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1.
Tatsuto Kajimura I Nyoman Widiarta Kazuya Nagai Kenji Fujisaki Fusao Nakasuji 《Researches on Population Ecology》1995,37(2):219-224
The reproduction ofSogatella furcifera was investigated in a chemically fertilized rice field and an organically farmed field. In the latter, the density of immigrants
was significantly higher, while the settling rate of female adults and the survival rate of immature stages of ensuing generations
were lower. The number of eggs laid by a female of the invading and following generations was smaller, and the percentage
of brachypterous females in the next generation was also lower. Consequently, the density of nymphs and adults in the ensuing
generations decreased in the organically farmed field. For an experimental comparison, potted rice plants were cultivated
using seedlings and soil from the chemically fertilized or the organically farmed fields. WhenSogatella furcifera was reared on these plants, both the reproductive rate and the appearance rate of brachypterous female adults were lower
in the organic treatment. Egg hatchability was also lower in the organic treatment. This experiment suggested that a specific
nutritional condition in rice plants suppressed the population ofS. furcifera in the organically farmed field. 相似文献
2.
I Gusti Ngurah Aryawan I Nyoman Widiarta Yoshito Suzuki Fusao Nakasuji 《Researches on Population Ecology》1993,35(1):31-43
Summary Population dynamics ofNephotettix virescens was studied in 17 paddy fields transplanted at intervals of about 1 month in 1988–1990. The adult density was highest either
in the immigrant or the 1st generation and sharply decreased to the 2nd generation. The survival rate of the 1st generation
was lowest in the transition season when areal population density increased. Key factor analysis revealed that the nymphal
and adult mortality of the 1st generation (kn) was the principal source of population fluctuations. No significant correaltion
was found between kn and natural enemy density, natural enemy density/healthy egg density, or the precipitation during the
nymphal period. On these bases adult emigration was suspected to be the key factor. Areal population build-up ofN. virescens in the transition season was considered to occur as a result of increasing immigration to young stages of rice.
Contribution from Indonesia-Japan Joint Program on Food Crop Protection (ATA 162), which was implemented by the Directorate
of Food Crop Protection, Ministry of Agriculture, Indonesia and Japan International Cooperation Agency, Japan. 相似文献
3.
I Nyoman Widiarta Kenji Fujisaki Fusao Nakasuji 《Researches on Population Ecology》1991,33(2):257-267
Summary The three year (1988–1990) life tables ofNephotettix cincticeps were constructed, and the daily survival rate and longevity of female adults were estimated by Hokyo and Kiritani’s (1967)
method for the overwintering and the first-generations on the foxtail grass in Okayama, southwestern Japan. The life tables
and the population parameter values estimated were compared with those in the other generations on rice. The FARMCOP suction
sampler was employed to survey the population density.
The durations of pre-ovarial maturation of female adults of the 1st generation on foxtail grass and rice seedling were similar.
Longevity of adults of the overwintering and the first generations which emerged on the wild host was longer than that of
the other generations (2nd and 3rd generations) on the rice plants. Fecundity of females decreased successively as the generation
proceeded and it became lowest in the final 3rd generation.
Only about 3.5 percent of first-instar nymphs of the 1st generation emerged as adults in the fallow field. The survival rate
of nymphs on foxtail grass was always lower in comparison with that on rice plants. However, the survival rates of nymphs
on foxtail grass and rice seedling were not significantly different from each other under laboratory conditions. In the fields,
senescence of foxtail grass occurred in the midst of nymphal period of the 1st generation. The survival rate of nymphs on
foxtail grass decreased with the increasing in the nymphal density. Abundance of spiders during the 1st generation was higher
than that in the early stage of rice plants. 相似文献
4.
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
5.
Demographic attributes of the adults of an introduced herbivorous lady beetleEpilachna niponica (Coleoptera: Coccinellidae) were investigated from 1975 to 1981 in the Botanical Garden of Kyoto University. Population growth
rate varied from 4.8 to 16.8 throughout the study period. Fecundity and mortality in the late larval period contributed most
to annual changes in the population growth rate. Population growth rate was negatively correlated with the density of overwintering
adults. Adult survival from emergence to the reproductive season, which varied from 0.03 to 0.36 throughout the study, was
almost completely determined by survival during the pre-hibernation period. Adult survival to the preproductive season changed
in a size- and sex-dependent manner. Larger adults survived better than smaller individuals; male-biased mortality occurred
from adult emergence to the reproductive age. Severe intraspecific competition among late instar larvae due to host plant
defoliation produced a higher proportion of small-sized adults, resulting in lower adult survival to hibernation. The introduced
population had a higher population growth rate and a lower adult survival to the reproductive season than the source population. 相似文献
6.
