bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differential responses to UVR by bacterioplankton and phytoplankton from the surface and the base of the mixed layer
Authors: Xenopoulos Marguerite A. , Schindler David W. 
Published: March 2003

SUMMARY 1. We tested the influence of ultraviolet radiation (UVR) and shallow stratification on phytoplankton and bacterioplankton from the surface and the base of the mixed layer in two boreal lakes in north‐western Ontario, Canada.2. We measured phytoplankton biomass and production, bacterioplankton production and plankton respiration after transplantation under three solar radiation treatments: ambient radiation (Photosynthetically active radiation (PAR) + ultraviolet‐A (UVA) + ultraviolet‐B (UVB)), minus UVB (PAR + UVA) and PAR only. We repeated this experiment on three occasions in each lake during the summer.3. Solar stress (measured as reduced growth and photoinhibition) was generally only found in the ‘base phytoplankton’ (i.e. originating from the base of the mixed layer). No inhibition of photosynthesis by UVB exposure was found in near‐surface phytoplankton. On the other hand, production of near‐surface bacterioplankton was reduced following a 4‐h UVR exposure but had increased after a 48‐h exposure to both UVA and UVB compared with the PAR only treatment.4. Negative effects of UVR on phytoplankton and bacterioplankton were not ubiquitous. We emphasise the importance of conducting experiments repeatedly, particularly those which test the effects of UVR on different community assemblages from different lakes.
Reaction distance of Bythotrephes longimanus, encounter rate and index of prey risk for Harp Lake, Ontario
Authors: Muirhead Jim , Sprules W. Gary 
Published: March 2003

SUMMARY 1. Some predatory zooplankton, such as the large cladoceran Bythotrephes longimanus (Leydig), have a large compound eye, hence vision may play an important role in prey detection and encounter. Our objectives were to quantify, under different light regimes, the reaction distance of Bythotrephes to an assortment of zooplankton prey and to model encounter rate with prey from Harp Lake, Ontario. Reaction distance to prey increased at higher light intensity.2. Results from the encounter model show that small, slow‐moving prey faced the greatest risk from Bythotrephes and most encounters occurred in the upper 10 m of the water column throughout the 24‐h period. The model was highly sensitive to ambient light. Encounter rate and prey risk were two to three orders of magnitude more sensitive to swimming velocity of the predator than to that of the prey.
Measurement of three‐dimensional structure of plants with a simple device and estimation of light capture of individual leaves
Authors: Takenaka A. , Inui Y. , Osawa A. 
Published: March 2003

1. A simple device called a ‘pocometer’ (POlar COordinate METER) was developed to measure three‐dimensional structure of plants. It consists of a tape‐measure to measure distance and two protractors to measure zenith angle and azimuth angle. 2. The pocometer can determine locations of points within a few metres distance with a resolution of less than 1cm. Location of any point on a plant can be measured in 10 to 30s depending on the ease of pulling the tape measure to the point of interest. 3. A system to use data obtained with the pocometer to calculate plant light capture was developed. The degree of shading at any point on a plant is estimated by checking obstruction by other plant parts of the view toward the sky at that point. 4. Photon flux density (PFD) on leaf surfaces was estimated for Aucuba japonica, a broad‐leaved evergreen shrub, using the above system. The estimated PFDs for individual leaves of a plant corresponded to the sensor‐measured PFDs with correlation coefficients of 0·67 to 0·92.
Economics of spider orb‐webs: the benefits of producing adhesive capture thread and of recycling silk
Authors: Opell B. D. 
Published: March 2003

1. The replacement of dry, fuzzy cribellar prey capture thread by viscous, adhesive capture thread was a major event in the evolution of orb‐weaving spiders. Over 95% of all orb‐weaving species now produce adhesive threads. 2. Adhesive thread achieves its stickiness with a much greater material economy than does cribellar thread. 3. Transformational analyses show that, relative to spider mass, adhesive orb‐weavers invest less material per mm of capture thread and produce stickier capture threads than do cribellate orb‐weavers. 4. The total cost of producing an orb‐web that contains cribellar thread is reduced by 32% when a spider recycles its silk and another 34% when these capture threads are replaced by adhesive threads of equal stickiness. 5. The increased economy with which adhesive capture thread achieves its stickiness may have been an important factor that favoured the origin and success of modern orb‐weaving spiders that produce adhesive capture threads.
Photoinhibition in tropical forest understorey species with short‐ and long‐lived leaves
Authors: Lovelock C. E. , Kursar T. A. , Skillman J. B. , Winter K. 
Published: March 2003

