bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of environmental change, including drought, on water use by competing Calluna vulgaris (heather) and Pteridium aquilinum (bracken)
Authors: Gordon C. , Woodin S. J. , Mullins C. E. , Alexander I. J. 
Published: March 2003

1. Competition for water between Calluna vulgaris (heather) and Pteridium aquilinum (bracken) was studied in conditions of increased temperature, drought and increased nitrogen supply. All these factors increased the intensity of competition for water, with the combination of drought and increased nitrogen having the greatest effect on water use. 2. Both species increased water‐use efficiency in response to increased nitrogen and drought. The effects of temperature were however, equivocal. Calluna had a greater water demand than Pteridium but acclimated to water stress more readily. 3.
Calluna was the superior competitor for water; its water‐use efficiency was reduced as a consequence of its roots depleting water from the Pteridium rooting zone. Pteridium, the poorer competitor, increased water‐use efficiency to cope with reduced water availability owing to competition. 4. There was a strong relationship between carbon isotope discrimination (Δ) and instantaneous water‐use efficiency for both species, but discrimination provided a more sensitive measure of seasonal water‐use efficiency. Reconstruction of the plant's history of water‐use efficiency by retrospective measurement of Δ proved a useful technique for Calluna leaves but was inappropriate for Pteridium rhizome.
Effects of long‐term exposure to elevated CO2 and increased nutrient supply on bracken (Pteridium aquilinum)
Authors: Caporn S. J. M. , Brooks A. L. , Press M. C. , Lee J. A. 
Published: March 2003

1. Bracken (Pteridium aquilinum) is an important fern with a global distribution. Little is known of the response of this species to elevated CO2. We investigated the effects of high CO2 (570 compared with 370 μmol mol–1) with and without an increased nutrient supply (a combined N, P, K application) on the growth and physiology of bracken, growing in containers in controlled‐environment glasshouses, over two full growing seasons. Results of growth and physiology determinations are reported for the second season. 2. Elevated CO2 had little impact on the growth or allocation of dry mass in bracken. No significant changes were detected in dry mass of the total plant or any of the organs: rhizomes, roots and fronds. In contrast to the small effects of high CO2, the high nutrient treatment caused a three‐fold stimulation of total plant dry mass and an increase in the allocation of dry mass to above ground when compared with low nutrient controls. 3. Net photosynthetic rates in saturating light were increased by both high CO2 and nutrient treatments, particularly in spring months (May and June). Growth in elevated CO2 did not cause a down‐regulation in light‐saturated rates of photosynthesis. The increased carbon gain in the high CO2 treatments was accompanied, in the low‐nutrient plants, by higher concentrations of carbohydrates. However, in high‐nutrient plants the CO2 treatment did not cause an accumulation of carbohydrates. The absence of a growth response to elevated CO2 in bracken despite significant increases in photosynthesis requires further investigation.
Echolocation constraints of Daubenton’s Bat foraging over water
Authors: RYDELL J. , MILLER L. A. , JENSEN M. E. 
Published: March 2003

1. Daubenton’s Bats (Myotis daubentonii) foraging over a stream concentrated their activity over calm surfaces, avoiding an adjacent area with small ripples (< 3 cm high). Aerial insects were most abundant over the ripples, so insect distribution could not explain why the bats avoided this area. 2. The bats flew low over water and always (N = 22) directed the head forwards, presumably emitting the echolocation beam parallel to the surface, thus minimizing clutter. At an angle of incidence of 30° there was significantly more clutter from the rippled water. 3. The ripples produced ultrasonic noises in the form of transient pulses at an average rate of 6·2 per second. In the present case, such pulses were common enough potentially to interfere with target detection by the bats. Transient noises and echo clutter from moving ripples may be the principal reason why bats generally avoid foraging low over turbulent water. 4. The target strength of a potential insect prey at the water surface and the source levels of the bats’ searching signals were measured to use in estimating the echo level at the bat when it detects the prey. The echo level at detection (+ 38 dB sound pressure level) was about the same as the clutter level extrapolated to the detection distance. This suggests that Daubenton’s Bat operates at very low signal‐to‐noise ratios when foraging for insects near the water surface.
Short‐term and long‐term effects of food supply on parasite burdens in Tawny Owls, Strix aluco
Authors: Appleby B. M. , Anwar M. A. , Petty S. J. 
Published: March 2003

