bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for micropatch partitioning and effects of boundaries on patch use in two species of gerbils
Authors: Fierer N. , Kotler B. P. 
Published: March 2003

Abstract1. Spatial heterogeneity in resource abundance creates opportunities to exploit patchiness at different scales. The ability to subdivide patches into smaller micropatches is termed micropatch partitioning. At various scales, patches can be recognized by distinct boundaries or by vague boundaries delineated by changes in resource abundances. The ability to micropatch partition was tested for and the effect on foraging of vague vs distinct boundaries was assessed for two species of coexisting desert rodents, the gerbils Gerbillus allenbyi and G. pyramidum. To do so, the distribution of seeds in experimental resource patches in a large enclosure were manipulated.2. Both G. allenbyi and G. pyramidum are imperfect micropatch assessors. When seeds were concentrated into micropatches, there were lower patch‐wide giving‐up densities (GUDs) than if seeds were randomly distributed throughout the patch. Both species could micropatch partition at scales of 0·14 m2.3. GUDs in experimental micropatches were greater than expected for perfect assessors.4. With G. allenbyi, a micropatch with fewer vague boundaries was foraged to a lower GUD. In contrast, GUDs for G. pyramidum were similar regardless of the types of patch boundaries.5.  Gerbillus allenbyi showed greater error in the assessment of micropatch size.6. These results have implications for diet selection and coexistence. These species coexist via temporal partitioning, with G. pyramidum biasing its activity to early in the night when resource patches are richer and G. allenbyi biasing its activity to later in the night. Gerbillus pyramidum encounters a richer and more variable environment where errors in patch assessment are costlier, and micropatch partitioning is more valuable. Gerbillus allenbyi encounters a poorer environment where resources vary at larger spatial scales.
On the measurement of growth with applications to the modelling and analysis of plant growth
Authors: M. L. Roderick 
Published: March 2003

Abstract1. In this paper, a theoretical framework for the analysis of growth is described. Growth is equated with change in volume (V) and the growth rate is given by the equation; dV/dt = (dm/dt)(1/ρ) − (dρ/dt)(m/ρ2) wheremis the mass andρthe density. The volume is inclusive of internal air spaces.2. The second term of the growth equation (see above) can be ignored if density is constant over time. Data for humans (and presumably other large animals) show that while composition changes over time, the density is approximately constant at about that of water. In that case, the growth rate can be estimated from measures of the rate of change of mass. However, the density of plants is variable (c. 0·4–1·2 g cm−3) and measures of mass and density are necessary to analyse plant growth.3. To use the theory as the basis of plant growth models, it is necessary to develop simple methods for estimating the surface area of roots, stems and leaves assuming that the mass and volume are known. A literature review found that the surface area to volume ratios of leaves and roots generally increase with the mass concentration of water. Theoretical arguments are used to predict that in woody stems, the situation should be reversed such that the surface area to volume ratio increases with the mass concentration of dry matter. Those relationships should be very useful in the development of plant growth models.4. Measures of plant dry mass and estimates of the rate of change in dry mass are shown to be very difficult to interpret because of differences in the mass concentration of dry matter between individuals and over time.5. It is concluded that measures of mass and density will be necessary before plant growth analysis can achieve its full potential. A framework for extending the theory to include the forces necessary for growth to occur is described.
Seed bank dynamics: the role of fungal pathogens and climate change
Authors: Leishman M. R. , Masters G. J. , Clarke I. P. , Brown V. K. 
Published: March 2003

