Population structure and dynamics of Pinus massoniana Lamb. on mount Jinyun,Sichuan, China

Masson Pine (Pinus massoniana Lamb.) is a pioneer in forest succession in the subtropics of East Asia. However, the species persits, though with decreasing abundance, throughout the various successional phases. Agestructure, spatial pattern, density, population biomass, and their dynamics are described for a population in Sichuan, China, on the basis of a census of all individuals in the population while substituting space with time. In the course of succession, the population density increases and its rate of growth decreases until self-thinning starts; during the phase of self-thinning density decrease and continues to decrease even afterwards, but the rate of growth increase markedly after self-thinning has stopped. The development of population biomass (Bp) during the early succession from shrub-grassland to the early stages of mixed pine and broad-leaved forest can be described by a logistic equation. Later, Bp decrease rapidly. These changes are governed partly by inherent biological features of P. massoniana and partly by the invasion, establishment and development of shade-tolerant evergreen broad-leaved trees. Both self- and alien-thinning occur. Soil conditions affect the rates of these processes.     

A preliminary study on quantitative relations among growth,reproduction and mortality in fishes

As a quantitative approach to the life histories of fishes, the present paper attempted to predict a relation among reproduction, growth and mortality numerically with a technique of control theory, the discrete maximum principle. A method for predicting the relation was derived on the postulate that natural selection maximized the net reproductive rate subject to a few constraints. The derived method was applied to Atlantic cod and Atlantic herring populations in the Southern Gulf of St. Lawrence as numerical examples. The examples demonstrated that the theoretical reproductive effort and body weight were well consistent with the observed ones every age but the theoretical survival rates were slightly different from the observed ones. For the reasons mentioned below, however, it should be interpreted that the examples rather support the adopted postulate to a certain degree. First, in general, it is very difficult to obtain good estimates of the rates with traditional methods. Second, intense fishing pressure possibly changes the life history parameters to some extent in fish populations. Moreover, the examples also suggested that, to examine the postulate in further detail, similar analyses had to be made with the data of many fish populations on which intense fishing pressure had not been exerted.     

Control of insecticide resistance in a field population of houseflies,Musca domestica,by releasing susceptible flies

Susceptible houseflies, Musca domestica, were released at a waste disposal site to control insecticide resistance in a field housefly population. In the first experiment, a total of 163,000 pupae of the susceptible Takatsuki strain were released in October–November 1977. LD₅₀ values to fenitrothion and diazinon decreased to about one-sixth in April 1978, five months after the releases, of those before the releases. For the second experiment, a susceptible colony was derived by cross and backcross between a white-eyed substrain of the Takatsuki and a field colony. This susceptible colony consisted of whiteeyed flies with low activity and normal-eyed flies bearing no or one white eye gene. The results of large cage experiments suggested that the normal-eyed males of the susceptible colony had half the mating competitiveness of wild males. Approximately 31,000–46,000 susceptible pupae were used in each of five releases from October to November 1980. The population number of each sex, estimated by a mark-release-recapture method, increased from 12,000 in late September to 35,000–43,000 in middle November and then decreased to 5,000–8,000 in early December. The frequency of field-collected males bearing one white eye gene and those bearing one male determining factor, which were characteristics of the susceptible colony released, increased gradually during the period of releases. The susceptibility of the field population to fenitrothion and diazinon was examined five times in the period from September to December 1980. With time, the dosage-mortality regression gradually shifted towards that of the susceptible colony after starting the releases. LD₅₀ values to fenitrothion and diazinon decreased to about one-sixth and one-fifth, respectively, in June 1981, six months after the second series of susceptible fly releases, of those before the releases. Ratios of the wild flies to the released fiies were estimated to be between 4.7∶1 and 9.8∶1 in males and between 3.0∶1 and 3.9∶1 in females by taking the quality of the released colony and the population parameters of the field houseflies into consideration. Under several assumptions, the manner of resistant phenotype reduction was discussed, based on the dosage-mortality regressions and the ratios of released flies. These results showed that the releases of susceptible flies were successful in suppression of insecticide resistance in the field housefly population.     

