Simulation model of a predator-prey system comprised ofPhytoseiulus persimilis andTetranychus urticae. II. Model sensitivity to variations in the life history parameters of both species and to variations in the functional response and components of the numerical response

Summary A detailed sensitivity analysis of a model of a predator-prey system comprised ofTetranychus urticae andPhytoseiulus persimilis was performed. The aim was to assess the relative importance of the life history parameters of both species, the functional response, and the components of the numerical response. In addition, the impact of the initial predator-prey ratio and the timing of predator introduction were tested. Results indicated that the most important factors in the system were relative rates of predator and prey development, the time of onset of predator oviposition, and the mode of the predator's oviposition curve. The total oviposition of the predator, the effect of prey consumption on predator oviposition, and predator searching were important under some conditions. Factors of moderate importance were the adult female predator's functional response, total prey oviposition, the mode of the prey's oviposition curve, abiotic mortality of the pre-adult predator, and the effect of prey consumption on predator development and on the immature predator's mortality. Factors of least importance were the variances of the predator's and prey's oviposition curves, the abiotic mortality of the adult predator, the abiotic mortality of the pre-adult and adult prey, the functional response of the nymphal and adult male predators, and the effect of prey consumption on adult predator mortality. The sex ratios had little effect, except when the proportion of female predators was very low. The initial predator-prey ratio and time of predator introduction had significant impacts on system behavior, though the patterns of impact were different.     

Systems analysis of an acarine predator-prey system II: Interactions in discontinuous environment

Summary An acarine predator-prey system in a circular stepping-stone environment was described with a simulation model to elucidate the factors responsible for persistence of the system. The main assumptions in this model are: (1) The prey are inevitably eliminated in patches in which predators exist. (2) The density of prey declines and becomes extinct by plant defoliation due to feeding by prey. In this regard this model is different from the models which mimickedHuffaker's (1958) experiments and assumed stable plant-prey relations. Analyses showed that the critical factor in persistence of the predator-prey system was the plant-prey relations, at any combination of other parameters involved in the model. The predator-prey system did not persist long under the unstable relationship of prey and plant. Otherwise the system persisted longer especially when I used a larger number of patches, a larger amount of plant in each patch, and long-distance-migrations of the prey. In particular, frequent emigration of the prey regardless of plant conditions was most effective.     

Predator-prey system structure in patchy and ephemeral phytotelmata: Aquatic communities in small aroid axils

Mechanisms allowing the persistence of an aquatic predator-prey system in tiny pools (the mean ca. 0.5 ml) held by taro axils were analyzed from the viewpoint of temporal and spatial patterns of habitat use. Predatory larvae of a mosquitoTopomyia tipuliformis concentrated in young axils, while 9 other taxa utilized both young and old axils or concentrated more in older axils. The total prey density was lower in axils with the predator but the density of each prey taxon (except for a few cases) and the number of prey taxa did not differ between axils with and without predators. This indicates thatT. tipuliformis is a general predator and does not influence prey community organization through selective removal of particular prey taxa. Inter-axil distribution ofT. tipuliformis was aggregated in the first instar but uniform in the third and fourth instars due to intraspecific cannibalism, which assures the survival of a single individual under short food supply. Distributions of prey taxa were mostly aggregated, fitting the negative binomial distribution. Thirty seven out of 45 associations of 10 taxa were independent with 3 negative (between the predator and some late-colonizing prey) and 5 positive (between some prey taxa) associations. Probabilistic refuges (produced by independent aggregated distributions) reduced interspecific encounters which may result in competition and predation, and thus probably facilitated prey coexistence. There was no evidence for the importance of predation in structuring the prey community. This system may be prey-dominated in that predator persistence depends on prey community existence but prey community structure depends less on predation.     

Simulation of the interactions of predatoryTyphlodromus mites with the European red mite,Panonychus ulmi (Koch)

Summary Interactions ofTyphlodromus mites and their prey, the European red mite, in orchard settings were examined through computer simulation. In particular, the consequences of very slow dispersal by the predators, compared with the weather-dependent higher rates of prey dispersal, were elucidated. In simulations of the interactions of the predator and its prey, both dispersal and temperature strongly affected the available supply of juvenile prey, and thus could determine whether the predators on an individual tree survived or perished.     