Abstract1. One of the climate change scenarios predicted for the UK is warmer winters and additional summer rainfall, which may favour growth and survival of fungal pathogens. We tested several hypotheses on the fate of persistent seeds in the soil and the role of fungal pathogens under this predicted climate change.2. We buried seed bags containing fungicide‐treated and non‐fungicide‐treated seeds of four species with persistent seed banks (Convolvulus arvensis L., Lotus corniculatus L., Medicago lupulina L. and Rubus fruticosus L.) under control and simulated climate change (winter warming plus supplemented summer rain) conditions, and monitored seed survival over 1 to 2 years.3. Fungicide treatment resulted in a significant increase in the percentage of intact seeds recovered for only two of the four species, M. lupulina and R. fruticosus. Seeds of M. lupulina that were treated with fungicide remained viable in the soil for longer than non‐treated seeds. Thus, the effect of fungal pathogens on seed persistence in the soil appears to be species specific.4. There was no significant effect of the simulated climate (winter warming plus supplemented summer rain) on seed persistence in the soil, for any of the four species. Neither was a significant climate × fungicide treatment interaction found for any of the four species. Thus, it does not appear that the conditions provided in the simulated climate plots favoured the growth and survival of fungal pathogens affecting the soil seed banks of the four species studied here.5. The use of fungicides in manipulative experiments and the importance of field experiments that simulate predicted climate change are discussed.
Locomotor performance and dominance in male Tree Lizards, Urosaurus ornatus
Authors: Robson M. A. , Miles D. B. 
Published: March 2003

Abstract1. The importance of locomotor performance to the social status of male lizards may lie in its effect on the outcome of agonistic interactions and territorial contests. Presumably, dominant males are able to acquire and defend larger territories, encounter more potential mates and have greater reproductive success.2. Therefore, the hypothesis that dominance status should covary with locomotor performance was tested using the Tree Lizard, Urosaurus ornatus.3. Two components of locomotor performance, maximum sprint speed and stamina, in males were measured. The former variable was estimated as the fastest speed on a 0·25‐m length along a 2‐m long racetrack. The second variable was measured as the elapsed time a lizard could sustain a walking pace on a canvas belt moving at 0·50 km h−1.4. The relative social status of size‐matched males was independently determined by staging paired encounters in a novel arena. Dominance was measured by behavioural scores of aggression and submission.5. The dyadic encounters resulted in the unambiguous determination of dominant individuals for 48 of 50 trials. Dominant males were significantly faster than submissive males. In addition, endurance capacity of dominant males exceeded the submissive males.6. Dominance behaviour and locomotor performance are strongly associated. Although the exact underlying mechanism is unknown, the results suggest a link between hormones, performance and behaviour in territorial lizards.
Constraints on the plasticity of Daphnia magna influenced by fish‐kairomones
Authors: Stibor H. , Navarra D. Müller 
Published: March 2003

Abstract1.  Daphnia magna reproduced at a smaller size (body mass) when exposed to fish‐kairomone than D. magna growing up without this cue.2. The total egg mass for first reproduction was the same in both groups, but the proportion of clutch mass to total body mass was about 11% higher in daphniids exposed to fish‐kairomone. This difference was about the same for low and high food concentrations (0·5 or 1·5 mgC l−1).3. Although egg mass was the same, triglyceride (TAG) content of the egg material was significantly lower when daphniids were exposed to fish‐kairomones for both food concentrations.4. The TAG content of the clutch was lowered to the extent that the TAG proportion in the clutch in relation to the somatic mass of the animal was the same for animals treated with fish‐kairomone and controls (5% of body mass at first reproduction).5. The lower TAG content per clutch resulted in a lower quality of the individual egg in daphniids exposed to fish‐kairomone. The resulting higher susceptibility to starvation under low food conditions is a substantial cost of the plastic response to fish‐kairomones.6. This cost may set a limit on the plastic response in resource allocation of Daphnia magna exposed to fish‐kairomones. However, daphniids living in a system with fish predation are more likely to be eaten by fish than to starve to death.
Effect of drought on the growth of Lolium perenne genotypes with and without fungal endophytes
Authors: Cheplick G. P. , Perera A. , Koulouris K. 
Published: March 2003

