bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kin‐related social organization in a winter population of the vole Clethrionomys rufocanus
Authors: Ishibashi Yasuyuki , Saitoh Takashi , Abe Syuiti , Yoshida Michihiro C. 
Published: December 2007

AbstractKinship among Clethrionomys rufocanus was investigated during the winter of 1992/93 in a 3‐ha enclosure using both molecular and catch‐mark‐release techniques. Forty‐six adult voles (22 males and 24 females) having high heterozygosities, which were collected from several natural populations, were released into the enclosure on 29 September 1992. Most fall‐born individuals of both sexes stayed in their natal site during the non‐breeding period (December–March), although reproductively active females dispersed during the fall breeding season (October–November). These philopatric individuals aggregated and formed an maternal family in the winter. Several females which failed to reproduce were solitary during this season. Some individuals which were derived from several families also aggregated into a mixed lineage group. Survival rate of fall‐born voles from earlier litters was higher than that from later ones. Maternal families broke up soon after the onset of spring reproduction. Most females established a territory near the wintering site and made a kincluster, in which close relatives neighbored each other. Maternal families in winter bring about female kin‐clusters in spring, which may influence reproductive output in the breeding season.
The population dynamics of the vole Clethrionomys rufocanus in Hokkaido, Japan
Authors: Saitoh Takashi , Stenseth Nils Chr , Bjørnstad Ottar N. 
Published: December 2007

AbstractPopulation dynamics of the gray sided‐vole, Clethrionomys rufocanus, in Hokkaido, Japan were described on the basis of 225 time series (being from 12 to 31 years long); 194 of the time series have a length of 23 years or longer. The time series were classified into 11 groups according to geographic proximity and topographic characteristics of the island of Hokkaido. Mean abundance varied among populations from 1.07 to 21.07 individuals per 150 trap‐nights. The index of variability for population fluctuation (s‐index) ranged from 0.204 to 0.629. Another index for population variability (amplitude on log‐10 scale) ranged from 0.811 to 2.743. Mean abundance and variability of populations were higher in the more northern and eastern regions of the island. Most populations, except for the southernmost populations, exhibited significant direct density‐dependence in population growth. Detection rate for delayed density‐dependence varied among groups from 0% to 22.6%. Both direct and delayed density‐dependence tended to be stronger in the more northern and eastern populations. The proportion of cyclic populations was higher in the northern‐eastern areas than that in the southern‐western areas. There was a clear gradient from the asynchronous populations in southwest, to the highly synchronized populations in the northeast.
Mapping the regional transition to cyclicity inClethrionomys rufocanus: Spectral densities and functional data analysis
Authors: Bjørnstad Ottar N. , Stenseth Nils Chr , Saitoh Takashi , Lingjærde Ole Chr 
Published: December 2007

AbstractWe study the regional transitions in dynamics of the gray‐sided vole,Clethrionomys rufocanus, within Hokkaido, Japan. The data‐set consists of 225 time series of varying length (most from 23 to 31 years long) collected between 1962 and 1992 by the Forestry Agency of the Japanese Government. To see clearly how the periodic behavior changes geographically, we estimate the spectral density functions of the growth rates of all populations using a log‐spline method. We subsequently apply functional data analysis to the estimated densities. The functional data analysis is, in this context, analogous to a principal component analysis applied to curves. We plot the results of the analysis on the map of Hokkaido, to reveal a clear transition from relatively stable populations in the southwest and west to populations undergoing 3–4 year cycles in the northeast and east. The degree of seasonality in the vegetation and the rodent demography appear to be strongest in the cyclic area. We briefly speculate that the destabilization of the rodent dynamics is linked to increased seasonalforcing on the trophic interactions in which the gray‐sided voles are involved.
Seasonal forcing on the dynamics of Clethrionomys rufocanus: Modeling geographic gradients in population dynamics
Authors: Stenseth Nils Chr , Bjørnstad Ottar N. , Saitoh Takashi 
Published: December 2007

