Use of the regression of mean crowding on mean density for estimating sample size and the transformation of data for the analysis of variance

Summary An approximate method for estimating the sample size in simple random sampling and a systematic way of transformation of sample data are derived by using the parameters α and β of the regression of mean crowding on mean density in the spatial distribution per quadrat of animal populations (Iwao, 1968). If the values of α and β have been known for the species concerned, the sample size needed to attain a desired precision can be estimated by simply knowing the approximate level of mean density of the population to be sampled. Also, an appropriate variance stabilizing transformation of sample data can be obtained by the method given here without restrictions on the distribution pattern of the frequency counts. Contribution from the Entomological Laboratory, Kyoto University No. 418. Contributions from JIBP-PT No. 52. Aided in part by a grant from the Ministry of Education for the special project research, ‘Studies on the dynamic status of biosphere’.     

Dispersion analyses and resource utilization of aphid parasitoids in a non-depletable environment

Summary Dispersions and resource utilization of primary and secondary parasitoids developing in non-depletable primary host populations were determined for an aphid-parasitoid community occurring on strawberries. Analyses of dispersions based onGreen's coefficient andLloyd's Patchiness Index indicated parasitized aphids were highly aggregated initially, became less aggregated as density increased, and remained aggregated following collapse of the aphid populations. The “index of aggregation” values calculated usingTaylor's Power Law concurred with results from the other indices, and the similarity of the regression coefficients from both seasons suggests that the index of aggregation may be characteristic for communities as well as species. Analysis withIwao's regression of mean crowding on the mean generated similar results when population data were stratified temporally, and also indicated that the individual was the basic unit of the population. In a non-depletable environment, oviposition of individuals exhibiting an aggregated dispersion pattern within clumps of hosts provides primary parasitoids with a suitable trade-off between energy utilization or genetic potential, and losses associated with hyperparasitism.     

Studies on the spatial distribution pattern of larvae of the mosquito,Anopheles sinensis, in rice fields

Summary The spatial distribution patterns of the population ofAnopheles sinensis larvae were studied in the rice field area in the suburb of Urawa city in Japan, during the summer seasons in 1973 and 1974. The distribution pattern of the larval population within the field, analysed by the m−m regression method, indicated that the basic component of larval distribution was not a group of individuals but a single individual and such components were distributed contagiously over the field. This basic pattern did not change significantly according to developmental stage, census date or field. Therefore, we could describe the distribution pattern of the population in a rice field by the single linear regression, x=0.021+1.339x(r²−0.912). Also, the relation for the whole population in the field area including the five fields could be shown by the linear regression, x=0.049+1.749x(r²−0.959). The value of α remained to be nearly equal to zero, but the value of β became larger than the value for the single-field relation. Such a change in distribution pattern seemed to reflect the greater heterogeneity in conditions among the fields than within individual field. Using the information on the distribution patterns mentioned above, some considerations were given on the sampling plans for mosquito larvae, including samplesize determination and application of sequential methods to estimate population size as well as to classify population level.     

A model of the species rank-abundance relation for a community in an open habitat

Summary A mathematical model is proposed to describe the relationship between the abundance and the rank of species in order from the most abundant to the least in a community in an open habitat. This model is derived as a corollary of a species-area equation (Kobayashi, 1975) which could be expected in the case where the individuals of each species are uniformly distributed over a habitat area. Numerical simulation reveals that a rank-abundance curve for a universe results in different species-area or species-individual curves according to the spatial distribution of individuals, and that the relative abundance of each species in a sample varies with sample size unless the spatial distribution of individuals is uniform. A species-individual curve obtained bySanders’s (1968) rarefaction method agrees with that observed actually only for the spatially uniform distribution. Change in the pattern of rank-abundance curve with species diversity and with sample size is discussed in relation to the present model.     

