bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of temperature on the web‐building behaviour of the common house spider, Achaearanea tepidariorum
Authors: BARGHUSEN L. E. , CLAUSSEN D. L. , ANDERSON M. S. , BAILER A. J. 
Published: November 2003

1. Because spiders are ectothermic animals, the temperature regime of the microhabitat in which an individual finds itself may affect important performance traits of that individual. The present study examined the effects of temperature on attributes of webs spun by Achaearanea tepidariorum (C. L. Koch), as well as testing temperature preference in this species. The effects of temperature on the amount of silk per web produced by Achaearanea tepidariorum and the prey‐capture efficiency of webs produced at different temperatures were determined by using webs constructed at 5, 10, 15, 20, 25 and 30°C. The temperature preferences of A. tepidariorum within a thermal gradient were also determined. 2. Web mass was related to temperature, exhibiting a quadratic relation with a maximum web mass occurring at approximately 20°C. 3. Number of strands per cm3 of webs varied directly with web mass; webs with greater strand densities were more efficient at capturing flies. 4. The number of spiders observed in each temperature range in the thermal gradient indicated a non‐uniform distribution, with the spiders avoiding temperatures in the highest range (27·3±2·0°C). 5. These data suggest an optimal temperature for web construction at which webs produced are more efficient at capturing prey. The data also suggest that this species may avoid sites that do not provide an adequate thermal environment.
Mass regulation in juvenile Starlings: response to change in food availability depends on initial body mass
Authors: WITTER M. S. , SWADDLE J. P. 
Published: November 2003

1. The adaptive mass‐regulation hypothesis suggests that birds should respond to worsening or unpredictable foraging conditions by increasing body mass and energetic reserves. However, previous work on adult European Starlings, Sturnus vulgaris L., has revealed that the response to worsening foraging conditions varies according to the seasonal status of the birds. Photosensitive birds respond to decreased time available to feed by increasing mass, whereas photorefractory birds regulate mass at a fixed level. Juvenile Starlings are in a state of photorefractoriness until puberty. In this paper, we examine whether photorefractory juvenile Starlings respond to worsening foraging conditions by regulating mass at a fixed level, like adults, or whether they increase in mass, in accordance with the adaptive regulation hypothesis. 2. Birds were divided into two treatment groups: control and food deprived. Control birds remained on food ad libitum throughout the experiment. Food‐deprived birds had their food removed for 5h every other day over a 6‐week period. The effects of these manipulations on the resulting changes in body mass and fat reserves were examined. 3. Food‐deprived birds increased fat reserves and body mass in comparison with controls. However, the response to food availability depended on the initial body mass of the birds. Birds with the lowest initial mass exhibited the largest response to the manipulation. This may be because birds with low energetic reserves are more severely affected by changes in the availability of food. 4. Juvenile photorefractory Starlings show a response to changes in food availability that is unlike the response of photorefractory adults. We suggest that the mechanism of responding to environmental change, in addition to being modulated seasonally, may be age structured. We speculate that the function of this age effect may be related to the low competitive status of juvenile Starlings. This subdominant age‐class may be displaced to less favourable feeding or roosting sites; as a result, they may have to respond flexibly to a rapidly changing and unpredictable energetic environment.
Ecophysiological responses to simulated canopy gaps of two tree species of contrasting shade tolerance in elevated CO2
Authors: E KUBISKE M. , PREGITZER K. S. 
Published: November 2003

