Population dynamic consequences of competition within and between age classes

We investigate the population dynamics of a semivoltine species whose juvenile development takes two years to complete, and is followed by a very short reproductive adult stage. Reproduction is synchronized so at any given time the juvenile population consists of two cohorts. Coexistence of the two cohorts requires that the strength of intea-cohort competition exceeds that of inter-cohort competition, an extension of the competitive exclusion principle. The population may exhibit population cycles with low integer period. We identify two mechanisms for two-year cycles, and note that four-year cycles are a natural consequence of overcompensation. Three year cycles can occur and we discuss the mechanisms involved.     

A genetic linkage map of Picea abies Karst., based on RAPD markers,as a tool in population genetics

Norway spruce (Picea abies Karst.) is a most important species among European forest trees for both economical and ecological reasons. However, this species has suffered from a lack of information on the genetic side due to the scarcity of linkage data. In this study we have used a population of 72 megagametophytes from a single tree in a natural Italian stand to produce a genetic linkage map by means of RAPD markers. Ninety-six random decamers used as primers yielded 185 polymorphic loci showing Mendelian inheritance. Analysis of the segregation by multipoint analysis allowed us to define 17 major linkage groups covering a total distance of 3584 cM, with an average spacing between markers of 22 cM. Possible uses of a genetic linkage map with respect to population ecology and genetics are discussed.     

A simple derivation of the partitioning of genetic differentiation within subdivided populations

The genetic differentiation within a subdivided population can be partitioned into two proportions, one due to differentiation within sub-populations and the other due to differentiation among subpopulations. A simple mathematical derivation of this procedure, known as Nei's G _ST -statistics, is presented. The significance of considering the differing relative sizes of subpopulations is stressed. Possible fields of applications for breeders and conservationists who are concerned with the establishment of genetically diverse populations are mentioned.     

A population analysis of Robertsonian and Ag-NOR polymorphisms in brown trout (Salmo trutta)

An analysis of Robertsonian polymorphism and variation in the number of active NORs has been carried out in several populations of brown trout (Salmo trutta) from Northwestern Spain. The karyotype of this species appears to be soundly established, and essentially no variation has been found in chromosome number. Interindividual and interpopulation variation in arm number was detected, with figures ranging between 100 and 102 among individuals, and between 100.10 and 100.80 among populations. This variation in arm number is solely attributable to the polymorphism of the short arm of the main NOR-bearing pair 11, which can appear from acrocentric to metacentric in different individuals. Most populations analyzed showed the standard distribution of active NORs previously observed in this species. The Miño drainage basin, and specially the Chamoso population, showed a multi-chromosomal distribution of active NORs, with several new locations, always telomeric. In most cases no concordance was observed between previously detected rDNA sites in S. trutta and the new Ag-NOR locations. This fact suggests a transposition mechanism rather than an activation of silent rDNA sites to explain this multichromosomal NOR pattern.     

Morphometric and DNA investigations into European water frogs (Rana kl. esculenta Synklepton (Anura, Ranidae)) from different population systems

The population specific variability of diploid and triploid R. kl. esculenta individuals was investigated by means of morphometric methods (canonical discriminant analysis, UPGMA cluster analysis) and DNA fingerprinting. As a result of the morphometric investigations, as well as of the DNA investigations, a clear separation of single populations was possible. However, no correlations between the morphometry and different population systems could be recognized. Clear morphometric differences could be seen between diploid ♀♀ and ♂♂ and triploid ♀♀ on the one hand, and triploid ♂♂ on the other. While the diploid ♀♀ and ♂♂ and the triploid ♀♀ were located in the intermediate area between the parental species R. lessonae and R. ridibunda according to their morphometric parameters, the triploid ♂♂ showed a great overlap with R. lessonae. Up to now, this phenomenon has not been explained. The first results of the DNA investigations provided further hints at the high inter-individual and population-specific variability of R. kl. esculenta. R. kl. esculenta individuals of the R. lessonae/esculenta population Toter See could be distinguished from conspecific individuals of the R. ridibunda/esculenta-♀♀ population Alte Oder according to their fingerprint patterns. Moreover, in the R. lessonae / esculenta population, the fingerprints or the diploid R. kl. esculenta-♀♀ and the investigated R. lessonae-♀ were very similar. Furthermore, in this population, many R. kl. esculenta genotypes resemble R. lessonae in their morphometric features. This finding suggests the occurrence of recombination in R. kl. esculenta. In general, every population seems to have its own genetic background. A classification of water-frog populations according to population systems is only possible under certain conditions.     

