Density fluctuations in populations (1982–1986) and biological observations ofPotamopyrgus Jenkinsi in two trophically differing lakes

The hydrobiid snailPotamopyrgus jenkinsi (E.A. Smith), characterized by parthenogenesis and ovovivipary, was quantitatively sampled monthly between June, 1982, and December, 1986, on sandy bottoms in the shallow zones of the meso-oligotrophic Lake Maarsseveen I and the eutrophic Lake Maarsseveen II. The snail demonstrated a very clumped distribution in both lakes. The mean numbers of juveniles and adults taken together fluctuated strongly. Organisms in Lake I showed relatively high densities (up to 25,000 per m²) in 1982, followed by a sudden drop to values approaching zero in December, 1982, with a subsequent rapid increase in densities, fluctuating between 2,000 and 200 per m². In Lake II, densities of snails fluctuated between 13,000 and 300 per m² with decreases in the spring of 1985 and 1986. The various types of decreases in the lakes are extensively discussed, but no explanation is presently available. The reduction in Lake I was of catastrophic proportions, but the speed of recovery of the population was remarkable.Floating was observed only in Lake I, and only during the occurrence of the highest densities on the sediment. Burrowing behaviour was very common, but strongly suppressed under an uninterrupted dark regime. A shift of temperature from 15 to 22°C had the same effect. A number of submerged macrophyte species from Lake I proved to attractP. jenkinsi in the absence of sandy substrate, though these plants were only covered by the snail during the period of the highest densities in 1982. Temperatures of 20°C or lower were well tolerated, unlike temperatures of 25 and 30°C. Growth was distinct at 10, 15 and 20°C. Keeled individuals were encountered in much higher numbers in Lake I than in Lake II.     

自交作物群体的遗传组成分析

用数学方法推导出了自交作物群体遗传组成的分析公式。根据所推出的公式,可以计算出任何自交世代群体的基因型频率和同一表现型中各基因型的频率。对自交群体遗传组成的分析可用于质量性状的选择,确定选择时需要的有效群体大小和选出有效群体的大小,亦有助于确定选择的最佳世代。     

伊蚊(纷蚊亚属)一新种——功果伊蚊的记述

1979年7月至1980年3月,作者在云南云龙县的功果采集到蚊类标本一批,发现伊蚊属纷蚊亚属(Finlaya)一新种,特记述如下。 功果伊蚊Aedes (Finlaya) gonguoensis,新种 雌蚊 中型黑色蚊虫,翅长3.5—4.2毫米。 头部 头顶前部平覆深褐宽鳞,中央区和后部具白弯鳞;头顶后部和后头有黑色窄竖鳞,并杂有少数白竖鳞;有眶白鳞线;头侧大部平覆白色宽鳞,仅前部有一褐鳞区。触角梗节内侧有淡色鳞。唇基光裸;喙约为前股的1.1倍长,一致暗黑色;触须约为喙     

云南壮异蝽属及娇异蝽属新种记述(半翅目:异蝽科)

云南地区的壮异蝽属(Urochela Dallas)和娇异蝽属(Hrostylis Westwood)截止到目前共记录23种。本文记述了在该省西部地区发现的5新种,现描述如下。模式标本保存于天津南开大学生物系。 钩壮异蝽Urochela hamata,新种(图1,2) 体黄褐色,具黑褐色花斑及黑色刻点。触角第4节中部及第5节基半部为淡黄色;     

Models for age structured populations with distributed maturation rates

In the use of age structured population models for agricultural applications such as the modeling of crop-pest interactions it is often essential that the model take into account the distribution in maturation rates present in some or all of the populations. The traditional method for incorporating distributed maturation rates into crop and pest models has been the so-called distributed delay method. In this paper we review the application of the distributed delay formalism to the McKendrick equation of an age structured population. We discuss the mathematical properties of the system of ordinary differential equations arising out of the distributed delay formalism. We then discuss an alternative method involving modification of the Leslie matrix.     