1. Shade‐tolerant species that inhabit the understorey have a range of leaf lifetimes (from 1 to 8 years), which may indicate a variety of strategies for dealing with increases in light associated with tree‐fall gaps. We hypothesized that species with long‐lived leaves should be more tolerant of an increase in light levels than species with short‐lived leaves. 2. In understorey plants of 12 shade‐tolerant rain‐forest species, photoinhibition, measured as a reduction in the chlorophyll fluorescence parameter Fv/Fm when leaf discs were exposed to 1h at 1000μmol m–2s–1, was greater in species with short‐lived leaves than species with long‐lived leaves. 3. Less photoinhibition in species with long‐lived leaves was not associated with higher levels of non‐photochemical dissipation (NPQ) of absorbed light, but may be the result of a higher yield of photosystem II compared with short‐lived leaves. 4. Thus, species with long‐lived leaves are more tolerant of abrupt increases in light that occur when tree‐fall gaps are formed than species with short‐lived leaves. 5. Discs from leaves of all species growing in tree‐fall gaps had higher levels of NPQ, yield of photosystem II and more rapid recovery from photoinhibition than leaves developed in the understorey; however, there were no differences among species with short‐ and long‐lived leaves.
Contrasting digestive strategies of fruit‐eating birds
Authors: Witmer M. C. , Van Soest P. J. 
Published: March 2003

1. Sugary fruits dominate the annual diet of Cedar Waxwings (Bombycilla cedrorum), whereas lipid‐rich foods dominate the diets of frugivorous thrushes. Nutrient utilization and preferences of Cedar Waxwings and thrushes fed sugary and lipid‐rich natural fruits were assessed to ascertain the potential for nutrient‐based specializations that could explain diet selection in nature. 2. Compared allometrically, Cedar Waxwings showed higher rates of sugar assimilation from sugary fruits than did thrushes, by virtue of higher intake rates, and achieved the highest energy assimilation rates when eating a sugary fruit. A trade‐off to this digestive strategy appears to be less efficient utilization of lipids when eating exclusively lipid‐rich fruits. 3. Thrushes digested lipids more efficiently than Cedar Waxwings as a function of intake rate or estimated retention time, and thrushes achieved the highest energy assimilation rates when eating a lipid‐rich fruit. Specialization to a diet rich in lipids appears to limit the rate at which sugary fruits can be processed. 4. Within each bird species, sugar digestive efficiencies were high and were not reduced at higher intake rates. Lipids were consumed at lower rates than sugars, and lipid digestive efficiencies declined with increasing intake rates. Frugivorous birds modulated digestive processing of fruits according to the time needed for efficient digestion and/or absorption of sugars and lipids, respectively. 5. Rate of nitrogen intake, not sugar assimilation, positively influenced body mass changes of birds. Sugary fruits appear nutritionally rich in energy, but limited in protein for avian frugivores. Relatively high intake rates and low protein requirements of Cedar Waxwings suggest that specialization to sugary, low‐protein diets involves traits that facilitate acquisition and conservation of protein/amino acids. 6. Cedar Waxwings and thrushes show digestive specialization to the utilization of sugars and lipids, respectively, as dominant dietary nutrients. These traits explain patterns of food selection by these birds in the laboratory and in nature. Variation in the value of particular fruit nutrients to different birds renders the dietary descriptor of ‘frugivore’ ambiguous in a nutritional context.
Limits to water transport inJuniperus osteospermaandPinus edulis: implications for drought tolerance and regulation of transpiration
Authors: Linton M. J. , Sperry J. S. , Williams D. G. 
Published: March 2003