Abstract

Grass leaves are often inhabited by fungal endophytes that can enhance host growth. In some forage species, endophytes improve host resistance to, and recovery from, drought.
Our objective was to determine if the growth of genotypes of Lolium perenne L. was improved by endophytes during recovery from drought.
Thirteen infected genotypes were cloned into ramets. Half were treated with a systemic fungicide to eliminate the endophyte (E−); half were untreated and retained high endophyte levels (E+). In a glasshouse, half of all E− and E+ ramets were watered regularly, whilst half were exposed to a 2 week drought on two occasions, each followed by a 3 week recovery period.
After the first drought and recovery period, endophytes significantly reduced tiller production in the drought‐stressed group.
After the second drought and recovery period, effects of drought on live leaf area and dry mass were highly dependent on host genotype, but not endophytes. The mean tiller mass of E+ ramets after drought was significantly less than that of watered E+ ramets, but this was not true in E− ramets. For six genotypes there was greater mass allocation to storage in the tiller bases of E− ramets after drought.
This perennial ryegrass population showed marked genotypic variation in the ability to recover from drought stress, but endophytes played little or no role in this ability. For some host genotypes there may be a metabolic cost of harbouring endophytes during environmentally stressful conditions.
Effects of temperature on the development of an arctic Collembola (Hypogastrura tullbergi)
Authors: Birkemoe T. , Leinaas H. P. 
Published: March 2003

AbstractEmbryonic development, juvenile moulting and growth rates, and maximum size of the arctic collembolanHypogastrura tullbergiwere investigated at 5, 10 and 15 °C in laboratory experiments. The embryonic development was also investigated at 21 °C.The lower temperature threshold of the embryonic development (t0) was −1·3 °C, possibly reflecting a slight cold adaptation. The temperature of maximum development rate exceeded 21 °C.Instar duration rate was linearly related to temperature. Growth per instar, however, was thermally dependent, giving an overall non‐linear correlation between growth and temperature. This emphasizes the importance of studying growth and moulting as separate processes in Collembola.Development of genital area (number of hairs) over succeeding instars was affected by the temperature, suggesting that a higher proportion of individuals reached the adult stage in an earlier instar at 15 than at 10 °C.Contrary to the general pattern in ectotherms of increasing size at lower temperatures, adultH. tullbergireached a larger maximum size at 15 than at 10 °C.No aspects of postembryonic development inH. tullbergishowed any signs of cold adaptation, probably because it is more important to be able to efficiently utilize high temperatures that frequently occur in the microhabitat during sunny periods in summer.
Seasonal nitrogen storage and remobilization in the forb Rumex acetosa
Authors: Bausenwein U. , Millard P. , Thornton B. , Raven J. A. 
Published: March 2003

Summary

The contribution of N storage and remobilization to the vegetative and reproductive growth of the forb Rumex acetosa was quantified using 15N labelling techniques with plants derived from semi‐natural grasslands in Scotland.
The contribution of remobilized N to the total N in the new above‐ground tissues was highest at the beginning of the growing season at 58%. New leaves and reproductive organs contained equal amounts of remobilized N.
During early vegetative growth, the taproot was the main source of remobilized N, whereas during reproductive growth, N was additionally remobilized from fine roots and leaves.
Free amino acids (mainly arginine and glutamine) and proteins were identified as the main storage compounds in the taproots. The protein pool did not show any seasonal variations that indicated the existence of a vegetative storage protein, indicating that such proteins are not a necessary component of N storage/remobilization in all species.
The ability to store and remobilize N provides a mechanism for growth in the spring when the availability of soil N is low, and means that growth depends upon environmental conditions during more than one year.
Leaf respiration in two tropical rainforests: constraints on physiology by phosphorus, nitrogen and temperature
Authors: Meir P. , Grace J. , Miranda A. C. 
Published: March 2003

