large roots) of the stand: 427 and 471 g C m−2 year−1, respectively. The difference may be explained by a release of CO2 from the decomposition of woody debris.

6. Ecosystem C loss by respiration was 800–1000 g C m−2 year−1. Gross C gain was 1000–1300 g C m−2 year−1. Ecosystem respiration therefore played a major role in the annual C balance of this forest.
Leaf‐level resource use for evergreen and deciduous conifers along a resource availability gradient
Authors: Kloeppel B. D. , Gower S. T. , Vogel J. G. , Reich P. B.
Published: March 2003

1. We compared leaf‐level carbon, nitrogen and water use for a deciduous (Larix occidentalis Nutt.) and sympatric evergreen (Pseudotsuga menziesii, Beissn., Franco, or Pinus contorta Engelm.) conifer along a resource availability gradient spanning the natural range of L. occidentalis in western Montana, USA.

2. We hypothesized that leaf photosynthesis (A), respiration (r), specific leaf area (SLA) and foliar nitrogen concentration (N) would be higher for deciduous than sympatric evergreen conifers in mixed stands, and that these interspecies differences would increase from high to low resource availability. We also hypothesized that leaf‐level nitrogen and water‐use efficiency would be higher for the co‐occurring evergreen conifer than L. occidentalis.

3. In general, mass‐based photosynthesis (Am) was significantly higher for L. occidentalis than co‐occurring evergreen conifers in the drier sites, but Am was similar for evergreen and deciduous conifers at the mesic site.

4. Mass‐based foliar nitrogen concentration (Nm) was positively correlated to SLA for all species combined across the gradient (R2 = 0·64), but the relationship was very weak (R2 = 0·08–0·34) for evergreen and deciduous species separately. Mass‐based Am and rm were poorly correlated to Nm for all species combined across the gradient (R2 = 0·28 and 0·04, respectively).

5. For each site‐species combination, daily maximum Am was negatively correlated to vapour pressure deficit (VPD) (R2 = 0·36–0·59), but was poorly correlated to twig predawn water potential (R2 < 0·04).

6. Instantaneous nitrogen‐use efficiency (NUEi; Am divided by Nm) and water‐use efficiency (δ13C) increased significantly (P = 0·05) from high to low resource availability for both evergreen and deciduous conifers, except for NUEi in L. occidentalis.
Indirect, physiological assessment of reproductive state and breeding chronology in free‐living birds: an example in the Marbled Murrelet (Brachyramphus marmoratus)
Authors: Vanderkist B. A. , Williams T. D. , Bertram D. F. , Lougheed L. W. , Ryder J. L.
Published: March 2003

An indirect, physiological method to assess reproductive state in individuals of unknown status is described. The plasma levels of two main yolk precursors, vitellogenin (VTG) and very‐low density lipoproteins (VLDL), are focused on as indices of egg production, for the characterization of fecund females.

Data for a species where breeding chronology could be directly assessed, at the population level (Cassin’s Auklet,Ptychoramphus aleuticus), confirmed the validity of this approach: plasma VTG levels were highest during the defined egg‐laying period, and the highest proportion of females were defined as ‘egg‐producing’ in this period.

Analysis of samples for Marbled Murrelets (Brachyramphus marmoratus) caught off‐nest (i.e. where all individuals were of unknown status), clearly identified a putative egg‐laying phase, with a single, protracted laying period (cf. multiple‐broodiness).

Analysis of body mass confirmed our characterization of ‘egg‐producing’ females: birds with elevated plasma VTG were on average 40 g heavier than other females, equivalent to the mass of the single egg (36–41 g).

Indirect, physiological assessment of reproductive state provided valuable information on the breeding biology of Marbled Murrelets which would have been difficult to obtain in any other way (e.g. proportion of fecund females, breeding phenology, singlevsmultiple‐clutch breeding pattern). Despite some limitations, this technique should be applicable to any oviparous vertebrate population where essential information on breeding biology cannot be obtained by more traditional methods.
Carbon allocation in calcareous grassland under elevated CO2: a combined 13C pulse‐labelling/soil physical fractionation study
Authors: P. A. Niklaus , E. Glöckler , R. Siegwolf , C. Körner
Published: March 2003

To test whether plant–soil C fluxes in natural grassland increase under elevated atmospheric CO2 concentration, intact calcareous grassland monoliths exposed to ambient or elevated CO2 were pulse‐labelled and the dynamics of the 13C label followed throughout the rest of the growing season.

 The experiment revealed no increased fluxes of C to soils at elevated CO2. The only changes found were relatively small shifts towards increased C allocation to roots by the end of the growing season. This effect was probably because wetter soil under elevated CO2 prolonged the growing period. At elevated CO2, plant C pools increased below ground (+28%) at the end of the season, resulting in slightly increased root : shoot ratios. Plant 13C pools increased significantly below ground. There were no effects of CO2 enrichment on 13C in soil microbes, fine roots or earthworms.

 Elevated CO2 caused a shift in soil particle size distribution towards smaller aggregate sizes, but had no effect on the total C and 13C content of low‐ and high‐density soil fractions.