Somchai Isichaikul Koichi Fujimura Toshihide Ichikawa 《Researches on Population Ecology》1994,36(1):23-28
Nymphs ofNilaparvata lugens were experimentally reared from the 2nd instar in a cage covering part of the leaf sheath of an individual rice plant grown
in a Wagner pot. Plants were covered with the cage from the water surface of the pot to 10 cm above the surface (lower cage-group)
or from 10 cm to 20 cm above the surface (upper cage-group). Temperatures measured at three different parts of the cage remained
fairly constant in both groups at around 25°C (23.7–25.2°C in mean value). In the lower cage-group, relative humidities measured
at the three heights in the cage in (76.3–90.5% in mean value) markedly increased with the approach to the water surface.
The nymphs of this group, particularly during the molting period, aggregated close to the surface. Eighty-two percent of the
released nymphs emerged in this group. Relative humidities measured at three heights of the upper cage-group were 69.5–72.7%
in mean value, and all the nymphs in this group died within 3 days after their release although half of them stayed on the
rice plants within 6 h after their release. The role of relative humidity as a limiting factor on the range of the microhabitat
and the population density ofN. lugens in rice fields was discussed on the basis of the results. 相似文献
7.
The cyclically stable population relaxes the stable population assumption of fixed vital rates and replaces it with the assumption of a recurring sequence of schedules of vital rates. From any point (or stage) in one cycle of the sequence to the same stage in the next cycle, the cyclically stable population grows at a constant rate (λ). While the age composition of the cyclically stable population is different at different stages of the same cycle, it always has the same age composition at the same stage of every cycle. The essential dynamics of the cyclically stable model are captured by its birth projection matrix (BPM). The dominant eigenvalue of the BPM is growth rate A, and the right eigenvector associated with λ gives the within cycle‐birth sequence. An important special case occurs when λ = 1, and a cyclically stationary population arises. Such populations challenge simplistic ideas about “Zero Population Growth.”; A population projection based on the sets of rates observed in the United States, 1970–90, shows a cyclically stationary population arising in less than 100 years. While it experiences no long term growth, that cyclically stationary population exhibits fluctuations in total size and considerable variability in age structure. 相似文献
8.
Beaujot RP 《Population bulletin》1978,33(2):1-48
In Canada the current 1.3% population growth rate is causing some concern. Those concerned argue that such a rate of growth in combination with high levels of consumption could jeopardize the country's resource base and its comfortable style of living. Many Canadians are questioning high levels of immigration, for now that the fertility level is below replacement level, net immigration contributes substantially to population growth (over 1/3 in 1976). The growing proportion of non-Europeans among recent immigrants is causing resentment, and, in a tight job market, immigrants are regarded as threats to the World War 2 baby boom cohort who are now at working ages. The baby boom generation also puts stress on housing and health services, and it will increase the need for pension checks as it ages. Although French fertility is no longer high and immigration is no longer dominated by the British, the French group's 200-year struggle to preserve its identity continues on in the current effort of the Quebec government to enforce the use of French language by law within that province. Geography and climate dictate another demographic fact that divides the country and pervades its history. In addition to intense regionalism, uneven population distribution is responsible for 2 other concerns: the rapid growth of several already large cities and depopulation of many small communities. Focus in this discussion is on Canada's population growth in the past and as projected for the future, historical and current fertility, mortality and immigration trends, the search for a new immigration policy, the impact of the baby boom generation on the population's age structure and the problems this creates, and recent shifts in population distribution and in the country's ethnic and linguistic makeup. The population policy proposals evolved thus far involve to a great extent the use of immigration as a lever for achieving given population objectives. 相似文献
9.