Summary

Leaf respiration is a major component of the terrestrial carbon cycle, but is poorly quantified for tropical forests. We measured dark respiration, R, and nutrient concentration (nitrogen, N and phosphorus, P) of leaves within two forest canopies: in Reserva Jarú, south‐west Brazil; and Mbalmayo Reserve, central Cameroon. The data, expressed on a leaf area basis (Ra, Na, Pa) and a leaf mass basis (Rm, Nm, Pm), were used to quantify the temperature sensitivity of R and to test the hypothesis that leaf metabolism is more strongly constrained by phosphorus than by nitrogen in these lowland rainforests.
Leaf respiration rate (Ra, at 25 °C) at Jarú was nearly half that at Mbalmayo (the range in Ra from near the ground to the upper canopy was 0·11–0·78 µmol m−2 s−1 at Jarú versus 0·22–1·19 µmol m−2 s−1 at Mbalmayo), and the mean Q10 for respiration at each site was 2·3 ± 0·9 (1 SD) and 2·0 ± 0·5 (1 SD), respectively. There were significant differences (P < 0·01) between sites in leaf phosphorus concentration, but not in leaf nitrogen concentration: Pm was very low at Jarú (0·2–0·7 mg g−1) but higher at Mbalmayo (0·5–2·4 mg g−1), whilst Nm was similar at both forests (10–45 mg g−1).
Rm was not significantly associated with canopy position or specific leaf area (SLA, m2 g−1) in either forest, but a significant relationship between SLA and Nm was found for both sites (P < 0·05), consistent with existing data. At Jarú, Rm was strongly related to Pm (P < 0·001) and less strongly related to Nm (P < 0·05), but at Mbalmayo, Rm was not significantly related to either Pm or Nm.
Ra was linearly related to Na and Pa at both sites (P < 0·01), principally because of changes in leaf mass per area (LMA, g m−2) associated with canopy position. At Mbalmayo, LMA explained 70% of the variation in Ra, but only 20% at Jarú. For Jarú, the strongest relationship with Ra was obtained by combining LMA with Pm in a multiple regression (r2 = 0·53); further inclusion of Nm did not improve the regression. At Mbalmayo neither Nm or Pm improved the regression of Ra on LMA.
These results indicate a strong influence of LMA on the relative rates of Ra within the vertical gradient of each canopy. They also suggest that at JarúPm constrains respiration more strongly than Nm, and further, that the very low Pm at Jarú may explain the lower absolute values of respiration there relative to Mbalmayo, where Pm was higher. The leaves at both sites are typical of lowland tropical rainforests in not having particularly low Nm, and consistent with this, Nm was a weaker predictor of respiration than Pm or LMA.
Active brood care in Cancer setosus (Crustacea: Decapoda): the relationship between female behaviour, embryo oxygen consumption and the cost of brooding
Authors: Baeza J. A. , Fernández M. 
Published: March 2003

Summary

Previous studies have shown that oxygen is limiting in embryo masses of marine invertebrates. It has been suggested that several behaviours found in brooding females of brachyuran crabs are used to ventilate and provide oxygen to the embryo masses.
The relationship between female brooding behaviour, oxygen consumption of embryos and oxygen provision to the brood mass for embryos at different developmental stages was studied, using the marine crab Cancer setosus. The changes in oxygen consumption of brooding females associated with changes in oxygen provision to the brood were also estimated.
Brooding females of C. setosus behaved differently from non‐brooding females. Abdominal flapping was associated with an increase in oxygen availability in the centre of the brood mass; the frequency of abdominal flapping increased with embryonic development, as oxygen demand of crab embryos increased. Oxygen consumption of brooding females also increased throughout embryonic development. The difference in oxygen consumption between brooding and non‐brooding females was used as an indicator of the cost of oxygen provision (brooding).
These results provide the first evidence – among crabs and other marine invertebrates – of a direct link between active brood care and oxygen provision. It is possible that parental care in marine invertebrates is strongly linked to oxygen provision, since oxygen limitation has been reported for several brooding taxa. The simple physiological constraint of oxygen provision in marine invertebrates may have important ecological and evolutionary consequences.
The balanced‐growth hypothesis and the allometry of leaf and root biomass allocation
Authors: Shipley B. , Meziane D. 
Published: March 2003