AbstractWe interpret gradients in population dynamics of the gray‐sided vole from the southwestern part of the island of Hokkaido to its northeastern part within the framework of a phenomenological model involving the relative length of summer and winter. In Hokkaido, as in other northern regions, both spring and fall is considered as short transition periods between the two main seasons — summer (the primary breeding season) and winter (the non‐reproductive or secondary breeding season). We show that the geographic transition in dynamics may be understood as the combined consequence of different patterns of density‐dependence during summer and winter, and geographically varying season lengths. Differences are shown to exist between summer and winter with respect to strength of density‐dependence. Direct density‐dependence, in particular, is stronger during winter than during summer. A model is presented to show how relative lengths of seasons can induce both stable and periodically fluctuating population dynamics. The results are compared and contrasted with what is otherwise known about the gradient in rodent dynamics in Fennoscandia.
The role of vole populations in prevalence of the parasite (Echinococcus multilocularis) in foxes
Authors: Saitoh Takashi , Takahashi Kenichi 
Published: December 2007

AbstractEffects of population fluctuation of the gray‐sided vole (Clethrionomys rufocanus) on the prevalence (infection rates) of the parasite Echinococcus multilocularis in red fox (Vulpes vulpes) populations was investigated from 1985 to 1992 in eastern Hokkaido (Abashiri, Nemuro, and Kushiro area), Japan. This parasite needs two hosts to complete its life cycle; the gray‐sided vole as its intermediate host and the red fox as its final host. We found that: (1) Infection rates in foxes depended on the current‐year abundance of voles in all three study areas, particularly in Abashiri. (2) In addition to this direct density‐dependence, delayed density‐dependence between the infection rate and the prior‐year abundance of voles was detected in Nemuro and in Kushiro. (3) The regional differences in density‐dependence pattern were related to regional differences in the winter food habits of red foxes: in Abashiri the proportion of voles in the fox's diet greatly decreases in winter, while the proportion remains high in winter in Nemuro and in Kushiro, probably because of shallower snowpack. These results suggest that infection rates in foxes in Abashiri were less influenced by the prior‐year prevalence, since the infection cycle might be interrupted in winter, when voles became less important in fox's diet. In contrast, the state of the prevalence may carry over from year to year in Nemuro and in Kushiro, because red foxes continue to eat a considerable amount of voles throughout year. The regionally contrasted results for the relationship between infection rate in foxes and vole abundance were parallel to the regional difference in fluctuation pattern of vole populations, which are highly variable in Abashiri area, but less variable in Kushiro‐Nemuro area. Drastic change in vole populations appears to affect the host‐parasite system.
The demography ofClethrionomys rufocanus: From mathematical and statistical models to further field studies
Authors: Yoccoz Nigel G. , Nakata Keisuke , Stenseth Nils Chr , Saitoh Takashi 
Published: December 2007

AbstractUntil recently, most studies on microtines have focused on patterns in population dynamics or demography without providing a quantitative assessment of the robustness of the inferred patterns as well as a link between demography and population dynamics. Developments in statistical time‐series analysis on the one hand and in capture‐recapture statistical modelling on the other hand, now allow for improved analyses. We review some of the recent developments in the capture‐recapture statistical methodology — restricting ourselves to methods most relevant to the demography of small mammals. A 5‐years study of the gray‐sided voleClethrionomys rufocanusin Hokkaido, Japan was used as an example to explore some models. We then provided a framework for further demographic analysis of microtine populations, includingC. rufocanus.Investigating the relative importance of the different demographic parameters (e.g. survival, maturation, dispersal) will require studies done on larger scale than is commonly done today, with more effort devoted to the low density phase. Special emphasis is given to study‐design, and to experimental designs tailored to the study of specific demographic mechanisms.
The population biology of coevolution
Authors: Thompson John N. 
Published: December 2007