1.An air‐injection method was used to study loss of water transport capacity caused by xylem cavitation in roots and branches ofPinus edulis(Colorado Pinyon) andJuniperus osteosperma(Utah Juniper). These two species characterize the Pinyon–Juniper communities of the high deserts of the western United States.Juniperus osteospermacan grow in drier sites thanP. edulisand is considered the more drought tolerant.2.Juniperus osteospermawas more resistant to xylem cavitation thanP. edulisin both branches and roots. Within a species, branches were more resistant to cavitation than roots forP. edulisbut no difference was seen between the two organs forJ. osteosperma. There was also no difference between juveniles and adults inJ. osteosperma; this comparison was not made forP. edulis.3.Tracheid diameter was positively correlated with xylem cavitation pressure across roots and stems of both species. This relation suggests a trade‐off between xylem conductance and resistance to xylem cavitation in these species.4.During summer drought,P. edulismaintained higher predawn xylem pressures and showed much greater stomatal restriction of transpiration, consistent with its greater vulnerability to cavitation, thanJ. osteosperma.5.These results suggest that the relative drought tolerance ofP. edulisandJ. osteospermaresults in part from difference in their vulnerability to xylem cavitation.
Survival of colour‐polymorphicEristalis arbustorumhoverflies in semi‐field conditions
Authors: Ottenheim M. M. , Wertheim B. , Holloway G. J. , Brakefield P. M. 
Published: March 2003

1.The theory on adaptive phenotypic plasticity assumes different fitness optima in different environments. To demonstrate these fitness differences in the field or under laboratory conditions can be difficult.2.The size of the coloured patches on the abdomen ofEristalis arbustorumvaries with rearing temperature. At low temperatures small patches develop and at higher temperatures larger patches develop. Consequently, the colour patch size varies seasonally.3.To study the relative fitness of two extreme phenotypes in abdominal coloration in the summer, a total of 591 laboratory‐reared flies were released in six large population cages. As a measure of fitness, survival was estimated.4.In all replicate cages the survival of the pale phenotypes was higher than that of the dark phenotypes, indicating a higher fitness for the pale flies under summer conditions.5.The fat content of flies reared under identical conditions to those released in the cages was measured. Pale flies had ≈ 0·7 mg more fat than dark flies (± 25% extra fat). However, it is argued that this difference in fat reserves could not have been the only cause of the observed difference in survival.6.The results are discussed in relation to mimicry and thermoregulation.
Elemental stoichiometry of Drosophila and their hosts
Authors: Markow T. A. , Raphael B. , Dobberfuhl D. , Breitmeyer C. M. , Elser J. J. , Pfeiler E. 
Published: March 2003

1. Nitrogen (N) and phosphorus (P) availabilities are important ecological determinants of resource use in nature. Despite the wide range of hosts used by species of the genus Drosophila, elemental composition of natural resources of these flies has never been investigated. 2. Total body N and P contents were determined in seven species of wild‐caught Drosophila, their natural hosts, and artificial diets routinely used to rear these flies in the laboratory. The flies tested included D. hydei, D. arizonae, D. simulans and D. pseudoobscura collected from rotting fruit (melons), and the cactophilic D. nigrospiracula, D. mojavensis and D. pachea collected from their specific host plants, Saguaro, Organpipe and Senita cactus, respectively. 3. Natural hosts varied in elemental composition, with fruit showing higher N (2·8–4·3% dry mass) and P (0·50–0·67%) levels compared with cacti (0·5–1·6% N; 0·01–0·29% P). No consistent differences in N and P levels were found between healthy and necrotic cactus tissue. 4. Total body N and P also varied among Drosophila species. This variation mirrored the levels of N and P found in the respective hosts and laboratory diets. N:P ratios were consistently lower in female flies compared with conspecific males suggesting phosphorus demands during oogenesis are high. 5. Potential mechanisms by which Drosophila deal with N or P limitation in nature are discussed.
Acclimation of photosynthesis to light: a mechanistic approach
Authors: Kull O. , Kruijt B. 
Published: March 2003

