bluuebunny/crossref_metadata_2025_split huggingface dataset:
Predator–prey instability: individual‐level mechanisms for population‐level results
Authors: BEISNER B. E. , MCCAULEY E. , WRONA F. J. 
Published: November 2003

1. In previous work we established that increasing temperature led to a destabilization of the population dynamics of the invertebrate carnivore Mesostoma ehrenbergii and its prey Daphnia pulex, which ultimately resulted in the local extinction of Daphnia at higher temperatures. Two mechanisms are proposed to explain the population‐level phenomena: (1) quantitative changes in carnivore vital rates with increasing temperature led to stronger functional and numerical response and (2) qualitative changes in the dynamic allocation of energy to reproduction by the predator with increasing temperature introduces inverse density dependence in the predator’s response. 2. The growth of individual M. ehrenbergii was monitored under various food conditions to determine the effect of two temperatures (18 and 24 °C) and five food levels on rates of growth, prey consumption and reproduction and on reproductive allocation patterns. 3. The first mechanism was supported by both higher consumption rates (stronger functional response) and faster growth rates with earlier age at maturity and shorter generation time (stronger numerical response). 4. Evidence for mechanism two was also provided by an alteration of the reproductive allocation pattern with temperature. Viviparous (subitaneous) eggs were more likely to be produced by this carnivore at low food levels at 24 °C, while at 18 °C, high food levels were required before individuals made this switch. This shift actually introduces inverse density dependence in the predator’s numerical response which is highly destabilizing. 5. Based on the results of this study, the differential effect of M. ehrenbergii on the dynamics and structure of its D. pulex prey populations can be attributed to changes in both physiological rates and reproductive allocation patterns with temperature.
Physical and chemical response of juvenile Acacia tortilis trees to browsing. Experimental evidence
Authors: GOWDA J. H. 
Published: November 2003

1. Changes in nutritional value and accessibility of leaves following browsing are important in the dynamics of plant–herbivore interactions because they influence the fitness of the plant attacked and the future utilization of it by the herbivore. 2. Hand pruning of Acacia tortilis, a spinescent tree common in savanna ecosystems of eastern Africa, resulted in higher biomass of spines and new shoots in pruned trees than in unpruned controls. 3. Pruned trees allocated a higher proportion of shoot biomass to spines than unpruned ones, whereas the proportion of leaf biomass in new shoots was slightly reduced. Because increases in spine biomass and density following pruning are coupled with an increase in shoot production, it is concluded that higher production of spines is an inducible response of Acacia tortilis to pruning. 4. No significant changes in the concentration of total phenolics, condensed tannins or leaf nitrogen were induced by pruning. 5. Irrespective of treatment, high foliar concentrations of nitrogen were correlated with an increase in twig production for a given leaf biomass and a reduction in the concentration of secondary substances in leaves. This relation may lead to a conflict between foraging efficiency and nutrition for browsers of A. tortilis.
Intrathalline and size‐dependent patterns of activity in Lasallia pustulata and their possible consequences for competitive interactions
Authors: HESTMARK G. , SCHROETER B. , KAPPEN L. 
Published: November 2003

1. In dense populations of the saxicolous lichen Lasallia pustulata the margins of adjacent thalli overlap each other in intraspecific competition for space and light. 2.
In situ non‐destructive monitoring of hydration‐dependent potential photosynthetic activity by modulated fluorescence systems in different parts of the thallus shows that the activity is structured by a centre‐to‐margin gradient, with the centre of the thallus remaining active for substantially longer periods than the margins when the thalli dry up after being activated by wetting. The pattern reflects the water status of different parts of the thallus; the margins which are thin and exposed dry up first. 3. The activity pattern within individual lichen thalli suggests that marginal overlapping between neighbours may have a less detrimental effect on the shadowed individuals than expected from a pure consideration of the amount of area shadowed. Because the centre of the lichen thallus is active for longer periods, shadowing of this region may possibly be more harmful per area unit than an overlap at the less active margins. 4. Larger thalli are active for substantially longer periods than small ones. Even the margins of larger thalli tend to be active for a longer period than the centre of small thalli.
The ecological function of extrafloral nectaries: herbivore deterrence by visiting ants and reproductive output in Caryocar brasiliense (Caryocaraceae)
Authors: OLIVEIRA P. S. 
Published: November 2003