1. The relationships among food supply (Field Voles, Microtus agrestis), reproduction and blood parasites was investigated in Tawny Owls, Strix aluco, in Kielder Forest, Northumberland, in 1994 and 1995. Vole populations were significantly lower in 1995 than in 1994. 2. Birds did not lose parasites after initial infection, and the level at which infections were maintained was characteristic of individual birds. 3. In 1994, the number and intensity of parasites was higher in adult owls that had experienced low food supply when they themselves were reared. This indicated that food supplied to chicks in the nest has a long‐term effect on the parasite burden of adults. 4. In addition, there was evidence that parasite burdens of adults were influenced by their current food supply. Birds that suffered a decline in food abundance on their territories between 1994 and 1995 showed an increase in parasite load over the same period. In 1995, there was also a significant negative correlation between the parasite loads of owls and vole abundance on their territories. 5. The best predictor of parasite number of chicks reared in 1995 was the parasite load of their fathers. The parasites chicks developed were not the parasites with which their fathers were heavily infested. This result could be due to inherited immunity. 6. Our results indicated that food resources should be measured when investigating interactions between parasites and their hosts, and that offspring quality as well as quantity might suffer when food abundance is low.
Effects of foraging mode and season on the energetics of the Marine Iguana, Amblyrhynchus cristatus
Authors: Drent J. , Van Marken Lichtenbelt W. D. , Wikelski M. 
Published: March 2003

1. Marine Iguanas (Amblyrhynchus cristatus) inhabiting the rocky shores of the Galápagos Islands apply two foraging strategies, intertidal and subtidal foraging, in a seasonal climate. Effects of both foraging strategy and seasonality on the daily energy expenditure (DEE) were measured using doubly labelled water. 2. Difference in foraging mode did not result in significant differences in DEE. 3. On Santa Fé the DEE in the warm season was significantly higher than in the cool season (67·8 ± 21·8 kJ kg–0·8 day–1vs 38·0 kJ kg–0·8 day–1). This difference can be explained by body temperature. A model estimate of the body temperature was used to predict monthly DEE figures, giving a year round budget. On average a 1‐kg iguana would need only 47 kJ day–1, or 17 mJ year –1. This is lower than previous estimates in which body temperatures were not taken into account. 4. The water flux of the Marine Iguana increases with increasing foraging time. The linear rise per minute foraging is roughly two times as high for subtidally foraging animals as for intertidal foragers.
Insectivore life histories: further evidence against an optimum body size for mammals
Authors: Symonds M. R. E. 
Published: March 2003

1.This study tests a model of the relationship of body mass to reproductive power (the rate of conversion of energy from the environment to an organism’s offspring). Specifically tested is the prediction that the regression of life‐history variables on body size will change slope and sign about an ‘optimum’ body mass of 100 g.2.Life‐history data from the mammalian order Insectivora have been collated and analysed using a phylogenetic comparative method to test this prediction.3.The analyses showed little evidence for significant changes in slope or sign around 100g body mass, or other possible optimal body masses, contradicting the predictions of the model. These findings agree with those of similar analyses on life‐history variables of bats.
Daily energy expenditure of free‐living male Wood Mice in different habitats and seasons
Authors: Corp N. , Gorman M. L. , Speakman J. R. 
Published: March 2003