1. One‐year‐old seedlings of shade tolerant Acer rubrum and intolerant Betula papyrifera were grown in ambient and twice ambient (elevated) CO2, and in full sun and 80% shade for 90 days. The shaded seedlings received 30‐min sun patches twice during the course of the day. Gas exchange and tissue–water relations were measured at midday in the sun plants and following 20 min of exposure to full sun in the shade plants to determine the effect of elevated CO2 on constraints to sun‐patch utilization in these species. 2. Elevated CO2 had the largest stimulation of photosynthesis in B. papyrifera sun plants and A. rubrum shade plants. 3. Higher photosynthesis per unit leaf area in sun plants than in shade plants of B. papyrifera was largely owing to differences in leaf morphology. Acer rubrum exhibited sun/shade differences in photosynthesis per unit leaf mass consistent with biochemical acclimation to shade. 4.
Betula papyrifera exhibited CO2 responses that would facilitate tolerance to leaf water deficits in large sun patches, including osmotic adjustment and higher transpiration and stomatal conductance at a given leaf‐water potential, whereas A. rubrum exhibited large increases in photosynthetic nitrogen‐use efficiency. 5. Results suggest that species of contrasting successional ranks respond differently to elevated CO2, in ways that are consistent with the habitats in which they typically occur.
Body size, granivory and seasonal dietary shifts in desert gerbilline rodents
Authors: DEGEN A. A. , KHOKHLOVA I. S. , KAM M. , NAGY K. A. 
Published: November 2003

1. Desert gerbilline rodents consume mainly plant material, in particular seeds. However, seeds are less available following winter rains than in summer and many rodents shift their diets from predominantly seeds to ones containing more vegetation. This shift results in a proportionately greater preformed water intake and, as these rodents do not drink, an increase in the water influx to field metabolic rate ratio (WI : FMR; ml kJ–1). Thus, this ratio is indicative of the food consumed, being low when gerbils are consuming seeds and high when consuming green vegetation. 2. Smaller animals are more dependent on a highly digestible, high energy diet such as seeds and are more vulnerable to extreme air temperatures than are larger animals. It was predicted that: (1) gerbils consume less seeds in winter than in summer but the difference between seasons in seed intake is less pronounced in smaller than in larger rodents; and (2) smaller gerbils are more sensitive to extreme air temperatures than are larger gerbils. To examine these hypotheses, two coexisting desert gerbils, Gerbillus henleyi (8–12 g) and Meriones crassus (50–110 g), were studied. 3. It was predicted that: (1) the WI : FMR ratio would be greater in winter than in summer in both species, but the proportionate increase would be smaller in G. henleyi than in M. crassus; and (2) energy expenditure would be greater in winter than in summer in both species, but the proportionate increase would be greater in G. henleyi than in M. crassus. To test these predictions, winter and summer water influx and field metabolic rates in these species were measured under free‐living conditions using doubly labelled water. 4. The WI : FMR ratio in summer was 0·048 in G. henleyi and 0·069 in M. crassus, indicating that G. henleyi was consuming proportionately more seeds than M. crassus. In winter, the ratio was 0·052 in G. henleyi, indicating that there was little change in dietary composition and that this species was still consuming mainly seeds. In contrast, the ratio in M. crassus rose to 0·127, indicating a shift to a diet containing more green vegetation. The relatively higher seed intake by G. henleyi than M. crassus in both seasons and the small, if any, seasonal change in seed intake in G. henleyi agrees with the hypothesis of body size and seed intake in gerbils. Winter FMR increased over summer FMR in both species, as predicted; however, the expected greater increase in G. henleyi relative to M. crassus did not occur. The winter FMR was 1·52 times the summer FMR in G. henleyi and 1·53 times the summer FMR in M. crassuss.
Natural thermal stress and heat‐shock protein expression in Drosophila larvae and pupae
Authors: FEDER M. E. , BLAIR N. , FIGUERAS H. 
Published: November 2003

