bluuebunny/crossref_metadata_2025 huggingface dataset:
Reproductive success of the rotifer Brachionus calyciflorus feeding on ciliates and flagellates of different trophic modes
Authors: Mohr Silvia , Adrian Rita
Published: March 2003

SUMMARY 1. The nutritional value of the bacterivorous ciliate Tetrahymena pyriformis and the algivorous ciliate Coleps sp., as well as the heterotrophic flagellate Chilomonas paramecium and the autotrophic flagellate Cryptomonas ovata, were investigated in population growth experiments using the rotifer B. calyciflorus. The two ciliates, both flagellates, which were of similar size, shape and mobility, were each offered as a sole diet and as a supplement to the alga Monoraphidium minutum, known to support reproduction of B. calyciflorus.

2. To further test nutritional differences between the prey organisms, prey selection experiments were conducted in which B. calyciflorus was able to select between the bacterivorous and algivorous ciliate, and between the heterotrophic and autotrophic flagellate.

3. The results demonstrated that both ciliates and the heterotrophic flagellate were not sufficient to support reproduction of B. calyciflorus when offered as a sole diet. They were, however, a good supplement to algal prey (except for the bacterivorous ciliate T. pyriformis). In the prey selection experiments, B. calyciflorus positively selected for the algivorous Coleps sp. and the autotrophic C. ovata.

4. Overall, ciliates and heterotrophic flagellates may enhance survival of B. calyciflorus, but reproduction of the rotifer is likely to rely on algal prey. Both higher population growth of B. calyciflorus when fed the algivorous Coleps and the autotrophic Cryptomonas, along with their positive selection, give evidence for prey specific differences in nutrition, with algivorous or autotrophic prey species tending to be of higher nutritional value.
Nutrient dynamics and successional changes in a lentic freshwater biofilm
Authors: Sekar R. , Nair K.V.K. , Rao V.N.R. , Venugopalan V.P.
Published: March 2003

SUMMARY 1. Colonisation, species composition, succession of microalgae and nutrient dynamics in biofilms grown under light and dark conditions were examined during the initial phases of biofilm development in a lentic freshwater environment.

2. Biofilms were developed on inert (perspex) panels under natural illuminated and experimental dark conditions and the panels were retrieved for analysis after different incubation periods. Analysed parameters included biofilm thickness, algal density, biomass, chlorophyll a, species composition, total bacterial density and nutrients such as nitrite, nitrate, phosphate and silicate.

3. Biofilm thickness, algal density, biomass, chlorophyll a and species richness were significantly higher in light‐grown biofilms, compared with dark‐grown biofilms. The light‐grown biofilms showed a three‐phased succession pattern, with an initial domination of Chlorophyceae followed by diatoms (Bacillariophyceae) and finally by cyanobacteria. Dark‐grown biofilms were mostly dominated by diatoms.

4. Nutrients were invariably more concentrated in biofilms than in ambient water. Nutrient concentrations were generally higher in dark‐grown biofilms except in the case of phosphate, which was more concentrated in light‐grown biofilms. Significant correlations between nutrients and biofilm parameters were observed only in light‐grown biofilms.

5. The N : P ratio in the biofilm matrix decreased sharply in the initial 4 days of biofilm growth; ensuing N‐limitation status seemed to influence biofilm community structure. The N : P ratios showed significant positive correlations with the chlorophycean fraction in both light and dark‐grown biofilms, and low N : P ratio in the older biofilms favoured cyanobacteria. Our data indicate that nutrient chemistry of biofilm matrix shapes community structure in microalgal biofilms.
Effects of catchment perturbations by logging and wildfires on zooplankton species richness and composition in Boreal Shield lakes
Authors: Patoine A. , Pinel‐Alloul B. , Prepas E. E.
Published: March 2003

SUMMARY 1. Forest logging and wildfires are important perturbations of the boreal forest, but their effects on lake biota remain largely unknown. Here, we test whether zooplankton species richness and species assemblages differed among three groups of lakes in Eastern Canada characterised by different catchment conditions: logged in 1995 (n=9); burnt in 1995 (n=9); unperturbed (n=20). Lakes were sampled in June, July and September 1 year after catchment perturbations.

2. Cumulative species richness in reference lakes averaged 46 (33–60) of which 63% were rotifers. Mean cumulative species richness and mean diversity in logged and burnt lakes did not differ from those in reference lakes.

3. Lake species assemblages were described by the density of 62 species (41 rotifers and 21 crustaceans). Among‐group differences in species assemblages were not significant. Eighteen per cent of the total variability in species assemblages could be explained by 13 environmental factors, among which dissolved oxygen concentration and cyanobacteria biovolume were the most important. About 5% of species assemblage variability was attributed to covariation between environmental factors and time of sampling, while 4.1% was attributed to temporal variation.