Spatial pattern of pine wilt disease caused byBursaphelenchus xylophilus (Nematoda: Aphelenchoididae) within aPinus thunbergii stand

Summary To understand the mechanism of spread of pine wilt disease caused by the pinewood nematode,Bursaphelenchus xylophilus, which is vectored by a cerambycid,Monochamus alternatus, the spatial distribution of trees weakened by the nematode was examined within aPinus thunbergii stand from June to October for 4 years. The weakened trees were distributed in a clumped pattern in 1980 and 1981, at an early stage of infestation. In many cases, they showed a double-clumped pattern. The degree of aggregation was higher in June or July than after August. They were uniformly distributed in June or July 1982 and in June 1983 whereas they showed a double-clumped pattern after August. The trees were frequently weakened in June or July when they were near the trees weakened during the previous year. At quadrat sizes of more than 25 m², spatial overlapping was pronounced between trees weakened during June–July of the current year and those weakened in the previous year. The seasonal changes in spatial distribution of weakened trees were explained by the interaction amongM. alternatus, B. xylophilus andPinus trees.     

Continuous population estimates forDendroctonus frontalis Zimm. (Coleoptera: Scolytidae) occurring in infestations

Summary Infestations ofDendroctonus frontalis Zimm. are often observed to enlarge continuously by the colonization of new hosts in a pattern similar to a forest fire. This pattern of infestation growth presents unique problems in quantitatively estimating populations ofD. frontalis. Beetle populations on each infested tree in an infestation go through five processes: attack, oviposition, reemergence, survivorship, and emergence. These processes, which have been described mathematically in the literature, each take several days for completion. In order to follow the distribution and abundance ofD. frontalis throughout the course of development of a spot, we need a daily estimate of the number of beetles involved in each process on every tree. Since it is not practical to sample each tree daily, we developed a procedure whereby quantitative estimation procedures for within-tree populations were used in combination with the mathematical models for the life processes to produce a daily record of the number of adults successfully attacking trees, the number of eggs oviposited, the number of beetles reemerging, number of beetles surviving within the trees, and the number of beetles emerging. These daily estimates were then summarized for all trees in the spot for the duration of the infestation. The daily record of populations ofD. frontalis, used with information on infestation geometry, were suggested to be of value in describing and elucidating several important facets of population dynamics including dispersal patterns within infestations, between tree beetle loss (mortality), and time lags among the various population processes. The information reported can be used to develop simulation models of population dynamics or to validate existing models. Texas Agric. Experiment Stn. TA No. 14689.     

Pit-relocation of antlion larvae in relation to their density

Of the biotic factors potentially affecting the foraging behavior of pit-building antlion larvae,Myrmeleon bore Tjeder, we focussed on the density effects and examined experimentally influences of larval density on pit construction behavior, spatial distribution and pit relocation rate. Moreover the mechanism of mutual interference among larvae was examined.

Anopheles culicifacies giles: Adult ecological parameters measured in rural punjab province, pakistan using capture-mark-release-recapture and dissection methods, with comparative observations onAn. stephensi liston andAn. subpictus grassi

Summary Dispersal, immigration and emigration rates, horizontal and vertical survivorship and absolute population size were estimated for micropopulations ofAn. culicifacies, An. stephensi andAn. subpictus at a series of cattle sheds in rural Punjab Province, Pakistan, during November 1979 and May 1980 using capture-mark-release-recapture and dissection methods. Dispersal was temperature-related, with populations more vagile during May. Mean dispersal distance per individual was low for all species. More than 70% of all recaptures were taken at the point of release and the longest detected flight was 1250 meters. Horizontal survivorship was greater during November and was always less than vertical survivorship calculated from dissection agegrading data. Survivorship during the nulliparous period was greater than survivorship throughout total life, indicating the survivorship curve may be slightly sigmoid. Daily population sizes of endemic and immigrating females and males were calculated usingBailey's (1952) modification of the Lincoln Index, with the daily captures adjusted for immigration which was highest in May. Daily additions to the indoor resting population exclusive of immigrants were estimated using the method ofManly andParr (1968). The relationship of the present findings to malaria transmission and genetic control were discussed.     

