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1.
Akiko Kashiwagi Tadashi Kanaya Tetsuya Yomo Itaru Urabe 《Researches on Population Ecology》1998,40(2):223-226
Closely related competitors comprising ofEscherichia coli strains having the same metabolic system and differing only with a few bases on the glutamine synthetase gene in the plasmid
pKGN were previously shown to coexist in a chemostat. The differences among these closely related competitors can be considered
large enough to allow coexistence as the level of enzyme activity is different. To bring the difference among competitors
to the slightest possible, the mutation was introduced on the noncoding region of the plasmid pKGN harbored in the wild-type
strain (strain W). The new strain, strain W’, carries the plasmid pKGN’ with a 4-base insertion at theHind III site in the polycloning site of pKGN. As the noncoding region is a nucleotide segment that is not translated into amino
acids, the relatedness between strains W and W’ is the closest possible from the genetic point of view. Interestingly, though
both strains are almost identical, they can coexist stably in a chemostat irrespective of the initial population size. These
experimental results suggest that in the natural ecosystem, no matter how akin competitors are, coexistence is not impossible. 相似文献
2.
The mathematical model presented here aims to elucidate the essential mechanisms of coexistence of species, especially those
of closely related forms, as a result of competition in the same environment. It describes a system where the fate of the
competitors or mutants is observed at the initial stage of evolution. The model encompasses both the external variables and
the internal state of the competitors, which differ only in one of the metabolic rate constants. Results of simulations, even
with the simplified form of the model, show that stable coexistence of closely related forms in a uniform environment is possible.
In addition, the model allows the analysis of the limitations on the level of differences and similarities among the competitors
for achieving a state of coexistence. The essential mechanisms for the coexistence of closely related competitors are proposed
to be the involvement of the metabolic network in allowing the same growth rate of competitors which have different internal
states, and the interplay between the internal states of the competitors and the external variables of their environment. 相似文献
3.
Masakazu Shimada 《Researches on Population Ecology》1985,27(2):203-216
Summary Effects of niche shift in ecological time scale on the population dynamics of competing species were studied in the experimental
populations of two parasitoid wasp species,Anisopteromalus calandrae andHeterospilus prosopidis (both are solitary parasites), on a host, the azuki bean weevil,Callosobruchus chinensis. Four resource conditions were set up with combination of kind of bean (azuki or black eye), and host distribution (uniform
or clumped). In each resource condition, four developmental stages of hosts were provided as a resource spectrum for parasitoid
wasps.
Population dynamics of the two wasp populations were investigated in each resource condition in Multi-Generation Competitive
Systems (MGCS), in which fresh hosts of four developmental stages were periodically introduced and were parasitized competitively
by the two wasp species. Competitive coexistence of both wasps occurred in the azuki-clumped condition, where the peaks of
the resource utilization curves separated in the two species; pupae inA. calandrae and the early or late fourth instar inH. prosopidis, A. calandrae was eliminated in the azuki-uniform condition andH. prosopidis went extinct in two black eye conditions irrespective of host distributions. The degrees of overlap of the resource utilization
patterns of the two wasp species during population dynamics were not significantly different among resource conditions irrespective
of the results of coexistence or extinction. Even in the azuki-clumped condition, however, extinction ofA. calandrae was observed when resource partitioning could not be realized with only the late fourth instar larvae available to wasps.
Further analytical experiments showed that parasitizing ability ofA. calandrae increased with host density per bean with azuki beans, butA. calandrae could express higher parasitizing ability with black eye beans thanH. prosopidis irrespective of host density per bean.
The flexibility in parasitizing ability byA. calandrae for various host stages under different resource conditions was thought to be the major factor in determining the competitive
coexistence or the extinction of either species under different resource conditions. The present experiments also suggested
that different second-best host stages between competitors could be a major contributing factor to competitive coexistence. 相似文献
4.
