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Surficial sediments from 32 Danish lakes were screened for subfossil chydorid (Cladocera) assemblages. Two data sets from 1965 and 1992 were examined by cluster analysis and nonmetric multidimensional scaling (NMDS) for lake classification. The best environmental variable to explain the 1992 species data was total phosphorus (TP) (r = 0.58, Spearman rank correlation), and NMDS defined three lake classes that were significantly different in communities (p < 0.01, ANOSIM) and in TP values. Canonical correspondence analysis found a strong relationship between the species data and log(TP) (axis 1 eigenvalue = 0.30, total inertia = 0.85, log(TP) intraset correlation = 0.92). Environmental variables were tested by forward selection and six variables were found to be statistically significant by 99 unrestricted Monte Carlo permutations. Weighted averaging regression and calibration models were established from the 1992 chydorid data and corresponding contemporary log-transformed TP data. The model's predictive ability was assessed by the bootstrapped coefficient of determination and the bootstrapped root mean squared error of prediction ( r2boot=0.79 , RMSEboot = 0.24). The patterns of changes in chemical and biological variables (diversity, Bray-Curtis dissimilarity) over the 27-year period placed the 32 lakes in six different response groups.

From 1979 to 1981 we followed the movement, diet, and growth of yellow perch,Perca flavescens, for their first 70 days after hatching in Lake Itasca, Minnesota. Perch spawned inshore during early spring; hatching occurred 10–20 days after spawning. Newly hatched perch were 5.6–6.2 mm total length (TL). Soon after hatching the larvae moved into the limnetic zone where they began feeding. This movement is probably a mechanism to escape intense predation in the littoral zone. Normally the first food of perch was immature copepods, but within a week they incorporated all common zooplankters into their diet. When the perch reached 25 mm TL (about day 40) they returned to the littoral zone, where they ate larger and more abundant prey than was present in the limnetic habitat. There is no correlation between growth rates and zooplankton abundances, which suggests that food quantity is not a limiting factor in the early life history of perch in Lake Itasca.

Population dynamics of chyorids from Elk Lake, Minnesota, were followed from May through October 1971 by means of three collecting methods. Emphasis was placed on data obtained by use of artificial substrate. This method was found to collect most species of chydorids living in the underlying substrate. A second method, funnel trapping, collected animals that migrated 10—20 cm vertically from their substrate into the funnel traps. Funnel trapping was found to be not very efficient at collecting all chydorid species, but to be useful for following overall population trends and for exploring the vertical movements of some species. A third method, called pattern sampling, was tried experimentally. It appears to collect most chydorid species, and also shows the mocro—distributions (or spatial arrangements) associated with population densities. Most chydorid species increase in population numbers during spring and fall, and decrease during midsummer. Chydoris have clumped or contagious patterns that fit the neg...

Microfossil remains from surficial sediments of 20 Danish and 14 northern Indiana Jakes were counted, and their relative percentages calculated. Using the function H = — Σp°ilog2°° species diversity was calculated for each lake. Indices of diversity for each lake and data on primary production and transparency were subsequently ranked and Spearman's rank correlation coefficient was determined between species diversity and production, and species diversity and transparency. Interpretation of results within the framework of information theory was not satisfactory. It is sugested that species diversity of chydorids is controlled primarily by complexity of the thier habitat, the rooted aquatic macrophytes of lakes. See full-text article at JSTOR

Es wurden die Uberreste von Chydoriden aus den oberflachennahen Ablagerungen von 80 danischen Seen untersucht, um den Zusammenhang zwischen der Artenzusammensetzung und den Seetypen festzustellen. ...