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81.
中国九个人群耵聍的遗传多态性 总被引:6,自引:2,他引:4
报道了九个人群的耵聍位点基因。计算表明中国各族人群在耵聍位点上的遗传分化程度非常大,固定指数F_(ST)=0.22。本文根据耵聍基因频率在我国和邻近地区的分布趋势,认为亚洲东北地区应是干型基因的起源地,目前世界上耵聍位点基因频率分布格局主要是基因扩散的结果,而非选择作用造成的。 相似文献
82.
运用聚丙烯酰胺凝胶等电聚焦(PAGIF)和免疫吸引技术,研究了3个地区汉族人群的C6多态性。得到的基因频率如下:漳州市——C6*A:0.4634、C6*B:0.5000、C6*R:0.0366(C6*B2:0.0317);成都市——C6*A:0.4975,C6*B:0.4484,C6*R:0.0545(C6*B2:0.0395);哈尔滨市——C6*A:0.4708,C6*B:0.5219,C6*R:0.0073(C6*B2:0.0073)。蒙古人种的C6*A频率一般都低于0.5,高加索人种的C6*A频率一般都高于0.6。黑人则介于两者之间。蒙古人种与高加索人种的另一个区别在于前者的C6*B2频率在0.03到0.07之间,而后者几乎没有C6*B2。 相似文献
83.
Cannibalism as a life boat mechanism 总被引:2,自引:0,他引:2
Under certain conditions a cannibalistic population can survive when food for the adults is too scarce to support a non-cannibalistic population. Cannibalism can have this lifeboat effect if (i) the juveniles feed on a resource inaccessible to the adults; and (ii) the adults are cannibalistic and thus incorporate indirectly the inaccessible resource. Using a simple model we conclude that the mechanism works when, at low population densities, the average yield, in terms of new offspring, due to the energy provided by one cannibalized juvenile is larger than one. 相似文献
84.
Synopsis We present ways to test the assumptions of the Petersen and removal methods of population size estimation and ways to adjust
the estimates if violations of the assumptions are found. We were motivated by the facts that (1) results of using both methods
are commonly reported without any reference to the testing of assumptions, (2) violations of the assumptions are more likely
to occur than not to occur in natural populations, and (3) the estimates can be grossly in error if assumptions are violated.
We recognize that in many cases two days in the field is the most time fish biologists can spend in obtaining a population
estimate, so the use of alternative models of population estimation that require fewer assumptions is precluded. Hence, for
biologists operating with these constraints and only these biologists, we describe and recommend a two-day technique that
combines aspects of both capture-recapture and removal methods. We indicate how to test: most of the assumptions of both methods
and how to adjust the population estimates obtained if violations of the assumptions occur. We also illustrate the use of
this combined method with data from a field study. The results of this application further emphasize the importance of testing
the assumptions of whatever method is used and making appropriate adjustments to the population size estimates for any violations
identified. 相似文献
85.
Microgeographical variation in shell morphology of the rock-dwelling land snail Chondrina clienta , collected from 30 sites within an area of 0.5 km2 on the island of Öland, Sweden, was examined in relation to its own population density and that of a potential competitor (the land snail Balea perversa ) and to environmental factors. Dispersal of marked individuals averaged 83 cm per year within a stone pile and 291 cm in an area of exposed bedrock. Local population density of active C. clienta ranged from 5 to 794 individuals per m2 . Shell characters were highly intercorrelated, both within and between populations. Principal component analysis revealed that most of the interpopulational variation could be expressed by the single character of shell height, which ranged from 5.54 to 6.94 mm. In all populations, snails of a given size had the same whorl number. Shell size was not influenced by habitat type (exposed rock surface, stone pile or stone wall) or proportion of calcareous stones within habitat. It was, however, negatively correlated with local population density, indicating intraspecific competition, and positively correlated with the degree of plant cover within the habitat. Analysis of variance revealed additionally a density effect of B. perversa on shell size in C. clienta , probably as a result of interspecific competition. Breeding experiments using C. clienta from different sites and carried out under unifrom conditions caused most of the phenotypic variation to disappear, demonstrating the high phenotypic plasticity of the species. 相似文献
86.
蚤数量与宿主数量关系 总被引:9,自引:5,他引:4
无论在自然条件下或在人为条件下,蚤指数和染蚤率的高低与宿主密度的高低是一致的.宿主密度的升降,会导致其寄生蚤指数和染蚤率的升降. 本文讨论了宿主数量下降导致其寄生蚤数量下降的原因,仅是分析推测,提出几方面的看法. 相似文献
87.