4. Variations in zooplankton species richness and assemblages in Boreal Shield lakes are important, both among lakes and among sampling dates. They seem to depend on environmental factors unrelated to catchment‐based perturbations, at least on the short‐term of 1 year.
Effects of deforestation on fish community structure in Ecuadorian Amazon streams
Authors: Bojsen B. H. , Barriga R.
Published: March 2003

SUMMARY 1. There is little information on the impacts of deforestation on the fish fauna in neotropical streams, and on parameters influencing species diversity and community structure of fish. We analysed these aspects in 12 stream sites in the Ecuadorian Amazon. The stream sites represented a large gradient in canopy cover and were located in an area of fragmented forest. While some streams had been deforested, they had not suffered gross degradation of the habitat.

2. The species richness of stream fish was not related to deforestation. Local fish diversity (Fisher's Alpha) was positively related to the surface area of stream pools (m2). Beta diversity was higher among forested than deforested sites, indicating greater heterogeneity in species composition among forested than deforested sites. The percentage of rare species was positively correlated with canopy cover.

3. Total fish density increased with deforestation, and the fish community changed from dominance by omnivorous and insectivorous Characiformes at forested sites to dominance of periphyton‐feeding loricariids at deforested sites.

4. Multidimensional statistical analysis of fish community structure showed that six environmental variables (the area of stream bottom covered by leaves, relative pool area, particulate organic matter, mean depth, conductivity and suspended solids) were related to the ordination axes. The presence of leaves, which was strongly correlated to canopy cover, was the variable most closely related to fish community structure, while relative pool area was the second strongest variable. Thus, fish community structure was strongly affected by deforestation.
Microform bed clusters: are they preferred habitats for invertebrates in a flood‐prone stream?
Authors: Matthaei C. D. , Huber H.
Published: March 2003

SUMMARY 1. Microform bed clusters are bedform microunits in streams. They consist of an obstacle clast (a large surface stone) against which other stones are stacked in a specific manner. Stream ecologists have suggested that these clusters are better flood refugia and more valuable habitats for invertebrates than single surface stones because of their higher stability during high‐flow events and their greater diversity of microhabitats available for colonisation.

2. To test these predictions in the Schmiedlaine, a flood‐prone prealpine stream, we sampled invertebrates on clustered and single stones on a total of seven occasions including before and after a moderate spate, two major floods and a minor spate. We also monitored surface particle stability during the second major flood and the minor spate.

3. Before the second flood (return period 1–2 years), we determined the exact positions of 60 clusters (60 obstacle clasts with 136 associated smaller particles) and 50 single stones in a 250‐m reach. We sampled the fauna on stones in the clusters, on well‐embedded single stones, and on loose single stones. Only six obstacle clasts and one single stone remained after the flood, implying movement of almost the entire surface layer. Therefore, we sampled the invertebrates on stones in newly formed clusters, on well‐embedded and single loose stones 3 and 11 days after the flood. The minor spate, in contrast to the second flood, moved only one of 495 monitored surface particles.

4. Three days after the flood, invertebrate density on clustered stones and both single stone categories were similar and equalled 34% of the mean pre‐flood density. Eight days later, density had almost doubled. The relatively high survival and rapid recovery suggest that invertebrates found refugia during the flood. However, the very low stability of clusters and single stones implied that surface particles were unimportant as refugia.

5. Total invertebrate density and taxon richness were never higher on clustered than on single stones (regardless of the timing of sampling relative to the last previous high‐flow event). Densities of the seven most common taxa and invertebrate community structure were also generally similar between particle types. We conclude that microform bed clusters cannot be regarded as more valuable invertebrate habitats than single surface stones in the Schmiedlaine.
Comparison of losses of planktivorous fish by predation and seine‐fishing in a lake undergoing long‐term biomanipulation
Authors: Wysujack Klaus , Mehner Thomas
Published: March 2003

SUMMARY 1. Piscivore stocking at artificially high densities and fishing are the two common approaches to reduce the amount of planktivorous and benthivorous fish in lake biomanipulation programmes. Both measures have advantages and disadvantages, but their relative efficacy has not previously been directly compared.

2. We calculated the average annual catch of roach and bream in a lake undergoing long‐term biomanipulation (Feldberger Haussee, Germany) by seining each year between 1992 and 1998. We compared this value with a bioenergetics estimate of annual consumption rates of the dominant cohorts of piscivores, pikeperch and pike, in 1997 and 1998. We also determined species composition and length distribution of prey fish in stomachs of the piscivores.

3. Roach was the dominant prey species of both pikeperch and pike, whereas bream was rarely taken by either piscivorous species. Seining removed on average larger specimens of roach than were found in the stomachs of the piscivores.

4. Based on stocking densities of the piscivores, published mortality rates, and individual consumption rates, feeding of pikeperch and pike on roach exceeded the manual removal of roach by seining by a factor of 4–15 (biomass) in 1997 and 1998.