1. Shrubs of Caryocar brasiliense are intensively visited by many ant species in the cerrado vegetation of south‐east Brazil. Ants collect nectar from the extrafloral nectaries (EFNs) located on the buds at the apex of the plant. 2. The proportion of C. brasiliense shrubs occupied by ants greatly surpassed that of neighbouring plants without EFNs and this resulted in many more termites being attacked and removed on this plant than on plants lacking EFNs. Ant attacks on Caryocar were more frequent near the EFNs. 3. Ant‐exclusion experiments with Caryocar shrubs revealed that ants significantly reduce the infestation levels by the butterfly Eunica bechina, the sucking bud Edessa rufomarginata, the bud‐destroying fly Prodiplosis floricola and by a stem‐galling wasp. Ants had no effect on the infestation by a leaf‐galling wasp. 4. Control (ants present) and treatment (ants excluded) plants produced equal numbers of buds but flower and initial fruit production was significantly greater for ant‐visited plants. Higher abortion rates of initial fruits by control plants resulted in similar final fruit and seed sets for plants in either experimental category. 5. The extremely low fertility of cerrado soils is suggested as a possible factor constraining the ability of Caryocar shrubs to provide the resources necessary for growth and development of their heavy fleshy fruits. Higher production of initial fruits by ant‐visited shrubs would be neutralized by competition among developing fruits and subsequent abortion. 6. Possible ant‐derived benefits to C. brasiliense include: protection of vegetative tissues during plant growth, larger floral display and increased attractiveness to bat pollinators, increased male contribution to fitness through pollen donation and selective abortion of genetically inferior progeny as the maternal investment is adjusted to match available resources.
Variation in leaf longevity of Pistacia lentiscus and its relationship to sex and drought stress inferred from leaf δ13C
Authors: JONASSON S. , MEDRANO H. , Flexas J. 
Published: November 2003

1. Leaf formation, loss, retention, longevity and biomass on male branches of the evergreen mediterranean shrub Pistacia lentiscus, L. correlated strongly with water‐use efficiency inferred from leaf δ13C across a gradient of precipitation on the island of Mallorca, Spain. 2. The correlations suggest that the leaf phenology is under control of drought‐induced constraints on the carbon balance. 3. In fruiting female branches, the correlations between the inferred water‐use efficiency and number of formed and retained leaves, leaf biomass and leaf longevity were non‐significant. Leaf formation was strongly reduced by fruiting and the females compensated the reduced photosynthetic capacity by retaining older leaves for a longer time than male plants. 4. It is suggested that leaf longevity in females is under strong control of resource allocation to fruit formation which is ‘overlaid’ on the drought‐induced carbon stress, which led to the observed longer leaf longevity in females than in males.
Sexually dimorphic eggs, nestling growth and sibling competition in American Kestrels Falco sparverius
Authors: ANDERSON D. J. , REEVE J. , BIRD D. M. 
Published: November 2003

1. American Kestrel (Falco sparverius) nestlings are sexually dimorphic, with daughters larger than sons. The larger daughters have an advantage during sibling competition for food in excess of their higher per capita food requirements, and we predicted that parents would reduce this competitive disparity by differentially enhancing the growth of sons, specifically by laying them in larger eggs. 2. In a captive breeding population, eggs producing sons were significantly larger than eggs producing daughters; laying order effects were controlled. 3. The influence of sibling egg size ratios on post‐natal size relationships persisted through the nesting period, providing parents with a tool to manipulate size‐related phenomena in their offspring.
Thermal influences on foraging ability: body size, posture and cooling rate of an ambush predator, the python Morelia spilota
Authors: AYERS D. Y. , SHINE R. 
Published: November 2003