Summary Microhabitat of the nymphs and the adults of the rice brown, planthopper,Nilaparvata lugens is known to be the lower parts of rice plants. In this study, possible environmental factors determining the range of the
microhabitat were experimentally analyzed by using the nymphs under laboratory conditions. Thirty individuals of the 1st or
the 3rd instar nymphs were released to a potted rice plant covered with a transparent acrylic cylinder. When the top of the
cylinder was kept opening (open condition), the temperatures in the cylinder were almost constant, and relative humidities
in the cylinder decreased with the increase of the height from the water surface of the pot. In the open condition, most nymphs
and all exuviae were found on the basal parts of rice plants where the humidity was more than ca. 90% r.h. When the top of
the cylinder was kept closing with parafilm (closed condition), the temperatures in the cylinder were almost constant, and
relative humidities in the cylinder were more than 95% r.h. In the closed condition, the nymphs and the exuviae were distributed
sparsely to the whole parts of rice plants. In both of the open and the closed conditions, patterns of nymphal distributions
on rice plants during the dark regime were the same as those during the light regime under 25±2°C and 16L∶8D. Four different
temperatures ranging from 20°C to 35°C did not influence on the microhabitat in the open condition. It was concluded from
the results that relative humidity is the important environmental factor to determine the microhabitat of the nymphs ofN. lugens which showed to prefer very humid condition more than ca. 90% r.h. 相似文献
10.
Hiroichi Sawada Ayi Kusmayadi S. W. Gaib Subroto Edi Suwardiwijaya Mustaghfirin 《Researches on Population Ecology》1993,35(1):113-137
Summary Population dynamics of the brown planthopper (BPH),Nilaparvata lugens St?l, were investigated in paddy fields in the coastal lowland of West Java, Indonesia, where rice is cultivated twice a
year, in the wet and dry cropping seasons. Distinct differences in the basic features of population dynamics were detected
between the two rice cropping seasons: (1) In the wet season, BPH populations multiplied rapidly in the period from initial
to peak generation, reaching quite often the destructive level despite the low density of initial immigrants. However, in
the dry season, the population growth rate and the peak population density were much lower than those in the wet season. The
abundance of natural enemies such as arthropod predators played a major role in determining such a difference in seasonal
population development. (2) The density at the peak generation or the occurrence of outbreaks in each field was predictable
in the wet season with fairly high accuracy on the basis of the density at the initial or previous seasonal generations. In
the dry season, however, the rate of population growth and the peak population density widely varied among the fields depending
on the water status in each field. (3) Density-dependent processes to regulate the population density were detected in both
cropping seasons. In the wet season, the regulatory processes were only detected in such high densities as cause the considerable
deterioration of host plants, which suggested that the processes were largely attributable to intra-specific competition.
In the dry season, however, the regulatory processes operated at a much lower density in the earlier stages of the crops.
The results of an analysis of adult longevity or residence period suggested that the density-dependent dispersal of macropterous
adults played an important role in stabilizing the population fluctuation among the fields in the early dry season. 相似文献
11.
Ronald Demos Lee 《Mathematical Population Studies》2013,20(3):265-288
A simple model of Malthusian population growth combined with population‐induced technological progress generates accelerating growth. The model may be relevant for a first stage of growth in which natural resource limitations can be overcome through technological progress; it is not applicable to a later stage in which resource constraints are more resistant. Parameter values are roughly inferred from historical experience. Exogenously more rapid population growth initially depresses income, perhaps for up to several centuries, then raises it without limit. More rapid population growth is desirable only when the social discount rate is less than the ratio of the parameters for induced technical progress and static diminishing returns. Imposed population fluctuations cause inverse movements in incomes, so that induced progress is very difficult to detect empirically even for population fluctuations up to 500 years. 相似文献
12.
I Nyoman Widiarta Yoshito Suzuki Hiroichi Sawada Fusao Nakasuji 《Researches on Population Ecology》1990,32(2):319-328
Summary The population dynamics ofNephotettix virescens, a vector of rice tungro virus disease was investigated in a synchronized transplanting area at Jatisari (1984–1986), West
Java and in a staggered transplanting area at Sidan (1986–1988), Bali, Indonesia. The FARMCOP suction sampler was employed
for population censuses ofN. virescens and its natural enemies. The population growth pattern was affected by transplanting pattern: In the staggered transplanting
area, the population density increased from the immigrant generation to the first generation, and sharply decrease thereafter,
while in the synchronized transplanting area the population density often reached the highest peak in the second generation.