Midori Tuda 《Researches on Population Ecology》1998,40(3):293-299
In an insect host (the cowpea weevilCallosobruchus maculatus)- parasitoidHeterospilus prosopidis) experimental system, the population densities of the component species oscillated for the first 20 generations and then
abruptly stabilized as the parasitoid density decreased. Examination of the host and parasitoid after the 40th generation
in the long-term experiment showed that (1) host larvae exhibited contest-type competition (killing other larvae inhabiting
the same bean), in contrast to the founder population being scramble-type competitors and (2) the parasitoid attack rate on
the host did not change. There was also an evolutionary trade-off between body size and the rates of larval survival and development,
suggesting a cost of contest competition on larval survivorship and development. I tested model predictions (Tuda and Iwasa
1998) that (1) host equilibrium population size should gradually decrease as the proportion of the contest type increases
and that (2) random attacks of the parasitoid on the host should reduce the rate of increase in proportion of the contest
type, and the effect should become manifest especially during the first 20 generations. Two of three host-only replicates
showed significant decrease in population sizes. Although the density of emerging adults per bean did not differ between replicates
of the host-only and host-parasitoid systems, comparison of the host body size between them on day 270 (at the 13th generation)
showed that the host was more contest-type in the host-only system than in the host-parasitoid system, as the model predicted,
and later on day 650 the effect of the parasitoid had disappeared. 相似文献
5.
Intra- and interspecific larval interactions that take place in a host body were investigated for two tachnid fliesEpicampocera succincta andCompsilura concinnata (Diptera: Tachinidae) parasitizingPieris butterfly larvae.E. succincta, a specialist onPieris butterflies, showed contest-type intraspecific competition, eliminating all the other conspecific larvae. On the other hand,
an extreme generalist parasitoidC. concinnata exhibited scramble-type competition, sharing the host with other conspecifics and suffering reduced body size as a result.
However, when these two species occurred together in a single host,C. concinnata had a much higher chance of survival. Moreover,C. concinnata could often survive in the presence of a parasitoid waspCotesia glomerata (Hymenoptera: Braconidae) whileE. succincta could not. The high tolerance ofC. concinnata could be attributable to its being an extreme generalist: To attack and survive on many different hosts, one has to be able
to deal with various competitors. The competitive inferiority of the specialistE. succincta, on the other hand, may be a result of relatively recent encounter with, those competitors. 相似文献
6.
Among wild plants ofHydrangea serrata (Hydrangeaceae) in Japan, there are sweet plants whose leave contain a kind of isocoumarin, phyllodulcin, which happens to
be 350 times as sweet as sucrose to the human tongue. In a primary beech forest in Ashu, Kyoto, the spatial distribution of
sweet plants and temporal and the spatial distribution of phyllodulcin within and among plants were investigated using a high
performance liquid chromatograph. The distribution of sweet plants was confined within a valley and was parapatric with non-sweet
plants. A plant's characteristic phyllodulcin accumulation did not change, even when transplanted into the different habitats.
The phyllodulcin content of the sweet plants varied greatly among plants, and the population mean peaked in July when the
plants flowered. Within a plant, phyllodulcin content was elevated by partial defoliation. We examined the possible effect
of phyllodulcin on herbivory by a specialist leafmining herbivore,Antispila hydrangifoliella (Lepidoptera: Heliozelidae). We transplanted sweet and nonsweet plants reciprocally between their original habitats, excluded
attacks by parasitoids, and compared performance of the leafminer. Leafminer colonization and larval survivorship on transplanted
andin situ plants was not significantly different between sites. The fact that accumulation of phyllodulcin did not augment a defensive
function, at least against herbivory by the leafminer, and the sporadic distribution of phyllodulcin-accumulating plants,
suggest that the genotypes synthesizing phyllodulcin emerged independently at separate localities by mutation, and that the
genotypes are almost adaptively neutral in defence against the specialist herbivore. 相似文献
7.
The outbreak mechanisms of the green rice leafhopper,Nephotettix cincticeps Uhler, in northern Japan
Intraspecific regulatory processes keep the population ofNephotettix cincticeps stable at a low density in southern Japan. In northern Japan, however, the yearly population density of the insect fluctuates
violently, and large outbreaks occasionally take place. To clarify the difference in the population dynamics between the two
regions, we analyzed light-trap and sweep-net sampling records from prefectural and national agricultural experimental stations.
The survival rate of the overwintering population decreased with increases in the period of continuous snow cover (PCSC) in
the north, and initial population densities in the years of long PCSC were too low for populations to reach equilibrium density
by the end of the active breeding season. This made yearly population fluctuations in the north much larger than in the south.
The equilibrium density in the north was higher than in the south. The higher equilibrium density presumably permits the higher
population density and larger yearly population fluctuations in the north. A major factor responsible for the difference in
equilibrium densities between the two regions is the difference in heading dates of the host plant (rice). Qualitative differences
among rice plant varieties, and among biotypes ofN. cincticeps, may also be important. 相似文献
8.