5. Based on these results, a combination of fishing and piscivore enhancement is recommended. Whereas the stocks of adult roach and bream have to be reduced mainly by fishing, the predation of piscivores should be directed predominantly towards the juvenile zooplanktivorous fish. Therefore, small size‐classes of piscivorous fish should be promoted by fisheries management, including stocking and harvest regulations.
Changes in the fish community and water quality during seven years of stocking piscivorous fish in a shallow lake
Authors: Skov C. , Perrow M. R. , Berg S. , Skovgaard H.
Published: March 2003

SUMMARY 1. Piscivores (annual stocking of 1000 individuals ha−1 of 0+ pike and a single stocking of 30 kg ha−1 of large 20–30 cm perch) were stocked in seven consecutive years in a shallow eutrophic lake in Denmark. The stocking programme aimed at changing food‐web structure by reducing zooplanktivorous and benthivorous fish, with resultant effects on lower trophic levels and ultimately water quality.

2. The fish community and water quality parameters (Secchi depth, concentrations of total phosphorus, chlorophyll a and suspended solids) were monitored between 1996 and 2000 and relationships were evaluated between predatory fish and potential prey and between zooplanktivorous or benthivorous fish and water quality parameters. In addition, potential consumption of piscivorous fishes was calculated.

3. The density of fish feeding on larger zooplankton or benthos (roach >15 cm, crucian carp >15 cm) declined distinctly during the study period. This effect was attributed to predation by large (>50 cm) pike. Based on scale readings, we cautiously suggest that the stocking of 0+ pike boosted the adult pike population to produce an unexpected impact in later years. Conversely, no direct impact of stocked 0+ pike was detected on 0+ roach.

4. A major decline in the recruitment strength of 0+ roach was observed in 2000. A combination of (i) the indirect effect of large pike preying on adult roach, with negative effect on roach reproduction and (ii) the direct predation effect of 0+ pike and/or 1+ and 2+ perch recruited in the lake, provides the most likely explanation of this phenomenon.

5. A marked increase in Secchi depth in 2000 and declining trends in suspended solids, chlorophyll‐a and total phosphorus concentrations were observed. These changes may also be attributable to changes in the fish community, although the relationships were not straightforward.

6. This 7‐year study indicates that piscivorous fish may be a significant structuring force in shallow eutrophic lakes, suggesting that stocking piscivores can increase predation pressure on cyprinids. However, the general lack of impact of 0+ pike points to the need of refining current stocking practices in several countries across Europe.
Critical flow velocities for the growth and dominance of Anabaena circinalis in some turbid freshwater rivers
Authors: Mitrovic S. M. , Oliver R. L. , Rees C. , Bowling L. C. , Buckney R. T.
Published: March 2003

SUMMARY 1. From measurements at several weir pool sites along the turbid and freshwater Barwon‐Darling River, Australia, the development of persistent stratification (for periods of >5 days) was related to river discharge. For the sites examined, the required discharge to allow the development of persistent stratification was between 100 and 450 ML day−1 during the hotter months. High discharge during the hotter months did not allow the formation of persistent stratification, although diel stratification did occur. Low discharge through the cooler months resulted in diel stratification, although persistent stratification lasting for a few days could occur at times.

2. The growth and dominance of Anabaena circinalis at these sites was closely related to the establishment and maintenance of persistent and strong thermal stratification. Growth only occurred during extended periods (>5 days) of persistent stratification. These conditions not only restrict the displacement of A. circinalis downstream, they also allowed the alga to accumulate in surface waters.

3. The discharge levels required to suppress the formation of persistent stratification at the study sites were variable because of large differences in channel cross‐sectional area. To compensate for this variation, the discharges were converted to flow velocities. A critical velocity of 0.05 ms−1 was sufficient for the suppression of persistent thermal stratification and concurrent A. circinalis growth for all sites. The turbulent velocity (u*) under weak wind mixing at the study locations varied between 2.66 × 10−3 and 2.91 × 10−3 ms−1 at the critical flow velocities. These values may have potential to be applied to other rivers in similar climatic zones to suppress nuisance cyanobacterial growth.
Affinity for CO2 in relation to the ability of freshwater macrophytes to use HCO–3
Authors: Maberly S. C. , Madsen T. V.
Published: March 2003

1. The affinity of photosynthesis for CO2 is calculated here as the initial slope of net‐photosynthetic rate against concentration of CO2. The affinity for CO2 for pairs of freshwater macrophytes with similar leaf morphology but able or unable to use HCO–3 as a carbon source was compared.

2. Species restricted to CO2 had a higher affinity for CO2 than species that were also able to use HCO–3 when rates were expressed on the basis of area, dry mass and content of chlorophyll a.

3. Published values for the affinity for CO2 and the concentration of CO2 which half‐saturated rate of photosynthesis were compiled and compared. Despite a large range of values, affinity for CO2 was greater for species restricted to CO2 than for those also able to use HCO–3 and statistically different when the slope was expressed on the basis of dry mass and chlorophyll a content.

4. The difference in affinity is consistent with predicted benefits of a high permeability to CO2 for species relying on passive diffusion of CO2 and a lower permeability for species able to use HCO–3 in order to reduce efflux of CO2 from a high internal concentration generated by active transport.

5. The implications of the different affinities are discussed in terms of species distribution.
Genotypic variation in the regrowth of Lolium perenne following clipping: effects of nutrients and endophytic fungi
Authors: Cheplick G. P.
Published: March 2003

1. The objective of this research was to determine the extent to which regrowth rate after clipping and the specific leaf area (SLA) of genotypes of Lolium perenne were influenced by soil nutrients and endophytic fungi.