Evaluation of the role ofMicrovelia douglasi atrolineata (Bergroth) (Heteroptera: Veliidae) as predator of the brown planthopperNilaparvata lugens (St?l) (Homoptera: Delphacidae)

Summary The biology of the veliid bugM. d. atrolineata, its predatory behavior, and the effects of plural hunting were studied to evaluate its role as a predator of the brown planthopperNilaparvata lugens in the Philippines. The probability of planthoppers falling onto the water surface and provision of habitat continuity was measured by a sticky trap placed at the base of rice hills in a greenhouse and in paddy fields. The developmental period of immature stages combined was 21 days. If given prey, females laid 25 eggs on the average during an adult life span of 18 days. Starved adults could survive for only 3–5 days. The functional response to prey density was sigmoid, and the maximum number of prey killed was 7 per day. Prey feeding was completed in 12–36 min. The percentage of successful prey attacks averaged 5–8%, decreasing with higher (and larger) developmental. stages of prey, but adult prey were found the soonest. Plural hunting increased the probability of capturing prey by as much as 2.5 times that by individual hunting. Late-instar nymphs, which may be more active, fell from rice hills in a greenhouse more than early-instar nymphs, and the number falling increased with density. In the field the percentage of planthoppers falling to the water in 1 day varied considerably, from 1% for nymphs in one field to 67% for adults in another field. On the basis of work described above and given the high density of veliid predators in flooded paddy fields of tropical Asia,M. d. atrolineata is considered one of the most important natural enemies of the brown planthopper.     

A population dynamic model of Batesian mimicry

Summary A population dynamic model of Batesian mimicry, in which populations of both model and mimetic species were considered, was analyzed. The probability of a predator catching prey on each encouter was assumed to depend on the frequency of the mimic. The change in population size of each species was considered to have two components, growth at the intrinsic growth rate and carrying capacity, and reduction by predation. For simplicity in the analyses, three assumptions were made concerning the carrying capacities of each population: (1) with no density effects on the mimic population growth rate; (2) with no density effects on the model species; and (3) with density effects on both species. The first and second cases were solved analytically, whereas the last was, for the most part, investigated numerically. Under assumption (1), two stable equilibria are possible, in which both species either coexist or go to extinction. Under assumption (2), there are also two stable equilibria possible, in which either only the mimic persists or both go to extinction. These results explain the field records of butterflies (Pachliopta aristolochiae and its mimicPapilio polytes) in the Ryukyu Islands, Japan.     

Studies on the basic components of the predation ofPhytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae)

Summary The basic components of the predation ofPhytoseiulus persimilis Athias-Henriot feeding upon eggs ofTetranychus urticae Koch were studied in an open system where the predator could disperse freely. The type of the functional response of the predator to the density of its prey was the same as that studied so far in a closed system, i.e.,Holling's Type 2. The search rate of the predator, however, was much lower in comparison with the result from a closed system. The oviposition of the predator per day was only weakly related to prey densities higher than 10 per leaf disc. But the emigration rate was inversely dependent upon the initial prey density up to 60 per leaf disc. The searching behaviour of the predator was influenced by both the web density spun byT. urticae and the density of the prey: the predator searched for its prey intensively only after it had contact with web. Mutual interference was observed in prey consumption, but not in the emigration rate. The emigration rate was largely dependent upon the prey density available per predator.     

An analysis of the predator-prey system in the paddy field

Summary A predator-prey system involvingLycosa pseudoannulata as predators and both the green rice leafhopper,Nephotettix cincticeps and the brown planthopper,Nilaparvata lugens as prey was studied in an experimental paddy field. Daily predation rates on the prey and weekly disappearance rates ofLycosa females were related to densities of both predators and prey by multiple regression. During the off-season of reproduction for predators and prey, it proved possible to simulate the interaction betweenLycosa and its prey.     

A new method for describing predator-prey relations in discontinous environments

Summary I propose a new method for anlysing predatorprey interactive systems in discontinuous environments. The basic index used here is a generalized version ofLloyd's (1967) “interspecies mean crowding”, which is defined as the number of individuals of one species existing in a given patch per that of the other species in either the same or different patches at either the same or different times. Four indices are derived from different combinations of the numbers of the prey and the predator in habitat patches. Then, the correlation coefficients between the numbers of individuals in patches in both different locations and times are derived by modifying the above new indices. Using this technique, dynamical changes of the joint distributions of the numbers of predators and prey which reflect variation in local conditions, can readily be described. As an example, this method was applied to an analysis of the outcomes of a multi-patch version of theLotka-Volterra model of predator-prey interactions.     

Group predatory behavior by the assassin bugAgriosphodrus dohrniSignoret (Hemiptera: Reduviidae)

Summary Nymphs ofAgriosphodrus dohrni Signoret (Reduviidae) have a strong gregariousness and show group predatory behavior. This study was conducted to clarify adaptive significance of group predation of this species, including laboratory observations and 6-year field surveys. In the laboratory, observations on both solitary and group attacking against armyworms were made at varying prey size classes to compare the capture success rate by solitary predators with that by groups. The efficiency in capturing the prey was significantly higher in group attacking at any prey size class compared. Data obtained from the field surveys indicated the tnedency for searching nymphs to feed in group and to increase the number of predators feeding per prey item with increasing prey size. Average sizes of prey captured were also larger in group feeding throughout the nymphal stage. In particular, it was remarkable that, when prey were “creeping” types, the upper size limit of prey eaten was dramatically increased.     

