Dynamic Regimes in a Model of Single-Locus Density-Dependent Selection

A model of density-dependent selection in a Mendelian single-locus population was analyzed in the case where the fitnesses of genotypic forms are exponential functions of the population size. Analytical and numerical studies of the model were performed for a diallelic locus, and parametric regions were established for different dynamic behaviors of the model. The diallelic model of density-dependent selection was generalized to a multiallelic locus; the results of its analysis are described.     

Experimental Examination of Intraspecific Density-Dependent Competition during the Breeding Period in Monarch Butterflies (Danaus plexippus)

A central goal of population ecology is to identify the factors that regulate population growth. Monarch butterflies (Danaus plexippus) in eastern North America re-colonize the breeding range over several generations that result in population densities that vary across space and time during the breeding season. We used laboratory experiments to measure the strength of density-dependent intraspecific competition on egg laying rate and larval survival and then applied our results to density estimates of wild monarch populations to model the strength of density dependence during the breeding season. Egg laying rates did not change with density but larvae at high densities were smaller, had lower survival, and weighed less as adults compared to lower densities. Using mean larval densities from field surveys resulted in conservative estimates of density-dependent population reduction that varied between breeding regions and different phases of the breeding season. Our results suggest the highest levels of population reduction due to density-dependent intraspecific competition occur early in the breeding season in the southern portion of the breeding range. However, we also found that the strength of density dependence could be almost five times higher depending on how many life-stages were used as part of field estimates. Our study is the first to link experimental results of a density-dependent reduction in vital rates to observed monarch densities in the wild and show that the effects of density dependent competition in monarchs varies across space and time, providing valuable information for developing robust, year-round population models in this migratory organism.     

Intraspecific Competition in a Natural Stand of Betula ermanii

Density and size of naturally regenerated Betula ermanii weremonitored for six years in a 100 m² plot located in Hokkaido,northern Japan. Natural thinning of 10- to 15-year-old treesoccurred at a negative exponential rate related to tree volume,demonstrating the –3/2 power rule of self-thinning. Diameterdistributions were unimodal at ages 10–13 years and bimodalat 14 and 15 years. Changes in diameter distribution were accompaniedby changes in structure, from a one- to two-storied stand. Mortalitywas highest among smaller trees and where density was greatest.The spatial distribution of trees changed from random to uniformwith increased stand age. Betula ermanii Cham., Self-thinning, mortality, spatial distribution, size distribution     

Optimal rates of dispersal II. Diploid populations

The problem of how an individual should divide its progeny into dispersed and non-dispersed descendants is investigated for a number of haploid models. In each model, a unique optimal ratio of dispersed to non-dispersed has been found, where the type with this optimal strategy has a selective advantage over all other types. Although the survival ability of a dispersed offspring is reduced (compared to that of a non-dispersed offspring), the optimal strategy implies that a substantial part of the progeny will be dispersed.     

The Ribosomes of Drosophila II. Studies on Intraspecific Variation

Electrophoretic comparisons of 40S and 55S ribosomal subunit proteins from 18 strains of Drosophila melanogaster revealed the virtual absence of allelic variation. More detailed two-dimensional studies on the large subunit proteins in 6 of the strains demonstrated additional complexity but still no interstrain variation. The significance of these results is discussed with respect to present estimates of genic heterozygosity in natural populations.     

Habitat Partitioning in a Patchy Environment: Considering the Role of Intraspecific Competition

Coexistence of many size groups of conspecifics in habitat patches may complicate resource partitioning and increase intraspecific interactions. The objectives of my study were to determine partitioning of habitat among age groups of rainbow trout, Oncorhynchus mykiss, coexisting in pool habitat of a headwater stream, and to determine the role of intraspecific competition for such resource partitioning. The trout population showed size and age specific patterns of habitat use, and trout selected locations based on depth and longitudinal position. This habitat use pattern decreased intraspecific overlap among the trout age groups for use of pool space. I used a removal experiment to determine if two-year old trout constrained habitat use by the smaller conspecifics. Although the experimental results imply that recent intraspecific competition was not present, the absence of competitive exclusion was not clearly demonstrated because of low experimental power. While this study identified habitat partitioning among the trout age groups, it remains unclear whether biotic interactions or size specific requirements were causing the habitat use patterns.     

Sexual isolation in Drosophila. II. Intraspecific variation in mate recognition systems

A simple behavioral model is used to investigate whether differences in the specific-mate-recognition system (SMRS), occur within species of the Drosophila genus. This model takes into account, and overcomes, the distorting effect of vigor differences on experimental results. Analysis shows significant deviations from the expected values under the assumption of identical SMRSs in around one fifth of the multiple-choice experiments performed with natural strains of twelve different Drosophila species. Different selection procedures raise the number of significant assortative mating results between strains of D. melanogaster and D. pseudoobscura from 3.0% to 32.8%. Finally, sub- or semispecific taxa show variations in their SMRS even more frequently (74.5%). Differences in male vigor and female receptivity are also found. These results show that a classification of Drosophila species based on SMRS stability, as proposed by the “Recognition concept of species”, is virtually impossible.     

