bluuebunny/crossref_metadata_2025_split huggingface dataset:
IsEcheveria gibbiflora(Crassulaceae) fecundity limited by pollen availability? An experimental study
Authors: Parra‐Tabla V. , Vargas C. F. , Eguiarte L. E. 
Published: March 2003

1.An experimental approach, manually pollinating all the flowers of individual plants, was used to measure the effect of pollen limitation on female fecundity of the hummingbird‐pollinated perennial shrubEcheveria gibbiflorain the ecological preserve of Pedregal de San Angel around México City, México. Eleven randomly selected plants were manually over‐pollinated in all their flowers and another 11 were left to be freely visited by natural pollinators.2.Manually pollinated plants produced significantly more fruit and seeds than control plants (1·38 and 1·74 times, respectively). There was no change in average mass of fruits.3.Considering individual fruit production per plant sampled three times in one season, decreases in fruit mass and average seeds per fruit were observed within the same reproductive season for both treatments. For the manually pollinated plants, from the start to the end of the reproductive season, seed set decreased 55·9%; while in control plants seed set decreased 33·4% in the same period. For both treatments, average fruit mass decreased 26%.4.Vegetative growth was not significantly different between control and experimental plants but hand‐pollinated plants showed a smaller reproduction probability for the following year.5.It is concluded that female fecundity inE. gibbiflorais limited by pollen early in the reproductive season and by resources in the middle and the end of the season.
Induced thermotolerance and associated expression of the heat‐shock protein Hsp70 in adult Drosophila melanogaster
Authors: Dahlgaard J. , Loeschcke V. , Michalak P. , Justesen J. 
Published: March 2003

1. Inducible heat‐shock proteins are synthesized when temperatures are increased to levels substantially above normal. The functional role of these proteins is well known at the cellular level. Today increasing interest has been directed towards the importance of heat‐shock proteins for resistance of whole organisms to high‐temperature stress and other environmental stressors. 2. Here the functional relationship between the heat‐shock protein, Hsp70, and thermal resistance in adult Drosophila melanogaster was examined by comparing thermal resistance, i.e. survival at 39 °C for 85 min, and levels of Hsp70 at various times elapsed (2, 4, 8, 16, 32 and 64 h) after thermotolerance was induced by short‐term acclimation/heat hardening at 37 °C for 55 min. 3. Levels of Hsp70 in both males and females were highest 2 h after heat hardening and declined with longer times elapsed. The rate of decrease initially was very fast but diminished with increasing time. After 32 h the level of Hsp70 approached the level in flies that were not hardened. Levels of Hsp70 in males exceeded that of females during the entire period. 4. Survival of both sexes increased with increasing time after heat hardening and reached an optimum between 8 and 32 h. Thereafter resistance decreased with longer times elapsed. Survival of females generally exceeded that of males except after 16 and 64 h. 5. Regression analysis applied to the data on Hsp70 levels revealed that the model describing these data could not explain the data for survival. Also, higher levels of Hsp70 in males compared with females were not associated with greater survival in males. However, statistical analysis on paired measurements of Hsp70 and survival revealed a positive association between Hsp70 level and survival at each time elapsed after induction of thermotolerance.
Modelling the time–temperature relationship in cold injury and effect of high‐temperature interruptions on survival in a chill‐sensitive collembolan
Authors: Nedve˘D O. , Lavy D. , Verhoef H. A. 
Published: March 2003

1. Temperature‐ and time‐dependent mortalities were studied and modelled in insects exposed in regimes with constant and alternating temperatures. In these experiments, freezing was not a cause of death. 2. Survival rates at a range of constant low temperatures (– 5 to + 1 °C) and for different exposure periods (1–14 days) were measured in the summer acclimated springtail Orchesella cincta. 3. Daily interruptions of the cold exposure with short intervals at high temperature reduced mortality or slowed the increase of mortality. This effect was stronger at higher temperature (19 vs 5 and 12 °C) and increased with the duration of the interruption (0·25–2 h). 4. The injury was reversible when the cold exposure was limited to 2 days. 5. Survival in desiccated animals (14% water loss) was reduced. 6. It is suggested that the mortality of summer acclimated springtails is caused by a complex metabolic disorder and membrane changes at low temperatures.
Using elasticity analysis of demographic models to link toxicant effects on individuals to the population level: an example
Authors: HANSEN F. , FORBES V. E. , FORBES T. L. 
Published: March 2003