1. The interface between thermal biology and foraging mode has attracted little scientific attention, but may be crucially important to the biology of ectothermic predators. Slip & Shine (1988c) suggested that the ability of large heavy‐bodied snakes to ambush nocturnally active mammals relied on the snakes’ control of cooling rates through their thermal inertia (via body size and postural adjustments) and microhabitat selection. 2. We tested assumptions underlying this hypothesis, using Diamond Pythons (Morelia s. spilota) from southeastern New South Wales. Our laboratory studies confirmed that larger body sizes and coiled postures significantly retarded cooling rates, and that body temperature affected the snakes’ ability to detect potential prey items. 3. The magnitude of these effects on cooling rates was great enough to extend the time period substantially over which an adult Diamond Python, lying in ambush in a suitable microhabitat, would be able to detect and capture nocturnally active prey. For example, the times taken for pythons to reach thermal equilibration under our experimental conditions (cooling from 33 to 12°C) were <1h for hatchling pythons regardless of posture, 1 h for outstretched juveniles, 2 h for coiled juveniles and outstretched adults, and almost 8 h for coiled adults. 4. The high rates of cooling of juvenile pythons, even when they are tightly coiled, may force them to rely upon diurnally active prey rather than crepuscular or nocturnal species.
Feeding behaviour of Red Deer (Cervus elaphus) offered Sitka Spruce saplings (Picea sitchensis) grown under different light and nutrient regimes
Authors: HARTLEY S. E. , IASON G. R. , DUNCAN A. J. , HITCHCOCK D. 
Published: November 2003

1. In addition to exhibiting preferences for particular plant species, vertebrate herbivores select particular individuals of these species whilst leaving others undamaged. This pattern of diet selection may reflect differences in the chemical composition (and hence nutritional quality) between individual plants, and/or variability in the physical constraints on intake rate, such as plant structure. 2. An experiment was conducted to test the effects of environmental manipulations on the morphology and chemical composition of Sitka Spruce saplings, and to evaluate the consequences for herbivory by Red Deer. Fertilizing the trees increased tree height, branch span and leader length, twig width and needle width, and decreased the concentrations of total phenolics, condensed tannins, fibre and lignin but monoterpene content was not altered. Shading also reduced phenolic and tannin concentrations. 3. When the fertilized and shaded trees were offered to deer in feeding trials, the probability of a tree being visited by a deer and the biomass removed were influenced by tree morphological variables, as were the bite rate and intake rate of the deer. More biomass was removed from larger trees. 4. Once the effects of tree morphology had been taken into account, there was no effect of the fertilizer and shade treatments on deer browsing behaviour that could be attributed to changes in chemical composition of the trees. The relationship between intake rate and bite size at each tree varied between individual deer, but the functional response relationship between intake rate and bite size was not influenced by the treatments applied to the trees. 5. Tree morphology may have a larger influence on deer feeding behaviour than tree chemical composition.
Seedling growth of four fire‐following Mediterranean plant species deprived of single mineral nutrients
Authors: HANLEY M. E. , FENNER M. 
Published: November 2003

1.
Anthyllis vulneraria, Cistus creticus, Hippocrepis unisiliquosa and Pinus brutia are frequent post‐fire colonizers whose seedlings are subjected to the mineral conditions imposed by ash in the early stages of growth. We test the hypothesis that the effective internal supply of mineral elements in the seeds of these species may complement the external availability of specific nutrients. 2. Newly germinated seedlings were grown in nutrient solutions, each deficient in one of the following elements: nitrogen, phosphorus or potassium. Control treatments consisted of full nutrients and distilled water. Seedling growth was monitored over 12weeks. The final dry masses of the seedlings were taken as a measure of the availability of each element from the seeds’ own stored reserves. 3. For the two legume species nitrogen was the most limiting element followed by phosphorus. Potassium deficiency had no effect on the final legume dry biomass. For Cistus, the order was nitrogen followed by potassium, while phosphorus deprivation had no effect on growth during the 12weeks of the experiment. Deprivation of single minerals had no significant effect on seedling growth of Pinus over the same period. The two legumes and Cistus when denied nitrogen had relatively greater relative root ratios than control plants. 4. The relative seedling requirements of each species for early external supplies of the various nutrients for establishment in the field are discussed with reference to the adaptation of the four species to post‐fire regeneration.
Effect of the canopy of Retama sphaerocarpa on its understorey in a semiarid environment
Authors: MORO M. J. , PUGNAIRE F. I. , HAASE P. , PUIGDEFÁBREGAS J. 
Published: November 2003