2. Twelve infected genotypes were cloned into ramets. Half were treated with a systemic fungicide that greatly reduced endophyte levels; half were untreated and retained high endophyte levels. Ramets of each genotype were subjected to low, medium or high levels of nutrients in a glasshouse for 11 weeks.

3. Plants were clipped at soil level at 11 weeks, allowed to regrow for 14 weeks and clipped again. SLA was determined at 11 and 25 weeks. Regrowth rate was calculated based on changes in leaf area and leaf dry mass between 11 and 25 weeks.

4. As a main effect, endophytes had no influence on regrowth rates and mean endophyte levels, as measured by hyphal counts within the leaves of five genotypes at high and low nutrients, were not correlated with regrowth rates. However, after clipping, regrowth responses to soil nutrients and endophytes were genotype‐specific. Some genotypes in the high endophyte group showed an enhancement of regrowth, whilst others showed no response or a depressive effect of endophytes.

5. At the time of leaf clipping, SLA was significantly affected by genotype, nutrients and endophytes. At medium nutrients, the SLA of high endophyte plants was significantly lower than that of low endophyte plants. However, the SLA of the regrowth was affected by nutrients but not endophytes. Mean endophyte levels, as measured by hyphal counts within the leaves of five genotypes at high and low nutrients, were not correlated with SLA at 11 or 25 weeks.

6. For both high and low endophyte plants, regrowth rate was negatively correlated with SLA.

7. Perennial ryegrass possesses genotypic variation in the ability to regrow following defoliation and this ability is conditioned by abiotic (nutrients) and biotic (endophyte) factors.
An open‐top chamber for measuring soil respiration and the influence of pressure difference on CO2 efflux measurement
Authors: Fang C. , Moncrieff J. B.
Published: March 2003

1. A new open‐top chamber for measuring CO2 efflux from the soil is reported here. The new design enables measurement of the equilibrium CO2 efflux, when there is no detectable pressure difference between the chamber and outside nor leakage of CO2 into or out of the chamber.

2. In previous dynamic‐chamber techniques, the measured CO2 efflux is dependent on the pressure difference between the inside and outside of the chamber, and a negative pressure difference of –1Pa may cause an order of magnitude increase in measured CO2 efflux. Although the measured CO2 efflux is less sensitive to a positive pressure difference than to a negative one, a positive pressure difference of even a few tenths of a Pa will lead to a considerable underestimation in soil CO2 evolution.

3. The influence of pressure difference on measured CO2 efflux is negligible in the new design and the estimated CO2 efflux is close to the undisturbed soil respiration rate. Flow rates up to 8lmin–1, or air movement over the soil surface up to 55cmmin–1, will not affect CO2 evolution from the soil. The influence of pressure difference is related to the type of soil being measured and this has also been reported here for the new design.
Diet mixing in the omnivorous tortoiseKinixys spekii
Authors: Hailey A. , Chidavaenzi R. L. , Loveridge J. P.
Published: March 2003

1.Mixed diets are common in vertebrates, and may be explained by several hypotheses including the availability and nutrient composition of different types of food, the presence of toxins, associative effects in digestion or non‐nutritional factors such as foraging efficiency or predation. This study investigated diet mixing in the omnivorous tortoiseKinixys spekii, which consumes fungi, vascular plants and invertebrates in the field. Tortoises feedingad libitumon these three diets had a higher intake of digestible energy from fungi than from leaves or millipedes (69, 42 and 31 kJ kg–1day–1respectively).

2.Tortoises offered pairwise combinations of foods chose mostly that giving the highest rate of digestible energy intake; 73:27 fungi:leaves, 92:8 fungi:millipedes, and 91:9 leaves:millipedes, by wet mass. Nevertheless, some of the food giving a lower energy intake was eaten.

3.Tortoises feedingad libitumon a mixed diet (90:10 leaves:millipedes by wet mass) had similar food intake rates and gut retention times to those feeding on leaves. The digestibility of energy was lower for the mixed diet than for diets of leaves or millipedes; a significant negative associative effect.

4.The rate of intake of dry mass did not differ between the three pure diets, the selected diets, or the mixed diet, though this was about 50% higher at 30 °C than outdoors, and represents a limitation due to digestion or appetite. Intake of other foods decreased the intake of dry mass of the preferred food, fungi, by an equal amount.

5.The three foods had similar levels of protein as a proportion of dry mass, partly because of the high ash content of millipedes. The digestibility of protein was higher in millipedes, but the rate of intake of total and of digestible protein was in the same rank order as that of energy (fungi > leaves > millipedes). Although the quantity of protein provided no nutritional explanation for inclusion of lower energy foods in the diet, the quality of protein may differ between food types.