Summary1. Many ecological models of plant growth assume balanced growth: that biomass is allocated preferentially to leaves or roots to increase capture of the limiting external resource. An alternative explanation is based on nonlinear (allometric) allocation as a function of plant size. The objective of this study was to test between these two alternative explanations.2. A total of 1150 plants from 22 different herbaceous species were grown in hydroponic sand culture in factorial combinations of high (1100 µmol m−2 s−1) and low (200 µmol m−2 s−1 PAR) irradiance crossed with a full‐strength and a 1/6 dilution of Hoagland’s hydroponic solution. Plants were harvested at 15, 20, 25, 30 and 35 days postgermination, and dry mass was determined for leaf and root components. These data were used to test the hypotheses of balanced growth and of allometric allocation.3. Both irradiance and nutrient supply affected the slope and intercept of the root : shoot allometry, contrary to the allometric hypothesis but in agreement with the hypothesis of balanced growth; decreased nutrient supply increased allocation to roots; and decreased irradiance increased allocation to leaves.4. Plants allocated relatively more biomass to roots than to leaves as plants grew larger. In order for the balanced‐growth hypothesis to be correct, the net rate of nutrient uptake per unit root mass must have been decreasing relative to the net rate of carbon gain per unit leaf mass.5. We suggest two reasons why this might be the case: (i) older roots decreased their efficiency of nutrient uptake; and (ii) larger root systems more rapidly decreased the available nutrients between flushes of hydroponic solution.6. These results support the notion of balanced growth that is found in many ecological models of plant growth.
Decreased heat‐shock resistance and down‐regulation of Hsp70 expression with increasing age in adult Drosophila melanogaster
Authors: Sørensen J. G. , Loeschcke V. 
Published: March 2003

Summary 1. Adult Drosophila melanogaster Meigen were examined for Hsp70 expression level and heat‐shock resistance from 0 to 8 days of age – the latter being close to the mean life span in natural D. melanogaster populations. 2. Over the 8 days, both induced Hsp70 expression level and induced heat‐shock resistance showed a linear decrease. Heat‐shock resistance without prior hardening also decreased, but at a lower rate than both induced Hsp70 expression level and heat‐shock resistance after hardening. 3. The results suggest that the decrease in induced Hsp70 expression level in D. melanogaster with age is regulatory and not due to a reduced ability to express Hsp70 as a result of senescence. 4. The changes in induced Hsp70 expression level with age are likely to be determined by natural selection and are evolutionarily adaptive. The decrease with age in stress resistance after hardening may then be considered a direct consequence of age‐dependent reduction in expression levels of induced Hsp70.
Roads as barriers to movement for hedgehogs
Authors: Rondinini C. , Doncaster C. P. 
Published: March 2003

Summary1. Movements of hedgehogs,Erinaceus europaeusL., were analysed in relation to roads by recording their nocturnal foraging trajectories in urban areas adjacent to major road systems. Four male and four female hedgehogs at each of two sites were each tracked over five replicate trajectories of more than 3 h, using radio‐telemetry and direct observation.2. Frequency of road crossings and use of habitat were compared to simulated random trajectories. For each observed trajectory, 100 trajectories were simulated with the same distribution of speeds as observed, but with random direction.3. Observed trajectories had lower rates of crossing large but not small roads than simulated, indicating that hedgehogs treat large roads as barriers during nightly foraging activities. Most hedgehogs were never observed to cross roads, whereas almost all simulated trajectories did cross both large and small roads.4. Crossing behaviour differed by site, but not by sex.5. Roads and road verges had the lowest rank in a habitat preference analysis at both sites, while playing fields, gardens and urban areas were preferred habitats. These results are discussed in relation to the regional scale preference for urban areas, and the attraction to road verges while dispersing, shown by hedgehogs.