. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 130 DAVID M. PRATT teristic of the species.) A staining period of 12 to 24 hours in pond water tinged with a few drops of a concentrated Neutral Red solution rendered the animals distinguishable from untreated individuals for several days. Two precautions were exercised in the selection of substitutes: 1. they were matched for size with the original members still living in the population, and 2. only individuals without eggs were chosen for this purpose. Thus, in so far as it was possible to estimate it, the substitutes' con
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 130 DAVID M. PRATT teristic of the species.) A staining period of 12 to 24 hours in pond water tinged with a few drops of a concentrated Neutral Red solution rendered the animals distinguishable from untreated individuals for several days. Two precautions were exercised in the selection of substitutes: 1. they were matched for size with the original members still living in the population, and 2. only individuals without eggs were chosen for this purpose. Thus, in so far as it was possible to estimate it, the substitutes' contribution to the total density effect was proportional to their number, and all of the young produced in the population were born of charter members. A. Experiments at 25°. Thirty tests were made at a density of one animal per 50 cc., four at densities 5 and 10, and two at densities 25, 50 and 75. The survival curve of the 30 single animals and the average survival curves for the five higher densities are plotted on Graph V. To facilitate a quantitative. ' *v 3O 40 TIME IN DAYS GRAPH V. Survival at different constant population densities, 25° C. Legend: population density 1 population density 5 -o-o-o-o-o population density 10 population density 25 -• •-• — •- population density 50 - population density 75 - comparison of survival at the six densities tested, the total number of animal days lived by each population was divided by the number of original members to give the mean duration of life at each population pressure. These data are plotted on Graph VI, which discloses the noteworthy fact that the greatest mean longevity occurs in populations of five, rather than at the minimal density, and that animals even at a density of ten per bottle lived longer, on the average, than did those in isolation. Two interpretations of this phenomenon suggest themselves. MacArthur and Baillie (1929) have developed the thesis that the mean longevity of Daphnia magna is an inverse
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