华中地区小家鼠生物学特性观察

华中地区农村小家鼠的个体较小,主要栖息于农舍,终年繁殖,繁殖高峰期为７月和８月,１－３月为繁殖低谷期;种群数量高峰在９月,低谷期在７－８月,冬季的种群数量水平较高,呈后峰型。在较高的密度条件下,雌鼠的怀孕率降低,性成熟延缓。     

Morphometric analysis of the genusHemerocallis L. (Liliaceae) in Korea

To better understand the patterns of variability and distributions ofHemerocallis in Korea, 53 locations were visited and measurements of 19 morphological and phenological characters were taken on plants directly from their natural habitats. For morphometric analysis, 10 plants from each of 34 populations and five herbarium specimens ofH. middendorffii were used and the data from 12 quantitative characters was analyzed using univariate analysis. Except the littoral populations of Cheju, Hong, Taehuksan, and Sohuksan Islands (H. hongdoensis M. Chung & S. Kang), three peninsular KoreanHemerocallis species can be recognized mainly in South Korea:H. hakuunensis Nakai (=H. micrantha Nakai, growing on southern, central, and northwestern Korea);H. thunbergii Baker (=H. coreana Nakai, found on southeastern and central Korea); andH. middendorffii Tr. et Mey. (central and northeastern Korea). Morphological and phenological features contributing to recognition of the three groups were; color of perianth, shape of roots, shape of inflorescence, flowering time, odor, length of inflorescence, width of the lowest bracts, length of perianth tube enclosing a ovary, width of the inner perianth lobes. Natural hybridization seems to be rare in KoreanHemerocallis. It appears that the KoreanHemerocallis species are relatively well characterized by their distribution patterns, phenology, and habitats compared with the JapaneseHemerocallis species.     

“8455”小麦植株化学成分与麦蚜（长管蚜、二叉蚜）种群消长的关系

通过对两种肥力条件下的“8455”小麦植株化学成分与麦长管蚜和麦二叉蚜种群消长关系的研究与分析,结果表明可溶性糖、含钾量、含水量是影响麦二叉蚜种群消长的主要因子,胱氨酸是影响麦长管蚜种群消长的主要因子。     

The regeneration niche of the grey mangrove (Avicennia marina): effects of salinity,light and sediment factors on establishment,growth and survival in the field

Field observations of seedlings and saplings of Avicennia marina showed patterns that correlated with salinity, light and sediment. Models that account for these observations were subsequently tested in a series of field experiments. Establishment varied within an estuary under controlled conditions but was not related to salinity or sediment type. Seedling survival was uniform over 3 years regardless of position in estuary and sediment type. Seedling densities and survival under canopies or in canopy gaps were not significantly different. However, seedling growth and density of saplings were greater in canopy gaps. Experiments involving manipulations of canopies showed no differences in seedling survival under canopies or in light gaps, but addition of slow-release fertilizer enhanced growth and survival in canopy gaps and under canopies. Long-term comparison of areas denuded of a canopy and with sediment disturbance showed enhanced establishment and survival when compared with areas with canopy gaps but with undisturbed sediments. Overall there appears to be no restriction to establishment of propagules within mangrove stands other than the supply of propagules and tidal or wave action. In contrast, recruitment to the sapling stage appears to be restricted by light and sediment resources. We suggest that propagules need to establish in a regeneration niche for seedling recruitment to the sapling stage. This differs from the view that seedlings in the under-storey are analogous to a seed pool in the soil.     

环境因子对荒漠沙蜥种群密度影响的研究

本文研究人类改造荒漠的活动,植被,潜在的可利用的食物资源,竞争种的密度,土壤理化性质等坏境因子对荒漠沙蜥种群密度的影响。结果说明：人类的活动对沙蜥种群密度没有显著影响;决定沙蜥种群密度的主导因子是潜在的可利用的食物资源,植被,土壤含水量,竞争种的密度。这些因子的任何改变都能改变沙蜥的种群密度,均具有调节种群的作用。