1. A simple two‐stage population model was applied to data from a previously published life‐table response experiment (LTRE), which examined the toxicity of 4‐n‐nonylphenol to life‐history traits of the polychaete Capitella sp. I. Population growth rates (λ) and the relative sensitivities (= elasticities) of λ to changes in each of the individual life‐history traits were calculated. 2. In the present study, the life‐history parameters measured in laboratory‐reared individuals were manipulated to simulate potential effects of competition and predation on fecundity, time to reproductive maturity and juvenile survival to explore how such factors might influence the sensitivity of population growth rate to toxicant‐caused changes in individual life‐history traits. 3. Dramatic changes in elasticity patterns among simulations indicate that population growth rates may respond very differently to toxicant exposure depending on the extent to which other demographically limiting factors (e.g. competitors and/or predators) are operating on the population. 4. Effectively predicting the population‐level consequences arising from toxicant effects measured on individuals can be improved by exploring the elasticity pattern of λ for the population over a range of realistic ecological situations.
Differential fractionation of δ13C and δ15N among fish tissues: implications for the study of trophic interactions
Authors: PINNEGAR J. K. , POLUNIN N. V. C. 
Published: March 2003

1. Stable isotopes of nitrogen and carbon are widely used in the evaluation and understanding of trophic interactions, and especially so in aquatic food‐webs. However, differences among tissues which occur in consumers such as fish may confound resolution of these ecological relationships, and greatly affect dietary compositions calculated through mass‐balance equations. 2.δ13C and δ15N were determined for homogenized whole fry (≈ 2·7 g) and particular tissues (white muscle, red muscle, liver and heart) of juveniles (≈ 20·6 g) of Rainbow Trout Oncorhynchus mykiss. 3. Differences in δ13C and δ15N were observed among tissues; removal of lipid resulted in these tissues becoming statistically indistinguishable but more variable in δ13C, particularly in tissues with higher lipid content. Differences in δ15N among tissues may be related to the relative composition of ‘essential’ and ‘non‐essential’ amino acids. 5. Acidification, which is used to reduce variability caused by the presence of inorganic carbonate, had a significant effect on δ15N, while having a non‐significant effect on the δ13C. This was the case for whole ground fish‐fry, which contained 22·6% inorganic carbonates in the form of bones and scales, and for individual fish tissues which contained only very small amounts of inorganic carbonate. 6. White muscle was found to be less variable in δ13C and δ15N than all other tissues, and is probably the best tissue for use in ecological work. Red muscle, which is often closely associated with white muscle, is more variable in δ13C and may constitute a source of significant error in source material identification and dietary overlap.
Life‐history variation in closely related generalist predators living in the same habitat: a case study with three Cyclosa spiders
Authors: Miyashita T. 
Published: March 2003

1. Generalist predators sharing similar food resources and phenologies as well as having no competitive interactions are expected to have a similar life‐history pattern, but some closely related web spiders show different life‐history traits. The present paper clarifies possible selection pressures affecting life‐history traits of the three coexisting Cyclosa spiders and explores the significance of the life‐history variation. 2.
Cyclosa argenteoalba had lower daily survival rate and higher growth rate, C. sedeculata had higher daily survival rate and lower growth rate, and C. octotuberculata showed intermediate levels. This implies that the selection pressures these spiders experience differ appreciably even in the same habitat. 3. The significance of the life‐history characteristics of the three species was evaluated by general life‐history theories. Cyclosa argenteoalba showed distinguishing reproductive traits: shorter time to maturation, larger reproductive effort, larger relative clutch size, decreased clutch size with the number of clutches, and smaller egg size. These characteristics may have evolved in response to the larger ratio of juvenile to adult survivorship. Cyclosa octotuberculata had a clutch size much larger than the other two species, but relative clutch sizes accounting for body size were similar between C. octotuberculata and C. sedeculata. Also, the two species showed a similar time to maturation despite having different selection pressures. Probably, higher growth rate compensates for lower survivorship, leading to the similarity in some reproductive traits.
Decomposition and nutrient dynamics of Quercus pubescens leaf litter in a naturally enriched CO2 Mediterranean ecosystem
Authors: Cotrufo M. F. , Raschi A. , Lanini M. , Ineson P. 
Published: March 2003

1. The chemical composition (i.e. N, P, C, lignin and polyphenol concentrations) of Quercus pubescens leaf litter derived from a natural CO2 spring in Tuscany (Italy) was analysed and compared to litter from a nearby reference site. Litter was incubated for 25 months at both the natural CO2 spring and the reference site, and monitored for decomposition rates, nutrient and lignin concentrations. 2. Long‐term exposure to elevated CO2 concentrations from the natural spring was associated with a change in the chemical composition of the Oak leaf litter, with decreases in P and polyphenol concentrations and increases in lignin. No differences in N concentrations were observed between the enriched CO2 litter from the natural spring and the reference litter. 3. Decomposition was reduced in the CO2 spring, with the lower P concentration of the native litter, combined with the lack of soil fauna observed at that site, being the factors most probably responsible for the measured decreases in mass loss. However, litter from the CO2 spring and reference litter decomposed at the reference site showed similar rates of decomposition. 4. All litter showed similar N concentrations during decomposition, with N being mineralized throughout the incubation period from both litter regardless of the site of incubation. In contrast, P dynamics differed between litter, with P being immobilized in the litter derived from the spring, and mineralized from the reference litter. When the litter from the spring was incubated at the reference site, there was a trend for net P uptake from the surrounding environment. The chemical composition of decomposing litter from the spring appeared to match that of the reference litter after 3 months of incubation at the reference site. 5. The results from the CO2 spring suggest that litter decomposition may be retarded under elevated levels of atmospheric CO2. However, results from field surveys around CO2 vents should be viewed with caution because differences may relate to factors other than the known differences in CO2 concentrations.
Metabolic costs of growth in free‐living Garter Snakes and the energy budgets of ectotherms
Authors: Peterson C. C. , Walton B. M. , Bennett A. F. 
Published: March 2003