1. Whether Drosophila larvae and pupae naturally experience temperatures that can cause heat damage or death is poorly understood, but bears directly on numerous investigations of the thermal biology and heat‐shock response in Drosophila. Accordingly, the temperatures of necrotic fruit, which Drosophila larvae and pupae inhabit, the temperatures of larvae and pupae outside the laboratory, and the levels of the heat‐shock protein hsp 70 expressed by larvae in nature were examined. 2. When necrotic fruit was sunlit, internal temperatures rose to levels that can harm indwelling insects. Fruit size and evaporative water loss affected these temperatures. Temperatures of larvae and pupae in the field commonly exceeded 35 °C, with living larvae recorded at >44°C and pupae at >41°C. Natural mortality was evident, presumably because of heat. 3. In the laboratory, these temperatures kill larvae rapidly, with LT50s (time taken for half the sample to be killed) of 30 min at 39 °C, 15 min at 40 °C and 8·5 min at 41 °C. Gradual transfer from 25°C to these temperatures resulted in no lesser mortality than did direct transfer. 4. Hsp 70 levels in lysates of whole larvae were measured by ELISA (enzyme‐link immunosorbent assay) with an hsp 70‐specific antibody. For larvae within necrotic apples experimentally transferred from shade to sun and within necrotic fruit in situ, hsp 70 levels equalled or exceeded levels detected in parallel laboratory studies of whole larvae or cells in culture. 5. These data provide an ecological context for studies of thermal stress and the heat‐shock response in Drosophila that has heretofore been lacking.
The impact of grazing on plant fractal architecture and fitness of a Mediterranean shrub Anthyllis cytisoides L.
Authors: ESCÓS J. , ALADOS C. L. , EMLEN J. M. 
Published: November 2003

1. We examined natural grazing by livestock (sheep and goats) on Albaida Anthyllis cytisoides L. with the aim of determining whether variation in the allometric relationships between plant parts provides a sensitive indicator of the impact of grazing. 2. The intra‐individual variation in translatory symmetry with scale and increased complexity of fractal structures reflect environmental disturbance under heavy grazing pressure and lack of grazing. 3. Fitness consequences of grazing were also investigated. Grazing promotes growth and adult survival, and a drop in seed production as a consequence of consumption. In spite of that, total inclusive fitness (population rate of change) tends to increase with grazing. 4. Moderate grazing, while promoting growth, also enhances stability of vegetative structures. The favourable effect of moderate levels of herbivory on A. cytisoides is reflected in the homeostatic maintenance of its translatory symmetry and in the increased complexity of its fractal structures.
Energy allocation in polymorphic Brown Trout
Authors: JONSSON N. , JONSSON B. 
Published: November 2003

1. To evaluate differences in energy allocation to gonadal development of resident and anadromous Brown Trout, Salmo trutta, we analysed tissue composition and energy contents of adults of the two morphs from three small streams in southernmost Norway. Somatic energy per unit mass of anadromous spawners (5·0 ± 0·6 kJ g–1 wet weight) was 1·1 times that of the residents. This difference was chiefly due to a 1·4 ‐times higher lipid content in anadromous (4·9 ± 1·5%) than resident trout. The somatic protein and carbohydrate contents per unit mass were higher in resident than anadromous fish. 2. Somatic energy content per unit mass increased linearly with body length in resident but not anadromous fish. This increase was due to a significant increase in lipid content with fish size in resident contrary to anadromous trout. 3. The mass‐specific energy content of the ovaries was higher for residents (8·4 ± 0·4 kJ g–1 wet weight) than anadromous (7·81 ± 0·5 kJ g–1 wet weight) trout. This was due to higher lipid and protein contents per unit mass in resident than anadromous females. In males, no similar differences between morphs were found (5·9 ± 0·8 kJ g–1 wet weight). The mass‐specific energy content of the ovaries was c. 1·4 higher than that of the testes, mainly caused by a 2·3–2·6 higher lipid content per unit mass of eggs. 4. The mean gonadosomatic index (kJ %) was higher in anadromous (34·0 ± 9·4) than resident (28·6 ± 5·5) females, but not in males (≈ 3%). In females, but not in males, gonadal energy increased linearly with increasing somatic energy of the fish. 5. Female gonadal energy at corresponding somatic energies was higher than that of males. On average, the energetic investment in gonads relative to soma of first‐time spawners in the year of maturation was estimated at 11% in males and 67% in females.
Trade‐off between height growth and stem diameter growth for an evergreen Oak, Quercus glauca, in a mixed hardwood forest
Authors: SUMIDA A. , ITO H. , ISAGI Y. 
Published: November 2003