Selection for Mating Reluctance in Females of a Diploid Parthenogenetic Strain of DROSOPHILA MERCATORUM

A diploid parthenogenetic strain of Drosophila mercatorum was outcrossed to produce genetic variance among the impaternate female offspring. Selection experiments were carried out for reluctance of the parthenogenetic females to mate.After only two cycles of selection, a parthenogenetic strain which is significantly less receptive to males from three different bisexual strains was obtained. It was also found that there is some degree of sexual isolation among the three bisexual strains used. The results support the idea that selection can render a newly produced diploid parthenogenetic strain behaviorally different from its bisexual ancestor. This appears to provide a framework which can explain the natural coexistence of diploid bisexual and diploid parthenogenetic biotypes in some species of insects.     

Effects of Intraspecific Competition and Host-Parasitoid Developmental Timing on Foraging Behaviour of a Parasitoid Wasp

In a context where hosts are distributed in patches and susceptible to parasitism for a limited time, female parasitoids foraging for hosts might experience intraspecific competition. We investigated the effects of host and parasitoid developmental stage and intraspecific competition among foraging females on host-searching behaviour in the parasitoid wasp Hyposoter horticola. We found that H. horticola females have a pre-reproductive adult stage during which their eggs are not mature yet and they forage very little for hosts. The wasps foraged for hosts more once they were mature. Behavioural experiments showed that wasps’ foraging activity also increased as host eggs aged and became susceptible to parasitism, and as competition among foraging wasps increased.     

Estimation,variance and optimal sampling of gene diversity II. Diploid locus

Nei's analysis of diversity at a diploid locus is extended to a population subdivided into a large number of subpopulations. The diversities and the heterozygotes frequency are defined with respect to the total population and unbiasedly estimated in a two-stage random cluster sampling. The fixation indices F _IS, F _IT andF _ST are derived, then inter- and intra-population variances of the estimated parameters are studied. We show that there is a unique sample size per population which yields the best accuracy in estimatingF _ST and F _IS, respectively, at a given locus. These results are illustrated with an analysis of DNA diversity in a forest tree and compared to those obtained under the Hardy-Weinberg assumption.     

Studies in the Dynamics of Genetically Variable Populations. I. Frequency- and Density-Dependent Selection in Experimental Populations of DROSOPHILA MELANOGASTER

Changes in genetic composition and in fitness of karyotypes in synthetic populations of Drosophila melanogaster carrying fourth chromosomes marked with recessive mutants in repulsion were measured as functions of initial population composition and density. There was no detectable influence of initial population density on the magnitude of chromosome frequency change or on adaptive values of karyotypes, but both measures proved sensitive to population composition. That fitness be measured zygote-to-zygote is argued to be of dubious necessity in all contexts except demonstration of frequency-dependent selection. Some prior reports cited as evidence of the operation of density-dependent selection, like the present study, contain no evidence that the rate of natural selection is influenced by population crowding. Reports that do demonstrate density-dependent selection suggest that the relationship between fitness and crowding differs from that assumed in most theoretical treatments. Further work is needed to elucidate the interaction between fitness, population crowding, and population composition.     

含有食饵自庇护的食饵-捕食模型的模糊滑模控制

针对一类令布食饵自虞护的食饵-捕食系统,当环境变化时,系统参数的扰动处于动态状态,利用其扰动边界的特性,通过设计模糊滑模控制器将失控系统引至平稳轨道,并使系统全局稳定,从理论上实现了失控系统的有效控制,为防治食饵种群灭绝,引起食物链断裂,导致生态平衡破坏提供了一定的理论依据．最后的仿真结果表明了此方法在理论上的有效性．     

Fertility in Crosses Involving Diploid and Autotetraploid Raspberries: II. Fruit and Seed Development

Variation in fruit and seed development following crosses betweendiploid and autotetraploid forms of raspberry cultivars is described. Drupelet set was sensitive to a large number of influences,and varieties differed in their response to such crosses but,once set, fruit growth was largely independent of seed development.Mailing Jewel had a high drupelet set as a seed parent. Chromosomedoubling reduced the fertility of both male and female gametes,but the effect was greater in the pollen where the ability toinduce set was impaired. This is ascribed to physiological ratherthan chromosomal causes. It is suggested that seed size in infertile crosses betweenplants of different ploidy depended on a balance between earlygrowth following the stimulus of fertilization and later slowergrowth due to a weakness in the endosperm. The rate of fruit maturation was more rapid on tetraploid seedparents, but otherwise showed few consistent features.