1. A dense understorey of annual and perennial herbs grow under the canopy of Retama sphaerocarpa shrubs in semiarid environments of south‐east Spain, influencing plant productivity and diversity at a regional scale. We investigated the facilitation by the shrub on its understorey in field and laboratory experiments with Barley designed to explore the mechanisms of interaction between both vegetation layers and their spatial variation. 2. There was a gradient of spatial heterogeneity in soil chemical fertility under the shrub canopy, with organic matter and soil nitrogen contents higher at the centre than at the edge of the canopy. Dry mass production of Barley was also higher in soils from intermediate positions, and lower in soils from both the centre and edge of the canopy. 3. In the field, pots sown with Barley placed near the centre, at an intermediate position and at the edge of the canopy of Retama shrubs showed significant differences in productivity, suggesting a mulching effect of the canopy that also affects seedling establishment. 4. Micro‐climatic measurements showed significant differences in total radiation reaching the soil, mean air and soil temperatures and maximum temperature among different positions in the understorey, increasing radially from the centre to the edge of the canopy. 5. These results and field observations suggest that the optimal association of climatic factors under the canopy would combine with a high soil fertility mediated by litter decomposition to increase biomass production mid‐way between the centre and the edge of the canopy. Overstorey and understorey thus interact to increase nutrient retention locally, which benefits both the shrub and the herb layer.
Allelopathic effect of Cistus ladanifer on seed germination
Authors: CHAVES N. , ESCUDERO J. C. 
Published: November 2003

1. The allelopathic effect of the exudate secreted by Cistus ladanifer leaves was tested on different plant species. Cynodon dactylon and Rumex crispus, species absent from C. ladanifer scrub (jarales), were clearly inhibited by the exudate. 2. Species present in the jarales, Medicago polymorpha and Lolium rigidum, showed no direct inhibition of germination, but the process this was delayed, and cotyledon and root size was diminished. This implies inhibition of seedling growth, and may explain the low abundance of these species inside the jarales. 3. The active constituents in the inhibition of germination are low molecular weight phenolic compounds. The flavonoids appear to exert no direct effect on germination of the species tested, but do provoke a reduction in cotyledon and root size, and could thereby inhibit subsequent seedling development.
Increased drag, and thus lower speed: a cost for morphological defence in Bosmina (Eubosmina) (Crustacea: Cladocera)
Authors: LAGERGREN R. , HELLSTEN M. , STENSON J. A. E. 
Published: November 2003

1. The swimming speed of two forms, an extreme and a typical, within the cladoceran subgenus Eubosmina were examined using a three‐dimensional video‐technique. The extreme form has a very high carapax and extremely long antennule, features probably involved in predator defence. 2. It was found that the extreme form swam almost 40% slower than the typical form. 3. Calculations show that the extreme form had to work at least 12% harder to swim at the same speed, or if it used the same amount of energy to swim, the extreme form would swim 6% slower. Increased drag, because of its distinguishing carapax and antennule, is thus the most likely explanation for the slower swimming speed of the extreme form, assuming it selects the same power output. 4. Swimming speed can be correlated to food intake either by the frequency of hits to edible food particles or by the time to swim from a poor food patch to a good one. So the reduced speed is probably a great cost for the extreme form.
Nestling obesity and variability of food delivery in Manx Shearwaters, Puffinus puffinus
Authors: HAMER K. C. , HILL J. K. 
Published: November 2003