1. We developed a mechanistic model to explain acclimation of photosynthesis to the radiation distribution within plant canopies. The model predicts the amount of photosynthetic apparatus in any leaf from the balance between supply of carbohydrates by photosynthesis and the demand for resources by enzyme synthesis and turnover and export to sinks elsewhere in the plant. 2. The turnover of the photosynthetic apparatus is assumed to depend on the amount of available resources: nitrogen and carbohydrates. Leaves export carbohydrates into a common pool of carbohydrates and take nitrogen from the common nitrogen pool. All leaves of one plant are assumed to share these common pools. 3. The model allows description of the dynamics of the acclimation process known to occur within weeks after changes in the environment. The model also adequately explains measured leaf nitrogen distributions and total leaf area in a multispecies canopy. 4. According to our model, differences between species in leaf nitrogen distribution with respect to PPFD can be explained with differences in plant common pools of carbohydrates and nitrogen. 5. Although canopies cannot be treated as a big leaf in a simple way because mechanisms predicting amount of photosynthetic apparatus in a single leaf and in entire canopy are different, total canopy nitrogen can be used as an estimate for canopy total photosynthesis.
Acclimation in dynamic models based on structural relationships
Authors: MÄKELÄ A. 
Published: March 2003

1. A number of recent tree growth models have been based on the assumption that tree structure follows certain empirical rules and carbon allocation is performed so as to maintain these rules when growth and senescence occur simultaneously. This paper introduces a method of combining structural rules with adaptive regulation in a carbon balance model. 2. The method is based on regulating gross growth but situations are analysed where increased senescence of tissue functions as an alternative means of re‐establishing the balance. 3. The model does not aim to be mechanistic but merely to describe the process of regulation, or acclimation to changing environments and situations, as constrained by the carbon balance. The method incorporates parameters that describe the rate of returning to the balance after disturbance or after a change in the goal, which can be determined empirically. 4. Two models are given as examples of the use of the method, and the requirements and limitations of control in a carbon balance framework are discussed. 5. The method is best applied as a technical tool to describe variations and disturbance in balanced growth models when the variations are present but not very large. In addition, it can be used as a theoretical framework for the analysis of regulation as constrained by the conservation of mass.
Assessing the benefits of aggregation: thermal biology and water relations of anomalous Emperor Moth caterpillars
Authors: Klok C. J. , Chown S. L. 
Published: March 2003

1.Three hypotheses have been proposed to account for the maintenance of aggregation behaviour in caterpillars. While the benefits of aggregation for defence and for the elevation of growth rates have been investigated in some species, both of these hypotheses have been criticized, and in many cases the alternative hypothesis regarding the benefits of physiological regulation has not been investigated.2.In this paper the field thermal biology and water relations of solitary caterpillars (instars IV–V) and aggregations of caterpillars (instars I–III) are examined inImbrasia belina(Westwood) (Lepidoptera: Saturniidae), a species where an instar‐related change in aggregation behaviour is obligatory (instars I–III always aggregate, instars IV–V are always solitary), and where the benefits of defence and of overwhelming inducible host plant defences are unlikely to be significant.3.Aggregations of instars II–III maintain body temperatures equivalent to those of larger solitary individuals of instars IV and V, but significantly higher than those of operative models of single caterpillars of instars II–III. In addition, behavioural thermoregulation is not used to elevate body temperatures, although hanging behaviour takes place when upper lethal temperature limits are approached. Nonetheless, solar radiation has a marked influence on the temperature of aggregations because of the accumulation of higher heat loads by the larger masses of large aggregations.4.Instars IV–V can survive higher temperatures than instars I–III, and this may be because of their accumulation of very high heat loads in the field. Instars I and III can avoid these high heat loads by partial dispersal from the aggregation. In contrast, instars I–III have significantly lower critical thermal minima than the later instars, which may allow larvae to regain aggregations if they are separated from them.5.Water loss rates of real aggregations, of a given size, within a particular instar are lower than the sum of the rates of the same number of individual caterpillars of the same instar. In addition, survival of water loss tends to be higher in individuals from aggregations than in single individuals.6.Using this evidence in conjunction with studies that demonstrate significant predation in all instars, aggregation in the early instars irrespective of whether outbreaks take place or not, and the absence of inducible defences in the major host (Colophospermum mopane) ofI. belina, it is concluded that physiological regulation, of temperature and water balance, is the most likely explanation for the maintenance of aggregation behaviour in this species.
Host specificity in parasitic mistletoes (Loranthaceae) in New Zealand
Authors: Norton D. A. , De Lange P. J. 
Published: March 2003