Associations between quantitative traits and enzyme loci in the F2 population of a maize hybrid

Summary Univariate and multivariate analyses were used to identify associations between eight enzyme marker loci and 11 quantitative traits of maize (Zea mays L.). The material analyzed included inbred lines Wf9 and Pa405, single-cross hybrid Wf9 X Pa405, and the F2 generation of the selfed single-cross hybrid. Each enzyme locus assayed was associated with at least one quantitative trait, and all quantitative traits were associated with genotypes at particular enzyme loci. Significant associations also were found between the level of heterozygosity per individual and nine of 11 quantitative traits. The total contribution to heterosis, for seed yield per plant, of genes linked with the eight enzyme loci, was 27% of the F2 mean and 18% of the difference in mean between the F1 hybrid and the inbred parents. Genes linked with Glu1 accounted for nearly one third of the total dominance effect detected by the eight enzyme loci. The chromosome segments marked by loci with significant effects on seed yield were markedly overdominant. The large heterotic effects of chromosome segments marked by particular loci suggest that enzyme loci could be used to help transfer genes responsible for heterosis to inbred lines. We conclude that analyses of additional inbred lines, F1 hybrids, and F2 populations in more environments will halp identify specific associations between enzyme loci, or chromosome segments which they mark, and important agronomic traits.Cooperative investigations of the USDA, ARS and Dept. of Plant Sciences, South Dakota State Univ. (SDSU), Brookings, Journal Series No. 2039; and the Institute of Animal Resource Ecology, Univ. of British Columbia, Vancouver, B.C. V6T 1W5, Canada     

Spatial relationship among individuals of the Japanese lacertidTakydromus tachydromoides (Sauria,Lacertidae)

The home range ofTakydromus tachydromoides was studied in a grassland area from April 1977 to November 1978. The mean size of home range did not differ markedly between sexes; 136.5 m² for males and 130.8 m² for females. Home ranges of adults overlapped greatly in each sex, and the lizard was considered to be non-territorial. Individuals showed return movement to a definite area (sleeping site) within the home range, and the home range did not shift within a year or between years. Characteristics of the home range of this grassland-inhabiting lizard were discussed in relation to resource abundance and predation pressure.     

Ecdysteroids in the haemolymph and the ovaries of the firebrat Thermobia domestica (Packard) (Insecta,Thysanura): Correlations with integumental and ovarian cycles

Ecdysteroids were analysed with radioimmunoassay (RIA) and high-performance liquid chromatography (HPLC) in females of the apterygotous insect Thermobia domestica, which ahs overlapping moulting and reproductive cycles. During each moulting cycle, a peak in the haemolymph concentration of ecdysteroids occurs at day 9 (in the 11-day standard cycle), which can be correlated with apolysis and the beginning of new cuticle deposition. The ovaries show a peak of ecdysteroids at day 5 (i.e. one day before egg-laying), which suggests that these hormones are also involved in the reproductive cycle. In both cases, HPLC analysis combined with RIA suggests that the main ecdysteroid is 20-hydroxyecdysone. This duality in the function of ecdysteroids is discussed.     

Regulatory processes and population cyclicity in laboratory populations ofAnagasta Kühniella (Zeller) (Lepidoptera: Phycitidae). III. The development of population models