6.Herbivorous tortoises are known to face limitations from calcium and sodium balance. Fungi had a lower level of calcium and a lower ratio of sodium:potassium than leaves; millipedes had values higher than leaves. Foods that are non‐optimal in terms of energy are probably included in the diet for micronutrients such as minerals or essential amino acids.
Sperm co‐operation in the Fishfly, Parachauliodes japonicus
Authors: Hayashi F.
Published: March 2003

1. Males of the Fishfly Parachauliodes japonicus (McLachlan) produce sperm in bundles. Each bundle consists of hundreds of sperm with their heads agglutinated. At copulation, on average 500 bundles are packed in a single spermatophore which is attached externally to the female genitalia. The bundles swim forward by synchronous flagellate movements in viscous seminal fluids and finally enter a spermatheca of the female. Females detach the spermatophore without guarding by the male; males guard the spermatophore for 5 h.

2. In this study, the effects of sperm‐bundle size and medium viscosity on their swimming velocities were examined. As sperm‐bundle mass increased, the amount of time it took to move a unit length decreased. As viscosity increased, those sperm‐bundles with greater mass moved faster than sperm‐bundles with less mass.

3. The distance sperm move seems to be longer in P. japonicus than in most other insects that ejaculate directly or place the spermatophore internally in the female storage organs. Thus, large sperm‐bundles may be an advantage for sperm of P.japonicus who move over a long distance in a viscous environment.
Allometry of resource capture in colonial cnidarians and constraints on modular growth
Authors: Kim K. , Lasker H. R.
Published: March 2003

1. Indeterminacy in growth of colonial organisms, such as corals, is commonly attributed to their modular construction which frees the colony from the allometric constraints that limit the size of single modules. However, as a colony grows, there may be a decrease in resource availability to interior modules because of active depletion and/or passive deflection by modules on the exterior. The effects of ‘self‐shading’ on resource capture in modular animals are modelled using a simple allometric growth function.

2. The model assumes that resource capture by a module scales as an exponent (γ) of colony size (i.e. number of modules). Data taken from the literature indicate that model values of γ for light and prey capture range from – 0·80 to – 1·16 for branching and encrusting corals. Module‐specific rates of resource use (i.e. metabolism) are less affected by colony size. Therefore, as a colony grows, net resource state eventually reaches zero, making further growth unsustainable or determinate.

3. The model also predicts an inverse relationship between module size and colony size such as that observed in Caribbean corals. This negative correlation results from the additive effects of module size and colony size on the degree of self‐shading.

4. Resource capture is affected by growth form and flow regime, and the interaction between them can account for some of the morphological variation in corals and other colonial suspension feeders.
Effects of simulated N deposition on understorey vegetation of a boreal coniferous forest
Authors: Nordin A. , NÄsholm T. , Ericson L.
Published: March 2003

1. We report the short‐term effects of simulated nitrogen (N) deposition on the understorey of a boreal forest in northern Sweden. Doses of 15N double‐labelled NH4NO3 (0·5, 12·5, 25·0 and 50·0 kg N ha–1) were applied to 1 m2 plots in the summer of 1995 and plants were harvested the following autumn.

2. No significant treatment effects were found in either above‐ or below‐ground biomass which was distributed as follows: the ericaceous shrub Vaccinium myrtillus contributed 76%, the grass Deschampsia flexuosa 4%, and the bryophytes Dicranum majus and Pleurozium schreberi 20%.

3. The recovery of applied N in these species was 24, 27, 27 and 32% of the 0·5, 12·5, 25·0 and 50·0 kg N ha–1 applications, respectively, and thus the recovery increased with the N dose.

4. In the 0·5 kg N ha–1 treated plots, the highest concentrations of fertilizer‐derived 15N were found in the bryophytes, while in plots given the three higher N applications, leaves of D. flexuosa had the highest concentrations.

5. N application resulted in elevated concentrations of free amino acid N, which indicate increased storage of N in plant tissues. Furthermore, the N application resulted in increased damage to V. myrtillus by natural enemies. The severity of disease caused by two foliar parasitic fungi showed a clear numerical response to N treatment, as did the amount of herbivory as a result of Lepidoptera larvae.
Does reproductive investment change with age in tsetse flies, Glossina morsitans morsitans (Diptera: Glossinidae)?
Authors: Langley P. A. , Clutton‐Brock T. H.
Published: March 2003

1. Viviparous insects such as tsetse (Glossina spp.) provide unusual opportunities to compare age‐related changes in the proportion of maternal resources transferred to offspring.

2. In laboratory populations of Glossina morsitans morsitans the survival of females was high for the first 60 days of adult life but declined rapidly thereafter.

3. Average longevity did not differ significantly between mated and unmated females (93·6 and 90 days, respectively).

4. Nutritional state in terms of fat content and residual dry mass did not decline with adult female age.

5. The fecundity of mated females was constant for the first 60 days of adult life and declined only slightly thereafter.

6. Offspring size did not change towards the end of the adult female lifespan and there was no evidence of an increase in the allocation of resources to reproduction in older females.