Influence of parental density on the distribution pattern of eggs in the common cabbage butterfly,Pieris rapae crucivora

Summary To investigate the relation between the distribution pattern of eggs and the parental density in the common cabbage butterfly,Pieris rapae crucivora, the countings of egg number per plant were made on both cabbage plants cultivated in the farm and planted in the net house in which the female butterflies were released at various densities. The frequency distribution of eggs fits well to the negative binomial excepting the cases where they agree withPoisson series, and the degree of aggregation expressed as the reciprocal of the parameter, 1/k, tends to decrease as the egg or parental density increases. At the same parental density, however, the distribution of eggs can be described by the negative binomial with a common parameter,k _c, regardless of the difference in the density of laid eggs. In the case where a single female butterfly lays eggs, the spatial pattern of egg distribution is always lean, while its frequencies conform toPoisson or the negative binomial series. This lean changes toward patchy with increasing the parental density. From these results, it is concluded that the degree of aggregation in the distribution of eggs decreases with the increase of the parental density.     

Studies on the distribution pattern of the pine needle gall midge,Thecodiplosis japonensisUchida etInouye (Diptera: Cecidomyiidae) in a pine forest

Summary Numerical changes and distribution patterns of the pine needle gall midge,Thecodiplosis japonensis Uchida etInouye, were studied during the period from 1978 to 1979 in a young plantation ofPinus thunbergii in Shiga Prefecture, Japan. The survivorship curve of this species was characterized by a low mortality of larvae in galls and two high mortalities before the formation of galls and during the overwintering period in soil. The within and between-trees distributions of eggs and larvae in galls were examined by using the regression method. The egg distribution per shoot was aggregative both within and between host plants. The within-tree variations in numbers of eggs per shoot were related to the differences in the abundance of available needles for oviposition per shoot among the canopy layers. The between-tree variations reflected the heterogeneous emergence of adult females in the study plot. The degree of aggregation increased from egg to gall stage in both within- and between-tree distributions and the increase was explained by the different mortality of larvae within trees and the inversely density-dependent mortality between trees. The distribution patterns in the soil habitat stages were examined by the patchness index ( ). This species showed aggregative distributions in soil stages. There was a correlation in spatial patterns of adult emergence between the successive generations. The distribution properties of this species were discussed in connection with the population dynamics and the availability of host plants in the study plot.     

Stabilization effects of spatial aggregation of vectors in plant disease systems

Stabilization effects of spatial aggregation of vectors were examined in insect-borne plant disease systems by constructing a model that describes the yearly dynamics of rice stripe virus disease transmitted by the small brown planthopperLaodelphax striatellus (Fallén). Two transmission paths between vectors were considered: vertical transmission from parents through eggs, and horizontal transmission from infected plants by acquisition feeding. In this model, a paddy field was divided into quadrats and horizontal transmission was assumed to occur within each quadrat. A negative binomial distribution was used to describe the frequency distribution of vectors per quadrat. The parameters of the model were estimated using field data collected in Ibaraki Prefecture, Japan. The model showed that (1) the disease cannot invade into an epidemiological system if the mean crowding of vectors is less than a critical value, (2) the proportion of infected vectors is maintained at about 30% irrespective of the vector density if vectors are highly aggregated, and (3) the proportion of infected plants is maintained at a low level irrespective of the vector density if vectors are highly aggregated. It was also shown that these stabilization effects of aggregation in this epidemiological system come from a mechanism that is common to other systems such as single-species systems and competition systems.     

Anopheles subpictus Grassi: Observations on survivorship and population size using mark-release-recapture and dissection methods

Summary A mark-release-recapture experiment to estimate population survivorship and absolute size was performed with wild-caughtAn. subpictus adults at the village of Khano-Harni, Lahore District, Punjab Province, Pakistan during September 1978, the end of the monsoon rainy season, when temporal population abundance was maximized. Daily survival rate estimated from the recapture sequence of marked adults was low, males=0.192 and females=0.343. Survivorship for females estimated by several vertical age-grading procedures ranged from 0.347 to 0.628. Both stage- and age-specific life tables were calculated from vertical age-grading data determined by the dilatation method. Female and male population size was estimated byBailey’s modification of theLincoln Index and was found to average 4478.4 and 6106.8, respectively. The bionomics, survivorship and population size ofAn. subpictus in the Lahore are indicated that this species was probably not important in the transmission of human malaria.     