 The absence of effects of CO2 on the labelling of soil microbial biomass, and of C and 13C accumulation in low‐density macro‐organic fractions, suggest that there is no significant effect of elevated CO2 on root exudation or turnover, agreeing with published labelling studies, but conflicting with CO2‐exchange budgets.
Nectar ‘theft’ by hummingbird flower mites and its consequences for seed set in Moussonia deppeana
Authors: C. Lara , J. F. Ornelas
Published: March 2003

Mites (Acari: Mesostigmata: Ascidae) that live and feed in the flowers of about 100 plant species are transported in the nares of hummingbirds (Trochilidae). Mites may compete with hummingbirds for nectar secreted by the host plants, and this could affect the dynamics and reproductive outcomes of the mutualism between plants and their pollinating hummingbirds.

 Here we combined field observations and experimental manipulations to assess the role of hummingbird flower mites (Tropicoseius sp. nov.) on nectar secretion and reproductive output of protandrous Moussonia deppeana (Schlecht. & Cham.) Hanst. (Gesneriaceae) during their flowering period in a cloud forest remnant.

 During the 4 days that the flowers of M. deppeana last, flowers were visited exclusively by hummingbirds (Lampornis amethystinus). Bud production per inflorescence peaked in December. There were few open flowers per inflorescence in November, but numbers increased as the flowering season progressed (December and January).

 The availability of each flower phase differed over the flowering season. Staminate‐phase flowers were more abundant over the flowering season than pistillate‐phase flowers. These differences were statistically significant over time.

 Nectar availability was reduced by up to 50% in the presence of hummingbird flower mites. Over the 4 days of observation, significantly more nectar was secreted to flowers from which mites were excluded than to flowers with no mite exclusion. The same effect was observed during flowering, but mites consumed a greater percentage of the total nectar secreted in December.

 Significantly more nectar was secreted during the staminate phase than in the pistillate phase, independent of time and treatment.

 A manual pollination experiment suggested that mites act like secondary pollinators in this self‐compatible, non‐autogamous plant, at least in flowers that were not pollinated manually and had no access to pollinating hummingbirds.

 Although seed production was not reduced significantly by flower mites, our results suggest that the presence of floral mites can affect pollen transmission, as the amount of nectar available to hummingbirds was reduced drastically. This can directly affect hummingbird foraging patterns and reduce the fitness of the host plants.
Contrasting effects of different types of resource depletion on life‐history traits in Daphnia
Authors: Urabe J. , Sterner R. W.
Published: March 2003

1. Life‐history traits of animals are known to change according to food quantity, but there is another type of resource depression, namely depletion of food quality. To examine life‐history responses of herbivores to changes in resource quality, Daphnia obtusa Kurz, a common planktonic herbivore, were reared individually under several algal food regimes with different quantity and quality in terms of chemical composition.

2. Compared with Daphnia fed on a small quantity of nitrogen (N) and phosphorus (P) sufficient food, Daphnia fed on a large amount of P deficient food grew more slowly at young ages but continually grew until older ages. This trend was also found for Daphnia fed on a large amount of N deficient food.

3. However, the size‐specific reproductive investment (measured as biomass accrued per unit time) of Daphnia fed on a large amount of N or P deficient algae was similar to those fed on a small amount of N and P sufficient food, indicating complex life‐history responses to food quality and suggesting that nutritional requirements for reproduction differ from somatic growth.

4. Compared with individuals fed high‐quality and high‐quantity food, Daphnia fed on a large amount of P deficient food produced smaller eggs, while individuals fed on a small amount of P and N sufficient food produced larger eggs. Furthermore, 15–30% of eggs produced by individuals fed on P or N deficient food ceased to develop and were aborted.

5. These results demonstrate that life‐history responses to food quality differ from responses to food quantity. Since the chemical composition of algae is highly variable in nature, herbivorous plankton demographics may not be predictable from resource quantity alone.
Soil dilution as a surrogate for root competition: effects on growth of seedlings of Australian tropical rainforest trees
Authors: Metcalfe D. J. , Grubb P. J. , Metcalfe S. S.
Published: March 2003

Previous studies on the combined effects of light and nutrient supply on the growth rates of plants have involved adding nutrients to soils to levels rarely (or never) met by the plants in nature. As a better test of the likely response of plants to root competition for nutrients, we grew for 1 year seedlings of six species of Australian rainforest tree on forest topsoil undiluted and on soil diluted 50/50, 25/75 and 5/95 with coarse sand. Seedlings were grown in tall tubes in 6 and 9% daylight, equivalent to gap‐edge and gap‐centre conditions.

 The six species varied in their light requirements for establishment and onward growth.

 One species grew significantly and markedly more quickly on soil diluted 50/50 with sand (Elaeocarpus grandis). Improved aeration is the most likely explanation.

 The extent of inhibition by soil dilution correlated positively with the absolute amount of new dry mass accreted in one year, whether the larger accretion resulted from a combination of high relative growth rate (RGR) and small embryo size, or moderate RGR and larger embryo size.

 Soil dilution generally reduced leaf mass fraction and leaf area ratio, but had no significant effect on specific leaf area.

 In all species the overall concentration of nitrogen in the whole plant declined with soil dilution; in the four species tested, N concentration in leaves declined, and it is likely that the reduction in growth arose partly from a reduced unit leaf rate. Most species showed increases in the concentrations of P, K, Ca and Mg with soil dilution, or no change, but in Diploglottis bracteata the concentrations of Ca and Mg, especially in the older leaves, declined markedly with soil dilution, and one of these cations could have been limiting growth.

 Extrapolation of the results to the field suggests that in single‐treefall gaps the fastest growing species will the most inhibited by root competition.

 The soil‐dilution technique is likely to be more appropriate than nutrient addition as an indicator of sensitivity to root competition on a given soil.