1. The daily energy expenditure of free‐living adult male Wood Mice, Apodemus sylvaticus, from deciduous woodland and maritime sand‐dune was estimated using the doubly labelled water (DLW) technique and time–energy budget models. 2. Method of calculation had a small effect on the calculated energy demands. There were no significant differences in energy expenditure across sites or seasons despite large differences in home range among mice from different sites. Mice in winter, and on the sand‐dunes, had lower body masses, which offset the effects of larger home ranges and colder temperatures. 3. The daily energy expenditure for a Wood Mouse of mean body mass (20·5 g) was 67·9 kJ day–1 (n = 19) This was comparable to other similar size rodents (slightly higher), and did not deviate significantly from allometric predictions. 4. Variation in daily energy expenditure among individuals was not explained by ambient temperature, home range size, body mass, change in body mass, time spent active and the distance or speed of travel. 5. Sustainable metabolic rates approximated to five times basal metabolism and were within the range previously reported but higher than most other estimates of free‐living energy demands. 6. Rates of water influx and efflux were significantly greater for Wood Mice on the sand‐dunes (influx, 9·3 ± 1·14 ml day–1, efflux, 10·2 ± 1·10 ml day–1) than for animals in the woodland (influx, 6·3 ± 0·48 ml day–1, efflux, 6·2 ± 0·47 ml day–1). This was probably due to differences in the water content of their diets (seed in woodland and invertebrate on the sand‐dunes). 7. The time–energy budget models yielded estimates of energy expenditure considerably lower than the doubly labelled water estimate. Potential reasons for this discrepancy are discussed.
Do plant species with high relative growth rates have poorer chemical defences?
Authors: Almeida‐Cortez J. S. , Shipley B. , Arnason J. T. 
Published: March 2003

1. Most theories of plant strategies assume the presence of certain ‘trade‐offs’. One such evolutionary trade‐off assumes a decrease in growth rate with increasing investment in chemical defences in species adapted to different levels of habitat fertility. 2. To test this hypothesis, we grew 31 herbaceous species of Asteraceae under controlled conditions of temperature (25 °C), humidity (80%), light (500 μmol m–2 s–1) and photoperiod (16 h day–1) in a modified Hoagland hydroponic solution. The plants grew from seed for 35 days post‐germination and were harvested at 14, 21, 28 and 35 days. Relative growth rate (RGR) was calculated as well as a general measure of potential phytochemical toxicity (LC50) using an alcohol extraction of secondary compounds followed by Brine Shrimp bioassay and an assay of total phenolics. 3. The interspecific correlation between RGR and the potential phytochemical toxicity was weak and non‐significant (rS = 0·12, P = 0·53). The correlation between RGR and total phenolics was weak, positive but significant (rS = 0·40, P = 0·03). 4. These results suggest that such an evolutionary trade‐off does not exist in this group of Asteraceae.
Field studies of reptile thermoregulation: how well do physical models predict operative temperatures?
Authors: R. Shine , M. Kearney 
Published: March 2003

Abstract1. Field‐based studies on reptile thermoregulation increasingly rely upon physical models to estimate operative temperatures. Some investigators use models that mimic the size, shape, colour and posture of their study species, but such details may have little influence on thermal regimes (and hence, complex models may be a waste of time and money).2. Temperatures were measured at 10‐min intervals inside 48 hollow copper‐pipe models exposed to natural weather conditions over a 27‐day period, in a factorial design to examine the effects of model attributes on thermal profiles.3. These data clarify the ways in which model size, colour (reflectance), orientation and degree of contact with the substrate affect (a) mean, minimum and maximum temperatures, and (b) the number of hours per day that the models exceed specified thermal thresholds. Also examined are (c) interactions between model attributes in these respects, and (d) the ways in which such effects depend upon local weather conditions.4. Model temperatures were affected by all of the attributes tested, but with few interactions between these effects. Although statistically significant, the effects of model attributes upon operative temperature regimes were generally minor (<5% of mean values).5. Guidelines for the use of physical models in future research are provided.
Germination of CO2‐enriched Pinus taeda L. seeds and subsequent seedling growth responses to CO2 enrichment
Authors: Hussain M. , Kubiske M. E. , Connor K. F. 
Published: March 2003

Summary

Pinus taeda seeds, developed under ambient or elevated (ambient + 200 µl l−1) [CO2], were collected from Duke Forest, North Carolina, USA in October 1998. Seeds were germinated in nutrient‐deficient soil in either ambient or elevated [CO2] (ambient + 200 µl l−1) greenhouse chambers and allowed to grow for 120 days.
Seeds that developed in elevated [CO2] had 91 and 265% greater weight and lipid content, respectively, and three times the germination success, compared to those developed in current ambient [CO2].
Seedlings from the elevated [CO2] seed source had significantly greater root length and more needles regardless of greenhouse chamber, but there were no treatment effects on tissue or total biomass.
Severely limiting nutrient conditions resulted in significant photosynthetic downregulation by seedlings grown in greenhouse chambers with elevated [CO2], regardless of seed source.
Our hypothesis that greater seed reserves from CO2 enrichment would synergistically affect seedling growth responses to elevated [CO2] was not strongly supported. Nonetheless, seeds produced in a CO2‐enriched environment may have fundamental changes in their viability, chemistry and germination that may affect reproduction.
Genetic variation in thermal tolerance among natural populations of Drosophila buzzatii: down regulation of Hsp70 expression and variation in heat stress resistance traits
Authors: Sørensen J. G. , Dahlgaard J. , Loeschcke V. 
Published: March 2003