1. The metabolic or respiratory cost of growth (RG) is the increase in metabolic rate of a growing animal, and it represents chemical potential energy expended in support of net biosynthesis but not deposited as new tissue. 2. Two statistical methods (multiple non‐linear regression and analysis of regression residuals) were used to calculate RG from data (n = 68) from a doubly labelled water study of free‐ranging Garter Snakes (Thamnophis sirtalis fitchi) in northern California. 3. The sample‐wise (‘ecological’) cost of growth was 2·07 kJ per gram of net growth (equivalent to 8·63 kJ g–1 dry tissue); reanalysis of a subset of efficient growers yielded a more conservative ‘physiological’ estimate of 1·67 kJ g–1. 4. Our empirical estimate of RG, among the first reported for squamate reptiles and free‐living animals of any kind, compares closely with published, laboratory‐derived values for ectotherms. 5. The metabolic costs of growth accounted for an average of 30% of total field metabolic rates for these snakes, which were growing at a mean rate of 3% of body mass per day. However, our method probably underestimated the total ecological cost of growth for large animals, because potential growth costs that covary with body size were not included. 6. Distinction between conceptual and empirical energy budgets clarifies relationships among body size, metabolic rates, and the physiological and ecological costs of growth.
Growth hormone‐induced effects on mortality, energy status and growth: a field study on Brown Trout (Salmo trutta)
Authors: Johnsson J. I. , Petersson E. , Jönsson E. , Järvi T. , Björnsson B. TH. 
Published: March 2003

1.Growth hormone (GH) treatment increases the growth rate and competitive ability of salmonids under laboratory conditions. Since fast growth should increase fitness, why is endogenous secretion of GH not higher in wild fish? To address this question, three hypotheses were suggested. H1: high GH levels reduce antipredator responses and may therefore increase mortality from predation. H2: high GH levels reduce long‐term (e.g. over winter) survival by reducing allocation to critical energy reserves. H3: GH is not beneficial for growth under natural conditions.2.To test these hypotheses, the performance of GH‐treated juvenile Brown Trout (Salmo trutta) and control (placebo) trout was compared in an enclosed stream section subjected to natural predation. Four experiments were conducted during winter, spring, summer and autumn, respectively.3.Mortality rates were not significantly different between GH‐treated and control trout in any of the four experiments so H1was not supported. Energy reserves were generally lower in GH‐treated fish, which is consistent with H2, whereas growth rates in mass were higher in GH‐treated fish than in controls so H3was not supported. This suggests that GH promotes growth at the expense of investment in maintenance.4.Judging from growth and mortality rates, the fitness of GH‐treated and control trout appeared similar. Thus, escaped GH‐manipulated fish may compete successfully with wild fish.5.Hatchery‐raised trout with higher initial condition index suffered higher mortality rates than more slender fish. This novel finding may be explained by reduced escape ability related to body morphology, reduced behavioural responses towards predators by high‐condition trout, or predator preferences for high‐condition fish.
Proportional dry‐mass content as an underlying trait for the variation in relative growth rate among 22 Eurasian populations of Dactylis glomerata s.l.
Authors: Ryser P. , Aeschlimann U. 
Published: March 2003

1. Relative growth rate (RGR), proportional dry‐mass content of leaf and stem tissues, and biomass‐allocation pattern were assessed under controlled conditions for 22 populations of Dactylis glomerata s.l. from contrasting latitudes and altitudes in Europe, Israel and Kazakstan. Furthermore, width and thickness of leaves were measured in garden‐grown mature plants. 2. All these parameters varied significantly among the populations. RGR correlated negatively with dry‐mass content of leaves and stems, but not with biomass‐allocation parameters, leaf thickness or leaf width. We argue that the close association of RGR with variation in dry‐mass content among species and genetically distinct populations is a result of the larger volume of tissue, and correspondingly larger leaf area and longer root system, that a plant with a low tissue density can build per unit dry mass. 3. Leaf tissue dry‐mass content decreased and RGR increased with increasing latitude and elevation of the originating site, indicating that a high growth rate may be an advantage in habitats with a short growing season. This contrasts with earlier findings of a negative correlation between inherent RGR and altitude.
Thermoregulatory abilities of Alaskan bees: effects of size, phylogeny and ecology
Authors: Bishop J. A. , Armbruster W. S. 
Published: March 2003

1. The thermoregulatory capabilities of 18 species of Alaskan bees spanning nearly two orders of magnitude of body mass were measured. Thoracic temperature, measured across the temperature range at which each species forages, was regressed against operative (environmental) temperature to determine bees’ abilities to maintain relatively constant thoracic temperatures across a range of operative temperatures (thermoregulatory performance). 2. Previous studies on insect thermoregulation have compared thoracic temperature with ambient air temperature. Operative temperature, which integrates air temperature, solar radiation and effects of wind, was estimated by measuring the temperature of a fresh, dead bee in the field environment. It is suggested that this is a more accurate measure of the thermal environment experienced by the insect and also allows direct comparisons of insects under different microclimate conditions, such as in sun and shade. 3. Simple regression analysis of species and family means, and analysis of phylogenetically based independent contrasts showed thermoregulatory capability, ability to elevate thoracic temperature, and minimum thoracic temperature necessary for initiating flight all increased with body size. 4. Bumble‐bees were better thermoregulators than solitary bees primarily as a consequence of their larger body size. However, their thermoregulatory abilities were slightly, but significantly, better than predicted from body size alone, suggesting an added role of pelage and/or physiology. Large solitary bees were better thermoregulators than small solitary bees apparently as a result of body‐size differences, with small bees acting as thermal conformers.
Dynamics of food availability, body condition and physiological stress response in breeding Black‐legged Kittiwakes
Authors: Kitaysky A. S. , Wingfield J. C. , Piatt J. F. 
Published: March 2003

1. The seasonal dynamics of body condition (BC), circulating corticosterone levels (baseline, BL) and the adrenocortical response to acute stress (SR) were examined in long‐lived Black‐legged Kittiwakes, Rissa tridactyla, breeding at Duck (food‐poor colony) and Gull (food‐rich colony) Islands in lower Cook Inlet, Alaska. It was tested whether the dynamics of corticosterone levels reflect a seasonal change in bird physiological condition due to reproduction and/or variation in foraging conditions. 2. BC declined seasonally, and the decline was more pronounced in birds at the food‐poor colony. BL and SR levels of corticosterone rose steadily through the reproductive season, and BL levels were significantly higher in birds on Duck Island compared with those on Gull Island. During the egg‐laying and chick‐rearing stages, birds had lower SR on Duck Island than on Gull Island. 3. The results suggest that, in addition to a seasonal change in bird physiology during reproduction, local ecological factors such as food availability affect circulating levels of corticosterone and adrenal response to acute stress.
A theoretical approach to linking the composition and morphology with the function of leaves
Authors: Roderick M. L. , Berry S. L. , Noble I. R. , Farquhar G. D. 
Published: March 2003

1. In this paper we develop a theoretical framework for describing the composition and morphology of leaves on a volumetric basis which is inclusive of both the liquids and internal air space. That framework is then used to link the composition and morphology with the function of leaves. 2. Leaves are segmented into a functional scheme named a–u–s–V (air space–solution–structure–Volume basis) and a measurement scheme named a–q–d–M (air space–liquid–dry matter–Mass basis). Measurements of mass, liquid mass, volume and fractional air space are necessary to (partially) link the two schemes. 3. The liquid content of leaves can be used to infer the mode of mechanical support and, hence, the likely values of air space, solution and structure. For example, if a leaf has a high liquid content, then it cannot have a large volumetric fraction of structure (which is largely made of dry matter) and is unlikely to have large internal air spaces. 4. Based on measurements of individual leaf components, the specific gravity of the non‐gaseous fraction in leaves would usually be in the range 1–1·3. Consequently, the specific gravity of leaves would be most sensitive to variation in fractional air space. 5. For the dimensions typical of most leaves, the surface area to volume ratio of a leaf is determined by leaf thickness (or diameter). 6. Leaf design is considered in terms of light interception and gas exchange. The requirements for each are essentially incompatible and lead to a trade‐off on leaf thickness. However, that relationship is complicated because variation in fractional air space can potentially lead to broad optima for gas exchange at any given leaf thickness. 7. The theoretical predictions have not been assessed owing to a lack of measurements of leaf density, fractional air space and liquid content. However, published data were used to develop the following hypotheses: (1) the mass of nitrogen per unit mass of liquid is relatively constant within leaves; (2) the surface area to volume ratio of leaves is proportional to leaf liquid content. These hypotheses are tested in a subsequent paper.