Consequences of differences in body mass,wing length and leg morphology for nectar-feeding birds

Nectar-feeding birds are prominent in many parts of the world, and vary with respect to body size. Despite the availability of considerable morphometric data, few concerted efforts have been made to assess the influence of attributes such as mass, wing length and leg morphology upon the speed, acceleration, mode and energetic cost of movement by birds between flowers when foraging for nectar. This review attempts to consolidate and interpret available data and highlight areas where further investigations appear warranted. Australian honeyeaters are generally larger, and American hummingbirds smaller, than Hawaiian honeycreepers and sunbirds of Africa or Asia. Sunbirds, honeyeaters and honeycreepers generally perch while extracting nectar from flowers. Hummingbirds usually hover, apparently because suitable perches close to flowers are lacking, and not because hovering increases the speed at which flowers can be visited. Honeyeaters move from one flower to another at speeds that are at least as great as those for hummingbirds. Most passerine nectarivores need to ingest more nectar per day than hummingbirds in order to maintain energy balance, some species devoting more than 60% of the day to foraging. The major consequence of reduced foraging activity by hummingbirds, which spend only 5–30% of the day in this manner, appears to be male emancipation from nest construction and care of offspring. Large nectarivores have a greater capacity to store surplus food and to fast than smaller birds, and so can take advantage of short-lived peaks in nectar abundance. Nectarivores such as honeyeaters should therefore be favoured by the rapid diurnal changes in nectar availability which are characteristic of many Australian and African habitats. Body mass also determines the likely access to rich sources of nectar through size-related interspecific dominance hierarchies. In all families, larger species tend to monopolize the most rewarding nectar supplies, forcing smaller subordinate species to use poorer, more scattered sources. Within particular species, males usually have longer wings and greater masses than females. These variations imply that the two sexes differ with regard to their foraging ecology, although few supporting data are currently available.     

FACTORS INFLUENCING THE EFFICIENCY OF INCOMPLETE BLOCK DESIGNS IN SENSORY EVALUATION EXPERIMENTS

The efficiencies of incomplete block designs were investigated by comparing two hundred and twenty eight analyses from eleven trials using hedonic scales with corresponding randomized complete block analyses. Of the ten explanatory factors examined, only the panelist, the product type, the number of samples per session and the average score of the data had an effect on the efficiency of incomplete block designs. The effect of product type was attributed to influences of produce consumed outside the trial, and the effect of the data mean reflected decreased conscientiousness with products the panelists disliked. With three and four samples per session, incomplete block designs were 31 % and 2 % more efficient, respectively, than randomized complete block designs. When five or more samples were tested, the incomplete block designs were markedly less efficient. The practical implications of all these effects on experimental design are discussed.     

The function of the intramaxillary joint in the Round Island boa, Casarea dussumieri

The bolyeriid snakes Casarea dussumieri and Bolyeria multocarinata are unique among vertebrates in possessing an intramaxillary joint that separates the maxilla into anterior and posterior segments. In contrast to previous studies, which suggest that this joint permits enhanced elevation of the anterior maxillary teeth, our films of live Casarea show that the snout and anterior maxillary teeth are actively depressed 15° 20° below rest position through bilateral retraction of the palatomaxillary arches. Patterns of bone movement in living Casarea support the hypothesis that a caudally directed force is transmitted to the snout via the medial bones of the palatomaxillary arch, suggesting functional affinities between Casarea and higher henophidians.
The intramaxillary joint, in conjunction with the curvature of the mandibles, allows the jaws of Casarea to encircle hard, cylindrical prey held transversely in the mouth. Because the Mauritian terrestrial vertebrate fauna lacks mammals and is dominated by skinks and geckos, which Casarea is known to consume, we suggest that the intramaxillary joint functions in a manner analogous to that achieved by quite different maxillary modifications in colubrid scincivores. Although the origin of the bolyeriid intramaxillary joint remains unclear, its structural refinement and evolutionary stability may be due to selection pressures arising from limited prey diversity.     

Cyclic Variations in Nitrogen Uptake Rate in Soybean Plants: Uptake During Reproductive Growth

Net uptake of by non-nodulated soybean plants [Glycme max(L ) Merr cv Ransom] growing in flowing hydroponicculture was measured daily during a 63 d period of reproductivedevelopment between the first florally inductive photopenodand late seed growth Removal of from a replenished solution containing 10 mol m^– was determined by ion chromatography Uptake of continued throughout reproductive development The net uptakerate of cycled between maxima and minima with a periodicity of oscillation of 3 to 7 d during the floralstage and about 6 d during the fruiting stage. Coupled withincreasing concentrations of carbon and C:N ratios in tissues,the oscillations in net uptake rates of are evidence that the demand for carbohydrate by reproductiveorgans is contingent on the availability of nitrogen in theshoot pool rather than that the demand for nitrogen followsthe flux of carbohydrate into reproductive tissues. Key words: Nitrate uptake rate, carbon-nitrogen partitioning, Glycme max (L ) Merrill     

A Dynamic Growth Model of Vegetative Soya Bean Plants: Model Structure and Behaviour under Varying Root Temperature and Nitrogen Concentration