1.We quantify the degree of host specificity for the five extant New Zealand loranthaceous mistletoes (Alepis flavida, Ileostylus micranthus, Peraxilla colensoi, Peraxilla tetrapetalaandTupeia antarctica).2.Host specificity is highest forA. flavida, P. colensoiandP. tetrapetalawhich primarily parasitize species ofNothofagus, and lowest forT. antarcticaand especiallyI. micranthuswhich parasitize a wide range of host species.3.These patterns of host specificity support the suggestion that relative host abundance is a key factor determining the degree of host specialization in mistletoes (resource fragmentation hypothesis). While evolutionary history may be important in the specificity of the mistletoe–host relationship in some situations, our data suggest that for New Zealand mistletoes evolutionary history simply reflects the temporal component of relative host abundance.4.We conclude that it is the stability of host availability through time and space which is the dominant factor determining host specificity patterns.
Interaction between ants, extrafloral nectaries and insect herbivores in Neotropical coastal sand dunes: herbivore deterrence by visiting ants increases fruit set inOpuntia stricta(Cactaceae)
Authors: Oliveira P. S. , Rico‐Gray V. , Castillo‐Guevara C. Díaz‐Castelazo† and C. 
Published: March 2003

1.This study examines the anti‐herbivore effect of ants visiting the extrafloral nectaries (EFNs) ofOpuntia stricta(Cactaceae) and its possible influence on the plant’s reproductive output in Mexican coastal sand dunes.Opuntia’s EFNs are located in the areoles of the developing tissue of emerging cladodes and flower buds.2.Ants visited the EFNs ofO.strictaon a round‐the‐clock basis. The associated ant assemblage was formed by nine species distributed in four subfamilies, and the species composition of the principal ant visitors changed markedly from day to night period.3.Cladodes of control (ants present) and treatment (ants excluded) plants ofOpuntiawere equally infested by sucking bugs and mining dipterans. Damage to buds by a pyralid moth, however, was significantly higher on treatment than on control plants. Ant visitation toOpuntia’s EFNs translated into a 50% increase in the plant’s reproductive output, as expressed by the number of fruits produced by experimental control and treatment branches. Moreover, fruit production by ant‐visited branches was positively and significantly associated with the mean monthly rate of ant visitation to EFNs.4.This is the first demonstration of ant protection leading to increased fruit set in the Cactaceae under natural conditions. Although the consequences of damage by sucking and mining insects remain unclear forOpuntia, the results show how the association of EFNs with vulnerable reproductive plant organs can result in a direct ant‐derived benefit to plant fitness.
Microbial processes and carbon‐isotope fractionation in tropical and temperate grassland soils
Authors: ŠantRůČková H. , Bird M. I. , Lloyd J. 
Published: March 2003

Abstract1. The carbon content and δ13C value of soil organic carbon (SOC), microbial biomass (Cmic) and respired CO2 were measured in a range of grassland soils from tropical and temperate biomes to determine if isotope effect of microbial degradation can induce a shift in isotope composition of SOC and CO2. The soil from a depth of 0–2 cm was analysed. Cmic was measured using the chloroform fumigation extraction method, while CO2 was measured in a closed system after 3 and 10 days of incubation. Two soils, temperate and tropical, were used for a long‐term experiment, in which measurements were performed after 3, 10 and 40 days of incubation.2. SOC and Cmic decrease exponentially with increasing mean annual temperature. Cmic decreases more slowly than SOC, resulting in a higher proportion of Cmic in the SOC of tropical soils relative to temperate soils.3. The δ13C value of Cmic and respired CO2 reflects gross changes in the δ13C value of SOC in the corresponding sample. On average, Cmic is 13C‐enriched by c. 2‰ compared with SOC, while respired CO2 is 13C‐depleted by c. 2·2‰ compared with Cmic. Thus, the observed 13C‐enrichment in Cmic is balanced by a corresponding 13C‐depletion in respired CO2 resulting in the δ13C value of respired CO2 being approximately similar to the δ13C of SOC.4. The isotope effect of microbial degradation is of importance in soil. It can be induced by selective utilization of SOC and isotope discrimination during metabolism. Metabolic isotopic discrimination is dependent on the growth stage of the soil microbial population.