The effect of prey size and prey density on the functional response, survival, growth and development of a predatory pentatomid bug,Podisus maculiventris say

Summary Two experiments on the nymphal predation ofPodisus maculiventris were conducted usingSpodoptera litura larvae as prey. First experiment: The predator nymphs divided into three groups were reared individually from second instar to adult in a small vessel. Each nymph in the groups 1, 2 and 3 was allowed to attack the serially growing larvae (these were supplied at the rate of one per day) from 3-, 5- and 7-day old after hatching, respectively. The first prey used for the group 1 was so small that it was not only insufficient to satiate the predator but also was difficult to be searched out. But these disadvantages were soon recuperated due to the rapid growth of the prey and all nymphs could survive to adults. The survival rate of third and fourth instar nymphs in the group 3 was severely affected by vigorous counterattack of older prey larvae. Second experiment: The predator nymphs were individually reared either in a small vessel or in a large one at various rates of food supply (the prey larvae of 7-day old were used). The functional response curves obtained for each instar of the predator took a saturation type within a certain range of the prey density. The saturation level specific to each instar was generally higher for the predator reared in the large vessel than in the small one. The functional response of fourth and fifth instar nymphs was accelerated at a high prey density,viz. 16 larvae per vessel. Even at the low rate of food supply,viz. one larva per day per predator, the predator nymphs could survive to adults, but the size of resultant adults were abnormally small.     

An acarine predator-prey population infesting roses

Summary WhenPhytoseiulus persimilis was reared withTetranychus urticae, infesting roses propagated in a greenhouse at controlled daily temperatures of 24°C (12 hrs) and 18°C (12 hrs), prey numbers fluctuated with peaks of increasing amplitude. Differential dispersal of prey and predator species was one factor contributing to the inability of the natural enemy to control the pest population.     

Extinction of the trochid gastropod,Umbonium (Suchium) moniliferum (Lamarck), and associated species on an intertidal sandflat

On an intertidal sandflat in western Kyushu, Japan in 1979, the trochid gastropod,Umbonium (Suchium) moniliferum (Lamarck), and the thalassinidean ghost shrimp,Callianassa japonica Ortmann, densely inhabited the lower and upper zones, respectvely.Callianassa japonica subsequently expanded its distribution range considerably, having occupied almost the entire sandflat by 1983. Concurrently, theU. moniliferum population gradually declined, becoming extinct in 1986. Furthermore, the populations of 9 species associated withU. moniliferum (predators, an ectoparasite, and subsequent inhabitants of emptyU. moniliferum shells) had disappeared by the end of 1992. The extinction processes ofU. moniliferum and the two other most numerically dominant species, the ectoparasitic gastropod,Odostomia sp., and the hermit crab,Diogenes nitidimanus Terao, were described in detail. It is believed that the bioturbation of sediments byC. japonica was responsible for the extinctions, possible mechanisms involved being discussed. This is the first documented record of the extinction of a large part of a macrobenthic assemblage centering on a filter-feedingUmbonium species which is characteristic of the benthic communities on many intertidal sandflats extending from Japanese to Southeast-Asian waters.     

Niche modification and stability of competitive systems. II. Persistence of interspecific competitive systems with parasitoid wasps

Summary Effects of niche shift in ecological time scale on the population dynamics of competing species were studied in the experimental populations of two parasitoid wasp species,Anisopteromalus calandrae andHeterospilus prosopidis (both are solitary parasites), on a host, the azuki bean weevil,Callosobruchus chinensis. Four resource conditions were set up with combination of kind of bean (azuki or black eye), and host distribution (uniform or clumped). In each resource condition, four developmental stages of hosts were provided as a resource spectrum for parasitoid wasps. Population dynamics of the two wasp populations were investigated in each resource condition in Multi-Generation Competitive Systems (MGCS), in which fresh hosts of four developmental stages were periodically introduced and were parasitized competitively by the two wasp species. Competitive coexistence of both wasps occurred in the azuki-clumped condition, where the peaks of the resource utilization curves separated in the two species; pupae inA. calandrae and the early or late fourth instar inH. prosopidis, A. calandrae was eliminated in the azuki-uniform condition andH. prosopidis went extinct in two black eye conditions irrespective of host distributions. The degrees of overlap of the resource utilization patterns of the two wasp species during population dynamics were not significantly different among resource conditions irrespective of the results of coexistence or extinction. Even in the azuki-clumped condition, however, extinction ofA. calandrae was observed when resource partitioning could not be realized with only the late fourth instar larvae available to wasps. Further analytical experiments showed that parasitizing ability ofA. calandrae increased with host density per bean with azuki beans, butA. calandrae could express higher parasitizing ability with black eye beans thanH. prosopidis irrespective of host density per bean. The flexibility in parasitizing ability byA. calandrae for various host stages under different resource conditions was thought to be the major factor in determining the competitive coexistence or the extinction of either species under different resource conditions. The present experiments also suggested that different second-best host stages between competitors could be a major contributing factor to competitive coexistence.     

