bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphorus dynamics in Danish lakes and the implications for diatom ecology and palaeoecology
Authors: Bradshaw Emily G. , Anderson N. John , Jensen Jens Peder , Jeppesen Erik
Published: March 2003

SUMMARY 1. Seasonal phosphorus variability may be considerable in eutrophic lakes and patterns are influenced by internal, as well as external, nutrient loading. The strong seasonality of planktonic diatoms, with main growth periods in the spring and also in the autumn in meso‐ to eutrophic lakes, means that the measure of total phosphorus (TP) that is most relevant for diatom ecology may not be adequately assessed by single or few measurements during the year.

2. The diatom species assemblage of surface sediments can be used to infer in‐lake nutrient concentrations. Weighted averaging (WA) and weighted averaging partial least squares (WAPLS) regression and calibration models for diatoms and annual mean TP were developed for a 29‐site data set of Danish lakes based on (a) all diatom species and (b) planktonic species only. Jack‐knifed error statistics were: =0.37, root mean squared error of prediction (RMSEP)=0.28 log10μg TP L−1 and mean bias=0.04 log10μg TP L−1 for the WAPLS 2‐component model based on all species; =0.23, RMSEP= 0.32log10μg TP L−1 and mean bias=0.07 log10μg TP L−1 for the WA model with tolerance downweighting based on planktonic species only. These are comparable with similar, published data sets.

3. A subset of 23 sites was used to develop models based on seasonal TP measurements. Mean spring TP concentrations gave only slightly improved RMSEP values for models based on all species and plankton‐only (0.24 log10μg TP L−1 and 0.29 log10μg TP L−1, respectively).

4. Weighted averaging models derive environmental optima, for individual species, which are not necessarily of ecological relevance. However, good water chemistry data are required to model species' responses adequately and to develop calibration data sets.
Modulation of the bacterial response to spectral solar radiation by algae and limiting nutrients
Authors: Medina‐Sánchez J. M. , Villar‐Argaiz M. , Carrillo P.
Published: March 2003

SUMMARY 1. The response of bacterial production (measured as [3H]TdR incorporation rate) to spectral solar radiation was quantified experimentally in an oligotrophic high‐mountain lake over 2 years. Bacterial responses were consistent: ultraviolet‐B (UVB) was harmful, whereas ultraviolet‐A (UVA) + photosynthetically active radiation (PAR) and PAR enhanced bacterial activity. Full sunlight exerted a net stimulatory effect on bacterial activity in mid‐summer but a net inhibitory effect towards the end of the ice‐free period.

2. Experiments were undertaken to examine whether the bacterial response pattern depended on the presence of algae and/or was modulated by the availability of a limiting inorganic nutrient (phosphorus, P). In the absence of algae, [3H]TdR incorporation rates were significantly lower than when algae were present under all light treatments, and the consistent bacterial response was lost. This suggests that the bacterial response to spectral solar radiation depends on fresh‐C released from algae, which determines the net stimulatory outcome of damage and repair in mid‐summer.

3. In the absence of algae, UVB radiation inhibited bacteria when they were strongly P‐deficient (mean values of N : P ratio: 46.1), whereas it exerted no direct effect on bacterial activity when they were not P‐limited.

4. P‐enrichment of lake water markedly altered the response of bacteria to spectral solar radiation at the end of ice‐free period, when bacteria were strongly P‐deficient. Phosphorus enrichment suppressed the inhibitory effect of full sunlight that was observed in October, both in whole lake water (i.e. including algae) and in the absence of algae. This indicates that the bacterial P‐deficiency, measured as the cellular N : P ratio, was partly responsible for the net inhibitory effect of full sunlight, implying a high bacterial vulnerability to UVB.
Phenotypic plasticity and constancy of life‐history traits in laboratory clones of Daphnia magna Straus: effects of neonatal length
Authors: Barata C. , Baird D. J.
Published: March 2003

1. The phenotypic constancy of four laboratory Daphnia magna clones in fitness‐related life‐history traits, such as age and clutch size at maturity, was studied among consecutive experimental runs in differing food environments.

2. A significant part of the observed clonal and genetic‐by‐environmental variation in age and clutch size at maturity was explained by experimentally uncontrollable variations in neonatal body length.

3. Despite food availability, neonatal length determined the number of instars invested to maturity and thus maturation age. Clonal differences in neonatal length and thus in maturation instar occurrence across environments explained most of the clonal variability observed in maturation age.

4. Although interclonal differences in clutch size existed, most of the phenotypic plasticity observed for clutch size was mediated by clonal differences in neonatal length.

5. Clonal differences in neonatal length and in the occurrence of maturation instars across environments dramatically affected the body length of instar IM‐2 where provisioning of eggs take place. Since clutch size is determined from clutch mass and clutch mass was strongly related to the body length of instar IM‐2, clonal differences across environments in body length of instar IM‐2 mirrored clonal differences across environments in clutch size.