Summary Simulation model for niche shift in ecological time scale was constructed on the basis of the optimal foraging theory. In
accordance with the previous experimental study (Shimada andFujii, 1985), the model competitive system consisted of 2 parasitoid wasp species utilizing 4 host stages. Wasps were assumed to
choose host stages in the manner that they realized the maximal gain/cost values, where gain was represented by body weight
of a wasp progeny emerging from each host stage and cost was expressed by time required to search for and detect an unparasitized
host. The number of parasitized hosts in each host stage was calculated numerically by usingArditt's (1983) model for avoidance of superparasitism.
The model simulated well the experimental results ofShimada andFujii (1985) andShimada (1985). Sensitivity analysis of the model showed that the experimentally derived criterion for competitive coexistence (different
second-best host stages between competing species even with the common best) was not necessarily the indispensable condition
for niche shift and separation, but that if the criterion was not satisfied, stable competitive coexistence occurred only
in the narrow range of the parametric values. Further, niche shift in ecological time scale made the competitive coexistence
more stable than fixed niche on which the current niche theory stands. 相似文献
9.
S. Akimoto 《Researches on Population Ecology》1995,37(1):81-89
Closely related species of gall-forming aphids are often associated with a single host species. SixTetraneura species coexist on the Japanese elm,Ulmus davidiana, in Sapporo, northern Japan. This paper describes the probabilities of coexistence on macro- and microgeographic scales (i.e.,
on host trees and host leaves) and examines whether coexistence with conspecific or heterospecific galls on leaves or shoots
has any effect on the fecundity of each aphid species using multiple regression. A Monte Carlo simulation showed that the
frequency distribution of the numbers of species on individual host trees differed significantly from that expected from the
null model. There were significantly positive or negative associations between species.Tetraneura radicicola andsorini always coexisted with other species on trees they infested. Multiple regression revealed that the coexistence of conspecific
or heterospecific galls on individual leaves had no influence on the fecundity ofradicicola andsorini, but had a negative influence on that of sp. O. On average,radicicola andsorini produced a smaller number of offspring in galls than sp. O, and obviously consumed only a small part of resources available
on the galled leaves. Evidence available suggests that although amensalism does arise between sp. O and other species, its
influence in not so strong as to exclude sp. O competitively from theTetraneura community. 相似文献
10.
David Wool 《Researches on Population Ecology》1969,11(1):40-44
Summary The effect of larval age range on survival of twoTribolium castaneum strains in mixed cultures was studied in an experimental situation in which other selective forces were reduced to a minimum.
Increasing the difference in larval age setween the strains by one day resulted in a reduction of survival of the faster-developing
mutant strain, because more of its earlier pupae were cannibalized by the larvae. General aspects of the effects of pupal
cannibalism by larvae on the outcome of intra-specific competition (sensu lato) inTribolium are discussed. 相似文献
11.
以人的全面发展统筹解决人口问题 总被引:3,自引:2,他引:3
进入21世纪以来,我国人口发展面临着前所未有的复杂局面,稳定低生育水平的基础还不牢固,人口素质、结构、分布与经济社会发展的矛盾日益显现,人口发展越来越多地受到各种因素的综合影响。采取综合措施,以人的全面发展统筹解决人口问题,已经成为新时期我国人口和计划生育工作新的指导方针。 相似文献
12.
Three models were constructed for analyzing the population characteristics ofC. chinensis on stored beans; model A describing the whole reproductive process with a single equation, model B describing the three age-specific
processes (oviposition, egg survival and larval survival) with separate equations, and model C which describes all these processes
not for the whole habitat but for the individual beans comprizing it. The logit equation was employed here as a common basis
to describe the density-response relationship involved. All three models showed very good fit to the experimental data obtained
for both laboratory and wild strains of the weevil. The parameter values characterizing the population dynamics were, however,
widely different between the two strains; the laboratory one which had been reared for some 500 generations showed significantly
higher reproductive capacity, less sensitive and gentler response to crowding in both adult and egg stages, and more uniform
egg distribution among individual beans, as compared with the wild strain newly introduced. Sensitivity analyses using these
models suggested that these changes in population characteristics have been attained by the process of domestication or adaptation
to stable laboratory conditions through a long period of time. This process seemed in effect to have optimized the population's
performances in the laboratory environment. Evolutionary significance of such optimization was discussed with reference to
the selection pressure which may have acted upon individuals. 相似文献
13.