1. Patterns of stem growth of a mid‐successional evergreen Oak species (Quercus glauca) in a mixed hardwood forest were examined to explore the trade‐off relationship between stem‐diameter growth and height growth. 2. The mean cross‐sectional area (and the corresponding mean diameter) of a stem at a point in time was defined as the stem volume divided by tree height. Based on this definition, a simple equation representing the trade‐off relationship between the height growth and mean diameter growth was formulated. 3. In the long term, allocation to height growth was encouraged at the seedling stage and it gradually declined with time, with the decline in the suppressed seedlings being more pronounced than in the dominant trees. 4. However, both the suppressed and the dominant trees showed acceleration of height growth at various ages. Such a fluctuation in the allocation of biomass to height growth is likely to have been caused by chronological changes in light conditions, and meandered the trajectory of allometry between the height and mean diameter. 5. The observed stem growth patterns of the individual trees could explain the chronological changes in the diameter–height relationship of the population.
Geographical pattern in photosynthetic light response of Pinus sylvestris in Europe
Authors: LUOMA S. 
Published: November 2003

1. The geographical aspects in photosynthetic light response and stomatal conductance in the shoots of Pinus sylvestris were studied together with structural properties of shoots and needles. Seven stands within the natural distribution area of P. sylvestris in Europe were chosen. CO2 exchange, irradiance and stomatal conductance (gs) for water vapour were measured and the maximum photosynthetic rate (Pm) was determined from the CO2 exchange measurements. 2. There was a clear pattern in the average values of Pm along the latitudinal gradient. Highest values of Pm were found in the middle parts of the distribution area and they decreased towards both ends of the transect. The highest value was almost twice as high as the lowest one. 3. The between‐site variation explained 70% of the total variation in the maximum photosynthetic rate. Pm was not clearly correlated with any single climatic variable or nitrogen concentration in the needles. 4.
Pm was closely coupled with stomatal conductance (r2=0·74). The differences in Pm and gs between the sites is likely to reflect adaptation and acclimation to different climates.
Reproductive investment and parasite susceptibility in the Great Tit
Authors: ALLANDER K. 
Published: November 2003

1. Reproduction and parasite defence are assumed to be costly activities for hosts, and therefore trade‐offs might exist between reproduction and parasite defence. 2. Brood sizes were manipulated in a population of Great Tits (Parus major L.) to assess trade‐offs between reproduction and parasite defence. Blood samples were taken from males and females during the late nestling phase, and parasite prevalence was compared among parents raising enlarged, reduced and control broods. 3. A higher prevalence of protozoan blood parasites dominated by Haemoproteus majoris was found among parents with enlarged broods, as compared with parents with control and reduced broods, respectively. Brood size manipulation did not affect parasite prevalence between the sexes or between age classes differently. 4. Mean parasite intensity (number of parasites per microscope field) among adult birds only infected with H. majoris was higher for parents with experimentally enlarged broods than controls and reduced broods, respectively. 5. These results support the hypothesis of a trade‐off between parasite defence and reproduction.
The adrenocortical responses to stress in breeding Willow Warblers Phylloscopus trochilus in Sweden: effects of latitude and gender
Authors: SILVERIN B. , ARVIDSSON B. , WINGFIELD J. 
Published: November 2003