Temporal constancy in grasshopper assemblies (Orthoptera: Acrididae)

ABSTRACT.

• 1 Temporal constancy in the structure of grasshopper assemblies (about forty-five species each) from two types of North American grasslands was assessed; one site was followed 25 years and the other 7 years.
• 2 Densities and relative abundances varied but composition of assemblies based on ranks suggested significant structure when three or more species were included in the analysis.
• 3 Results compared favourably with other insect herbivore assemblies which have been examined; variability in population change was intermediate along the spectrum of organisms which have been studied.

     

Dispersion and Distribution of Pratylenchus scribneri and Hoplolaimus galeatus in Soybean Fields

Examination of dispersional characteristics of Pratylenchus scribneri and Hoplolaimus galeatus indicated that there were patches within soybean fields in which both survival and reproduction wexe enhanced in spite of apparent homogeneity of soil type and topography. Treatment with carbofuran reduced the patchiness (or increased the dispersion) for H. galeatus while it had the opposite effect for P. scribneri. P. scribneri was less highly dispersed in conventional tillage plots than in the zero tillage plots. Populations from quadrats contained entirely within the patches could be described by the normal distribution (in the case of P. scribneri) or by the Poisson distribution (in the case of H. galeatus), while populations from quadrats contained entirely outside the patches could be described by the Poisson distribution for both nematodes. None of the distributions tested (Poisson, normal, negative binomial, Neyman''s) gave an adequate fit when populations from both inside and outside the patches were considered together. In all instances, log₁₀ and ln transformations reduced the goodness of fit of the data to all of the distributions tested. Even with logarithmic transformations, parametric statistics were not appropriate for analysis of data in most instances.     

Suspending disbelief—of Wynne-Edwards and his reception

Critique of Wynne-Edwards' views on population regulation and sociality suppose a population of discrete, mutually exclusive groups essential to his thought. Yet both his past and present work focus on continually distributed, philopatric populations; his critics have argued the untenability of a position never his own. Wynne-Edwardsian ‘group selection’ focuses on local population productivity under philopatry. A ‘group’ is a local confluence of genotypes which need not be reified, and group selection consists of the differential replication (hence heritability) of the local social environment in which a genotype is embedded. Differential productivity contingent on social environment can eliminate some relational structures on genotypes in favor of others, creating an expanding wave of population productivity as in Wright's shifting balance metaphor. Such a process is inherent in the evolution of reciprocity, where cooperators must cluster to successfully invade a population of defectors. Regulation of resource exploitation in continuously distributed populations may be modeled as overlapping n-person Prisoner's Dilemmas, where each individual participates in several distinct commons and defection represents local over-exploitation of resources.     

Allozyme divergence between different gene arrangements in Drosophila subobscura

Allozyme and chromosomal polymorphism were analysed simultaneously in three population samples of Drosophila subobscura from Scotland, Germany and Italy. The study revealed significant genic divergence between the various chromosomal gene arrangements for the loci Acph, Lap and Pep, which are located inside inversions. No difference was found with the loci Me and Odh, which are both on the same chromosome but proximal to the structurally polymorphic region. Samples of a given gene arrangement taken from the different localities are genetically uniform. The data indicate that the observed non-random associations between enzyme genes and chromosomal inversions are the result of inhibited recombination in heterokaryotypes and gradual differentiation of the separated gene pools, rather than selection and coadaptation.     

Fertility interactions in Drosophila: Theoretical model and experimental tests

The results of 11 experiments with Drosophila species show that fertility is not a reducible property: the fertility of a mating pair cannot be predicted from the average fertility of the two genotypes involved. We propose a model of fertility selection that does not assume additivity (or multiplicativity) but assumes random mating and that the genotypic frequencies are in Hardy-Weinberg equilibrium. Numerical simulations show that removal of the assumption of Hardy-Weinberg frequencies does not significantly change the equilibrium frequencies predicted by the model.