Evaluation of statistical precision and design of efficient sampling for the population estimation based on frequency of occurrence

Summary The binomial sampling to estimate population density of an organism based simply upon the frequency of its occurrence among sampled quadrats is a labour-saving technique which is potentially useful for small animals like insects and has actually been applied occasionally to studies of their populations. The present study provides a theoretical basis for this convenient technique, which makes it statistically reliable and tolerable for consistent use in intensive as well as preliminary population censuses. Firs, the magnitude of sampling error in relation to sample size is formulated mathematically for the estimate to be obtained by this indirect method of census, using either of the two popular models relating frequency of occurrence (p) to mean density (m), i.e. the negative binomial model,p=1−(1+m/k) ^−k, and the empirical model,p=1−exp(−am ^b). Then, the equations to calculate sample size and census cost that are necessary to attain a given desired level of precision in the estimation are derived for both models. A notable feature of the relationship of necessary sample size (or census cost) to mean density in the frequency method, in constrast to that in the ordinary census, is that it shows a concave curve which tends to rise sharply not only towards lower but also towards higher levels of density. These theoretical results make it also possible to design sequential estimation procedures based on this convenient census technique, which may enable us with the least necessary cost to get a series of population estimates with the desired precision level. Examples are presented to explain how to apply these programs to acutal censuses in the field.     

Time-specific life tables for the pea aphid,Acyrthosiphon pisum (Harris ), on alfalfa

Summary Time-specific life tables were constructed for three pea aphid,Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), populations using a modification ofHughes' analytical procedure. All populations were studied on second-growth alfalfa (mid-June to mid-July) in south central Wisconsin; data for two populations were collected during 1980, and data for the third population were collected during 1982. The intrinsic rate of increase (r _m) estimated on a physiological time (day-degree) scale under field conditions but in the absence of natural enemies, provided a reliable estimate of potential population growth rate and was used in preference toHughes' approach of estimating potential population growth rates directly from stage structure data. Emigration by adult alatae and fungal disease were the major sources ofA. pisum mortality in each of the three populations studied. These factors were most important because of their impact on reducing birth rates within the local population. Parasitism was never greater than 9 percent. Mortality attributable to predation ranged from 0.0 to about 30.0%; however, even at the highest predator densitiesA. pisum populations increased exponentially.     

Geographical variation of elytral spot patterns in the phytophagous ladybird,Epilachna vigintioctopunctata (Coleoptera: Coccinellidae) in the Province of Sumatera Barat, Indonesia

Summary Geographical variation in the elytral spot patterns of a phytophagous ladybird,Epilachna vigintioctopunctata, was studied in the Province of Sumatera Barat, Indonesia. Populations ofE. vigintioctopunctata were divided into four major groups (I–IV) by the incidence of spot pattern variations. Group I, occurring in the coastal plains and inland lowlands, and Group IV, confined to the highlands, were the extremes of the spot pattern variations, the latter had many more non-persistent spots and confluences with larger body size and advanced melanism than the former. These two groups were connected with each other via the intermediate groups. A positive relationship was detected between the elevations of sample sites and the average number of non-persistent spots per elytron. Consequently, present results favor the view that the two previously recognized forms ofE. vigintioctopunctata (formae A and B inKatakura et al., 1988) represent a complicated intraspecific variation rather than two distinct sibling species. Elytral spot pattern variations were not different between the sexes or between the beetles collected from different kinds of host plants. Contribution No. 30 of Sumatra Nature Study (Entomology). Supported in part by grants from Japan Society for the Promotion Science for JSPS-DGHE Scientific Cooperation (1980, 1982) and for the RONPAKU program (toI. Abbas, 1984) and Grants-in-Aid for Overseas Scientific survey from the Ministry of Education, Science and Culture of Japan (Nos. 56041027 and 58041030).     