1. Life table data for interactions between Anagasta kühniella and its ichneumon parasite Venturia canescens in two room ecosystems (A & B) have been analyzed in an attempt to explain and model each room situation. The life table data have been presented in the form of a graphical key-factor analysis, and have been further analyzed by an investigation of the density relationships between the different mortalities and the Angasta densities upon which the mortalities act.
2. In room A (1.2 gm food per container), the parasites were present throughout the interaction. Egg and early larval mortality (k₁) appeared to be directly density-dependent and was the sole stabilizing influence when introduced into the model for room A. The area of discovery of the parasite was relatively constant and its mean value was used to calculate parasitism (k₃) in the model. All other mortalities were density-independent and treated as being constant at their mean values. The model predicts a series of oscillations of decreasing amplitude which are somewhat similar to those observed in the Anagasta population during the early stages of the interaction. The observed mean densities of host and parasite were very close to those predicted.
3. In room B, the parasites were absent for the first 8 generations (1- 2gm food per container). Model B₁ covers this period and includes a direct density-dependent component describing changes in k₁, the remaining mortalities being constant. The observed mean densities approximate to the calculated densities. The parasites were present from the ninth generation and after the eleventh generation the food per container was increased to 7.2 gm. Model B₂ covers the period in room B from generation 11. The most important component of k₁ after the parasites were established is a delayed density-dependent one which appeared to be due to wounding of very small larvae by the probing activities of the parasites. Since the changes in k₁ could not be suitably predicted, the observed values were used in model B₂. This delayed component was not detected in room A due to the relatively small range of parasite densities in room A compared with the 600-fold change in densities in room B. The calculated area of discovery for the parasite population in each generation was found to vary inversely with searching parasite density, and this ‘interference relationship’ was used in the submodel for parasitism. Again, this relationship was not detected in room A due to the much smaller range of parasite densities there. Model B₂ gives oscillations in host and parasite populations arising from parasitism being a delayed density-dependent mortality. The correspondence with the observed oscillations is partly due to the actual k₁-values being used and partly because the submodel for parasitism adequately describes the observed changes in k₃. The tendency for these oscillations to decrease in amplitude is due to both the damping effect of parasite interference and the direct density-dependent component of k₁.

     

Multivariate analyses of Canadian and Japanese populations ofGlycyphagus destructor (Schrank) (Acarina,Glycyphagidae)

Summary Two multivariate statistical procedures were used to determine the basic trends of morphologic and geographic variations between males of a common stored-grain mite,Glycyphagus destructor (Schrank) collected from Canada and Japan. All analyses were carried out on physical measurements of 25 morphological features. Three principal component analyses bases on the Canadian (50 specimens), Japanese (50 specimens) and the combined populations from the 2 countries (100 specimens) revealed that the first component, accounting for 40% of the variability in all 3 solutions represented a measure of the morphologic dimension of the body. The second component, which explained over 18% of the variability, is a measure of the leg dimension. Smaller clusters of variates characteristic of the population from each county were also evident. Discriminant analysis, performed with the Canadian and Japanese populations, identified the variates that differed between the 2 populations and provided an approximate appraisal of interrelations. The general conclusion based on these analyses is that the Canadian and the Japanese populations are morphologically distinct. The difference is most evident in the diameters of genu 2, lengths of the sensory seta W_I, lengths of the body, and the distances between the vertical external setae. Contribution No. 446, from Research Station, Canada Department of Agriculture, Winnipeg, Manitoba, Canada.     

Ecological studies on the population of isaza,Chaenogobius Isaza Tanaka,in Lake Biwa,with special reference to the effects of population density upon its growth

1. In order to get the knowledge on the age composition of “isaza” population in Lake Biwa and the effect of population density on growth, monthly distribution of mean body length and mean body weight has been analyzed on the basis of monthly haul by “isazabiki” trawl during 1949 to 1953 and also 1960 to 1965.
2. There is no apparent sex difference in the growth in the first and second years of life.
3. “Isaza” population is composed of two age groups, age 0 and 1 groups (1+fish), the latter occupying by far the greater part in commercial catch.
4. During the growth season fishes of both ages feed mainly on zooplankton, though in winter frequently take chironomid larvae, gammaridae and others in volume.
5. The growth season falls in the period from April to October in both age groups.
6. A considerable yearly variation occurring in growth is in close connection with the fluctuation of population density of all ages.
7. The influence affected by the density of age 1 group is larger than that by age 0 group.

     

A possible discrepancy between the exposed and the whole population depending on range-size and trap-spacing in vole populations

Population Ecology - From a field study for the vole population (Clethrionomys rufocanus) in Hokkaido in the late summer of 1965, it has been proved that the range length may decrease from 25 to 18...