中国人口出生控制成效的比较分析

中国 ①的计划生育工作起始于 2 0世纪 5 0年代。从 1 95 5年到 1 971年 ,中国推行的是一般性的家庭计划生育政策 ,从 1 971年至今 ,中国推行的是家庭计划生育与国家计划生育相结合的政策。如果不实行任何形式的计划生育政策 ,2 0 0 0年末中国人口将会达到 1 8 5 8亿 ,如果象印度那样只倡导自愿实行家庭计划生育 ,将会达到 1 5 3 2亿。过去 45年中 ,中国一共少生了 5 88亿人 ,其中由于实行国家计划生育政策少生了 2 6 2亿人 ,而一般性的家庭计划生育政策少生了 3 2 6亿人。计划生育为中国的社会经济发展做出了巨大的贡献     

Tables for the analysis of selective predation experiments

Summary This paper discusses the analysis of selective predation experiments with two types of prey when the prey are not replaced after they have been removed by the predators. In an earlier paper (Manly et al., 1972) consideration was given to situations where the replication of experiments allows the estimation of standard errors from the experimental results; in the present paper a table of standard errors is given for a large range of experiments and replication is therefore no longer necessary. The standard errors were calculated on an electronic computer by solving the exact equations given in the earlier paper. The suggested method of analysis is illustrated using some data where the prey were red and yellow artificial ‘maggots’ and the predators were garden birds.     

Simultaneous estimation of mortality and dispersal rates of an artificially released population

Mark-recapture methods cannot estimate both mortality and dispersal rates of a wild population simultaneously. However, when an artificially cultured population is released into an area, the initial population size and the initial population distribution are usually known. If artificially cultured individuals are released with marks or distinguished from wild individuals or if no wild individual exists in the study area, we can estimate both the mortality and dispersal rates of the artificial population. The numbers of dispersed and dead individuals are estimated from the dispersal rate from the diffusion model and the total decreasing rate estimated from a mark-recapture data. We can estimate both the time-dependent and time-independent dispersal rates from the data. We choose the best fit model that has the smallest value of Akaike's Information Criteria. We also consider ‘concentric circles approximation” of spatial distribution, in which the cumulative and frequency distributions are analytically obtained.     

Prey or host searching behavior that leads to a sigmoid functional response in invertebrate predators and parasitoids

Summary Invertebrate predators and parasitoids have long been characterized as having a hyperbolic (Type 2) functional response. Modifications were made to Holling's sand paper disc experiment which consisted of limiting the initial period of search during which a host must be contacted. Failure to contact a host during this initial period causes the predator to emigrate from the search area. The modification generated a sigmoid (Type 3) functional response. This response resulted from the low probability of encountering a host during the initial period of search at low host densities in the time allotted. A limited period of search has been found in several insect parasitoids. Such a strategy would minimize the time (energy) spent per offspring produced by minimizing the time invested in searching microhabitats in which hosts are scarce or absent. The work was supported in part by NSF Grant DEB-75-04223 and by a grant from the Netherlands Dranization for the Advancement of Pure Research (ZWO).     

Persistence of females that produce only female progeny in lepidoptera

Summary In Lepidoptera females that produce only female progeny, can be found in wild populations of at least 11 species. The genetic variation is passed on to each generation of female offspring. If genetically abnormal females produce more female offspring than normal females do and mating is random, then populations containing these abnormal females will have a biased population sex ratio. Unmated females will increase due to the scarcity of males and so the population as a unit will die out. Several possible biological explanations for the persistence of the genetic variation have been proposed. But experiments and observations have not verified those hypotheses. Simulations of Heuch's model (1978), however, have shown that the variation persists if the population is distributed, in patches and there is dispersal among patches, even when insects disperse at random. Abnormal females tend to persist at both low and high migration rates, but the probability of persistence is higher at high migration rates. It has been suggested that abnormal females in a population are an adaptation, but the results of this investigation show that this explanation, may not be plausible.     

延续香火的理想与普遍绝嗣的现实——基于家谱的人口数据

延续香火、专宗接代②是传统社会人们的普遍愿望和理想,然而,由于传统时代人口的高死亡率和极短的预期寿命,延续香火的理想对于大多数人来说难以实现,绝嗣现象普遍存在。本文依据家谱的人口信息,通过构建虚拟的家族支脉,考察了清代两百余年间家族支脉的繁衍状况。结果显示,仅有13.61%的人在经历了两百余年的生存竞争后,能够拥有自己的后代,而其他大多数都已绝嗣,传嗣的理想和现实之间存在巨大的落差。