- With a severe decline in prey density available per individual predator, the predators exhibited a marked behavioural change and dispersed to other areas.
- When two neighboring host plants did not touch with each other and the dispersal of the predators was possible only through a 20cm plywood “bridge” which connected the two plants, the rate of successful dispersal of the predators was only 20 to 25%, whereas it was 95% when the plants touched with each other.
- In the system where 32 host plants touched with each other, the predators succeeded in immigrating into all the plants by the 16th day, and they completely eliminated all the prey by the 33rd day.
- In another system, the 32 plants were equally divided into eight “patches” which were connected with each other with two of the bridges and the predators could move between them only through the bridges as mentioned above. In such a system the predators and their prey coexisted about three times longer than in the other one.
- It is suggested that for a longer continued coexistence of the predators and prey, it would be necessary to introduce more physical barrier against the dispersal of the predators and to provide more chances for the prey to disperse.
- With a severe decline in prey density available per individual predator, the predators exhibited a marked behavioural change and dispersed to other areas.
- When two neighboring host plants did not touch with each other and the dispersal of the predators was possible only through a 20cm plywood “bridge” which connected the two plants, the rate of successful dispersal of the predators was only 20 to 25%, whereas it was 95% when the plants touched with each other.
- In the system where 32 host plants touched with each other, the predators succeeded in immigrating into all the plants by the 16th day, and they completely eliminated all the prey by the 33rd day.
- In another system, the 32 plants were equally divided into eight “patches” which were connected with each other with two of the bridges and the predators could move between them only through the bridges as mentioned above. In such a system the predators and their prey coexisted about three times longer than in the other one.
- It is suggested that for a longer continued coexistence of the predators and prey, it would be necessary to introduce more physical barrier against the dispersal of the predators and to provide more chances for the prey to disperse.
- The slope b in the density-on-density regression between successive developmental stages has a general tendency to become smaller than 1, though the bias approaches zero if one or more of the following three conditions are satisfied: (a) the data cover a large number of generations, (b) the variance of the rate of population change for the period concerned is small relative to that for the residual period in a whole generation, and (c) the population has a distinct trend to either increase or decrease over generations.
- The variance for the generation-to-generation population fluctuation increases continually as the number of generations is increased, even if the population has no inherent trend to increase or decrease. For a fixed number of generations, however, the variance remains constant among different developmental stages.
- In this study, we have developed a new method to estimate population parameters and applied it to a concrete example on the situation that there are two fisheries resources which are depleted only by catch, and that these two resources are not caught equally because of the difference of prices.
- Switching function, which is originally used to describe the effort allocation that one predator eats two preys, has been introduced. We have constructed a model of fishery in which each fisherman pursues economical optimum.
- The population size of two species at the beginning of the fishing season, catchability coefficient and parameters of switching function are estimated by the criterion of minimum error sum of squares between CPUE (catch per unit effort) of data and that by model.
- We have applied it to the diver fishery of abalone in Ojika Island, Nagasaki Prefecture. The model describes well the situation during the season that CPUE of the less expensive species increases gradually as the population of the other species is depleted.
- The intimate relationship between sampling efficiency and Taylor's power law (TPL) was investigated with gypsy moth sample data. The data were used to compute sampling efficiency directly and indirectly by TPL.
- Comparison of TPLs and efficiency plots of male and female pupae confirmed the identities linking TPL with sampling efficiency. Divergence of sex-specific TPL plots indicated local scale density-dependent sex ratio.
- Egg mass sample data confirmed the sampling efficiency and TPL identities provided the same variance and mean vectors were used to compute TPLs. Small differences in sample numbers destroy the identities but approximate efficiency estimates are still obtainable from the TPLs. Sampling efficiency of timed walks, fixed area and variable area surveys were estimated and ranked.
- Rescaling moth catches per trap to number per unit volume changes slope, intercept and correlation coefficient while stretching the pattern of data points. Comparison of absolute density estimates over two different time intervals showed density-dependent variation declining with increasing sample interval.
- Fitting power laws by ordinary dependent regression is less efficient than fitting by geometric mean regression and produces biased regression parameters. The significance of this for the analysis and interpretation of ecological sample data generally is discussed.
- 1 Dispersion patterns of the protelean parasite, Allothrombium pulvinum Ewing, among individuals of an aphid host, Aphis gossypii Glover, were examined during spring 1991 in several cotton fields in Jiangsu Province, China.
- 2 The variance-to-mean ratios (i.e. dispersion index) of larval mites per host were greater than 1, indicating that the mite parasites were overdispersed among aphid hosts. The variance increased with the mean according to the power law, variance = 1.51 mean106, which explained 99.7% of the variation in the data.
- 3 The negative binomial distribution adequately describes the patterns of larval mite dispersion among aphid hosts in eight out of ten populations. The degree of clumping (1/k) decreased curvilinearly with parasite density (mites per host).
- 4 Mites were more clumped among adult aphids than among immature ones.
- 5 Ecological and evolutionary consequences of mite overdispersion within host populations are discussed. The role of Allothrombium in pest control is also discussed.
- So far as the population data thus far amassed go, commensal rats in residential habitats are of type II; house mice may be of type I or III in fields but might show type II in residences, and fieral species or subspecies may range from type I to III. Altogether alloresponsive populations seem to be much commoner than the isoresponsive.