1. Procellariiform seabirds such as Manx Shearwaters, Puffinus puffinus, accumulate large quantities of lipid during the nestling period, the purpose of which remains unclear. This paper examines temporal and age‐specific variation in the pattern of food delivery to nestling Manx Shearwaters, to determine whether food delivery was likely to be determined primarily by the availability of food to adults at sea or by a chick’s short‐term nutritional requirements. The variability in daily food delivery to chicks in the context of nestling obesity is then discussed. 2. For all but the youngest and oldest age classes, individual meals delivered by adults averaged 49 g, which was 12% of mean adult mass over the same period. More than 80% of chicks were fed each night and the maximum interval between feeding events for any chick was four nights. Feeding conditions did exert some influence over the ability of adults to feed their offspring, but deviations from expected values for both feeding frequency and meal size were restricted to a small number of nights, included values both higher and lower than expected and did not persist for more than one night in succession. These results were not compatible with the notion that large lipid reserves accumulated by chicks during their development provide insurance against prolonged interruptions to feeding. 3. Although adults did not appear to modulate food delivery over the nestling period, there was some evidence of short‐term adjustment of feeding frequency (but not meal size) according to a chick’s immediate nutritional requirements. This suggests that variation in the provisioning rates of chicks did not result solely from stochastic variation in parental foraging success. However, the effect was slight and despite such minor adjustments, the coefficient of variation in daily provisioning rate was not substantially lower than in other species where the chick has no influence on parental food delivery. This suggests that even among those species that feed their chicks at comparatively frequent intervals, lipid accumulation among Procellariiformes may result from chronic overfeeding of chicks in order to reduce the impact of variable food provisioning by individual parents.
Nitrogen fertilization affects interactions between the components of an insect–fungus–plant tripartite system
Authors: HATCHER P. E. , PAUL N. D. , AYRES P. G. , WHITTAKER J. B. 
Published: November 2003

1. The chrysomelid beetle, Gastrophysa viridula and the rust fungus, Uromyces rumicis both occur on leaves of Rumex obtusifolius growing in a wide range of soil nutrient conditions. We investigated the effect of fertilizing plants with eight nitrate and four ammonium concentrations on the components of this tripartite interaction in a controlled environment. 2. Leaf weight, area and total plant weight increased as both nitrate and ammonium concentrations increased up to 15mmol l–1. Between 15 and 50mmol l–1 added nitrate, leaf and total plant weight decreased. Total plant weight was unaffected by increasing ammonium fertilization from 15 to 25mmol l–1. 3. The density and percentage of U. rumicis pustules sporulating 8 days after infection decreased with increasing nitrate but were unaffected by increasing the concentration of ammonium fertilization. 4. Leaf area consumed and number of eggs laid by G. viridula decreased as the concentration of nitrate fertilization increased. Increasing the concentration of ammonium decreased leaf area eaten. 5. First instar mortality of G. viridula was increased and gregariousness and adult fecundity was decreased additively by the combination of U. rumicis infection and decreasing the nitrate concentration fed to plants from 10 to 1mmol l–1.
Pollen dynamics of bumble‐bee visitation on Echium vulgare
Authors: RADEMAKER M. C. J. , DE JONG T. J. , KLINKHAMER P. G. L. 
Published: November 2003

1. We quantified pollen deposition on the stigma, pollen removal from the anthers and pollen losses in Echium vulgare, visited by workers of Bombus terrestris under controlled conditions. We used dye as a pollen analogue. Bumble‐bees were trained to visit a sequence of non‐emasculated flowers to estimate pollen carryover and to visit individual flowers to estimate pollen loss. 2. Carryover of pollen grains and dye particles between flowers was similar, which justifies using dye as a pollen analogue. On average 93·8% of the dye particles on the bee were carried over to the next flower. Only a small fraction of the pollen grains was deposited on the stigma (0·15%). A much larger fraction (6·1%) was lost in another way: passively during flight, through grooming or on floral parts other than the stigma. The bees removed 44% of the pollen grains from a fresh flower and 50·3% of this removed pollen adhered to the bee. 3. We predict that, using the parameters mentioned above, during a single visit to a newly opened flower, a bee collects an amount of pollen grains which will bring about 60% geitonogamous self‐pollination in the next flower visited. The expected percentage of self‐pollination is considerably less if bees visit flowers that have been visited before.