1. In the present study we tested the hypothesis that birds suppress their adrenocortical response to stress when breeding in a severe environment. 2. We measured increases in circulating levels of corticosterone following capture and handling in populations of Willow Warblers, Phylloscopus trochilus, breeding in a rich deciduous forest in southern Sweden and in Willow Warblers breeding in a subarctic environment in Swedish Lapland. Data from an 8‐year study on survival rates and nest predation in southern and northern Sweden are also included. 3. By comparing the changes in corticosterone levels immediately following capture, handling and restraint, and then up to 1‐h post‐capture across gender and latitude, we were able to assess possible ecological influences. 4. Willow Warblers had about the same survival rates in northern and southern Sweden (0·27 and 0·30, respectively). Depredated clutches were normally replaced in southern Sweden (72%), but not in northern Sweden (1%). 5. A reduced adrenocortical response to stress was found in Willow Warblers of both sexes breeding in northern Sweden where conditions were more severe and the nesting season shorter than in southern Sweden. At the southern site, males had a significantly more robust adrenocortical response to stress than females, whereas at the northern site changes in corticosterone following capture were identical in males and females. Maximum corticosterone levels generated by the capture stress protocol were significantly higher in males at the southern site than in all other groups. 6. There were marked individual variations in the patterns of corticosterone changes following capture in all groups, but there were no significant relationships of dynamics of corticosterone changes to body mass or fat score in males. However, in females at the southern site, the maximum corticosterone level and the rate of corticosterone increase during the capture stress protocol were positively correlated with body mass. In contrast, at the northern site females showed negative correlations of body mass with maximum corticosterone and rate of corticosterone increase. These differences may reflect different ecological bases for modulation of the adrenocortical response to stress with latitude, and with gender.
The costs of becoming nocturnal: feeding efficiency in relation to light intensity in juvenile Atlantic Salmon
Authors: FRASER N. H. C. , METCALFE N. B. 
Published: November 2003

1. Most animals are active by day or by night, but not both; juvenile salmonids are unusual in that they switch from being predominantly diurnal for most of the year to being nocturnal in winter. They are visual foragers, and adaptations for high visual acuity at daytime light intensities are generally incompatible with sensitive night vision. Here we test whether juvenile Atlantic Salmon Salmo salar are able to maintain their efficiency of prey capture when switching between diurnal and nocturnal foraging. 2. By testing the ability of the fish to acquire drifting food items under a range of manipulated light intensities, we show that the foraging efficiency of juvenile salmon is high at light intensities down to those equivalent to dawn or dusk, but drops markedly at lower levels of illumination: even under the best night condition (full moon and clear sky), the feeding efficiency is only 35% of their diurnal efficiency, and fish will usually be feeding at less than 10% (whenever the moon is not full, skies are overcast or when in the shade of bankside trees). Fish were unable to feed on drifting prey when in complete darkness. 3. The ability of juvenile salmon to detect prey under different light intensities is similar to that of other planktivorous or drift‐feeding species of fish; they thus appear to have no special adaptations for nocturnal foraging. 4. While winter drift abundance is slightly higher by night than by day, the difference is not enough to compensate for the loss in foraging efficiency. We suggest that juvenile salmon can nonetheless switch to nocturnal foraging in winter because their food requirements are low, many individuals adopting a strategy in which intake is suppressed to the minimum that ensures survival.
Energetic costs of activity by lizards in the field
Authors: CHRISTIAN K. A. , BAUDINETTE R. V. , PAMULA Y. 
Published: November 2003

1. The available data related to the activity energetics of lizards in the field were collated with respect to three indices of activity energetics: the ecological cost of transport (ECT) expressed as a percentage of the total energy, the proportion of total energy used in all forms of activity (%AR), and the sustained metabolic scope (SusMS), defined as the ratio of the total energy expenditure to the total resting metabolism. 2. The ECT values of lizards ranged from 3 to 36% with five of 11 species having values >20%. The percentage AR ranged from 23 to 80% for lizards during active seasons, with most species having values > 50%. The SusMS ranged from 1·1 to 5·1. 3. Values of ECT are higher for lizards than for mammals, in part because the costs of maintenance metabolism are higher in mammals. 4. The percentage AR and SusMS values of mammals are higher than those of lizards. 5. It follows from the previous two points that the proportion of the total daily energy that is expended in non‐locomotory activities is disproportionately higher in mammals compared with lizards. 6. The energy expended in locomotion is a significant portion of the energy budget of lizards. This is generally true for all seasons in which there is activity.