The degree of contageousness in the spatial distribution ofN. virescens was negatively correlated with population density of the immigrant generation.
Contribution from Indonesia-Japan Joint Program on Food Crop Protection 相似文献
13.
This paper examines the long-term impact of constant immigration on the dependency ratio in an SI population (a stationary population through constant immigration) in the context of the stable population model. Our analysis has three main findings. First, in SI populations, a younger population (a lower aging ratio) does not necessarily have a lower dependency ratio. An SI population has a lower dependency ratio than a closed stationary population, provided immigration is concentrated around the youngest working age in the host population. Second, under the same condition, selecting high-fertility immigrants increases the dependency ratio. Third, also under the same condition, substituting working-age immigrants with young (dependent) immigrants increases the dependency ratio. Using the United Nations model age structures of immigrants, our empirical illustration confirms these analytical results. 相似文献
14.
Gendell M 《Population bulletin》1980,35(2):1-44
In this discussion of Sweden as it approaches zero population growth, focus is on the following: population growth in perspective, fertility trends (childbearing concentrated and cohort versus period fertility), marital status (non-marital cohabitation, out-of-wedlock births, and divorce), women's changing status (increasing education and increasing employment), constraints and supports for women's dual role (family allowances and housing), birth control (contraceptive methods and practice and abortion), mortality trends, changing age structure and the elderly (average population age and proportion of elderly and cost of elderly support), international migration (from emigration to immigration and demographic impact of immigration), immigration policy, recent population debate (immigration issues and facing zero population growth). Since 1900 the primary features of Sweden's demographic history are a continuing decline in the birth rate to very low levels -- relieved by some upward movement in the 1940s and 1960s -- and a marked shift in the migration balance from emigration to immigration. It is almost entirely because of immigration that Sweden's population growth rate has not yet turned negative. If Swedish women were to continue to bear children at the rate that all women in the reproductive ages actually did in 1978, each women would end up with an average well below the level necessary to exactly replace each adult in the population leaving migration out, an annual total fertility rate of 2.1 children per woman would have to be sustained for births and deaths to be in balance under the low mortality conditions prevaling in Sweden. 相似文献
15.
This paper reports on work aimed at extending stable population theory to include immigration. Its central finding is that, as long as fertility is below replacement, a constant number and age distribution of immigrants (with fixed fertility and mortality schedules) lead to a stationary population. Neither the level of the net reproduction rate nor the size of the annual immigration affects this conclusion; a stationary population eventually emerges. How this stationary population is created is studied, as is the generational distribution of the constant annual stream of births and of the total population. It is also shown that immigrants and their early descendants may have fertility well above replacement (as long as later generations adopt and maintain fertility below replacement), and the outcome will still be a long-run stationary population. 相似文献
16.
Population Reference Bureau PRB 《Population bulletin》1982,37(2):1-51
This Bulletin reviews recent trends in the dynamics and character of the U.S. population, the outlook for the remainder of the 1980s, and prospects for longterm growth. Estimated at 232 million as of mid-1982, the U.S. population is currently growing at about 1% a year, one of the developed world's highest growth rates. Natural increase (births-deaths) still adds some 1.7 million people a year, despite the rapid postbaby boom fall in fertility to a near-record low rate of 1.9 births/woman in 1981. With increasing numbers of refugees, net legal immigration averaged 600,000/year in 1979-81 and the net inflow of illegal immigrants may now be 500,000 a year. Uncertainty over potentially large numbers of immigrants complicates projections of future U.S. population size. Currently, the U.S. death rate is at an alltime low. More than 1/2 the population now resides in the South and West. Rural areas and small towns grew faster than urban areas in the 1970s for the 1st time in over a century. Educational attainment is at an alltime high, as is labor force participation, due to increasing employment among women and the baby boom generation's arrival at working ages. The age composition of the population, with the bulge of the baby boom generation surrounded by the older "depression" generation born during the 1930s and the younger "baby bust" generation born since the end of the 1960s, presents special problems for U.S. society. 相似文献
17.