7. Results contrast with those obtained recently for vertebrates and may indicate that age‐related changes in offspring size in Glossina are not adaptive, or that so few females reach old age under natural conditions that there is no selection for a strategy of terminal investment.
Photosynthetic nitrogen‐use efficiency in leaves of woody and herbaceous species
Authors: Hikosaka K. , Hanba Y. T. , Hirose T. , Terashima I.
Published: March 2003

1. Photosynthetic characteristics of an annual herb, Chenopodium album, and an evergreen tree, Quercus myrsinaefolia, were compared to clarify causes of the difference in photosynthetic nitrogen‐use efficiency (photosynthetic capacity per unit nitrogen) between leaves of herbaceous and evergreen species.

2. When leaves with the same nitrogen content on an area basis were compared, photosynthetic capacity of C. album was twice as high as that of Q. myrsinaefolia. Gas‐exchange measurements showed higher intercellular CO2 concentration in C. album. Biochemical analyses indicated larger allocation of nitrogen into ribulose‐1,5‐bisphosphate carboxylase, a key enzyme of photosynthesis, and higher specific activity of ribulose‐1,5‐bisphosphate carboxylase in C. album. However, these differences were not large.

3. Compositional deviation of 13C in leaves of the two species suggested that the drop of CO2 level between the intercellular space and the chloroplast was slightly larger in Q. myrsinaefolia when compared between the leaves with the same photosynthetic capacity.

4. It is concluded that the difference in photosynthetic nitrogen‐use efficiency between C. album and Q. myrsinaefolia is not caused by a sole factor that is markedly different between the two species but by several factors each of which is slightly disadvantageous to Q. myrsinaefolia compared with C. album.
Root growth dependence on soil temperature for Opuntia ficus‐indica: influences of air temperature and a doubled CO2 concentration
Authors: Drennan P. M. , Nobel P. S.
Published: March 2003

1. Root elongation as a function of soil temperature was determined for the CAM succulent Opuntia ficus‐indica, under three different day/night air temperatures (15 °C/5 °C, 25 °C/15 °C and 35 °C/25 °C) and an ambient (360 μmol mol–1) vs a doubled CO2 concentration (720 μmol mol–1) at 25 °C/15 °C, the optimum temperature for net CO2 uptake.

2. Root elongation occurred at soil temperatures from 12 °C (at 15 °C/5 °C) to 43 °C (at 35 °C/25 °C) with optimum temperatures of 27–30 °C, similar to other CAM succulents and consistent with the distribution of this shallow‐rooted species in warm regions. Although a doubled CO2 concentration did not alter the optimum or limiting soil temperatures, increases of up to 5 °C in these temperatures accompanied the 20 °C increase in day/night air temperatures.

3. Root elongation rates at optimum soil temperatures ranged from 5·4 mm day–1 (15 °C/5 °C), through 6·6 mm day–1 (25 °C/15 °C), to 10·4 mm day–1 (35 °C/25 °C) with a 25% increase under a doubled CO2 concentration. Highest root elongation rates at 35 °C/25 °C may reflect changing root vs shoot sink strengths in a species with a highly plastic root system.

4. At limiting soil temperatures, the length of the cell division zone was reduced by an average of 20% and cell length at the mid‐point of the elongation zone by 10%. Increased root elongation rates under a doubled CO2 concentration reflected increased cell elongation.

5. The temperature response for the roots of O. ficus‐indica and stimulation of elongation by a doubled CO2 concentration indicate that root growth for this highly productive species should be enhanced by predicted global climate change.
Effects of elevated temperature on multi‐species interactions: the case of Pedunculate Oak, Winter Moth and Tits
Authors: Buse A. , Dury S. J. , Woodburn R. J. W. , Perrins C. M. , Good J. E. G.
Published: March 2003

1. The effects of temperature on the Oak–Winter Moth–Tit food chain were studied at Wytham Wood, Oxford, and experimentally in the controlled environment solardomes at the Institute of Terrestrial Ecology, Bangor.

2. Tree cores from Wytham indicated that mature Oaks grew best at high temperatures and rainfall, but with low caterpillar populations. Young trees grew less well at elevated temperature, probably because they lost more water than they gained. Elevated temperatures advanced budburst, reduced foliar nitrogen and increased leaf toughness.

3. Moth eggs laid later or maintained at cooler temperatures than average required fewer heat units to hatch. Caterpillars took up to 50 days to complete growth at field temperatures but did so in only 20 days at a constant 15 °C.

4. The mass of Tit chicks at day 15 (day 1 = egg hatch) was positively correlated with temperature and negatively correlated with rainfall during the growing period.

5. At elevated temperature, budburst and moth egg hatch were synchronized, but earlier. Late feeding larvae and larvae fed on leaves from trees grown at elevated temperature produced smaller pupae. Pupal mass was unaffected when caterpillars and trees were maintained together under the same conditions.

6. Delaying egg hatch in Tits, to simulate conditions at elevated spring temperatures, resulted in reduced chick mass, body size and fledging success. This occurred because the chicks were fed later and prey quality was poorer, because the peak of caterpillar biomass was missed.