J P Paul 《Journal of homosexuality》1983,9(2-3):45-63
Theories of sexuality reflect popular notions by treating sexual identity as a simple dichotomy. There is research evidence for the coexistence of homosexual and heterosexual interest and behavior in a significant portion of the population. This paper examines how various conceptualizations of human sexuality have failed to adequately deal with bisexuality. The lack of acknowledgement by both the larger heterosexual society and the emerging lesbian/gay community, and its impact on the individual bisexual is examined by using the sociological concept of marginality. Some of the differences in self-labeling by women and men are noted in the light of social sex-roles. Finally, the implications of society's acceptance of bisexuality for evolving forms of relationships are suggested. 相似文献
14.
R. N. Coulson P. E. Pulley D. N. Pope W. S. Fargo L. J. Edson 《Researches on Population Ecology》1980,22(1):117-135
Summary Infestations ofDendroctonus frontalis
Zimm. are often observed to enlarge continuously by the colonization of new hosts in a pattern similar to a forest fire. This pattern
of infestation growth presents unique problems in quantitatively estimating populations ofD. frontalis. Beetle populations on each infested tree in an infestation go through five processes: attack, oviposition, reemergence,
survivorship, and emergence. These processes, which have been described mathematically in the literature, each take several
days for completion. In order to follow the distribution and abundance ofD. frontalis throughout the course of development of a spot, we need a daily estimate of the number of beetles involved in each process
on every tree. Since it is not practical to sample each tree daily, we developed a procedure whereby quantitative estimation
procedures for within-tree populations were used in combination with the mathematical models for the life processes to produce
a daily record of the number of adults successfully attacking trees, the number of eggs oviposited, the number of beetles
reemerging, number of beetles surviving within the trees, and the number of beetles emerging. These daily estimates were then
summarized for all trees in the spot for the duration of the infestation.
The daily record of populations ofD. frontalis, used with information on infestation geometry, were suggested to be of value in describing and elucidating several important
facets of population dynamics including dispersal patterns within infestations, between tree beetle loss (mortality), and
time lags among the various population processes. The information reported can be used to develop simulation models of population
dynamics or to validate existing models.
Texas Agric. Experiment Stn. TA No. 14689. 相似文献
15.
Koukichi Nagasaka 《Researches on Population Ecology》1991,33(1):115-128
Summary ThreeAthalia sawflies,A. japonica, A. rosae andA. infumata, feeding on cruciferous plants, coexist in Japan. However, it is not known what ecological strategies they use and what environmental
factors are crucial to such strategies. I attempted to explain these questions by examining the relationship between the spatio-temporal
distribution patterns of threeAthalia sawflies and their habitats in three districts (Lowland, Intermediate and Mountain).
The three sawflies have different spatio-temporal distribution patterns, though they usually used common cruciferous plants.A. japonica was abundant in spring and autumn but disappeared during summer in all the districts. In the Lowland, populations ofA. rosae andA. infumata, like that ofA. japonica, crashed in summer. HoweverA. rosae occurred mainly in summer in the Intermediate and Mountain. AlthoughA. infumata occurred in the same seasons asA. rosae in all districts, population levels ofA. infumata were always lower than those ofA. rosae.
The crucial factors controlling their population patterns were the availability of host plants and temperature. Population
crashes ofA. rosae andA. infumata were due to food depletion, and those ofA. japonica were due to heat stress. On the other hand, their population patterns may be interpreted as phenological synchronization
with their original host plants, though they all existed on common cruciferous plants.
The three sawflies may have evolved different strategies to escape from unfavorable habitat conditions. Such strategies are
speculated to be summer diapause inA. japonica, long distance migration inA. rosae, and local dispersal inA. infumata. 相似文献
16.
In May 1971, 45 adults of an herbivorous lady beetleEpilachna niponica (Coleoptera: Coccinellidae) from Asiu Experimental Forest were introduced into a botanical garden of Kyoto University, where
is 10 km south of the southern limits of its distribution with being 3–5°C warmer than the original site. The introduced population
of the lady beetle was thus investigated from 1975 to 1981. Mark-release-recapture experiments were applied to individual
adult beetles, to estimate population size and daily survival rate. Overwintering adults emerged from hibernation around early
April, reaching peak numbers in late April to early May, then gradually declined to late June. No adults remained at the end
of June. Adult survival was maintained at a high level to early May, and declined consistently until late in the reproductive
season. New adults began to emerge in late June and quickly reached a peak in early July; thereafter they decreased in number
and had entered hibernation by late October. In spite of seasonally deteriorating food resources and heat stress in summer,
new adults showed moderately high survival during the inimical period. New adults which emerged later in the season tended
to be smaller in body size than those that emerged early. The proportion of females in the new adult population gradually
increased throughout the pre-hibernating period, suggesting that male-biased mortality occurred during this period. When compared
to the source population, the introduced population had a higher rate of population growth. Coupled with the improved population
growth, heavy leaf damage during the larval period suggested that intensive intraspecific competition was most likely to occur
among larvae in the introduced population. 相似文献
17.