Izumi Washitani Yasushi Okayama Keiko Sato Hitomi Takahashi Takayuki Ohgushi 《Researches on Population Ecology》1996,38(2):249-256
Antagonistic biological interactions with flower consumers and pathogens may influence reproductive success of flowering plants,
affecting population dynamics and natural selection for floral traits. However, ecological and evolutionary consequences of
the interactions may depend on both spatial and temporal patterns of the interactions. In a forest metapopulation ofPrimula sieboldii E. Morren, an endangered clonal plant species, we measured between-subpopulation patterns of seed sets and interactions with
an influential flower consumer, a rove beetle,Eusphalerum bosatsu Watanabe, and a specific smut fungal pathogen,Urocystis tranzschelina (Lavrov) Zundel (Ustilaginales), for three years. Mean female fertility (seed set per flower) for individual subpopulations
fluctuated moderately among years but was highly variable within each year among the five subpopulations studied. In two subpopulations,
the impact ofEusphalerum beetle, was sufficiently large to result in almost complete failure in seed production over eight years including the three
study and five previous preliminary observation years. In the two other subpopulations, seed set failure was caused by infection
by the smut fungus. Infected capsules which constitute 10–30% of the capsules produced in the subpopulations were filled with
ustilospores instead of seeds. In the subpopulation that escaped flower damage byEusphalerum beetles and smut fungal infection, seed sets of both pin and thrum flowers were much higher than in the other subpopulations.
The spatial restriction of individual antagonistic agents to a part of subpopulations suggest that dispersal of the agents,
as well as the mode of spatial subdivision of the plant population would be important for determining the overall effects
of antagonistic interactions on plant performances at the metapopulation level. 相似文献
18.
引进外来移民是俄罗斯摆脱人口危机的现实途径之一。对引进中国劳动移民的利弊问题,俄学者对此看法各异,伴随着俄经济形势的好转,大多数俄学者肯定了中国移民对俄罗斯经济发展的作用,并提出形成完善的移民政策、引入适当数量的移民、避免非法移民流入及民族间冲突是解决俄罗斯人口危机和保证国家安全的有效方法。 相似文献
19.
The relation of the within-season and between-season patterns of shoot growth were compared in a clonal grass with long-lived
shoots,Festuca rubra, in a mown mountain grassland. The growth rate of shoot length from spring to summer in a year was almost constant for each
shoot irrespective of spring shoot length each year. The annual shoot growth rate from spring to spring was negatively correlated
with the shoot length in the first spring. Shoots of different length and age therefore tended to converge over time to a
population of identical shoot size, suggesting an equalizing effect of growth pattern on size structure. Shoot size (shoot
length and number of leaves) influenced the fates of shoots. Larger shoots showed an increased incidence of both flowering
and formation of intravaginal daughter shoots and a decreased incidence of death in the subsequent time period. The fates
of shoots were independent of their age. Although the negatively size-dependent springto-spring annual shoot growth rate acted
to decrease shoot size variation, the remaining variation within the shoot population was still sufficient to generate different
fates of shoots. These fates were not related to the previous life history of individual shoots. There was a significantly
positive effect of the shoot size at initiation on its life expectancy. This was mainly attributable to the positively size-dependent
survival rate of shoots in the early stage (<1 year old) of shoot life history. Later on (> 1 year old), shoot size had little
effect on the survival rate of shoots. Once small young shoots have survived this early stage (< 1 year old) in life history,
they can grow vigorously, little affected by competition regardless of shoot size, and converge to a stable size structure
of shoots of similar size. Only shoot size in the early stage ( < 1 year old) of life history is important for the persistence
of a shoot population. 相似文献
20.
Tim Futing Liao 《Mathematical Population Studies》2013,20(3-4):217-229
There has been public concern about the effect of immigration on population growth in the U.S. But how responsive is population growth to immigration? This paper examines the sensitivity of intrinsic population growth to immigration and situates such sensitivity in fertility and survival changes. The application of second derivatives on a modified Leslie matrix facilitates the analysis of situational sensitivity of U.S. population growth to immigration. The results show that the sensitivity to immigration is not as influential as the sensitivity to fertility, and that the sensitivity to immigration further depends on changes in fertility and survival. 相似文献