Summary

Thermal adaptation was investigated in the fruitfly Drosophila buzzatii Patterson and Wheeler. Two natural populations originating from a high‐ and a low‐temperature environment, respectively, were compared with respect to Hsp70 (heat shock protein) expression, knock‐down resistance and heat shock resistance.
Three main hypotheses were tested: (i) The expression level of Hsp70 in flies from the high‐temperature habitat should be down‐regulated relative to flies from the colder habitat. (ii) Flies having higher Hsp70 expression levels should be weakened most by a hardening treatment and go faster into coma, as Hsp70 level reflects stress intensity, and therefore display reduced heat knock‐down resistance. (iii) Heat shock resistance should be increased in the population with highest Hsp70 expression because the level of Hsp70 is positively associated with this trait.
The results generally matched the hypotheses. Hsp70 expression was reduced in the high‐temperature population. Knock‐down resistance was higher in the high‐temperature population and survival after heat shock was lower in the high‐temperature population.
This study showed genetic differences in thermal tolerance between populations, indicating that high temperature in nature may be an important selective factor. Moreover, knock‐down resistance in this study seems to be a more relevant trait than standard heat shock resistance for identifying thermal adaptation in natural populations.
The specialist seed predator Bruchidius dorsalis (Coleoptera: Bruchidae) plays a crucial role in the seed germination of its host plant, Gleditsia japonica (Leguminosae)
Authors: Takakura K. 
Published: March 2003

Summary

This paper describes the germination mechanism of hard seeds of a species of honey locust, Gleditsia japonica, which can germinate only when externally damaged, in relation to four germinating factors: feeding damage by two specialist seed predators, a bean weevil (Bruchidius dorsalis) and a cydid bug (Adrisa magna); feeding damage by a generalist seed predator, a wild mouse (Apodemus speciosus); and physical damage.
In laboratory experiments, both the bean weevil and physical damage facilitated germination, while damage by the cydid bug and wild mouse did not.
In contrast to laboratory findings, field censuses of G. japonica seed survival revealed that more than 99% were damaged either by B. dorsalis or A. magna. Therefore, less than 0·5% of the seeds remained intact, preventing formation of a seed bank.
In addition, all germinating seeds found in the field contained B. dorsalis larvae.
These results strongly suggest that damage by B. dorsalis is a prerequisite for G. japonica germination, in contrast to the conventional view that physical disturbance, possibly flooding, is the primary germinating factor for hard seeds.
Adjustment of tree structure in response to the environment under hydraulic constraints
Authors: Magnani F. , Grace J. , Borghetti M. 
Published: March 2003

Summary1. The hypothesis is tested that functional limitations, possibly related to the risk of disruptive xylem embolism, maintain the leaf water potential of trees within a safety range. This strategy would particularly apply to conifers.2. It is also hypothesized that homeostasis in water transport is achieved by a combination of short‐term stomatal regulation and the optimal allocation of resources between transpiring foliage, conductive sapwood and absorbing roots.3. The implications of this hypothesis for responses of plant structure to the environment are explored from a theoretical viewpoint, focusing in particular on the effects of temperature, vapour pressure deficit and soil water availability and texture.4. A comparison with published data sets confirms model predictions of greater allocation to transpiring foliage with increasing temperature, and lower allocation with increasing vapour pressure deficit and soil drought. Allocation to fine roots would respond more strongly to drought, and the effect would be magnified by coarse soil textures.5. The applicability of the model to other taxa remains to be determined, and the extent to which the observed structural adjustment is the result of phenotypic plasticity or long‐term adaptation is still unclear.
Insects as leaf engineers: can leaf‐miners alter leaf structure for birch aphids?
Authors: Johnson S. N. , Mayhew P. J. , Douglas A. E. , Hartley S. E. 
Published: March 2003