A differential equation model of vegetative growth of the soyabean plant (Glycine max (L.) Merrill cv. ‘Ransom’)was developed to account for plant growth in a phytotron systemunder variation of root temperature and nitrogen concentrationin nutrient solution. The model was tested by comparing modeloutputs with data from four different experiments. Model predictionsagreed fairly well with measured plant performance over a widerange of root temperatures and over a range of nitrogen concentrationsin nutrient solution between 0.5 and 10.0 mmol in the phytotron environment. Sensitivity analyses revealedthat the model was most sensitive to changes in parameters relatingto carbohydrate concentration in the plant and nitrogen uptakerate. Key words: Glycine max (L.) Merrill, dry matter, nitrogen uptake, partitioning, photosynthesis, respiration, sensitivity analysis     

The Uptake and Transport of 14C in Cells of Conocephalum conicum L. in Light

Dissolved inorganic ¹⁴carbon, fed to a small portion of thetissue of Conocephalun conicum, travelled along the tissuesfrom cell to cell at rates of about 2.0 to 1.7 µm 5^–1,which is of the same order of magnitude as streaming rates inthese cells. Trans-cellular transport can take place againsta pressure gradient, but pressure gradients of 200 kPa or morein either direction reduced the trans-cellular transport significantlywithout reducing streaming rate and are, therefore, thoughtto have induced ‘valving’ effects at the plasmodesmata.Ammonium ion reduced or inhibited transport without reducingstreaming rates and is, therefore, thought to have inhibitedan active component in the plasmodesmata. Thus the results obtainedfrom tandem cells of Nitella can be transferred to tissues. Key words: Conocephalum, transport, plasmodesmata     

Action of Sorghum Proteinase on the Protein Bodies of Sorghum Starchy Endosperm

Protein bodies isolated from the starchy endosperm of ungerminatedsorghum exhibited some autolytic activity but seemed incapableof significant self-hydrolysis. Enzyme assay, transmission electronmicroscopy, sodium dodecyl sulphate—polyacrylamide gelelectrophoresis and amino acid analysis revealed that a proteinaseextract from germinated sorghum could degrade the protein bodiesin a manner resembling that which takes place in vivo. The proteinbodies were degraded mainly from the periphery. Glutelin (matrixprotein) was first hydrolysed, followed by the prolamin proteinbody protein. Proteinase extracts from both the germ and endospermof germinated sorghum were capable of degrading the proteinbodies. This finding is consistent with the concept that theproteinase is synthesized in the germ and then secreted intothe starchy endosperm during germination. Key words: Sorghum bicolor, protein body degradation, proteinase.     

Potential Increase in Photosynthetic Efficiency from the Redistribution of Solar Radiation in a Crop

The efficiency of the conversion of photosynthetically activeradiation by C₃ plants falls off with increasing intensity.Hypothesis: an increase in the productivity of direct solarenergy will be achieved if, by redistribution, it is interceptedat a more uniform and lower intensity by a greater proportionof the leaf area of a crop. A model is developed which usesestimates of the proportions of clear and overcast conditionsfrom site records of solar radiation to calculate the resultantphotosynthetic productivity. The amounts of diffuse light anddirect light are estimated for clear conditions. The model predictsthat redistributing direct solar radiation over twice the leafarea at half the intensity would give an increase of 22% inannual productivity. The model gives reasonable values for theproductivity reductions reported for two shading regimes. Tomato plants were grown for 21 d in three cabinets under regimesthat differed from each other only in the distribution of PARenergy over the daily photoperiod: (a) 103 W m^–2 for halfthe photoperiod followed by 13 W m^–2, (b) 13 W m^–2followed by 103 W m^–2 and (c) 58 W m^–2 for the wholephotoperiod. The dry matter increase of plants under the uniformregime was 33% greater than the average of those in the twoasymmetric regimes. It is suggested that, in protected cultivation, screens of partiallyreflective material could be used to redistribute solar radiationfrom leaves exposed to high intensities on to shaded leavesand so raise the photosynthetic efficiency. Assuming an absorptionof direct light by the screens of 0.10, the increase in productivityis estimated to be 17%. Key words: Photosynthesis, C₃, canopy, solar energy, solar redistribution, light interception, partial reflection, growth cabinet, glasshouse, tomato     

Modeling Cretaceous-Tertiary boundary events with extant photosynthetic plankton: effects of impact-related acid rain

Griffis, K. & Chapman, D. J. 1990 10 15: Modeling Cretaceous-Tertiary boundary events with extant photosynthetic plankton: effects of impact-related acid rain. Lethaia , Vol. 23, pp. 379–383. OSIO. ISSN 0024–1164.
An acid rain phenomenon has previously been proposed as one of the consequences of a bolide impact contributing to the extinctions at the Cretaceous-Tertiary boundary. This hypothesis has been tested by observing the growth responses of four organisms under simulated acid rain conditions. Two of these phytoplankton, Ditylum (a diatom) and Thoracosphaera (a dinoflagellate). are genera that persisted through the boundary, while the other two, Coccolithus (a coccolithophorid) and Gonyaulax (a dinoflagellate), are post-boundary genera. Ditylum and Coccolithus survive the acid rain simulation. but with the loss of scales in Coccolithus . The two dinoflagellate are sensitive to acid rain simulations. with Gonyaulax unable to survive beyond seven days. The results indicate that acid rain may have contributed to the Cretaceous-Tertiary boundary extinctions. but that the changes resulting from the acid rain were not as severe as postulated or were short-lived and quickly dissipated. ▭ Acid rain, coccolithophorids. Cretaceous/Tertiary extinctions, diatons, dinoflagellates, phytoplankton .