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61.
Mutsunori Tokeshi 《Population Ecology》1992,34(2):249-273
Theoretical and analytical problems of the dynamics of distribution and abundance in animal communities were examined. In many communities, species with low abundance and of limited spatial occurrence (i.e., rare species) typically form a conspicuous peak when a frequency distribution of the number of species is constructed with respect to the proportion of sites occupied within an area of distribution. Models of distribution dynamics, including a new model proposed here, were compared with a range of animal community data using a new procedure to assess single- and bi-modal patterns in frequency distributions of spatial occurrence. Data reveal that single-modality with an excess of rare species occurs more frequently than bimodality. Even when bimodality is detected, the mode representing wide-spread species is in the majority of cases smaller than that for rare species. Thus, a new model in which the rate of local extinctions is assumed to be negatively related to patch occupancy (or population abundance) is in better agreement with observed data than earlier models. Some problems of analysis, in particular model assumptions and testing, are discussed. 相似文献
62.
B. K. Sharma 《Hydrobiologia》1990,199(1):29-33
Nine species and subspecies of the genus Testudinella are reported from North-Eastern India. Of these, six are new to India and eight to the North-Eastern region. Remarks are made on their distribution. 相似文献
63.
64.
H. Nthel 《Mutation research》1981,84(2):291-304
In earlier work, immature oocytes of the irradiated population RÖI4 of Drosophila melanpgaster were found to be radioresistant relative to those of the basic population RÖI and to those of the control population Berlin wild (+K). The resistance of RÖI4 relative to RÖI was previously attributed to a hypothetical “factor” rar-3. In the present paper, evidence is presented to show that rar-3 is a single, recessive genetic factor, located on chromosome 3 at a map position of about 49.8. The action of rar-3 is apparently independent of that of rar-1 and rar-2, the factors already present in RÖI. 相似文献
65.
Oxygen availability,redox and the distribution of some Turbellaria Schizorhynchidae and other forms 总被引:3,自引:3,他引:0
Patrick J. S. Boaden 《Hydrobiologia》1981,84(1):103-112
Records from a considerable number of meiofaunal samples are reexamined in relation to the depth within sediment distribution of various taxa especially Schizorhynchidae and the main turbellarian orders.Frequency and density records in samples with particular oxygen flow rates and redox potentials confirm that the ranges of Schizochilus, Proschizorhynchus and Neoschizorhynchus spp. within these factors may help account for congeneric occurrence within cores. However, statistical analysis of the records is seldom able to confirm apparent differences. There is, for example, a statistically significant difference in distribution in relation to redox potential between the red schizorhynchians Pseudoschizorhynchides ruber, Diascorhynchus rubrus and the red acoelan Paratomella rubra but not in relation to oxygen availability and depth within sediment. On one beach Gnathostomula aff. paradoxa was found at Eh and O2 availability values under which it must be assumed to be living anaerobically.Contingency and other analyses are extended to differences between higher taxa and the results discussed in relation to habitat evolution of the Turbellaria. The suggestion that structural complexity of turbellarians has increased with increased oxygenation of the environment is tentatively supported. 相似文献
66.
This paper reviews the systematic status and geographical distribution of 30 odd species of freshwater calanoid copepods in Southeast Asia. Three regions are delineated based on the diversity and abundance of these organisms; Region I being the Southasiatic element, Region II the attenuated belt of copepods and Region III rich in endemic species. The implication of a north-south diminishing of copepod species to inland fisheries is postulated. 相似文献
67.
68.
H. Walter Lack 《Plant Systematics and Evolution》1979,131(1-2):35-52
Three species of the genusPicris L. are native in Tropical Africa:P. abyssinica
Sch. Bip. (Ethiopia),P. xylopoda
Lack, spec. nova (Nigeria, Ethiopia) andP. humilis DC. (Senegal, Mali). There are indications that the two perennial species,P. abyssinica andP. xylopoda, are related to and have evolved from a primitive Central Asiatic stock in a manner parallel to many African species ofCrepis L.P. humilis, on the other hand, is a small annual plant with a high number of derived characters. The introduced species of European origin growing south of the Sahara are briefly mentioned. 相似文献
69.
A remark on the shape of the logistic distribution 总被引:3,自引:0,他引:3