Seasonal changes in the abundance of Microcrustacea in a small pond

Sampling methods, and methods used in extracting, identifying and counting the Microcrustacea in samples are outlined. Numbers of parthenogenetic females and young stages of Daphnia obtusa were highest from March/June to Sept./Nov., with a trough in July. Ephippial females were recorded during some or all of the months from March to Nov. with two numerical maxima, one in early summer and one in autumn. Males were present during the same period as ephippial females. Naupliar, copepodid and adult stages of Cyclops strenuus strenuus were recorded in every month; numbers of all three stages tended to be high from March to Nov. and low from Dec. to Feb. Females were present in smaller sumber than males. Females with eggs sacs occurred every month with two peaks of abundance in April–July and Oct. Adult Canthocamptus staphylinus were absent during the summer/early autumn from June/July/Aug. to Sept./Oct. Numbers were highest from Nov. to May/June with a peak in spring. Females carrying an egg sac were recorded each month with the highest proportion occurring sometime in the period Feb. to May. Possibly two peaks, one in early summer and one in autumn, of total numbers of Cyclocypris ovum were recorded. Comparisons with other available information on the life-cycle of the species are made. The effects on the species of a six-week period of drought in the autumn of 1969 are considered.     

Microspatial heterogeneity of allele frequencies at allozyme loci in the bivalveMytilus trossulus: Dependence on age and depth

Allozyme variability was investigated at 18 polymorphic loci in 9 samples of the bivalveMytilus trossulus (Gould, 1850) from Vostok Bay, Sea of Japan. Significant differences in allele frequencies at some loci were found between samples from different age cohorts and different depths. Genetic distances between samples were as great as (and often exceeded) those typically found between geographically separate populations in Peter the Great Bay. Some practical recommendations for experimental researchers are proposed.     

Cyclomorphosis inEubosmina longispina in a small North American pond

The cyclomorphosis exhibited by a population ofEubosmina longispina in Bullhead Pond, Rhode Island is documented and compared to that reported for similar species of Bosminidae. Cyclomorphosis inEubosmina longispina involves the same morphological characters that exhibit seasonal changes in related species, but the temporal patterns of these changes are quite distinct. We suggest that the cyclomorphosis exhibited byEubosmina longispina is caused by simultaneous, but very different selective predation by planktivorous copepods and fish.     

Population dynamics ofDaphnia rosea in a small eutrophic pond

The population dynamics ofDaphnia rosea were studied in a small, eutrophic fish-free pond during November 1986–November 1987.D. rosea showed two density peaks in 1987, a high peak in spring and a slightly lower one in autumn, but they disappeared in mid- and late summer when a smaller cladoceran,Ceriodaphnia reticulata, dominated. The rapid decline in density ofD. rosea in mid-May and the low density in June/July were preceded by or coincided with a period of increased male density, the appearance of ephippial females, smaller body length of adult females, decreased brood size, and increased frequency of empty brood chambers, all of which indicate a worsening food situation. The rapid density decline ofD. rosea in mid-May was considered attributable neither to increasing water temperature, nor predation by the dipteranChaoborus flavicans, but to insufficient food conditions for the maintenance of stable reproduction. Although edible phytoplankton was abundant in June/July, the general food situation was not suitable forD. rosea due to blooms of the large-celled dinoflagellate,Ceratium hirundinella, which probably inhibited the feeding activity ofD. rosea. TheC. hirundinella blooms might also be important for the shift of the dominant herbivore from the largerD. rosea to the smallerCeriodaphnia reticulata in August/September.     

Habitat selection and patchiness in Scapholeberis: horizontal distribution and migration of S.mucronata in a small pond

The horizontal distribution of Scapholeberis mucronata in asmall pond was studied by transect and pattern sampling. Densitiesare high (>1000 animals m^–2) in the littoral zone andlow in the open water (no aquatic vegetation; <<50 animalsm^–2). The preference for the littoral zone is, however,less well expressed during the night, indicative of a diurnalhorizontal migration. Within the littoral zone, the distributionof Scapholeberis is highly aggregated. The relative degree ofpatchiness is inversely correlated with density. The relativeabundance of males and ephippial females was not invariablyhigher in than out of patches. It is hypothesized that the observedhabitat preference, as well as the aggregative behaviour, ofScapholeberis are mechanisms to avoid predation by fishes.     

Carbon and nitrogen dynamics in a small pond in the maritime Antarctic

Small ponds and puddles are extremely common throughout the ice-free areas of the maritime Antarctic. The carbon and nitrogen dynamics in a typical pond on Livingston Island, South Shetland Islands were investigated during summer 1991. The pond vegetation consisted of a benthic mat of cyanobacteria, diatoms and chlorophytes. The mat was not limited by nutrient availability, both phosphorus and nitrogen being available in the overlying water and N:P ratios in both the water and the mat indicating a roughly balanced supply. Maximal rates of carbon fixation of 0.1–0.2 mgC g^–1 dry weight h^–1 were similar to those of other perennial Antarctic mat communities. Productivity appeared to be limited by physical factors, but the effects of irradiance and temperature could not be separated. Although carbon fixation rates were low, carbon loss processes were minimal leading to an accumulation of material in the mat approximating to one doubling per year. Atmospheric nitrogen fixation was not a significant component of the nitrogen budget of the pond, accounting for only 0.1 % of the nitrogen accumulation by the mat. Nitrogen uptake was largely from dissolved nitrogen sources, in particular as dissolved organic nitrogen. It is concluded that ephemeral water bodies may play a significant role in the nutrient dynamics of maritime Antarctic ecosystems.     

海洋浮游纤毛虫在世界海区的时空分布

作为微型浮游动物的重要组成部分,海洋浮游纤毛虫是连接微食物环和经典食物链的重要中介,在海洋浮游生态系统物质循环和能量流动中发挥重要的作用.从20世纪60年代至今,关于纤毛虫丰度和生物量的分布已经积累了大量的资料,目前纤毛虫丰度和生物量分布的研究大部分集中在温带海区,热带和极地海区的研究尚少.本文概述了世界海区纤毛虫丰度和生物量的水平分布、垂直分布特点及周年变化规律.纤毛虫丰度和生物量一般在饵料丰富、生产力较高的海区较高;纤毛虫倾向分布在水体的中上层;纤毛虫的丰度和生物量一年之内呈现双峰型或单峰型,纤毛虫群落的粒级组成一般春季较大,夏季较小,砂壳纤毛虫丰度占纤毛虫丰度的比例一般在夏季或秋季较高.     

Seasonal and spatial distribution of ciliates in the sandy hyporheic zone of a lowland stream

The seasonal and spatial distribution of abundance and biomass as well as the taxonomic composition of ciliates inhabiting the sandy hyporheic zone of a lowland stream were studied. The mean abundances varied between 0 and 895 cells ml⁻¹ sediment, and the mean ciliate biomass ranged between 0 and 5.3 μg C ml⁻¹ sediment. Ciliate numbers and biomasses were greatest at the sediment surface and declined significantly with increasing sample depth. Abundance and biomass varied seasonally, with maximum values in late autumn and early winter and minimum values in early summer. The community was dominated by small representatives of the Hymenostomatia and Peritrichia. Ciliate community composition changed with depth from a very diverse community at the sediment surface to a less diverse one at greater sediment depths. Ciliate abundance and biomass were two orders of magnitude lower in the channel water than in the hyporheic zone. Although representatives of all sediment taxa could also be found in the channel water, the greatest concentrations of Peritrichia and Suctoria were in the hyporheic zone. The species of the sandy Ladberger Mühlenbach sediment were ubiquitous; there was no single ciliate fauna that proved to be typical for this kind of freshwater biotope.     

Factors involved in the distribution pattern of ciliates in the water column of a transparent alpine lake

The recurrent depth preference of three ciliate species (two prostomatids and one haptorid) in a transparent alpine lake indicates the existence of niche partitioning among them involving potential factors such as avoidance of high ultraviolet radiation levels and zooplankton predation, as well as competition for food resources.     

A sequence-based analysis of the pointer distribution of stichotrichous ciliates

Micronuclear genes in stichotrichous ciliates are broken into blocks separated by noncoding sequences, sometimes with the blocks in a shuffled order, some even inverted. During reproduction, all blocks are assembled in the correct order and orientation. This process is possible due to the special structure of micronuclear genes: each coding block M ends with a short nucleotide sequence (called pointer) that is repeated at the beginning of the coding block that should follow M in the assembled gene. Many of the pointers have multiple occurrences along both strands of the gene. This yields a very high number of pointer-induced possible divisions into coding and noncoding blocks.We investigate the distribution of pointers for all currently sequenced micronuclear ciliate genes with the goal of identifying what distinguishes the real gene structure among all possible coding/noncoding divisions. We find a sharp criterion in the average a/t-content of the noncoding blocks: the real division has, in most cases, the maximum such content among all possible combinations. Even for pointers as short as two nucleotides, the real division is one of very few with an average a/t-content of its noncoding blocks over 80%. The separation is most clear when the loci of pointers of up to four nucleotides (even three in the case of unscrambled genes) are fixed (e.g., through a template-based recombination mechanism).     

Abundancy estimations of aDaphnia magna population in a small artificial pond

Practical difficulties in the application of correct statistical methods in field ecology are illustrated by a plankton abundancy estimation in a small pond. Random sampling was performed over a limited number of previously chosen sample places and times. A cylindric sampler was used, which caught the plankton within a whole water column (1 m). Relatively high numbers of samples were needed to achieve reliable estimates of population parameters, which was demonstrated by simultaneous sampling. The probability distribution of the number of daphnids per sample was shown to be approximately lognormal. However, the variances of the log-transformed data were not uniformly homogeneous, which reduces the applicability of familiar tests for parameter comparison. Arguments are presented to make comparisons of population abundancies through transformed data only.     

Predation and the distribution and abundance of a pulmonate pond snail

Summary The abundances of a freshwater pulmonate snail, Lymnaea elodes were studied in a temporary pond and a permanent, more productive pond in northeastern Indiana, USA. When snails from both populations were reared in each of the ponds in containers excluding predators, snails grew to be 1.3 to 2 times as large in the more productive pond, and laid 9 times as many eggs. However, field sampling data showed adults to be more abundant in the temporary pond. The only obvious difference between the two ponds was the presence of the molluscivorous central mudminnow (Umbra limi) in the permanent pond. These fish fed upon L. elodes when eggs and juvenile snails were abundant. In an experiment in the temporary pond, addition of mudminnows lowered egg and juvenile snail survival in pens where snail abundances had been increased. We suggest that vertebrate predators like the mudminnow can be significant sources of mortality for thin shelled species like L. elodes, possibly excluding them from habitats like lakes and rivers.Address for offprint requests     

Seasonal succession of a microphagotroph community in a small pond during litter decomposition

Temporal dynamics of a lentic microphagotroph community were studied during leaf litter decomposition from December to May. Small plastic vessels containing leaf litter were placed on a pond bottom. They were sampled periodically to collect microphagotrophs. Three abiotic factors and abundance of two food items were also measured to analyze the autogenic and allogenic phenomena during a microphagotroph succession. Three behavior types were recognized in dominant taxa: a free-swimming type, a vagile (creeps on substratum, sometimes swims) type, and a voluntarily fixed type. Dominant taxa changed from the free-swimming to the vagile type up to mid-March, and the reverse change occurred from mid-April. Principal component analysis (PCA) indicated four factors affecting the dynamics of the community: water temperature as a seasonal factor, detritus volume on the litter surface as a habitat factor, and densities of bacteria and small flagellates as food factors. Taxa replacement appeared to occur through two mechanisms. (1) Dominance of small holotrichs, a free-swimming type, was brought about by a high bacterial density caused by seasonal events, i.e., leaf fall in December and detritus formation by litter feeders in mid-April. This is an allogenic aspect of community dynamics. (2) The free-swimming type was replaced by the vagile one during the period with high taxa diversity. This replacement occurred through intertaxa competition for scarce food and/or selective predation by larger microphagotrophs. It is an autogenic process within the community.     

Vertical distribution of planktonic ciliates in strongly stratified temperate lakes

The vertical distribution of planktonic ciliates in eight strongly stratified temperate lakes was studied in summer 1998. Ciliate abundance and biomass were highest (mean 39.9 cells ml^–1 and 181.9 g C l^–1) in the epi-, and lowest (mean 8.2 cells ml^–1 and 97.6 g C l^–1) in the hypolimnion. The community of ciliates was dominated by five orders: Oligotrichida, Haptorida, Prostomatida, Scuticociliatida and Peritrichida. The community composition varied greatly with depth. In the epilimnion, the ciliate numbers were dominated by oligotrichs but small algivorous prostomatids, peritrichs and haptorids were also numerous. In the metalimnion, these groups were replaced by scuticociliates and mixotrophic prostomatids. In the hypolimnion species known as benthic migrants appeared. We found a positive significant correlation (p < 0.05) between ciliate numbers and Chl a and bacterial densities. Only in the hypolimnion, the correlation between ciliates numbers and Chl a was not significant.     

Light and assimilation number in a small desert,recharged-groundwater pond

Summary Measurements of irradiance, chlorophyll a concentration, respiration, and net and gross photosynthesis were carried out in a small desert pond containing recharged-groundwater from the Flushing Meadows water reclamation project at Phoenix, Arizona. Over the 6-month period May–October, chl. a concentration averaged 119 mg m^-3; and gross primary productivity in terms of the mean daily carbon fixation rate was 8.29 g C m^-3, which is roughly equal to productive fish and farm ponds but less than many polluted eutrophic lakes and streams. Both net and gross assimilation numbers were found to be satisfactorily represented by pure sine waves that implied total inhibition of those two processes near an underwater irradiance value of 0.32 cal cm^-2 min^-1.The maximum value of the gross assimilation number at 0.16 cal cm^-2 min^-1 of 30 mg C hr^-1 per mg chl. a ranked with some of the highest values that have been found world-wide.Joint contribution of the Department of Zoology, Arizona State University, and the Agricultural Research Service, U.S. Department of Agriculture. Portions of this work were supported by the Grace Ellis Ford Fellowship, American Association of University Women, awarded to Joyce M. Foster on July 1, 1971.     

Ecological characteristics of scale-bearing chrysophytes in a small eutrophic pond in The Netherlands

In a pool near Nijmegen (The Netherlands) a study was carried out regarding the ecological characteristics of scale-bearing chrysophytes (species and groups of species). The results confirm the relatively new thought, that chrysophytes are not indicating oligotrophic waters only, but the wider range of oligotrophic to eutrophic water. In this pool ammonia and nitrate appeared to be the most important chemical variables, determinatting the development of chrysophyte species. Total and ortho-phosphorus were important variables in the second place. From the physical factors, pH-value here had less influence, while conductivity and alkalinity had none at all. However, some species of Mallomonas are able to develop at higher levels of conductivity than usually assumed. In high concentrations, ammonia could be toxic. Confirming the knowledge from literature, temperature variation is an important factor for the quantitative development of species. In particular, high abundancies occur at temperatures below around 12–14°C, which explains the decrease of chrysophytes in summertime. The presence of organic matter complicates the results and must be taken into account in future studies. For biological assessment of water quality, the results underline the necessity of having knowledge of the ecological characteristics of the individual species.     

Microspatial genetic heterogeneity and gene flow in stray cats (Felis catus L.): a comparison of coat colour and microsatellite loci

We analysed levels of genetic differentiation between nine local urban colonies of stray cats using eight coat colour and nine microsatellite loci. Both types of markers revealed a strong differentiation between colonies (FST = 0.15 and 0.09 for coat colour and microsatellite loci, respectively). Three coat colour loci showed extreme levels of genetic differentiation comparatively to other loci and are strongly suspected to be under divergent selective pressures. Microsatellite loci showed significant heterozygote deficiency within colonies (FIS = 0.14), suggesting that coat colour loci are not appropriate to investigate genetic structure at a fine scale because coat colour allele frequencies are based on Hardy-Weinberg equilibrium. The reported pattern conformed to that predicted from the social structuring of cat colonies: aggressive exclusion of immigrants, inbreeding and very low dispersal rate.     

A model for acid and alkaline phosphatase activity in a small pond

Acid and alkaline phosphatase activity were determined in a small pond over a period of 24 months (64 samples). Activity of each phosphatase enzyme was positively correlated with chlorophyll concentration, viable bacterial count, total phosphate concentration, inorganic phosphate concentration, and temperature. Multiple regression analysis was used to formulate equations that described phosphatase activity in terms of these physical, chemical, and biotic factors. Corrected coefficients of determination were calculated, and the highest values were obtained when all parameters were included in the equation (r ²=0.776 and 0.659 for alkaline and acid phosphatase activity, respectively). However, there was little improvement in ther ² value obtained when only chlorophyll was used in the equation (r ²=0.654 and 0.624, respectively). Samples were then taken over a further 12 months (25 samples), and observed activity was compared with the activity predicted by application of the previously derived equations. For alkaline phosphatase, the best fit between observed and expected activity was seen with the equation containing all parameters, but for acid phosphatase the best fit was seen with the equation containing only chlorophyll and temperature as the determinants. In both cases there was a good fit between observed and expected data using the equation containing chlorophyll as the sole determinant. From this we have concluded that phytoplankton were the chief producers of phosphatase activity in this pond, although the influence of physical and chemical factors on enzyme activity could not be ignored.