Summary

This study examined the indirect impacts of leaf‐mining insects, Eriocrania spp. Zeller (Lepidoptera: Eriocraniidae) on a phloem‐feeding insect, Euceraphis betulae Koch (Homoptera: Drepanosiphinae). While many insect herbivores affect one another through changes to host plant chemical composition, Eriocrania also has the potential to affect E. betulae through structural modification of a shared leaf.
Euceraphis betulae mortality was higher when caged on leaves with Eriocrania leaf‐miners. Mortality was not affected by the amount of leaf mined or elevated phenolic compound concentrations in mined leaves, but leaf‐miner induced damage to the midrib was strongly correlated with poor aphid survival. In field surveys, E. betulae was significantly less abundant on mined leaves with midrib damage than on mined leaves with just lamina damage, or mine‐free leaves.
Experiments simulating leaf‐miner damage on B. pendula leaves pinpointed midrib damage as being associated with higher E. betulae mortality, whereas lamina damage had no effect on aphid mortality. Disruption of phloem hydraulics is proposed as the mechanism underpinning the negative impacts on the aphid.
Eriocrania larvae mining leaves with manually damaged midribs weighed more than those in which the midrib was intact. There was also a trend towards higher nitrogen concentrations in leaves in which Eriocrania had damaged the midrib. There could therefore be a selective advantage to leaf‐miners that damage the midrib if severance improves leaf nutritional quality, in addition to rendering the leaves unsuitable to potential competitors.
Determinants of postfire flowering in the geophytic grass Ehrharta capensis
Authors: Verboom G. A. , Stock W. D. , Linder H. P. 
Published: March 2003

Summary

We conducted a fertilization–defoliation experiment to investigate postfire flowering in Ehrharta capensis, a cormous grass native to the Cape fynbos.
Combined fertilization and defoliation produced a strong flowering response in E. capensis, suggesting that the strong postfire flowering pattern of this species can be explained largely by the effect of fire on soil nutrients and vegetation cover. Flowering was absent in control plants, and sparse in plants receiving single treatments.
Comparable treatment dependence of flowering was not observed in two congeneric species that lack specialized storage structures and in which flowering is not apparently fire‐dependent.
In E. capensis, flowering did not significantly reduce the dry mass of corms persisting from previous years, or the amounts of reserves these contained. We conclude that corm‐stored reserves do not contribute substantially to inflorescence production.
Flowering E. capensis plants produced significantly larger replacement corms than did nonflowering plants, indicating that sexual reproduction does not occur at a cost to asexual persistence.
The lack of a trade‐off between sexual and asexual reproduction may explain why E. capensis, and possibly other clonal geophytes, flower only when resource availability is high. Cost–benefit models, which predict a trade‐off, do not properly describe resource allocation in these species.
Phenotypic plasticity of body size at different temperatures in a planktonic rotifer: mechanisms and adaptive significance
Authors: Stelzer C. P. 
Published: March 2003

Summary

Larger body size at low temperatures is a commonly observed phenomenon in ectothermic organisms. The mechanisms that lead to this pattern and its possible adaptive significance were studied in laboratory experiments using the parthenogenetically reproducing rotifer Synchaeta pectinata.
At low temperatures of 4 °C mean body volume was 46% larger than in individuals cultured at 12 °C. Egg volume was 35% larger in low vs high temperatures.
Larger body size at low temperatures was caused by two mechanisms. First, when exposed to low temperatures, mothers laid larger eggs and the hatchlings of these eggs developed into larger adults (irrespective of temperature). Second, individuals cultured at low temperatures grew to a larger body size during their juvenile phase. The former mechanism had a greater influence on adult size than the latter.
The production of larger eggs at low temperatures seemed to be due to a higher reproductive investment into individual offspring as it occurred independently of differences in maternal size.
Life table experiments showed that offspring from small eggs (produced at high temperatures) had a significantly higher population growth rate than offspring from large eggs, when cultured at high temperatures. This was mainly due to an increase in fertility during the first days of adult life.