bluuebunny/crossref_metadata_2025_split huggingface dataset:
Genetic variation can promote system persistence in an experimental host‐parasitoid system
Authors: Imura Daisuke , Toquenaga Yukihiko , Fujii Koichi 
Published: February 2004

AbstractWe tested experimentally the effects of genetic variation in host population on the host‐parasitoid system persistence. The experimental systems consisted of one parasitoid wasp species (Heterospilus prosopidis), one bean weevil species (Callosobruchus chinensis), and one bean species, of which only the host species (bean weevil) was genetically manipulated. As control treatments with low genetic heterogeneity in the host population, we used two bean weevil strains (Kyoto and Niigata strains) which have several contrasting ecological traits. For the high genetic heterogeneity treatment, hybrid bean weevils which were generated by crossbreeding the strains Kyoto and Niigata were used. In the multiple‐generation experiments, all three treatments had different patterns of extinction. The control treatment with the Niigata strain was very prone to system extinction, whereas the treatment with hybrids showed coexistence of constituent species in almost all replicates and also showed stabilized population dynamics. The other control treatment, using the Kyoto strain, showed intermediate proneness. To interpret the results of multiple‐generation experiments, we conducted several short‐term experiments. The different persistence patterns between the two control treatments were explained by the shapes of the host‐finding abilities of wasps and the growth rate of the bean weevils. The mean values of many ecological traits of hybrid lines were not different from those of the Kyoto strain, but their variability increased. These outcomes corresponded well to the prediction of models by Doebeli [J Theor Biol (1997) 188:109–120]. We discuss the mechanisms in which the variability in host species population was effective for the prolonged system persistence.
Local survival after fire in Mediterranean shrublands: combining capture‐recapture data over several bird species
Authors: Pons Pere , Henry Pierre‐Yves , Gargallo Gabriel , Prodon Roger , Lebreton Jean‐Dominique 
Published: February 2004

AbstractPost‐disturbance survival is a key factor in the onset of secondary successions. Here we analyse capture‐recapture data from two before/after disturbance studies to estimate the effect of fire on local bird survival. Analyses of six bird species at two Mediterranean shrubland sites were combined using a meta‐analysis approach. Two warblers, Sylvia undata and S. melanocephala, were studied at one site altered by prescribed burning, and five passerines (Luscinia megarhynchos, Turdus merula, Parus major, P. caeruleus and S. melanocephala) at one site disturbed by wildfire. Based on the combined analysis, annual survival probability significantly decreased from 0.49 to 0.18 (i.e. a 64% decline) after the fire. Our results further suggest a trend for a higher decrease in annual survival associated with wildfire (−72%, from 0.51 to 0.14) than with prescribed burning (−35%, from 0.41 to 0.27), although this should be properly tested with a specific experimental design. In S. undata, a decline in survival in the ‘long‐term’ cannot account for the drop in density observed the first spring after fire. We suggest that a decrease in recruitment rate and an increase in the proportion of non‐breeders immediately after the fire may contribute more strongly to the decline in the breeding population. Our results tend to support the idea that bird populations may respond to moderate disturbances with noticeable time lags, because of individual site tenacity.
Population dynamics of the solitary digger bee Andrena vaga Panzer (Hymenoptera, Andrenidae) studied using mark‐recapture and nest counts
Authors: Bischoff Inge 
Published: February 2004