7. We predict that moth reproductive output will be retained at elevated temperatures because both leaves and caterpillars develop faster. Brood size in birds may be reduced because they cannot lay early enough to coincide with the narrower peak of food abundance.
Patch depression in grazers: the roles of biomass distribution and residual stems
Authors: Ginnett T. F. , Dankosky J. A. , Deo G. , Demment M. W.
Published: March 2003

1. In this paper the results are presented of two experiments designed to examine the relationship between sward structure variables and the nature of patch depression experienced by a large grazing herbivore, Bos taurus, grazing from small patches of forage. In experiment 1 the spatial distribution of leaves within patches was varied. In experiment 2 the role of reproductive stems of different lengths as potential intake rate inhibitors was examined.

2. Both experiments were conducted by offering cattle hand‐constructed swards of Orchardgrass (Dactylis glomerata) leaves attached to plywood boards. Each of three experimental animals was allowed to take 10, 20, 30, 45 or 60 bites from a patch and intake was estimated on the basis of pregrazing and postgrazing dry‐matter. All trials were videotaped and the trial length in seconds was determined from playback of the tapes.

3. In both experiments patch depression (reduction in instantaneous intake rate) was due to decreases in bite mass concomitant with patch depletion. Handling time per bite was unaffected by depletion level. In experiment 1, different spatial configurations resulted in markedly different gain functions ranging from linear to sigmoid. In experiment 2, the presence in the sward of long (15 cm) reproductive stems slowed cumulative gains by restricting bite mass and by increasing the per‐bite handling time relative to patches with shorter (5 cm) or no stems.

4. The study of patch depression mechanisms now needs to be generalized over a range of herbivore body sizes and feeding styles.
The effect of predator and prey density on the induced defence of a ciliate
Authors: Wiackowski K. , Starońska A.
Published: March 2003

1. The level of antipredator defence should be proportional to the actual attack probability to minimize the cost of defence and maximize the net benefit.

2. The hypothesis that the induced antipredator morphology of Euplotes octocarinatus is a graded response to the actual risk of predation by Stylonychia mytilus was tested by manipulating the density of both prey and predator populations.

3. The magnitude of the response was graded according to both predator and prey density. A dense prey population may be protective since a prey is more exposed to a predator's attack as a solitary individual.

4. The results suggest that Euplotes is able to ‘estimate’ the real risk of predation and respond appropriately, without mobilizing more resources than needed.

5. Separation of the prey and predator with a nylon net revealed that the response was not induced by a water‐transmitted factor but that direct cell‐to‐cell contacts were important. This finding departs from those of other studies.
Growth responses of 15 rain‐forest tree species to a light gradient: the relative importance of morphological and physiological traits
Authors: Poorter L.
Published: March 2003

1. Growth of seedlings of 15 rain‐forest tree species was compared under controlled conditions, at six different light levels (3, 6, 12, 25, 50 and 100% daylight).

2. Most plant variables showed strong ontogenetic changes; they were highly dependent on the biomass of the plant.

3. Growth rate was highest at intermediate light levels (25–50%) above which it declined. Most plant variables showed a curvilinear response to irradiance, with the largest changes at the lowest light levels.

4. There was a consistent ranking in growth between species; species that were fast growing in a low‐light environment were also fast growing in a high‐light environment.

5. At low light, interspecific variation in relative growth rate was determined mainly by differences in a morphological trait, the leaf area ratio (LAR), whereas at high light it was determined mainly by differences in a physiological trait, the net assimilation rate (NAR).

6. NAR became a stronger determinant of growth than LAR in more than 10–15% daylight. As light availability in the forest is generally much lower than this threshold level, it follows that interspecific variation in growth in a forest environment is mainly owing to variation in morphology.
The size–grain hypothesis and interspecific scaling in ants
Authors: Kaspari M. , Weiser M. D.
Published: March 2003

1. The size–grain hypothesis maintains that as terrestrial walking organisms decrease in size, their environment becomes less planar and more rugose. The benefits of long legs (efficient, speedy movement over a planar environment) may thus decrease with smaller body size, while the costs (larger cross‐sectional area limiting access to the interstitial environment) are enhanced.

2. A prediction from this hypothesis – that leg size should increase proportionately with body mass – is examined. Ants are among the smallest walking animals and extend the size gradient five orders of magnitude beyond the traditional ‘mouse to elephant’ curve. The mass of 135 species of worker ants spans 3·7 orders of magnitude (0·008–53 mg). Larger ants tended to be slimmer and longer legged. Ant subfamilies varied in their scaling relationships, but four out of five showed a positive allometry for hind leg length (b > 0·33). Mammals, in contrast, show isometry for leg length over six orders of magnitude.

3. It is suggested that ants make a transition from living in an interstitial environment when small to a planar environment when large, a habit continued by most terrestrial mammals. Head length and pronotum width are robust estimators of mass in ants.
Mediterranean Fruit Fly leks: factors affecting male location
Authors: Kaspi R. , Yuval B.
Published: March 2003

1. The mating system of Mediterranean Fruit Flies (Ceratitis capitata, Diptera: Tephritidae) is based on male leks which form within the canopies of certain trees. In this study the following hypotheses are tested: (a) fly location depends on microclimate and illumination and (b) larger and heavier males occupy preferred locations in leks. Accordingly, systematic quantitative observations of diel three‐dimensional (3‐D) locations of lekking C. capitata males were performed in field and field cage studies.

2. Fly locations were found to vary significantly during the activity hours.

3. Medflies were generally found calling from highest and most exterior locations during early morning and late afternoon hours. During the hottest hours (1200–1500) flies occupied lower locations within the tree canopy, and interior locations from 1000 to 1500.

4. Fly location (from 1000 to 1700) was correlated with the azimuth of the sun. However, the mean azimuth range of fly location was limited to 85° (59·45°–143·94°).

5. Both in the field and in the field cage the temperature, relative humidity and light intensity beneath the leaves on which the males perched were closer to the microclimate beneath fully shaded leaves than to microclimates beneath leaves exposed to direct sunlight.

6. It is concluded that male medflies occupy locations which confer suitable microclimates for calling and copulating, and suitable 3‐D locations within the canopy which provide protection from predators, wind, direct sunlight and water loss.
Reverse phenology and dry‐season water uptake byFaidherbia albida(Del.) A. Chev. in an agroforestry parkland of Sudanese west Africa
Authors: Roupsard O. , Ferhi A. , Granier A. , Pallo F. , Depommier D. , Mallet B. , Joly H. I. , Dreyer E.
Published: March 2003

1.Faidherbia (Acacia) albidais a multipurpose tree widely distributed in semiarid Africa, notably in agroforestry parklands. It is in leaf during the dry season and defoliated during the rainy season, displaying therefore a peculiar reverse phenology. The related water‐use strategy, including leaf water potential, sapflow, hydraulic conductance and depth of uptake, were monitored on adult trees in a Sudanese west‐African parkland.

2.Despite a severe drought in the superficial soil layers, the predawn leaf water potential ofF. albidadropped only toca.– 0·5 MPa during the end of the dry season, indicating only a moderate water stress.

3.Radial trunk growth ceased before the end of the dry season and could have been affected by the moderate drought stress. However, leafiness remained constant during the dry season. Leaf shedding occurred after the first rains and was probably independent of drought.

4.Faidherbia albidadisplayed large transpiration rates under favourable conditions but the ratio of sapflow to Penman evapotranspiration and the soil‐to‐leaf specific hydraulic conductance decreased severely towards the end of the dry season.

5.Roots ofF. albidawere distributed through the weathered rock, down to a depth of 7 m, and vanished in the vicinity of a permanent water‐table. The isotopic composition of oxygen in the xylem sap (δ18O) remained very close to the values recorded in the water‐table during the course of the year. Phreatophytism thus explained the maintenance of growth and transpiration during the dry season. Nevertheless, during early rains, δ18O of sap switched towards the composition of the superficial soil layers, indicating facultative phreatophytism.

6.Reverse phenology, low density and depth of water uptake ofF. albidaindicated a low competition with annual crops for water; the fraction of annual rainfall used by the trees was estimated to remain below 5%.
Costs of rapid growth: the risk of aggression is higher for fast‐growing salmon
Authors: Nicieza A. G. , Metcalfe N. B.
Published: March 2003

1. Agonistic behaviour can be an important trait in determining individual success under interference competition, but it also generates energetic and physiological costs. The ensuing trade‐off is expected to be dependent on the individual state. This study tests whether aggression patterns of juvenile Atlantic Salmon Salmo salar are linked to the recent growth history and the developmental pathway adopted by fish (early vs late migrants).

2. By manipulating growth rates over 1 month in the autumn, three groups of fish were produced differing in body size and thereby in the length increment necessary to achieve the threshold size for migration in the following spring. Fish that had experienced reduced rations or abnormally low temperatures during the manipulation period experienced ‘catch‐up’ growth after the resumption of standard growth conditions.

3. Aggression was strongly connected to growth bimodality and the underlying developmental polyphenism. Fast‐growing (upper modal group, UMG) fish (which would migrate in the spring) were more aggressive than slow‐growing (lower modal group, LMG) fish (which would delay migration for another year), but they were also more vulnerable to being attacked by conspecifics.

4. Aggressive acts initiated by UMG fish were strongly biased towards fish of the same category (57–77% of aggressive acts being against other UMG fish). Under illumination conditions simulating overcast nights, UMG individuals sharply reduced their aggressiveness and were not selective in their attacks. The aggression by LMG fish was more evenly distributed between modal groups (44–74% of attacks were against UMG) regardless of light levels.

5. Recent growth history had no consistent effect on aggression rates, although under overcast night conditions the rate of attacks received by non‐manipulated UMG fish was twice as high as that for fish undergoing compensatory growth.

6. These results demonstrate a link between developmental pathways and aggression patterns. They also show that individuals maintaining a fast growth strategy over the winter experience a more aggressive social environment than individuals adjusting feeding rates to ensure safe maintenance levels. The reduced involvement of LMG fish in agonistic encounters conforms to a strategy of avoidance of those energetic and physiological costs that ultimately could compromise overwintering survival.