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Laboratory experiments and computer simulations have been performed to study the influence of increased temperatures on the structure of cladoceran communities. Analysis of changes in the rate of population growth and demographic parameters has shown that smaller cladoceran species are less sensitive to decreased concentrations of food at any of the test temperatures (18, 21, and 27°C). An increase in temperature from 18°C to 27°C has been shown to facilitate the establishment of acute competition conditions. At 18°C, periods of food deficiency are shorter, and competition is therefore less manifested than at 27°C. According to the results of computer simulations, alleviation of competition in waters with 'low' temperatures results from reduction of the periods of food deficiency because of prolonged juvenile development. [ABSTRACT FROM AUTHOR]

We provide the first in-depth study of the Branchiopoda of the rain forests of Cameroon and also of the African continent. Surface water environments, Cameroon. Qualitative plankton samples were collected in all types of surface water environments present, ranging from big lakes to water collected in rock crevices or fallen fruit cavities. A tow or hand-held plankton net of mesh size 100 μm was used, and water volumes filtered were at least several m3 in large water bodies, or half to whole water volume in small water bodies. We recorded 61 species (53 first records for the country), based on 700+ samples collected between September 1998 and March 2002. Anomopoda (92%) was the dominant order, followed by Ctenopoda (6.5%) and Cyclestherida (1.5%). Chydoridae (67%) was the most speciose family followed by Macrothricidae (6.5%) and Daphniidae (5%). Alona (11%) was the dominant genus followed by Chydorus (10%) and Pleuroxus (8%). Several species of Chydorinae, especially of the genus Pleuroxus, are shared with continental Eurasia–North America, but are absent from the Mediterranean and desert–steppe–savanna zones of Africa (boreal–tropical disjunction). Daphnia was absent, as in most tropical lowlands. No single species was really abundant, and a majority were rare to very rare, and of restricted occurrence within the rain forest patches. Comparing Africa, South America and Southeast Asia, we found a current total of 196 species for the combined rain forest areas, out of a world total of 500+ species. Systematic trends in richness at three taxonomic levels were the same for all continents: Anomopoda–Ctenopoda–Cyclestherida at ordinal level, Chydoridae–Daphniidae–Macrothricidae–Sididae at family level and Alona–Chydorus–Macrothrix–Diaphanosoma at genus level. Southeast Asia was richest (111 species, 14 endemics) with South America a close second (110 species, 27 endemics). Africa was the most species-poor (95 species, of which only 5 are endemics). We hypothesize that the post-Miocene cooling and aridization of the world climate hit the freshwater biota of Africa particularly hard, with more extinction here than elsewhere, and little recolonization. Most extinction occurred in the savanna-desert belt, and eight disjunct boreal species (four Pleuroxus, Picripleuroxus laevis, Kurzia latissima, Alonella exigua, and Monospilus dispar) survive morphologically unchanged since pre-Pleistocene times in the Cameroon rain forest. Slow evolution thus appears typical of these cyclic parthenogenetic branchiopods in which sexual recombination occurs only at intervals. Illustrative of the same slow evolution is the fact that the two endemic cladocerans of Cameroon ( Nicsmirnovius camerounensis and Bryospilus africanus) belong to tropicopolitan genera of Gondwanan age. [ABSTRACT FROM AUTHOR]

1. The role of seasonal phenology in the emergence of zooplankton from diapause in patterns of seasonal abundance in the water column was investigated in Oneida Lake, New York. Replicate emergence traps, placed in contact with the lake sediments at two locations (one at a shallow site and one at a deep site), were monitored between May and August. 2. Although six rotifer taxa showed a clear seasonal succession in the water column throughout the study period, all but one taxon emerged exclusively in spring. Three cladoceran and three calanoid copepod species, also present in the water column throughout the study period, again showed predominantly spring emergence. In contrast, three cyclopoid copepod species had distinct seasonal periods of emergence that corresponded, at least in part, to the timing of abundance peaks in the plankton. 3. These results for a single lake are largely consistent with patterns observed or inferred by other investigators for other lakes: variable dependence of abundance in the plankton on diapause emergence for species with long-lived diapausing eggs (i.e. rotifers, cladocerans and calanoid copepods), and much closer dependence for species with short-lived diapausing immature stages (i.e. cyclopoid copepods). [ABSTRACT FROM AUTHOR]