ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01542.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

SummaryA typical marl lake of the Upper Great Lakes region has very few quantitatively important aquatic macrophytes. The macrophytes, however, dominate the total primary production of the lake. Submersed vegetation is extremely sparse on the shallow (less than I m) marl bench that characterizes the littoral of these lakes, and is completely dominated by one. little‐known species (Scirpus subterminalis Torr.) between 1 and 7 m.A detailed investigation of the spatial and seasonal distribution of macrophytic species and biomass showed that S. subterminalis strongly dominated the lake (79% of total biomass). S. suhterminalis represented an almost pure stand (to 200 g m−2mean annual ash‐free dry weight) at all times of the year at intermediate depths of macrophytic growth (1–6 m). Two species of Chara (of eight varieties and forms) were present in significant quantities (12% of total biomass; to 100 g m−2) but were severely limited to shallow depths (0‐S‐l m) and protected areas. Several annual submersed angiosperms were present (9% of total biomass), but only two species were quantitatively important. Potamogeton illinoensis Morong. and P. praelongus Wulfen formed brief summer peaks (less than 100 g m−2) at 3 and 4–6 m, respectively.A striking feature of the seasonal biomass distribution of Scirpus subterminalis was the higher, viable biomass (to 150g m−2) throughout the winter under ice cover. Cyclic fluctuations of the S. subterminalis populations were discerned at different depths, each with different periodicities. The population at 2 m exhibited a fall peak; that at 4 m had a summer maximum. The lowest overall biomass ofS. subterminalisoccurred in the 2 m population in June.Chara populationsat 0–2 m also exhibited a relatively constant biomass throughout the year. The appearance of Nitella at 7 m in July‐October and ofCharaat 5 m in September‐October was interpreted as an interaction between light, thermal, and carbon stratification.Estimates of macrophytic productivity of perennial (‘evergreen’) species populations whose biomass remains relatively constant throughout the year were made employing several different methods of calculation and turnover factors. All methods resulted in productivity estimates in good agreement with the conservative value of 178 g m−2year−1for the entire lake. In comparison to the other components (phyto‐planktonic, epiphytic and epipelic algae) of the primary production of Lawrence Lake, the aquatic macrophytes constituted a major portion (anuual mean 82·77 g C m−2year−1or 48·3 %) of the total production of the lake.The low diversity but relatively high quantitative importance of macrophytes in marl lakes is attributed to an adverse dissolved inorganic and organic chemical milieu which inhibits phytoplanktonic production and allows only certain adapted macrophytes to develop strongly. The phenomenon of perennial biomass levels throughout the year is believed to be much more common than previously suspected and has iikely resulted from adaptations of submersed macrophytes to ameliorated conditions of water and temperatures relati

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01543.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

SummaryActinomycetes of the family Actinoplanaceae, especiallyActinoplanes, are readily isolated from the flowing waters of local rivers and streams and it seems clear that such lotic environments are favoured for colonization by these organisms. In this contribution evidence is produced that part at least of this activity can be ascribed to the utilization of wood as a growth substratum. Some other aquatic Actinomycetes of less certain affinity were also shown to be capable of growth on wood, under the conditions of pure culture.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01544.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Summary(1) Analysis of data from samples of chub taken at monthly intervals from two tributaries of the Herefordshire Wye revealed an annual cycle of scale growth with the formation ofa check during May or June. The frequency distributions of ages deter‐mined from scale checks and the length‐frequency distributions showed close simi‐larities. It was concluded that age determinations based on an examination of the scales were valid, provided care was taken in the identification ofthe first scale cheek. The maximum age observed was 15 years.(2) Examination ofthe population structure revealed an overall sex ratio close to unity but there was a significant increase in the proportion of females in the 11 + and older age groups. Dominant year‐classes were observed. The strongest was 1959, which was attributed to exceptionally warm, dry, sunny weather during the period May‐September.(3) Female chub grew more rapidly and attained greater ultimate size than the males. Changes in the pattern of growth during the life‐span were attributed to the attainment of sexual maturity, especially in the females. The length‐weight relation‐ships of the sexes diflFered slightly but were almost identical for the same sex in the two rivers studied. Seasonal variations in the growth‐rate were followed. Most rapid growth occurred after check formation in May or June and continue

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01545.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01546.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

SummaryFewer species and more individuals of Tubificidae were present in the soft sediments of a polluted ditch than in the relatively unpolluted Bere Stream.Changes in width frequency of natural populations ofTubifex tubifexandLimno‐drilus hoffmeisterithroughout the year were similar at both the sites investigated.In laboratory experiments larger populations ofTubifex tubifexdeveloped in fine sediments than coarse. By means of a width‐dry‐weight relationship it was possible to estimate the weight of the experimental popula

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01547.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

SummaryThe paper presents information on factors influencing maximum feeding‐rates (measured in the laboratory) in larvae of the damselfly Pyrrhosoma nymphula, and compares estimates of feeding rates in the field with maximum feeding‐rates for larvae of the same size at the same temperature.Maximum feeding‐rates in Pyrrhosoma larvae of different sizes were measured at 4, 5, 10 and 15°C. At low temperatures (4–5°C) maximum feeding‐rate was depressed more than predicted either from the effects of temperature on the gut‐clearance time of larvae or their respiratory rate. Maximum feeding‐rate declined steadily throughout metamorphosis in the final instar and stopped completely prior to emergence of the adult.Feeding‐rates in the field were calculated from ‘balanced’ energy equations, i.e. from the sum of larval growth, respiration and the production of faeces and exuviae. Feeding rates in the field were always much less than maximum feeding‐rates for the same size of larva at the same temperature, and at the most were never more than 70% of the latter; they were closer to the maximum in summer than in winter, when they fell as low as 20% of the maximum.The relevance of these findings to studies on the efficiency with which carnivores utilize energy in the field, and the importance of Odonata larvae as predators in aquatic

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01548.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

SummaryFive species of helminth parasites were found in adults and tadpoles of the newtsTriturus helveticus, T. vulgaris, andT. cristatus, caught at eight different localities in Somerset. These parasites wereAcanthocephalus anthuris, A. ranae, Megalobatra‐chonema terdentatum, Thominx filiformisandOswaldocruzia molgeta. Mean worm burdens did not change through the year, and egg‐producing females ofAcantho‐cephalus anthurisandMegalobatrachonema terdentatumwere found throughout. There was no difference in the level of infection of male and female

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01549.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01550.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY