Characteristics of dispersal in sexually mature dragonflies

Abstract.

• 1 The population dynamics of a natural population of Sympetrum danae (Sulzer) were studied, by means of a mark—release—recapture method, to find indications of dispersal by mature adults. Additional information on orientation and the influence of phenotype (including age), density and weather was obtained by observations under natural conditions and in a large outdoor field cage.
• 2 80% of all mature adults caught around the natural pond were estimated to be immigrants. Considerable immigration was confirmed by the abdomen length of unmarked matures which did not accord with that expected from the locally emerged population. Total numbers captured and the minimum number known to be alive fell sharply at the time when most individuals were mature. At the same time, new matures continued to enter and disappear from the study area at an increasing rate.
• 3 Dispersive behaviour (escape flights) in the field enclosure was primarily age dependent in both sexes: it occurred from an age of 25–30 days onwards. This coincides with the time-lag between the emergence peak and increased dispersal in the field. Secondary effects on escape flights suggested that males tended to abandon low density areas.
• 4 Males flew relatively more southward than females.

     

Nonmetric cranial variation and biological distances between samples of six nontribal populations of India

Sixty-nine nonmetrical morphological variants of the cranium have been studied in six samples of non-tribal, state populations in India, and their incidence reported. Using C.A.B. Smith’s angular transformation of frequencies, the multivariate Thetasquare distances and their respective standard deviations have been presented. On the basis of nonmetrical cranial variation, it is clear that the samples from Uttar Pradesh, Andhra Pradesh and Bihar are closer to each other but distant from Madhya Pradesh, Karnataka and Maharashtra. On the other hand, Karnataka and Maharashtra samples are quite close to each other and both, in turn, are comparatively closer to Madhya Pradesh than to Uttar Pradesh, Andhra Pradesh and Bihar. Madhya Pradesh sample emerges as the most divergent group among the six population samples studied. This, in general, is in conformity with the picture that emerges from various analysis of morphometric and other biological data on various populations of India.     

Changes of Copepoda populations in Lake Kiret during 1969–1985

Long period analysis of Copepoda populations in Lake Kinneret indicated significant reductions in total biomass and production as well as densities of nauplii and adult stages, particularly females. The reduction of adult Mesocyclops sp. was statistically significant, but that of Thermocyclops sp. was not. Annual averages of eggs/female values and densities of copepodite stages did not show significant changes. Concentrations of adult Thermocyclops sp. became higher relative to the larger genus Mesocyclops sp. It is suggested that densities of large copepods were affected by intensification of predation pressure by particulate feeding fishes. The densities of nauplii were probably reduced by increased predation pressure of filter feeding fish.     

Morphology and life cycle of Ceratium rhomvoides nov. sp. (Dinophyceae) from the lake Plußsee (Federal Republic)

A new species of freshwater dinoflagellates, Ceratium rhomvoides nov. sp., is described from the Plußsee, northern West Germany, where it occurs regularly. C. rhomvoides nov. sp. is distinguished from closely related taxa by various aspects of the morphology of the vegetative cell and the cyst and by its sexual reproduction and seasonal distribution.     

Life history of a lacustrine ostracod

The ostracod Cypria turneri has one generation per year in Mirror Lake, New Hampshire. Juveniles hatch in January through May and reach maturity by August. The life history of this ostracod suggests that the turnover rate of the population is low.     

The effect of fish predation on Cyclops life cycle

Two populations of Cyclops abyssorum tatricus studied in neighbouring alpine lakes in Tatra Mountains (southern Poland) differed in their life cycles. In the lake with planktivorous fishes, Cyclops was typically monocyclic, with highly synchronized reproduction during two winter months, while in the fishless lake its reproduction was asynchronous and continued for six months. Direct and indirect effects of fish predation on Cyclops life cycles are discussed.     

The benthic phase of the life cycle ofParapenaeus longirostris (Crustacea,Decapoda, Penaeidae) along the Mediterranean coast of Israel

The population ofP. longirostris along the Mediterranean coast of Israel spends the benthic phase of its life cycle (from body size over 15 mm) on muddy bottom deeper than 45 m. New age groups are recruited within the depth zone of 45–300 m and migrate in both inshore and offshore directions. Inshore migration is limited by unsuitable sandy ground. The limiting line for offshore migration was not found.An age group could be detected during one year within a body size range of TL = 40 mm to TL = 84.5 mm for males and to TL = 102.5 mm for females. Reproductive activity in shallow water, down to a depth of 73 m, takes place during the whole year, while in depths of 150–300 m there is an arrest of reproductive activity from June to August.     

Sexual reproduction and life cycle of Ceratium furcoides (Dinophyceae) in situ in the lake Plußsee (F.R.)

The life cycle of Ceratium furcoides (Levander) Langhans which features sexual reproduction is described for the first time in situ from the lake Plußsee (northern West Germany). Anisogamic copulation occurs during the bloom period in July–August by incorporation of the male gamete by the female gamete, resulting in an overwintering planozygote. The planozygote develops into a benthic hypnozygote which germinates in spring to establish a planomeiocyte. The morphology and structure of the stages of the life cycle are described using light and scanning electron microscopy.     

Distribution pattern of the dinoflagellateCeratium hirundinella (O. F. Müller) Bergh in a reservoir

Horizontal distribution of the dinoflagellateCeratium hirundinella (O. F. Müller) Bergh in the Ishitegawa Reservoir, Ehime Prefecture, Japan, was investigated. Water quality was also surveyed. It was observed that the population ofC. hirundinella exponentially decreased in number from the head of the reservoir to the dam site. Further investigation proved thatC. hirundinella initiated growth at the head of the reservoir, and later gradually expanded downstream. It was found during the period of increase in water temperature that the cell density ofC. hirundinella at the uppermost station exponentially increased.