Spatial pattern analysis of the incidence of aster yellows disease in lettuce

The degree of aggregation of lettuce plants infected by aster yellows phytoplasma (AYP) was investigated in 12 fields from three experiments. Position of diseased and healthy plants was mapped in a 6–9×12-m section of each field; for most analyses, fields were divided into 10-plant quadrats. Mean disease incidence (p) ranged from 0.01 to 0.30. The frequency of diseased plants was described by the beta-binomial distribution, with an index of aggregation (θ) ranging from 0 to 0.17, positively correlated withp, and generally increasing over time within a field. Distance-class analysis revealed a core-cluster size of only a few plants. However, spatial autocorrelations ofp between quadrats were not significant, indicating that the scale of spatial pattern was small, generally less than 10 plants. An overall measure of aggregation was given by the slope parameter of the binary form of the power law, in which the log of the calculated variance is regressed on the log of the theoretical variance for a binomial distribution. The slope was 1.18 and significantly different from 1. Results for this “simple-interest” disease are interpreted in relation to the persistent transmission of AYP by its aster leafhopper vector.     

On the mode of selection inEscherichia coli

Summary Competition experiments between a lac⁺ prototroph and a lac⁻ auxotroph ofEscherichia coli were conducted by serial transfer procedure on four levels of sugar concentration. Changes of the relative frequencies of both genotypes were followed and the relative fitness was estimated. Fitness was proved to be density-dependent. No explicit dependence of fitness upon genotype frequencies could be detected by the simple method ofKosuda (1981).     

Host-attacking behavior of a eulophid parasite,Kratochviliana sp., to the leaf mining host,Phytomyza ranunculi (Diptera: Agromyzidae) during its stay on the leaf

Summary The present paper studies how the female parasite ofKratochviliana sp. visits and attacks its host larvae of Ranunculus leaf mining fly,P. ranunculi at a single leaf visit. The parasite visited its hosts at random on the leaf. The frequency of host visits was independent of the host density and the proportion of hosts survived from the parasite attack, in a leaf and its distribution was expressed as a single straight line. It almost always attacked living hosts at the first host visit after isolated from them for one day but with the rate of about 0.5 at the subsequent visits. In consequence, the relationships of the number of host attacks and killed hosts to the host density drew satulated curves in each. A model of host attack by this parasite at its single leaf visit was formulated by modifyingBakker et al.'s model (1972) basing upon these observations and the attack avoidance by the parasite to already attacked hosts previously reported. Ecological studies on the relationship between Ranunculus leaf mining fly,Phytomyza ranunculi Schrank (Diptera; Agromyzidae) and its parasite,Kratochviliana sp. (Hymenoptera; Eulophidae) from the viewpoint of spatial structure II. This paper constitutes a part of the Doctoral Thesis presented to the College of Agriculture, Kyoto University by the present author.     

Natural control of populations of the southern green stink bug,Nezara viridula

Summary Based on the results of five-year study on theNezara population, it was concluded that the level of abundance of the insect was determined partly by the combination and relative adundance of the host plants and partly by the climatic factors. The endless increase of the population was checked by the deleterious effects associated with the overpopulation which occurred locally. The degree of such overpopulation was determined by the relative abundance of host plants to the current level of the population. Therefore, even when the general level ofNezara population seemed to be low, there still exists the possibility of overpopulation in some areas. Winter was the critical period which threatened the persistence ofNezara population. The survival of the hibernating adults was partly dependent on the physiological state of adults which was determined in the period of pre-hibernation. But when the severity of a winter exceeded the tolerance limit of the insect, the only safety-valve which prevented the elimination ofNezara was the heterogeneity of hibernacula. Therefore,Milne's theory (1957) was closest to the known facts.