bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract1. 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

Abstract1. 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

Abstract1. 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

Abstract1. 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

Abstract1. 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

Abstract

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

Abstract

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

Abstract

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

Summary 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

Abstract1. 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.