AbstractNew populational approaches to the study of coevolution among species are confronting two major problems: the geographic scale at which coevolution proceeds, and the long‐standing issue of how species may coevolve with more than one other species. By incorporating the ecological structure of life histories and populations into analyses of the coevolutionary process, these studies are indicating that coevolutionary change is much more ecologically dynamic than indicated by earlier work. Rather than simply a slow, stately process shaping species over long periods of time, parts of the coevolutionary process may proceed rapidly (sometimes observable in less than a decade), continually molding and remolding populations and communities locally and over broad geographic scales.
Receptivity of female remating and sperm number in the sperm storage organ in the bean bug, Riptortus clavatus (Heteroptera: Alydidae)
Authors: Sakurai Tamito 
Published: December 2007

AbstractThis study examines the relationship between the number of sperm in the seminal receptacle (spermatheca) and the receptivity of female remating in the bean bug Riptortus clavatus Thunberg. On the 21 st day after the first mating when receptivity to remating was > 70%, females receptive to remating had significantly fewer sperm (< 40 on average) in the spermathecae than females reluctant to do (about 150 on average). However, averages of the number of eggs laid by receptive and reluctant females within 21 days were almost same. The proportion of fertilized eggs for receptive females at 15–21 days after copulation was significantly lower than that for reluctant females. Spermatozoa transferred from a male to a female's spermatheca were detected 5 min after copulation and then increased continuously to about 500 with the first hour. When copulation durations were manipulated artificially, the shorter the copulation period (=females had less sperm in their spermathecae), the higher the remating rate became. Females may perceive the number of sperm in their seminal receptacles and then determine whether they copulate or not. These results support the hypothesis that females mate multiply in order to replenish inadequate sperm supplies to fertilize all eggs produced.
Natural enemies for the cabbage webworm, Hellula undalis (Fabr.) (Lepidoptera: Pyralidae) in Malaysia
Authors: Sivapragasam A. , Chua T. H. 
Published: December 2007

AbstractFour species of larval parasitoids were reared from larvae of the cabbage webworm (CWW),Hellula undalis (Fabr.) (Pyralidae: Glaphyriinae) collected from various cruciferous plants and a capparidaceous weed, Cleome rutidosperma (DC). On cabbage, only two species were recorded, viz, Bassus sp. (Braconidae) and Trathala flavoorbitalis (Cam.) (Ichneumonidae). The other parasitoids were braconids, Chelonus sp. and Phanerotoma sp. Egg or pupal parasitoids were not recorded. The parasitoids were not an important mortality factor of CWW on cabbage because they were usually present at the end of the crop season and their numbers were generally low. On the other hand, predator‐exclusion experiments indicated that predators were important in determining the density of CWW on cabbage and the within‐generation survival in the field. The major predator was the fire‐ant, Solenopsis geminata (F.), which foraged on the prepupae and pupae.
Possible influences of habitat characteristics on the evolution of semelparity and cannibalism in the hump earwigAnechura harmandi
Authors: Kohno Katsuyuki 
Published: December 2007

AbstractThe possible influences of life history and habitat characteristics on the evolution of semelparity and cannibalism in the hump earwigAnechura harmandiwere studied. This species is univoltine and overwinters as an adult. Females laid single egg‐batches during winter in nests under stones at a riverside in a valley. They took care of the eggs which hatched in early spring and the offspring ate their mother before dispersing. The valley was sometimes flooded in summer. Nymphs emerged as adults and dispersed to elsewhere before the rainy season arrived. They returned to the riverside after the rainy season. The flooding and/or summer heat seemed to be the selective force for the evolution of dispersal behavior and semelparity in this species. The cannibalism of the female parent by her offspring seemed to have readily evolved after the evolution of semelparity. The unfavorable environmental conditions seemed to have a large effect on the evolution of semelparity and cannibalism in this species.
Deme formation in gall‐making aphids Adelges japonicus (Homoptera: Adelgidae)
Authors: Ozaki Kenichi , Itahana Naoei 
Published: December 2007

