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Adam Jeziorski Andrew M. Paterson Norman D. Yan John P. Smol 《Journal of Paleolimnology》2008,39(3):421-425
Despite reductions in atmospheric sulphur emissions and the resulting decline in acidic deposition, many lakes on the Canadian
Shield that have experienced acidification are either recovering at a rate slower than expected or not recovering at all.
This lack of recovery is believed to be partly the consequence of the depletion of exchangeable base cations (principally
calcium, Ca) from watershed soils. Although the implications of reduced Ca availability for biological communities remain
poorly understood, the effects on crustacean zooplankton populations may be severe, as Ca is the primary structural component
of the crustacean zooplankton exoskeleton. Because the daphniid resting egg is protected by a modified portion of the exoskeleton
(ephippia) and because these ephippia are well preserved in lake sediments, we investigated whether inter-specific differences
in Ca content are recoverable from Daphnia ephippia. However, using two methods, we did not find a recoverable Ca signal in the ephippia, indicating that future efforts
should be focused upon sedimentary taxonomic assemblage differences, not differences in ephippial Ca levels. 相似文献
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T. A. Davidson C. D. Sayer M. R. Perrow M. Bramm E. Jeppesen 《Journal of Paleolimnology》2007,38(1):117-134
To assess the similarity, not only in community structure, but also in the factors that shape cladoceran assemblages, we analysed
the contemporary zooplankton populations and their sub-fossil remains in 39 shallow UK and Danish lakes. Contemporary zooplankton
populations sampled from both the lake edge and the open water in August were compared with surficial sediment assemblages.
The sedimentary assemblage data combined counts of both ephippial and chitinous remains in order to provide some representation
of Daphnia and Ceriodaphnia. A relatively large volume of sediment (>5 cm3) was analysed for ephippial remains so as to include those species best represented by the larger ephippia. Ephippia were
identified to species level in the case of Daphnia magna, and to species aggregates for other groups such as Daphnia hyalina agg., Daphnia pulex agg. and Ceriodaphnia spp. In accordance with previous work several species found in contemporary samples (copepods and the cladocerans Polyphemus pediculus, Scapholeberis mucronata and Diaphanosoma brachyurum) were absent from the surface sediments. There were extensive supporting environmental data sets for the 39 sites. It was
therefore possible to determine the factors which influenced assemblage composition for the two datasets by a combination
of constrained ordination, in this case redundancy analysis (RDA), partial RDA and Procrustes rotation. The same two factors,
zooplanktivorous fish density and submerged macrophyte abundance, were not only the main structuring forces for both data
sets, but also explained very similar amounts of the variation in the different assemblages. Thus, we conclude that the living
communities and their sedimentary remains reflect the environment they are shaped by in broadly similar ways. Calibration
of sub-fossil cladoceran assemblages against modern environmental data to reconstruct environmental change can, therefore,
validly employ principles elucidated by contemporary studies to determine the most appropriate modelling technique. 相似文献
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《Limnologica》2020
The fitness of animals inhabiting highly unpredictable intermittent ponds depends on the effectiveness of the production of their resting stages. Daphnia living in such an environment produce sexual eggs as well as the males needed to fertilize them. We hypothesize that the strategy of permanent male presence should coexist with the synchronization of the production of males with that of sexual eggs. To test this hypothesis, we collected plankton samples from a model urban pond, two times a week, throughout the growing season. We analyzed in detail a number of environmental factors and the population dynamics of two Daphnia populations. The percentage of ephippial females and males periodically reached c.a. 50 % of the population. Depending on the moment of the growing season, this proportion was primarily influenced by population crowding, the richness of invertebrate predators in the habitat, extreme high temperatures and the occurrence of the autumnal photoperiod. Our results confirm the hypothesis that Daphnia produce simultaneously long-living males and males synchronized with receptive females. Additionally, we have shown that the number of resting eggs deposited by temporally-isolated populations varied significantly; thus the fitness of a particular genotype depends on the season and on the particular timing of its activation. 相似文献
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