6. The results reported in the present study show that maternally mediated traits such as neonatal length affect how genotypes respond to different environmental selection regimes (genetic‐by‐environmental interaction). Future research needs to focus on the effects of neonatal length on the heritability or genetic variation of the reaction norms, since prediction of the response to selection is a key research objective in quantitative genetic studies.
Haematological health state indices of reproducing Great Tits: methodology and sources of natural variation
Authors: Ots I. , MurumÄgi A. , HÕrak P.
Published: March 2003

1. A cornerstone concept of ecological immunology is that immune function, interacting with various aspects of individual health state, plays a central role in the life‐history trade‐offs between conflicting demands of survival and reproduction. In order to develop this research, more knowledge about the applicability and usefulness of different health state assays is needed.

2. Eleven, mostly hemato‐serological, health state indices are described and their suitability for sensing the condition of breeding Great Tits (Parus major L.) in terms of measurement precision, constancy in time, diurnal variation, and sex‐ and site‐related differences, is examined.

3. Measurement errors for the plasma albumin content, residual body mass, heterophile/lymphocyte ratio and total plasma protein content were relatively small compared with the total variation, suggesting these indices to be most adequate for ecological research. Measurement precision was lowest for the heterophile count and ‘buffy coat’ layer height (relative amount of leucocytes in total blood volume). Buffy coat layer height correlated weakly (r=0·21) with total leucocyte count estimated from blood smears and therefore appeared inappropriate for estimation of the leucocyte number.

4. Body mass (residual in respect to size) and intensity of Haemoproteus blood parasite infection were the least variable state indices during the nestling period (for both, the correlation between the values measured on the 8th and 15th days of the nestling period=0·71). Haematocrit, heterophile count and albumin/globulin ratio showed no individual constancy across the nestling period, while other traits revealed moderate but statistically significant correlations between 8th‐ and 15th‐day values.

5. Leucocyte (both lymphocyte and heterophile) counts were higher among females captured at night compared with those captured during the day.

6. Females had higher intensities of Haemoproteus infection, higher heterophile counts and higher heterophile/lymphocyte ratios than males. Contrary to published information, females had higher haematocrits than males.

7. Haematocrit values in both sexes, as well as total plasma protein and albumin concentrations in males, differed significantly between Great Tits breeding in urban habitat and rural woodlands, respectively.
Haematological health state indices of reproducing Great Tits: a response to brood size manipulation
Authors: HÕrak P. , Ots I. , Murumägi A.
Published: March 2003

1.A brood size manipulation experiment was performed in two Great Tit (Parus majorL.) populations in order to evaluate the effect of raising different numbers of nestlings on parental health state.

2.Brood enlargement resulted in elevated heterophile:lymphocyte ratios and decreased lymphocyte number in the peripheral blood, indicating that increased reproductive effort causes immunosuppression.

3.Haematocrit increased in response to brood enlargement, suggesting a response to the requirement of elevated oxygen‐carrying capacity of the blood during increased work load.

4.Parental body mass revealed a tendency to decrease in response to brood enlargement.

5.No effect of brood size manipulation on total leucocyte count, heterophile count, intensity ofHaemoproteusblood parasite infection or plasma proteins could be detected.

6.Health state indices were more sensitive to brood size manipulation in the Great Tits breeding in a rural habitat than urban birds.
Seasonal patterns of nitrogen fixation in termites
Authors: Curtis A. D. , Waller D. A.
Published: March 2003

1. Termite nitrogenase activity was highest in autumn and spring (≈ 3 μg N2 fixed termite fresh mass (g)–1 day–1) and lowest in winter and summer (≈ 0·8 μg N2 fixed termite fresh mass (g)–1 day–1).

2. The nitrogenase activity of worker termites was significantly higher than all other castes (1·58 ± 0·27 μg N2 fixed termite fresh mass (g)–1 day–1).

3. Worker termites constituted the largest proportion of all the castes throughout the study period (≈ 90%).

4. The localized input of fixed nitrogen by termites may reach 15·3 mg N log–1 day–1 and 5·6 g N log–1 year–1.
Random walks and the gas model: spacing behaviour of Grey‐Cheeked Mangabeys
Authors: Barrett L. , Lowen C. B.
Published: March 2003

1.Simple mechanical models (random walks and the ‘gas model’) were used to investigate the movement patterns and intergroup encounter rates of a high‐ and low‐density subpopulation of Grey‐Cheeked Mangabeys (Cercocebus albigena johnstoni,Lydeker) at two sites in the Kibale Forest, Western Uganda.

2.Random walk simulations showed that the presence of conspecific groups could act as ‘social barriers’ which constrained group movements, and promoted high levels of site attachment to a specific home range area.

3.Encounter rate models showed that in the low‐density subpopulation (Kanyawara), intergroup encounters occurred no more frequently than expected if groups were moving randomly and independently of each other. This was in contrast to previous analyses which suggested that Grey‐Cheeked Mangabeys employed a social spacing mechanism (mediated by male loud calls) in order to reduce the frequency of encounter to below chance levels.

4.Encounters in the high‐density subpopulation (Ngogo) were found to occur less frequently than expected at short range (within 100 m). This was suggested to be due to the operation of a territorial mate defence strategy by males at this site.
No support for socio‐physiological suppression effect on metabolism of paired white mice (Mus sp.)
Authors: Speakman J. R. , Rossi F. P.
Published: March 2003

1. Three experiments were performed on white mice (strain MF1) to establish if there was social or physiological suppression of metabolism, mediated by elevated ambient levels of CO2, when animals were in close contact. In the first two experiments the metabolism of two mice were each measured solitarily and paired together in the same chamber, both with and without a partition that allowed visual, auditory and olfactory communication but restricted physical contact.

2. Comparisons were made between the sum of the two solitary measurements, and the observed measurements of paired individuals. In the first experiment air flow was low and ambient CO2 was always at levels predicted to produce suppression (> 0·2%), independent of whether the animals were measured alone or paired.

3. The paired mice had greater metabolism than expected from the sum of their solitary metabolic rates whether the partition was present or absent. This increase was due to increased activity of the animals when in pairs. This experiment indicated that when CO2 levels were maintained in the range 0·2–0·5% there was no social suppression of metabolism.

4. In experiment 2 metabolic rates were measured of solitary mice exposed to subthreshold levels of CO2 (≈ 0·12%) and paired mice that experienced levels above the supposed threshold (≈ 0·24%). Again the observed metabolism of the paired mice exceeded the sum of their metabolic rates when solitary. The increase was also attributable to greater activity of the animals in pairs.

5. This experiment indicated no social suppression effect when CO2 varied in the range 0·12–0·24%. Moreover there was no significant difference between the oxygen consumptions of mice in experiment 2 compared with experiment 1, indicating that independent of the social context there was no suppressive effect of increases in CO2 concentration over the range 0·12–0·5% CO2.

6. Finally, in experiment 3, when two mice were placed in sequential separate chambers (allowing no social contact), their summed metabolism did not differ from the sum of their solitary measurements when a CO2 absorber was placed in the airflow linking the chambers. When the CO2 absorber was absent the observed metabolism of the pair exceeded the sum of the solitary measurements.

7. Overall, across all three experiments no evidence was found for either a social or a physiological suppression of metabolism mediated via CO2 (0·12–0·5%).
Comparison of seedling and adult palatability in annual and perennial plants
Authors: Fenner M. , Hanley M. E. , Lawrence R.
Published: March 2003

1.The relative palatabilities of the seedlings and adults of a range of British herbaceous plant species (14 annuals and 15 perennials) were compared using a generalist native herbivore (the slugDeroceras reticulatum) in a food‐choice experiment. A palatability index (0 to 1) was devised.

2.A general linear model analysis showed that, overall, there was a highly significant difference between seedling and adult palatability.

3.In the majority of cases, seedlings were more palatable than adults. However, in species with highly palatable adults the opposite tended to be the case.

4.No consistent difference between annual and perennial species was seen with respect to the relative palatabilies of adultsvsseedlings.

5.No evidence of a trade‐off between seedling palatability and relative growth rate was found.

6.In view of the role that selective seedling predation may play in determining species composition in the field, the results of this experiment indicate the need for caution in making ecological inferences from the exclusive use of adult material in palatability tests.
Stable coexistence of contrasted nitrification statuses in a wet tropical savanna ecosystem
Authors: Lata J. C. , Durand J. , Lensi R. , Abbadie L.
Published: March 2003

1. Wet tropical savannas are characterized by strong environmental constraints—particularly low soil nutrient availability—associated with high plant productivity. Nitrogen recycling, and especially nitrification, is supposed to be a strong determinant of the balance between conservation and loss of nutrients at the ecosystem level. Savanna facies dominated by the grass Hyparrhenia diplandra (Andropogoneae) are known to exhibit low levels of nitrification and thus avoid nitrate losses.

2. By comparing two sites in the Lamto area (Côte d’Ivoire, West Africa) with similar soil physico‐chemical characteristics and equally dominated by H. diplandra (80% of the grass cover), it was demonstrated that, within this facies, nitrification is highly heterogeneous, with a 240‐fold variation in potential nitrification within a specific site.

3. In order to test whether these differences can be considered as permanent in this ecosystem, nitrate reductase activities were compared on H. diplandra plantlets from the two sites, cultivated under identical conditions in the presence of nitrate. The leaves of plants originating from the high nitrification site were always able to reduce nitrate at a significantly higher rate than those from the low nitrification site. This observation indicates a long‐term adaptation of the plants and stable nitrification behaviour.

4. Lamto can thus be considered as a contrasted dual ecosystem relative to its nitrogen cycle. The two sites studied therefore constitute useful models to assess the determinism of nitrification in wet savannas and the role of this process on nitrogen retention in such ecosystems.
The effect of tree height and light availability on photosynthetic leaf traits of four neotropical species differing in shade tolerance
Authors: Rijkers T. , Pons T. L. , Bongers F.
Published: March 2003

1. Light‐saturated rate of photosynthesis (Amax), nitrogen (N), chlorophyll (Chl) content and leaf mass per unit area (LMA) were measured in leaves of trees of different heights along a natural light gradient in a French Guiana rain forest. The following four species, arranged in order from most shade‐tolerant to pioneer, were studied:Duguetia surinamensis, Vouacapoua americana, Dicorynia guianensisandGoupia glabra. Light availability of trees was estimated using hemispherical photography.

2. The pioneer speciesGoupiahad the lowest LMA and leaf N on both an area and mass basis, whereasDuguetiahad the highest values. In general, leaf variables ofVouacapouaandDicoryniatended to be intermediates. BecauseAmax/area was similar among species,Goupiashowed both a much higher light‐saturated photosynthetic nitrogen‐use efficiency (PNUEmax) andAmax/mass. Leaves ofVouacapouademonstrated the greatest plasticity inAmax/area, particularly in small saplings.

3. A distinction could be made between the effect of tree height and light availability on the structural, i.e. LMA, and photosynthetic leaf characteristics of all four species. The direction and magnitude of the variation in variables were similar among species.

4. LMA was the key variable that mainly determined variation in the other leaf variables along tree height and light availability gradients, with the exception of changes in chlorophyll concentration.Amax/area, N/area, LMA and stomatal conductance to water vapour (gs) increased, whereas Chl/mass decreased, with both increasing tree height and canopy openness.Amax/mass, PNUEmaxandAmax/Chl increased with increasing openness only. N/mass and Chl/area were independent of tree height and openness, except for small saplings ofGoupiawhich had a much lower Chl/area.
Phylogenetic tests of ecological and evolutionary hypotheses: checking for phylogenetic independence
Authors: Freckleton R. P.
Published: March 2003

1. Phylogenetic methods that account for the degree of relationship between species are increasingly commonly used for cross‐species comparisons of ecological data. In particular ‘phylogenetic contrasts’ are commonly used to generate data for analysis that are phylogenetically independent. The efficacy of this technique for removing phylogenetic correlations is rarely tested, however.

2. For a number of reasons, including non‐Brownian modes of evolution, phylogenetic contrasts may not always be phylogenetically independent. This lack of independence defeats the object of phylogenetic analysis and effectively invalidates the results of such analyses. Typically such problems may be overcome using simple data transformations but it is necessary to identify the correct transformation for each analysis variable.

3. Examples are presented for which contrasts have failed to control for phylogenetic correlation. This was because the correct transformation of the data was not identified prior to analysis. It is highlighted that the very act of transformation of data increases our understanding of the ecological variables being studied because the choice of transformation depends on how the character in question evolved.
The effects of diet switching and mixing on digestion in seabirds
Authors: Hilton G. M. , Furness R. W. , Houston D. C.
Published: March 2003

1. Animals modulate digestive function in order to optimize digestion of their current diet. Two seabird species were used to test the idea that, as a result, changing and mixing diets might adversely affect digestive performance.

2. When switched from an energy‐dense fish diet (Sprat, Sprattus sprattus (L.)) to an energy‐dilute diet (Whiting, Merlangius merlangus (L.)), Lesser Black‐Backed Gulls, Larus fuscus L. had worse digestive performance than birds that were acclimated to Whiting, indicating a cost of diet switching. However, when switched from Whiting to Sprat, Lesser Black‐Backed Gulls had better digestive performance than birds acclimated to the Sprat diet.

3. When switched from a Whiting to a Sprat diet some Common Guillemots, Uria aalge (Pont.), developed diarrhoea, although after acclimation birds were able to digest Sprat normally.

4. Common Guillemots, but not Lesser Black‐Backed Gulls, showed a reduction in digestive efficiency when given both diets in a mixed meal.

5. Common Guillemots appear to have a less flexible digestive system than Lesser Black‐Backed Gulls. This difference in response of the two species may be related to differences in their ecology.

6. Subtle diet shifts may affect digestive performance of animals, and therefore digestive effects, as well as factors such as prey availability and ease of capture, might affect food choice.
Reproductive strategies ofGammarus lacustris(Crustacea: Amphipoda) along an elevation gradient
Authors: F. M. Wilhelm , D. W. Schindler
Published: March 2003

1. The number of eggs, their size, mass and development time, and the starvation time of newly hatched young, was examined in four populations ofGammarus lacustrisalong an elevation gradient from prairie to alpine lakes (730 m to > 2300 m above sea level). Water temperature and ice‐free season decreased with increasing altitude.

2. Females in the alpine lake produced fewer but larger and heavier eggs than females in the prairie lake. Eggs produced by females in montane and subalpine lakes were intermediate in size, mass and number. Within populations, egg size was not related to the number of eggs or female size.

3. The development time of eggs declined with an increase in incubation temperature. At all incubation temperatures, large eggs had a longer incubation time than small eggs. All eggs incubated at 4 °C failed to produce young. Young from large eggs were larger in size than young from small eggs.

4. The starvation time of newly hatched young increased with decreasing temperature. However, slopes of regressions relating starvation time to temperature differed among populations. At 4 °C young from large eggs survived longer than young from small eggs.

5. The high phenotypic plasticity in reproductive traits contributes to the success ofG. lacustrisin a wide range of aquatic habitats. It is predicted that in response to climate‐induced warming, populations in currently cold montane and alpine lakes would shift their reproduction to produce more eggs of smaller size. However, the accurate prediction of the fate of populations between ecoregions will require knowledge of the extent to which these traits are under genetic control.
Above‐ground resource use increases with plant species richness in experimental grassland ecosystems
Authors: E. M. Spehn , J. Joshi , B. Schmid , M. Diemer , C. Körner
Published: March 2003

1. Diversity effects on canopy structure and the use of space and light were investigated in experimental grassland communities of one, two, four, eight or 32 species and of one, two or three functional groups (grasses, legumes and non‐leguminous forbs) in north‐western Switzerland.

2. Plant species and functional group richness improved the establishment of grassland assemblages and increased mean vegetation cover from 64% in monocultures to 100% in 32‐species mixtures.

3. Above‐ground biomass and leaf area index increased linearly with the logarithm of plant species number in all 3 years of the experiment. The most species‐rich communities produced 143% more biomass than the mean of all monocultures and 25% more biomass than the most productive monoculture in the third year of the experiment.

4. Plant light absorbance per unit ground area increased by 44% with diversity (32‐species mixtures compared with monocultures) for two reasons. (i) The lack of species complementarity in terms of success of seedling establishment and plant size in vegetation with low species diversity increased the gap area in the canopy, and consequently more light reached bare ground. (ii) Diverse ecosystems absorbed more light within their closed canopies (+20%) than did less diverse ecosystems, because of better three‐dimensional space filling and greater biomass density due to complementarity in plant architecture, particularly between grasses and dicots.

5. The overall canopy height was increased by 46% and the centre of gravity of the canopy was raised by up to 10 cm over the range of experimental diversity treatments from one to 32 species.

6. These results cannot be explained solely by a higher likelihood of the inclusion of more productive dominant species in the more diverse communities (sampling effect), which suggests that biomass production may be determined by the most productive species present in a community. For all important canopy characteristics of multispecies communities, we show that with increasing diversity, mixtures perform better than the best monoculture. This is a strong indication that part of the positive effect of diversity on biomass production is driven by complementary resource use.
Effects of defoliation on male and female reproductive traits of a perennial orchid, Dactylorhiza maculata
Authors: E. Vallius , V. Salonen
Published: March 2003

The effects of defoliation on male reproductive traits of plants have received little attention. We conducted two field experiments with Dactylorhiza maculata (L.) Soó to examine the effects of defoliation on both male and female reproductive traits. We removed 0, 50 or 100% of leaves prior to flowering. The quality of pollen was tested by transferring pollen from the differently treated plants to untreated plants of the same population.

The non‐defoliated plants did not differ from the defoliated plants in mass of pollinia. No differences were found in the weight of seed capsules or in the proportion of embryonic seeds raised by flowers receiving pollen from differently treated pollen donors.

The non‐defoliated and partially defoliated plants produced relatively more and heavier capsules than the completely defoliated plants.

Defoliation decreased leaf area, corm mass and the probability of flowering in the following year.

These results demonstrate that defoliation has no acute effects on male traits in the long‐living perennial orchid D. maculata. In this respect, D. maculata differs from the two other polycarpic species studied so far. Availability of resources appeared to be insufficient to prevent negative effects of defoliation on the later‐occurring and more costly female functions.
Architectural and allometric differences among Scaphium species are related to microhabitat preferences
Authors: Yamada T. , Yamakura T. , Lee H. S.
Published: March 2003

Interspecific comparisons were made among Scaphium species (Sterculiaceae): S. borneense (Merr.) Kosterm., S. longipetiolatum (Kosterm.) Kostermans, and S. macropodum (Miq.) Beumee ex Heyne to test the hypothesis that variations in their architecture and allometry are related to the microhabitat conditions of stands where the species regenerate preferentially.

The species studied are shade‐tolerant canopy trees. They occur in a tropical rainforest in Lambir Hills National Park, Sarawak, East Malaysia (sympatric at the community level), where the study was conducted, but show an allopatric pattern of distribution among microhabitats due to localized edaphic conditions. Scaphiumlongipetiolatum occurs primarily in stands on clay‐rich soils, whereas S. borneense occurs primarily in stands on sandy soils. Stands on clay‐rich soils are more shaded, and gaps form less frequently than in stands on sandy soils.

Scaphium
longipetiolatum initiated branching at a smaller tree size than S. borneense and S. macropodum, which did not produce branches until stems reached several centimeters in diameter.

The monoaxial saplings of S. borneense and S. macropodum expanded their crown area by producing bigger leaves. The branched saplings of S. longipetiolatum expanded their crown area by developing lateral branch systems.

An analysis of interspecific differences in above‐ground allometries revealed that the growth pattern of monoaxial saplings, which emphasizes leader growth, leads to rapid height growth. In contrast, that of the branching saplings of S. longipetiolatum prioritizes shade tolerance.

The architecture and allometry of each Scaphium species gave some potential advantage over the other Scaphium species in stands where the former regenerates preferentially, that is, the advantages of each phenotype were context‐dependent.
Manipulation of flooding and arbuscular mycorrhiza formation influences growth and nutrition of two semiaquatic grass species
Authors: Miller S. P. , Sharitz R. R.
Published: March 2003

Two semiaquatic grasses, Panicum hemitomon Schultes and Leersia hexandra Schwartz, were grown for 12 weeks in sterilized soil in experimental mesocosms, with and without the addition of arbuscular mycorrhizal (AM) fungal inoculum (as nonsterilized soil), under the following rooting‐zone flood regimes: waterlogged (W), free‐draining (D), beginning W and ending D (W–D), and beginning D and ending W (D–W). The purpose of the experiment was to determine whether these controlled water regimes affected both colonization of wetland grasses by AM fungi and the effects of the colonization on various plant parameters.

Water regime, addition of inoculum, and their interaction were highly significant effects on total and proportion of root length colonized by AM fungi. Trends were very similar for the two grass species. Colonization was less and plants smaller in the W and W–D than in the D and D–W treatments. The viability of mycorrhiza at the end of the experiment, as measured by vital staining techniques, was not affected by changes in water level.

Colonized plants in all water level treatments showed an improvement in phosphorus (P) nutrition over noncolonized plants. Colonized grasses of both species gained consistently more P per plant and had greater tissue P concentrations, with the greatest P concentration in the most heavily colonized plants (from the D and D–W treatments).

The effect of flooding on the mycorrhizal association depended largely on the extent to which the association was already established when the flooding occurred. Flooding reduced the initiation of colonization either directly or indirectly, but once the fungi were established in the roots they were able to maintain and expand with the growing root system.
Maternal provisioning of offspring and the use of those resources during ontogeny: variation within and between Atlantic Salmon families
Authors: Berg O. K. , Hendry A. P. , Svendsen B. , Bech C. , Arnekleiv J. V. , Lohrmann A.
Published: March 2003

The size and proximate composition of eggs and alevins (larvae) were measured from six full sibling families of Atlantic Salmon (Salmo salar), at six stages between fertilization and first feeding.

 Egg and alevin size measures (diameter, wet mass, dry mass) and proximate composition attributes (water, protein, fat, energy) were all highly correlated with each other (r = 0·89–0·99), suggesting that each is a reasonable surrogate for any other.

 Most of the variation in egg size (95·0–97·0%) and composition attributes (95·5–97·9%) was partitioned between, rather than within, females. Most of this variation was attributable to differences in female size, owing to the length of time spent at sea.

 Fat, protein and energy content varied less on a relative basis (controlling for egg size variation) than on an absolute basis, suggesting that certain combinations of egg attributes are optimal regardless of egg size.

 Stored fat decreased by 9·6 µg day−1before hatching but increased by 27·4 µg day−1after hatching. The increase after hatching suggests that alevins actively synthesize (probably from protein) and store lipids between hatching and first feeding.

 Stored protein decreased by 8·8 µg day−1before hatching and by 181·3 µg day−1after hatching. Assuming all metabolic energy was derived from stored protein, metabolic rate increased logarithmically from 0·115 J day−1to 5·43 J day−1. Rates of oxygen consumption estimated from protein loss (6·09–288·9 µl O2d−1) were similar to those reported in studies that measured oxygen consumption using respirometry.

 Alevins appear to convert protein to fat, a change that their mothers were unable or unwilling (in an evolutionary sense) to make. This may reflect the conflicting goals of parents and offspring for maximizing fitness.
Competition for light and nitrogen among grassland species: a simulation analysis
Authors: P. Schippers , M. J. Kropff
Published: March 2003

1. A plant competition model to analyse the competition among perennial grassland species was developed. It was used to find out whether complex perennial competition processes could be simulated accurately on the basis of ecophysiological principles; what crucial parameters and processes determine succession; and how spatial heterogeneity affects interspecies competition for light and nitrogen.

2. Simulation results were compared with results of a 2‐year replacement experiment involving Holcus lanatus, Anthoxanthum odoratum and Festuca ovina. Sensitivity analyses were performed to evaluate the importance of processes and parameters.

3. The model’s sensitivity to plant height, specific leaf area and turnover and the large interspecific differences indicated that these were key determinants of competition between species. Festuca’s low shoot turnover enabled it to survive the winter better and gave it an advantage in spring; this resulted in an unexpected recovery after winter in the second year.

4. Spatially explicit simulations showed that species patchiness reduced competitive asymmetry, especially under nutrient‐poor conditions.

5. The model’s ability to simulate complex perennial competition processes as observed in the experiment indicates its potential for analysing vegetation processes related to succession.
Functional significance of sexual dimorphism in Wandering Albatrosses, Diomedea exulans
Authors: Shaffer S. A. , Weimerskirch H. , Costa D. P.
Published: March 2003

1. The investigation covered whether sexual dimorphism could affect flight performance in a manner that is consistent with differences in at‐sea distribution of male and female Wandering Albatrosses, Diomedea exulans Linnaeus. Adult morphology was also compared to near‐fledged chicks to assess whether morphological differences are consistent with different at‐sea distributions of adults and fledglings.

2. Body girth, mass, wing span and area were measured on 24 females (16 adults and 8 chicks) and 32 males (20 adults and 12 chicks) breeding in the Crozet Archipelago.

3. On average, adult males had longer wings (4%, 311 ± 4 cm) with 6·8% more area (6260 ± 270 cm2), but were also 20·4% heavier (9·44 ± 0·59 kg) than adult females. As a result, wing loading in adult males was 12·1% greater than adult females.

4. When compared with adults, total wing area of chicks was lower resulting in higher wing loading because of the incomplete growth of chicks at the time measurements were collected. However, projected chick growth to fledging indicates that wing loading would be lower in fledglings than adults.

5. Because wing loading determines flight speed, it is conceivable that windier regions of the sub‐Antarctic/Antarctic are more optimal for male albatrosses because they have higher wing loading. Conversely, wing loading is lower in adult females and fledglings, which could make them better adapted to exploit lighter winds of the subtropical and tropical regions. Thus, size dimorphism may have a functional role in flight performance that influences the at‐sea distribution of adult and fledgling Wandering Albatrosses.
Relationships between physical and chemical attributes of congeneric seedlings: how important is seedling defence?
Authors: Hanley M. E. , Lamont B. B.
Published: March 2003

While herbivory is considered a major selective force operating in mature vegetation, much less is known about how herbivores affect the expression of defence at the seedling stage. In this study we quantified several chemical and physical properties, usually considered to affect seedling palatability, of 14 Western Australian Hakea species. We also determined whether seedling defences were related to other plant life‐history attributes.

Of all of the attributes measured, chemical defence (phenolic content of shoots) exhibited the most significant correlations with other traits (six of a possible eight). We also detected an apparent trade‐off between chemical (phenolics) and physical (spinescence) defence.

Seed mass, relative growth rate and specific leaf area are traits commonly held to have the most predictive power in simplifying our understanding of plant ecological and evolutionary processes across species boundaries. Within this genus, however, these attributes were poorly correlated with other traits.

We conclude that more extensive studies of seedling defence attributes are needed for a fuller understanding of what governs the evolution of plant life‐history traits.
Visit larger displays but probe proportionally fewer flowers: counterintuitive behaviour of nectar‐collecting bumble bees achieves an ideal free distribution
Authors: Ohashi K. , Yahara T.
Published: March 2003

1. Patterns of pollinator responses to variation in floral display size have significance for pollen flow among plants. Here we test a theoretical model for explaining such patterns by simultaneously assessing bumble bee behaviour and nectar availability in two native stands of Cirsium purpuratum with different spatial densities.

2. A bumble bee (Bombus diversus) foraging on a plant remembered and avoided only one or two flower heads that it had probed before, so that the flower‐head revisitation rate increased as it stayed longer on a plant. Moreover, the revisitation rate increased less rapidly on larger displays.

3. The number of heads probed per plant increased less than proportionally with display size, and this increase was smaller at higher plant density. This pattern is consistent with our expectation that a bee leaves a plant when the cost of flower‐head revisitation exceeds that of interplant movement. However, bees left plants slightly earlier than predicted.

4. As predicted, the visitation rate of bees per plant showed a decelerated increase with floral display size, and this increase was greater at higher plant density.

5. As a result of these complementary changes in the number of heads probed per plant and visitation rate per plant across plant densities, nectar rewards per head were equalized among displays (an ideal free distribution was achieved).
Spatial variation in ant and rodent post‐dispersal predation of vertebrate‐dispersed seeds
Authors: Rey P. J. , Garrido J. L. , Alcántara J. M. , Ramírez J. M. , Aguilera A. , García L. , Manzaneda A. J. , Fernández R.
Published: March 2003

Post‐dispersal predation of vertebrate‐dispersed seeds has received little attention in the Mediterranean region. We investigated the spatial variation in post‐dispersal seed predation of vertebrate‐dispersed plants and its potential implications for plant diversity in fleshy fruited plant communities of southern Spain.

An experiment was conducted in forests and open scrubland at mid‐ and high elevations to explore: (a) the possibility of differential seed predation by rodents and granivorous ants; (b) the spatial variation, between and within habitats, in post‐dispersal seed predation and predator abundance; and (c) whether the spatial distribution of predation covaries among plant species.

Rodents and granivorous ants proved to be important predators of vertebrate‐dispersed seeds, and showed significant variation in their preferences for different seed species. Granivorous ant preferences depended on seed size, as seeds heavier than 20 mg were hardly ever removed. Rodents were indifferent to seed size.

Sites safe from predators were more frequent at mid‐elevations. In contrast to other temperate communities, successional status (open scrubland vs forest) did not determine the probability of predation, probably because ants are more important as seed predators in the early successional stages of Mediterranean habitats than in other temperate communities. The large‐scale variations in the occurrence of safe sites for the seeds depended on resource abundance rather than on predator abundance.

We found a significant interaction in seed predation rates between microhabitat and seed species at mid‐elevations, but not in high‐elevation habitats, implying stronger covariance across plant species in the microhabitats adequate for recruitment (e.g. with lower predation risk) at high elevation. This pattern may contribute to the differential plant diversity at mid‐ and high elevations in Mediterranean fleshy fruited plant communities. Theoretical models predict that seed predators may contribute to the maintenance of species diversity if the spatial distribution of safe sites from predators is uncorrelated across plant species, as it was at mid‐elevations.
Competitive status influences tree‐growth responses to elevated CO2 and O3 in aggrading aspen stands
Authors: McDonald E. P. , Kruger E. L. , Riemenschneider D. E. , Isebrands J. G.
Published: March 2003

Competition effects on growth of individual trees were examined for 4 years in aggrading, mixed‐clone stands of trembling aspen (Populus tremuloides Michx.) at the Aspen‐FACE free‐air CO2 and O3 enrichment facility in northern Wisconsin, USA. During each growing season stands received one of four combinations of atmospheric [CO2] (ambient vs∼56 Pa) and [O3] (ambient vs∼1·5 × ambient).

Non‐destructive measurements of annual tree growth were compared within and among clones and treatments in relation to an index of competitive status based on the difference between a tree's height and that of its four nearest neighbours. Competitive status strongly influenced tree growth, and the positive growth response to elevated [CO2] was greater for competitively advantaged individuals than for disadvantaged individuals of most clones.

The magnitude of O3 effects on growth depended on clone and competitive status: for some clones, negative O3 effects were stronger with competitive advantage while others showed stronger O3 effects with competitive disadvantage. The interactive effects of CO2 and O3 differed among clones, with negative effects of O3 amplified or ameliorated by elevated CO2, depending on clone and competitive status.

Treatments modified competitive interactions by affecting the magnitude of growth differences among clones. These modifications did not alter clone rankings of competitive performance, but when CO2 and O3 were both elevated, the differences in competitive performance among clones decreased.
Multivariate responses to flooding in Arabidopsis: an experimental evolutionary investigation
Authors: Kolodynska A. , Pigliucci M.
Published: March 2003

Response to selection in different environments has been investigated in the model system Arabidopsis thaliana in order to determine the changes in heritabilities, reaction norms, relationships with reproductive fitness, and character correlations induced by the selection regimes and by alterations of environmental conditions (flood vs normal water levels).

Our artificial population responded to selection mostly by line sorting, where some of the initial genotypes increased significantly in frequency over three generations, while others went extinct. This is probably how selection works in natural populations of this species.

We observed changes in the heritabilities of various traits in response to selection and experimental treatments, with morphological characters exhibiting higher heritabilities than life‐history traits.

The selection process did not alter the overall shape of the reaction norms of various characters, but did lower the phenotypic means of several traits in the same direction of plasticity imposed by flooding. Most characters were under directional selection throughout the experiment, though in the opposite direction from the actual shift in their means at the end of the experiment.

The multivariate architecture of this plant was affected more by selection than by environmental changes.
Interplay between positive and negative elongation factors: drawing a new view of DRB
Authors: Yamaguchi Yuki , Wada Tadashi , Handa Hiroshi
Published: March 2003

DRB is a classic inhibitor of transcription by RNA polymerase II (pol II). Although it has been demonstrated that DRB inhibits the elongation step of transcription, its mode of action has been elusive. DRB also markedly inhibits human immunodeficiency virus (HIV) transcription, by targeting the elongation which is enhanced by the HIV‐encoded transactivator Tat. Two factors essential for DRB action have recently been identified. These factors, positive transcription elongation factor b (P‐TEFb) and DRB sensitivity‐inducing factor (DSIF), positively and negatively regulate pol II elongation, and are likely to be relevant to the function of Tat. In this review, we summarize the recent findings on these factors, and discuss a possible model for the molecular mechanism of DRB action.
Type I interferons are essential mediators of apoptotic death in virally infected cells
Authors: Tanaka Nobuyuki , Sato Mitsuharu , Lamphier Marc S. , Nozawa Hiroaki , Oda Eri , Noguchi Shigeru , Schreiber Robert D. , Tsujimoto Yoshihide , Taniguchi Tadatsugu
Published: March 2003

Background

The interferons (IFNs) have been extensively studied in the context of host defence against viral infection. In the established model of IFN action, virally infected cells secrete type I IFNs (IFN‐α/β) which induce an antiviral state in uninfected cells. However, it is not clear how IFNs function on the infected cells. It has been reported that cells infected by some viruses die by apoptosis.

Results

In the present study, we found that three types of viruses commonly induce apoptosis in primary cell cultures. Importantly, we observed that virus‐induced apoptosis was inhibited by anti‐IFN‐α/β antibodies, and in cells lacking either the type I IFN receptor 1 (IFNAR1) or its downstream mediator, Stat1 (Signal transducer and activator of transcription 1). IFN‐α treatment by itself did not induce apoptosis unless it was combined with transfection by double‐stranded RNA (dsRNA), which is normally generated during the course of viral infection.

Conclusion

These results indicate a novel antiviral function of the type I IFNs, i.e. the selective induction of apoptosis in virally infected cells. In effect, these IFNs have a bifunctional role in limiting the spread of virus; eliciting an antiviral state in uninfected cells while promoting apoptosis in infected cells. Our results may help explain why IFNs are sometimes useful in the treatment of viral diseases and will provide further insight into the mechanisms of virus‐induced pathogenesis