Effects of early adult experience on host selection in insects: Some experimental and theoretical results 总被引:2,自引:0,他引:2
John Jaenike 《Journal of Insect Behavior》1988,1(1):3-15
A field experiment with Drosophila melanogasterrevealed that when flies encounter a particular food type soon after emergence, the probability of their subsequently being attracted to such a resource is increased. In this experiment, the length of time flies experienced their postemergence environments was under the control of the flies themselves. The experiment thus realistically mimicked one form of experiential effect that may be important in nature. A theoretical model is developed which shows that enhanced adult preferences for the types of resources fed on as larvae can substantially increase the degree of host-based genetic subdivision within a polyphagous population. 相似文献
88.
Absract Three pedicellate-declinate-flowered species of Trillium (Liliaceae), T. vaseyi and T. flexipes , were studied for their life history characteristics, e.g., stage class structures of natural populations and reproductive features, including energy allocation to reproductive activities. The populations structures of all three species showed similar depletion structures characterized by a conspicuous decrease of individuals in the small juvenile stages, as was also observed in pedicellate-erect-flowered Trillium species However, with respect to reproductive characteristics, these three declinate-flowered species showed different features from erect-flowered species, although they belong to the same pedicellate-flowered group. That is, these declinate-flowered Trillium species exhibited low seed setting rates of 30% in T. catesbaei , 45% in T. vaseyi and 34% in T. flexipes , suggesting that they possess different mating systems from erect-flowered species which showed high seed setting rates of 50–90%. 相似文献
89.
Nobuhiko Ohga 《Ecological Research》1992,7(3):341-353
Herbaceous lomas in the Peruvian coastal desert, of South America establish in spring, and its habitat is limited to the southern
or southwestern slopes along the coast that are affected by thick fog. The time of appearance, the duration and the thickness
of the fog vary greatly from year to year, so the lomas can grow only in habitats with enough water to, sustain seed germination
and plant growth. This paper studies the species composition and density of the buried seed population, of the herbaceous
lomas of Loma Ancon in order to clarify the mechanisms of the lomas' establishment. The mean number of species with viable
seeds was about, 12 spp. m−2 and that of dead seeds was about 22 spp. m−2. The dominant species wereSolanum tuberiferum, S. pinnatifidum andNolana humifusa, both in viable and dead seeds. Viable seed density was about 5000–8000 seeds m−2, which is comparable with the seed densities of other herbaceous communities. Dead seed density was about 15000–27000 seeds
m−2, or nearly three times the viable seed density, because the rate of decomposition was slow in the extremely dry conditions.
The net increase of viable seeds by seed production was estimated at about 5000 seeds m−2 in 1980, and the increase in the number of dead seeds was 2200 seeds m−2. 相似文献
90.
Estimates of gene flow, genetic substructure and population heterogeneity in bracken (Pteridium aquilinum) 总被引:1,自引:0,他引:1
PAUL G. WOLF ELIZABETH SHEFFIELD F.L.S. CHRISTOPHER H. HAUFLER 《Biological journal of the Linnean Society. Linnean Society of London》1991,42(4):407-423
Bracken [ Pteridium aquilinum (L.) Kuhn] is a cosmopolitan species and is a noxious weed in many areas. Because of its abundance, particularly in Britain, bracken affords an ideal system for investigating various aspects of population genetics and evolution. High mobility of dispersal units (spores) suggests that rates of gene flow among distant populations should be high. Gene flow is a major evolutionary force that influences the genetic structure of populations. To examine the effects of gene flow on population heterogeneity and population substructuring in bracken, starch gel electrophoresis of enzymes was used to provide the necessary genetic database. Allele frequency data at 21 loci were obtained for seven British populations, one Majorcan and one from the eastern United States. A model was employed to estimate the amount of gene flow ( Nm ) at several levels. Gene flow among British populations was extremely high ( Nm = 36.51), one of the highest estimates reported for plants. Among eight European populations gene flow was lower (but still considered high) at Nm = 2.47. Trans-Atlantic gene flow was low ( Nm = 0.0926).
F -statistics were used to assess population heterogeneity and substructuring. The data indicate that, compared with other species, there is very little genetic differentiation among British populations of bracken. Indeed, it appears that the whole island is behaving as a single randommating population. This result is consistent with high levels of gene flow. Only one population (on the Isle of Arran) showed statistically significant genetic substructuring. Habitat heterogeneity on the island and age structure are hypothesized as possible causes of this result.
The data reported here support previous studies demonstrating that bracken is genetically polymorphic and is an outcrossing species. 相似文献
F -statistics were used to assess population heterogeneity and substructuring. The data indicate that, compared with other species, there is very little genetic differentiation among British populations of bracken. Indeed, it appears that the whole island is behaving as a single randommating population. This result is consistent with high levels of gene flow. Only one population (on the Isle of Arran) showed statistically significant genetic substructuring. Habitat heterogeneity on the island and age structure are hypothesized as possible causes of this result.
The data reported here support previous studies demonstrating that bracken is genetically polymorphic and is an outcrossing species. 相似文献