AbstractThe deme formation hypothesis in herbivorous insects states that herbivores differentiate genetically into small demes, each specialized in the idiosyncratic traits of individual plants. We examined this hypothesis in gall‐forming aphids, Adelges japonicus, by reciprocal transfers of aphids among three susceptible clones of Picea jezoensis standing in proximity. Performance of aphids transferred to their natal clone was compared with that of aphids transferred to other novel clones. ANCOVA showed no significant donor (source of aphids) by receptor (recipient of aphids) interactions for both total aphid performance on the host tree over a life cycle and its three subdivisions (q1,q2 and q3). In addition, the total performance on the natal clone was lowest among those in the three clones, which was explicitly against the prediction from the local adaptation. In contrast, there were significant receptor effects on q1 (fecundity of gallicolae multiplied by survivorship of fundatrices while feeding on needles) and q3 (fecundity of fundatrices multiplied by survivorship of gallicolae before emergence from the galls), suggesting genetic differences in resistance among clones. The two‐fold difference in q3 among clones was due to different gall size, which was highly correlated with the number of gallicolae that emerged from the gall. The two‐fold difference in q1 seemed to be caused by different survivorship of larval fundatrices while feeding on needles.
An island biogeographical approach to the analysis of butterfly community patterns in newly designed parks
Authors: Kitahara Masahiko , Fujii Koichi 
Published: December 2007

AbstractWe analyzed the butterfly communities in the newly designed city parks (area C), “newly opened habitat islands”, of Tsukuba City, central Japan. The area constituted a natural ecological experiment on the mainland for clarifying the pattern and process of faunal immigration. We compared butterfly communities in area C with those in two other areas in the light of the theory of island biogeography and the concept of generalist/specialist. Our results showed the following: (1) Fewer species were found in area C than in other areas, due largely to the absence of many specialist types, restricted and habitat specialists, and/or low density species in the area. Generalist types, widespread and habitat generalists, and/or high density species predominated in area C. (2) The difference in the species numbers among the three sections within area C could be explained by the habitat structure in and around the respective sections. (3) The densities of many species were low in area C, probably due to its man‐modified habitat structure. In particular, several species occurred at extremely low densities in area C, but at high densities in other areas. (4) The internal structure of the habitat island butterfly community in area C was almost perfectly consistent with that of “quasi‐equilibrium” communities that appear during the colonization of an island. Our results demonstrate that the synergetic application of the generalist/specialist concept and the island biogeography theory is effective for the understanding of the patterns and structures of habitat island communities.
Population stability in relation to resource availability in an introduced population of an herbivorous lady beetle
Authors: Ohgushi Takayuki , Sawada Hiroichi 
Published: December 2007

AbstractMechanisms responsible for population stability in relation to resource availability were studied in an introduced herbivorous lady beetle, Epilachna niponica. The introduced population was relatively constant over a seven‐year study period. Egg density was related to the variation in host‐plant abundance in different years, and was highly stabilized during the period from reproductive adult to egg stage. Two density‐dependent processes were identified in the reproductive season: (1) density‐dependent reduction in fecundity and (2) density‐dependent increase in female mortality and/or emigration, all of which operated early in the season. As a result, temporal variability in cumulative egg density was greatly reduced by mid‐May, by which time approximately 40% of total eggs were laid. A field cage experiment demonstrated that egg‐laying of individual females was largely limited by resource availability even at low levels of leaf herbivory. Since movement activity of ovipositing females increased in a density‐dependent manner, inter‐plant movement is more likely to cause density‐dependent reduction in fecundity and female loss, due to enhanced energy expendiditure. The introduced population was less stable than the source population, probably because of decreased inter‐plant movement of females and the unlikelihood of egg resorption, both of which contribute significantly to the temporal stability of E. niponica population densities.
Extinction of populations due to inbreeding depression with demographic disturbances
Authors: Tanaka Yoshinari 
Published: December 2007