An individual-based model forDrosophila is formulated, based on competition amongst larvae consuming the same batch of food. The predictions of the model are supported
by data for single speciesDrosophila populations reared in the laboratory. The model is used to build a simple discrete model for the dynamics ofDrosophila populations that are kept over a number of generations. The dynamics of a single species is shown to give either a stable
equilibrium or fluctuations which can be periodic or chaotic. When the dynamics of a species in the absence of the other is
periodic or chaotic, we found coexistence or two alternative states, on neither of which the species can coexist. 相似文献
18.
Summary Spatial distribution pattern of the brown planthopper (BPH) was analyzed at 9 experimental fields in the northern part of
West Java during two consecutive rice cropping seasons, i.e., wet and dry seasons.
The population of each developmental stage and wing form of BPH at each location showed consistent departure from the random
(Poisson) distribution, the variances of the densities in most cases exceeding their means. Namely, the distribution pattern
of BPH per hill of rice plant was found to have a general tendency to be aggregated or contagious and to fit fairly well to
the negative binomial model. The tendency for aggregation was further confirmed by both the β-values of
-m regression being larger than unity and theC
A
-values being larger than zero for each developmental stage.
Although significant variations in the distribution pattern as measured by β- orC
A
-value were observed between different developmental stages, between wing forms and among locations, the degree of aggregation
for a given developmental stage at each experimental field remained fairly stable throughout the crop period, despite wide
temporal changes in population density.
Possible factors to explain these characteristics of the spatial distribution pattern of the BPH in West Java were discussed
with reference to the process generating it. 相似文献
19.
Summary Populations of the two-spotted spider mite,Tetranychus urticae Koch collected from various localities and from various host plants in Japan showed wide variations in diapause attribute.
Diapause percentages at 18°C/9L15D varied from nearly 100% in the north to 0% in the south-west. At intermediate latitudes
the mites showed wide inter-population variations. Populations on herbaceous hosts in vinyl- or glass-houses gave significantly
lower incidence of diapause than those on roses and deciduous fruit trees. Presence of winter hosts and better host quality
under protected environments seemed to favour non-diapausing mites.
The temperature threshold for diapause expression also varied widely among local populations. Northern populations consistently
had higher and less variable thresholds than populations at intermediate latitudes with thresholds between 15 and 18°C. Inbred
lines derived from a population in Kyoto exhibited a wide variation in diapause percentage at 18°C. These results show that
diapause inT. urticae is a quantitative threshold trait and that populations in central Japan consist of a variety of genotypes with different
diapause traits. This might provide a genetic source for adaptation to local and temporal variations in environmental conditions. 相似文献
20.
Naota Ohsaki 《Researches on Population Ecology》1980,22(1):163-183
Summary Utilization of patchy habitats by adult populations of threePieris butterflies,P. rapae, P. melete andP. napi was studied throughout the flight season in an area of their coexistence, about 3×1.5 km, in a farm village in the mountains
in Inabu, Aichi Prefecture. Field study was by the mark-recapture method. Results were analyzed by dispersal distances and
recapture duration decay curves for adults of different age-classes estimated on the basis of physical condition of their
wings, together with supplementary information of daliy egg-laying rate of females, obtained in field cages.
Sexually immature, mated femals ofP. rapae after teneral stage showed a migratory flight. On the other hand, reproductive females and all males ofP. rapae were strongly resident within suitable habitats, and reproductive females begun to lay eggs abundantly at sunny places of
newly suitable areas within a short period.P. melete seemed to disperse gradually from emerged stites and females of this species continued to lay some constant numbers of eggs
for more than ten days over a wider area.P. napi appeared more likeP. melete thanP. rapae.
The habitats of the three species can be characterized as follows:P. rapae, temporary, continued for pre-reproductive females but localized for reproductive females and all males, and unstable;P. melete, permanent, widespread, and stable;P. napi, permanent, localized, and stable.
The numbers of generations ofP. rapae, P. melete andP. napi were estimated to be about six, three and three, respectively. Seasonal fluctuations in the number of adults were influenced
by the stability of their habitats, i. e., the population size fluctuated sharply inP. rapae, but it was much more stable inP. melete andP. napi. In view of these results, it can be said thatP. rapae fits the general characteristics of a r-strategist whereasP. melete andP. napi are more K-strategic thanP. rapae. 相似文献