AbstractThe population size of the solitary digger bee Andrena vaga was documented using mark‐recapture methods during 4 consecutive years (1996–1999). Additionally, the numbers of the parasitoids Nomada lathburiana and Bombylius major were estimated. For calculations of the daily population size, the Jolly‐Seber model for open populations with time‐dependent survival and capture rates was used. The mean daily population size corresponded well to the number of nests marked in the aggregation of A. vaga. The method of mark‐recapture achieved the most accurate data when the number of sampling periods and the capture probability was high. The results document a decrease in population size of the investigated A. vaga aggregation during 4 successive years. A population increase of its parasitoids B. major is considered to be one reason for the population decline of A. vaga in 1999. The sex ratio of A. vaga was biased toward females, contrary to the expected higher number of males. Results of the mark‐recapture studies showed that up to 50% of females left the aggregation or died at the beginning of the season. The females probably colonized new aggregations at distances further than 200 m away from their birth aggregation, as no marked females were observed in the environs of the study area. This behavior is interpreted as a parasite avoidance strategy. The bee populations in the study area form a web of interconnected aggregations. Apparently a flux of extinction and recolonization exists between the different aggregations.
Synchrony and geographical variation of the spruce bark beetle (Ips typographus) during a non‐epidemic period
Authors: Økland Bjørn , Bjørnstad Ottar N. 
Published: February 2004

AbstractSpatio‐temporal analyses of non‐epidemic bark beetle populations may provide insight in dynamics predisposing for outbreaks. The present article presents a spatio‐temporal analysis of the population dynamics of Ips typographus based on pheromone trap data from southeast and mid‐Norway in the post‐epidemic period 1979–2002. The analyses include regression analyses, hierarchical cluster analysis, and analysis of spatial synchrony of beetle time series and climatic data by means of nonparametric spatial covariance functions. The mean abundance of beetles declined linearly with latitude. In addition, the time series means were higher in areas with high forest productivity and rocky soils predisposed to drought. The time series patterns differed significantly between northern and southern study areas. The regional synchrony of the time series was fairly high (0.38), indicating that some large‐scale climatic factor may influence the dynamics. Windfelling was the external variable showing the most parallel pattern of correlation to the beetle dynamics. We thus posit that large windfall events may be a major instigator and synchronizer of beetle outbreaks in areas subjected to regionalized weather systems.
Intraspecific variation in the status of ant symbiosis on a myrmecophyte,Macaranga bancana,between primary and secondary forests in Borneo
Authors: Murase Kaori , Itioka Takao , Nomura Masahiro , Yamane Seiki 
Published: February 2004

AbstractA tree species,Macaranga bancana, distributed in South East Asian tropics has a mutualistic relationship with specific symbiotic ant species, which defend the plant from herbivores. To examine the intraspecific variation in the status of the ant‐plant symbiosis among microhabitats of different light conditions, we investigated the species composition of nesting ants and the herbivory damage onM. bancanasaplings by field observations and sampling in primary and secondary forests in Sarawak. In addition, the effectiveness of non‐ant (physical and chemical) defenses were estimated by feeding the larvae of a polyphagous lepidopteran withM. bancanaleaves from saplings in the two types of forests. All saplings in the primary forest were colonized by twoCrematogasterant species that had been known to be the obligate symbionts ofM. bancana,while in the secondary forest, about half of the saplings were occupied by several ant species that were not obligate symbionts. There was little herbivory damage on saplings colonized by the twoCrematogastersymbiont ants in both forest types, while the saplings colonized by the other ant species suffered a 10–60% loss of leaf area. Larval mortality of the polyphagous lepidopteranSpodoptera liturawas significantly higher when larvae fed on leaves ofM. bancanasaplings in the secondary forest than when fed on leaves ofM. bancanasaplings in the primary forest. These results suggest that the symbiosis between ants andM. bancanais looser and the non‐ant‐defenses are stronger in secondary forests, where light is more intense, than in primary forests.
Population dynamical consequences of reduced predator switching at low total prey densities
Authors: Abrams Peter A. , Matsuda Hiroyuki 
Published: February 2004

AbstractSeveral models of rapid switching by a predator in a two‐prey environment are analyzed. The goal is to determine how the dynamics of the system and the potential indirect effects between prey are affected by the dependence of switching on total prey density. In exploring this question, the difference between the population‐level consequences of switching in stable and cycling predator‐prey systems is also examined. We concentrate on reduced switching at low densities, a feature that is likely because of the difficulty of distinguishing between two very low densities. The main findings are: (1) switching in unstable systems can produce positive indirect effects of one prey species on the other; and (2) reduced switching at low densities can greatly alter the dynamics of the system and the indirect effects between prey. Both of the possibilities are only evident in cycling systems. Reduced switching at low total prey densities leads to heavier predation on the slower‐growing prey when both prey species are rare. As a consequence, there is a lag in the recovery of the slower‐growing prey species after predator densities fall, and the dynamics of the two prey become desynchronized. The net result is increased indirect interactions between prey, and a greater likelihood of exclusion of the slower growing prey. The analysis of these models suggests a need for more empirical work to determine whether switching is reduced by very low total prey densities, and to study the long‐term dynamics that occur in systems with switching predators.
Vulnerability and body size: tetrapods versus fish
Authors: del Monte‐Luna Pablo , Lluch‐Belda Daniel 
Published: February 2004

AbstractThe relationship between body size and risk of extinction has been the focus of much recent attention; however, it has only been stated for a few groups inhabiting restricted areas. Based on the IUCN list and other public records, we suggest that the relationship between vulnerability and body size is a trend among all vertebrates, especially tetrapods. In the case of fish, our results show that body size may be subordinate to another factor that we named concealment. Other plausible explanations about this difference could be the human preference for large terrestrial vertebrates and/or the inappropriateness of the current IUCN listing criteria for fish species.
Neighbourhood size, dispersal distance and the complex dynamics of the spatial Ricker model
Authors: Travis J. M. J. 
Published: February 2004

AbstractAmongst the most frequently made assumptions in simple population models are that individuals interact equally with every other individual and that dispersal occurs with equal likelihood to any location. This is especially true for models of a single population (as opposed to a patchy population or metapopulation). For many species of animals and probably for all plant species these assumptions are unlikely to hold true. Here one much‐studied population model—the Ricker model—is reformulated such that interactions occur only between individuals located within a certain distance of each other and dispersal distance is finite. Two alternative reformulations are presented. Results demonstrate that both limiting the interaction neighbourhood and reducing dispersal distance tend to stabilise the global population dynamics, although the extent to which this occurs depends upon the reformulation used. Spatial pattern formation is a feature of the simulated population. At lower intrinsic rates of growth (r) these patterns tend to be static, while for higherr, they are dynamic. Both the stabilisation of global dynamics and spatial pattern formation are well‐described features of metapopulation models. Here, similar effects are shown to occur on a single contiguous patch of habitat.
The genetic polymorphism linked to mate‐securing strategies in the male damselfly Mnais costalis Selys (Odonata: Calopterygidae)
Authors: Tsubaki Yoshitaka 
Published: February 2004

AbstractAlternative male mate‐securing strategies are widespread among animal taxa, but there are few well‐documented examples of genetic polymorphisms for them. In the Japanese calopterygid damselfly Mnais costalis, males occur as either orange‐winged territorial fighter males, or clear‐winged non‐territorial sneaker males. It has previously been suggested that this behavioral polymorphism is genetically controlled. However, there was no direct evidence for this. By rearing two groups of larvae from the same female but sired by different male morphs, I show that differential morph development is genetically controlled and consistent with a single‐locus two‐allele autosomal genetic polymorphism.
Mechanisms of density dependence in fluctuating vole populations: deducing annual density dependence from seasonal processes
Authors: Saitoh Takashi , Stenseth Nils Chr. , Viljugrein Hildegunn , Kittilsen Marte O. 
Published: February 2004

AbstractBased on recent advances in time‐series analyses of ecological dynamics using statistical and mathematical models, we summarise our recent results on the seasonal processes in the annual population dynamics of the grey‐sided vole Clethrionomys rufocanus (Sundevall, 1846) in Hokkaido, Japan, and report additional analyses on annual and seasonal density dependence. Annual direct density dependence was strong in almost all populations. In contrast, delayed density dependence was generally weak, although clear delayed density dependence was detected in some of the studied populations. Although seasonal density dependence was observed both in winter and summer, direct density dependence was much more profound during winter; thus, winter density dependence contributed most to the overall annual direct density dependence. We found no correlation between the seasonal components of annual direct density dependence; however, the corresponding seasonal components for annual delayed density dependence were positively correlated. We conclude that winter conditions influence the strength of annual direct density dependence most profoundly. Moreover, we conclude that direct density dependence during summer and winter may be generated by different mechanisms, whereas delayed density dependence seems to be generated by a common mechanism. Candidate mechanisms are discussed in relation to general knowledge of northern rodent populations and to specific insights provided by earlier studies of grey‐sided voles in Hokkaido.
How does spatio‐temporal disturbance influence species diversity in a hierarchical competitive system? Prospective order of species coexistence and extinction
Authors: Ohsawa Kyoko , Kawasaki Kohkichi , Takasu Fugo , Shigesada Nanako 
Published: February 2004

AbstractTo address how habitat destruction and hierarchical competition among species affect the spatio‐temporal dynamics of a multi‐species community, we present a compartment model in which multiple species undergo dispersal and competitive interactions in a patchy habitat arranged in a two‐dimensional lattice. We assume that disturbances are periodically imposed on some parts of the lattice in a block, followed by a period free of disturbance. For convenience, species are ranked in order of competitive ability. We further assume that the intrinsic growth rate of speciesi,εi, and the dispersal ability,Di, increase in decreasing order of rank. Our model can analytically determine the exact number of surviving species when disturbance is absent. In the presence of disturbance, we numerically examine how spatio‐temporal changes in environmental heterogeneity affect species coexistence and extinction, for the case in which the value ofεi/Dimonotonically increases or decreases with rank. The results demonstrate that (1) when the interspecific competition is smaller than the intraspecific competition, we can provide predictions on the prospective order of species to be driven extinct and the order of potential species to revive with increasing extents of disturbance; (2) when the interspecific competition is stronger than intraspecific competition, a small difference in the disturbance level can lead to drastic changes in the species composition, their densities and the order of species extinction. In addition, comparison with other similar models reveals that differences in species interaction in local population dynamics critically affect the disturbance‐mediated species diversity.
Cospeciation of figs and fig‐wasps: a case study of endemic species pairs in the Ogasawara Islands
Authors: Yokoyama Jun 
Published: February 2004

AbstractThe interactions between figs (Ficus, Moraceae) and fig‐wasps (Agaonidae, Chalcidoidea, Hymenoptera) are special plant‐pollinator relationships that are highly species‐specific, in that each fig species is pollinated by a single fig‐wasp species that can breed only in that particular fig species. This study examined the degree of pre‐mating isolation and genetic differentiation for three fig/fig‐wasp pairs endemic to the Ogasawara Islands. Simple Y‐tube tests revealed that fig‐wasps fromFicus nishimuraeand “Higashidaira type” chose their own host figs significantly more often, while fig‐wasps fromF. boninsimaedid not. Based on RAPD markers, the genetic differentiation among the fig species was low, butF. boninsimaeformed a cluster within theF. nishimuraecluster. The Higashidaira type has been derived from a subpopulation ofF. nishimurae. Five mitochondrial DNA haplotypes were found in the fig‐wasps and each haplotype correlated well with the fig species on their island of origin. These results led to a three‐step hypothesis on the cospeciation process: (1) spatial separation of fig/fig‐wasp populations arises; (2) gene flow is restricted and character differentiation of fig‐wasps occurs; (3) there is further restriction of gene flow and genetic and character differentiation of figs.
Dislocation Pile-up in Two-Phase Materials
Authors: Kuang J. G. , Mura T. 
Published: February 2004

Based on the theory of continuously distributed dislocations, the equilibrium equations for both edge-and screw-dislocation pile-ups in materials composed of soft and hard phases are formulated in terms of a singular integral equation. The integral equation is solved exactly by using the Wiener-Hopf technique with Mellin transforms.
The dislocation distribution function is found in explicit form. It is shown that the number of dislocations in the piled-up array can be determined directly from the Mellin transform of the distribution function without its inverse transform.
Extensional Mechanical Properties of Polyester- and Polyether-Based Polyurethanes
Authors: Klosner Jerome M. , Segai Alexander , Franklin Howard N. 
Published: February 2004

An investigation of the extensional mechanical properties of a polyester-based polyurethane (Texin 480 A Opaque 149004 B) and a polyether-based polyurethane is described.
Dynamic steady-state tests were performed over a frequency range of 1000–8000 Hz and a temperature range of 50°–110°F for the polyester material held at a constant elongation of 105%. The experiments on the polyether were conducted at 110% initial elongation over a range of frequency of 200–1600 Hz, and a temperature range of 50°–110°F.
The complex modulus was found for both materials and the reduced-variable concept applied. Master curves for the moduli at a reference temperature of 510°R (50°F) are presented.
Relaxation tests were performed on the same materials and the relaxation modulus determined. Finally, the relaxation spectrum was determined by using the data from the dynamic and relaxation experiments.
New Data on the Shear Stresses and Energies of ½ 〈110〉, {111} Edge Dislocations in Elastically Anisotropic fcc Metals
Authors: Duncan T. R. , Kuhlmann-Wilsdorf D. , Moore J. T. 
Published: February 2004

Numerical data and curves for the shear stresses and energies of ½ 〈110〉, {111} edge dislocations in elastically anisotropic fcc and diamond-type materials are presented, based on a previously published analytical solution, to supersede those contained in the earlier paper.
The corrected data are compared with data by Foreman, by Van Hull and Weertman, and by Seeger and Wobser, and are shown to be reliable.
Properties of a Ferromagnetic Powder in a Nonmagnetic Matrix
Authors: Baldwin John A. 
Published: February 2004

A study has been made of the magnetic properties of ferromagnetic powder suspended in a nonmagnetic matrix. The study was motivated by a desire to predict the properties of keepers employed in some fast computer memories. Expressions are obtained which give the static susceptibility and useful frequency range of such materials. The susceptibility is found to be small and relatively independent of that of the parent material. However, the useful frequency range is greatly increased.
The analysis is used to evaluate effective demagnetizing factors and interaction fields in quasiuniformly magnetized bodies. It is shown that the theory is consistent with certain experimental findings concerning polycrystalline ferrites and YIG. Finally, a suggestion is made for possible observation of domain-wall resonance.
Mechanical Aberrations of a Magnetic Quadrupole Quadruplet Lens
Authors: Kawakatsu Hisazo , Vosburgh Kirby G. , Siegel Benjamin M. 
Published: February 2004

The mechanical aberrations of a system of two or more magnetic quadrupoles have been studied. Displacement, rotation, and tilting of one quadrupole, and the effects of radial and rotational errors in alignment of one pole are considered as well as the inhomogeneity of the material used in the system. The changes in field distribution introduced by these errors are calculated and the corresponding aberration formulas are derived.
As a particular case, the mechanical aberrations of a quadruplet projector, are computed. The construction tolerances are estimated for an allowable image defect (magnification error) of 3% in the radial and rotatinoal directions. The calculations indicate that the projector system can be used in an electron microscope without excessive image defects. The image is most sensitive to rotational misalignment with a required tolerance of ±2×10−3 rad.
Precipitation of Iron Carbides in Tempered Martensite
Authors: Ron Moshe , Shechter Hanan , Niedzwiedz S. 
Published: February 2004

The precipitation of carbides in 0.7 wt%-carbon steel as a function of tempering temperature has been studied through the Mössbauer effect, magnetic measurements, and x-ray observations.
The magnetic behavior of the extracted precipitates is discussed. The tiny clusters obtained by extraction after the early stages of tempering (up to 250°C) show the relation of these clusters to martensitic bct cells (``Johnson clusters'').
The results obtained by further stages of tempering (250–500°C) show a decrease in the relative amount of the Johnson clusters, followed by a precipitation of ferromagnetic carbides. The behavior of the internal field, the TC and θD, as a function of the tempering temperature suggests a decrease of the relative carbon content with the increasing tempering temperatures. The Fe3C is formed toward 550°C.