AbstractThe process of population extinction due to inbreeding depression with constant demographic disturbances every generation is analysed using a population genetic and demographic model. The demographic disturbances introduced into the model represent loss of population size that is induced by any kind of human activities, e.g. through hunting and destruction of habitats. The genetic heterozygosity among recessive deleterious genes and the population size are assumed to be in equilibrium before the demographic disturbances start. The effects of deleterious mutations are represented by decreases in the growth rate and carrying capacity of a population. Numerical simulations indicate rapid extinction due to synergistic interaction between inbreeding depression and declining population size for realistic ranges of per‐locus mutation rate, equilibrium population size, intrinsic rate of population growth, and strength of demographic disturbances. Large populations at equilibrium are more liable to extinction when disturbed due to inbreeding depression than small populations. This is a consequence of the fact that large populations maintain more recessive deleterious mutations than small populations. The rapid extinction predicted in the present study indicates the importance of the demographic history of a population in relation to extinction due to inbreeding depression.
Competition and evolutionary stability of plants in a spatially structured habitat
Authors: Takenaka Yasuto , Matsuda Hiroyuki , Iwasa Yoh 
Published: December 2007

AbstractWe modelled the population dynamics of two types of plants with limited dispersal living in a lattice structured habitat. Each site of the square lattice model was either occupied by an individual or vacant. Each individual reproduced to its neighbors. We derived a criterion for the invasion of a rare type into a population composed of a resident type based on a pair‐approximation method, in which the dynamics of both average densities and the nearest neighbor correlations were considered. Based on this invasibility criterion, we showed that, when there is a tradeoff between birth and death rates, the evolutionarily stable type is the one that has the highest ratio of birth rate to mortality. If these types are different species, they form segregated spatial patterns in the lattice model in which intraspecific competitive interactions occur more frequently than interspecific interactions. However, stable coexistence is not possible in the lattice model contrary to results from completely mixed population models. This clearly shows that the casual conclusion, based on traditional well mixed population models, that different species can coexist if intraspecific competition is stronger than interspecific competition, does not hold for spatially structured population models.
Maintenance of diapause variability in the two‐spotted spider mite, tetranychus urticae, in a heterogeneous and stochastic environment
Authors: Tsuda Yoshio , Takafuji Akio , Kuno Eiji 
Published: December 2007

AbstractA simple nongenetic mathematical model analyzed the processes responsible for the variations in the diapause percentage among populations of the two‐spotted spider mite, Tetranychus urticae Koch. This model incorporates the following assumptions. 1) Mites have diapause (DD), non‐diapause (NN), and “plastic” (DN) populations (plasticity exists in the phenotypic expression of diapause in response to habitat conditions at the time of diapause induction). 2) A heterogeneous mite habitat consists of microhabitat L, in which all the non‐diapausing mites die during the winter due to the lack of winter host plants, and microhabitat O with winter hosts capable of supporting some of the non‐diapausing mites overwinter. 3) Temporal fluctuation of winter conditions which affect the survival and reproduction of non‐diapausing mites. Using these assumptions, we compared the fitness functions of the three populations and analyzed the conditions under which each population is favoured over the other two, thereby elucidating the processes involved in the maintenance of variability in diapause. Our analysis revealed: 1) frequent mild winters are of primary importance for the non‐diapause trait to be maintained, 2) the existence of winter hosts is also important for the nondiapause trait to be favoured, and this importance depends greatly on the degree of the adaptive diapause expression in the DN mites in response to habitat conditions, i.e., the better the phenotypeenvironment matching in DN, the higher the probability that DN will be favoured, 3) The combined effect of the temporal and spatial variation enhances the maintenance of variablity in the diapause trait of the mites.