The variation in the lengths of two co-occurring Daphnia species (Crustacea) in the Hubenov Reservoir in years when the chlorophyll-phosphorus ratio was low

0371697 - BC 2012 CZ eng J - Článek v odborném periodiku
Hrbáček, Jaroslav - Albertová, O.
The variation in the lengths of two co-occurring Daphnia species (Crustacea) in the Hubenov Reservoir in years when the chlorophyll-phosphorus ratio was low.
Acta Societatis Zoologicae Bohemicae. Roč. 75, 1-2 (2011), s. 23-35. ISSN 1211-376X
Výzkumný záměr: CEZ:AV0Z60170517
Klíčová slova: Daphnia * length distribution * temporal changes * congeneric competition * reservoir
Kód oboru RIV: DA - Hydrologie a limnologie

During the period 15 May 1975 – 22 June 1977 the mean body length of all the specimens of Daphnia pulicaria Forbes, 1893 measured was only slightly longer than that of D. galeata Sars, 1863 (1.13 against 1.09 mm). The range in size of individuals in samples collected approximately at three week intervals is 0.85 to 1.46 for D. p. and 0.87 to 1.40 for D. g. The distribution is far from normal. The standard deviation of the means is smaller than that of the medians and both are larger than that of the smallest and largest individuals. The seasonal patterns in these parameters and the skewness and kurtosis for the two species are not the same. This unexpected asynchrony is partly due to slight differences in when the two species start to actively reproduce each year. The expected increase in length in winter indicating a decrease in predation by fish when temperatures are low did not occur in either species. A clear predominance of young individuals among the specimens measured, which indicates a strong predation pressure, was not recorded except in a few samples. Logarithmic transformation shortens the right tail of the distribution of the lengths of the individuals but does not significantly in crease the predominance of young individuals or result in a distribution closer to normal. The linear regressions of the means, medians and the lengths of the smallest and largest specimens, against time, show a decrease in both species. Only the decrease in the length of the largest specimens in samples is statistically significant.The absence of both parallel trends in the seasonal distributions and a predominance of young individuals are discussed in relation to the size-selective effect of fish on zooplankton an dexpression of congeneric competition.
Trvalý link: http://hdl.handle.net/11104/0205158