- It is as yet little disclosed to what degree the differentiation of the type is correlated with speciation or subspeciation, even if only a proof that a subspecific population would hold type III as its fixed feature is given. The response types are supposed to be associated with the levels of population shyness. Hence some characters reflected in those may possibly be connected with sexual isolation provoking speciation.
- Some awkward respects due to the heterogeneous trappability, depending upon the trap-response type, among a mixed population of marked and unmarked animals have been confirmed regarding the methodology for estimating parameters.
- A study was made of the populations of Collembola in the pine forest. Among the eight species commonly found, Folsomia octoculataHandschin was numerically dominant.
- Seasonal population changes of these eight species were described over a year. It was found that many species show two peaks in number. As for F. octoculata, the dominant species, the changes in number was discussed in connection with the variation in age structure.
- The census data for each species were examined for the distribution pattern by using the regression method. None of these eight species was distributed at random in the soil and they could be classified into three groups based on the differences in the degree of aggregation in terms of coefficient β of the regression. It was suggested that such differences in the distribution pattern are largely due to differences in the response to heterogeneity of the habitat. In the case of F. octoculata, the changes of distribution pattern in the course of post-embryonic development were examined and it was found that (a) the component of distribution is a single individual rather than a colony, and (b) the degree of aggregation is decreased with the development of individuals.
- Using the relationship, the relation of the necessary sample size to the population density was derived for a fixed level of presision (D=S.E./m=0.2) and some suggestions were given concerning sampling plans for these insects.
- The population dynamics of two Salicornia species from the Bergen op Zoom salt marsh (south-west Netherlands) was examined. Based on the results of several field studies three preliminary life tables were constructed, two for S. procumbens agg. populations growing respectively on the mud flats and in the salt marsh, and one for S. europaea agg. living in the upper marsh.
- The life cycles are described and quantified in terms of eight phases and the transition probabilities between them, starting from a notional individual representative of each population.
- The models depicting the life cycle of S. procumbens show a mean offspring number of 4.26 individuals per parent for the mud-flat population and 0.18 for the salt-marsh population. The S. europaea model gives an output of 0.44 individuals per parent. These results reflect the fluctuations in population size observed in sample plots over the years 1976–78.
- Comparison of the transition probabilities reveals that on the mud flats most S. procumbens individuals die during pollination and seed germination, while the population in the salt marsh proper is thinned especially during the seed phase in winter time and during the growth from established seedlings to maturation. S. europaea behaves in a similar but less pronounced way to S. procumbens in the salt marsh.
- Probabilities for one flower or one seed to produce a mature flowering plant were calculated, and were compared with those found in the literature. They are roughly of the same order of magnitude as the probabilities for other annual species, but much higher than those reported for biennial species.
The Hindustan citrus mite, Schizotetranychus hindustanicus (Acari: Tetranychidae), is an invasive pest in South America and constitutes a threat to Brazilian citriculture. This study aimed to determine the contribution of weather variables to the seasonal abundance of S. hindustanicus and the best sampling scheme (sampling variable and unit) for this mite. Populations of S. hindustanicus were monitored monthly in an orange orchard for 31 months in Roraima state, Brazil. Eggs, mobile stages, and the symptoms caused by S. hindustanicus were sampled in different combinations of canopy quadrants, vertical tree strata, and branch sections. The optimal sampling variable and sampling unit for S. hindustanicus scouting were determined according to fidelity and precision criteria. Rainfall and high air temperature were the main factors reducing S. hindustanicus populations. The most suitable variable for S. hindustanicus sampling was egg count. The optimal sampling unit was a leaf collected in the central section of branches located in the middle tree stratum. In addition, the sample should be taken from the southwest quadrant. Collectively, this study adds to the understanding of S. hindustanicus population dynamics and provides a sampling scheme for better management of this pest.
相似文献- 1 Mark—recapture sampling must be stratified because populations of foragers and defenders are partitioned by trunk trails and order of emergence respectively.
- 2 Foragers and defenders form overlapping subsets of the total colony population, each of which is correlated with total colony population size.
- 3 Foragers and defenders have an average life expectancy of approximately 2 weeks.
- 4 The fluorescent marking procedure did not significantly affect harvester ant mortality and only temporarily affected their behaviour.
- 5 Combinations and mixtures of fluorescent ink allow at least eight groups in a colony to be distinctly marked for periods exceeding 4 months.
- Sex ratio in reproductives in a colony of haplodiploid species does not affect the direction of evolution, contrary to the hypothesis ofTrivers andHare (1976). Female biased sex ratio increases the rate of evolution irrespective of its direction.
- The only factor that determines the direction of evolution is the balance of benefit and cost of altruism of workers.
- The value of ratio of benefit to cost of altruism of workers when the change of gene frequency of altruistic allele does not take place is unity in both haplodiploid and diploid species. There is no theoretical reason that the eusociality through kin selection evolves more easily in haplodiploidy than in diploidy, contrary to the hypotheses ofHamilton (1964) andTrivers andHare (1976).
- The larger the colony size is, the lower the rate of evolution is irrespective of its direction.
- 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.
- There is no apparent sex difference in the growth in the first and second years of life.
- “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.
- During the growth season fishes of both ages feed mainly on zooplankton, though in winter frequently take chironomid larvae, gammaridae and others in volume.
- The growth season falls in the period from April to October in both age groups.
- A considerable yearly variation occurring in growth is in close connection with the fluctuation of population density of all ages.
- The influence affected by the density of age 1 group is larger than that by age 0 group.