Ecology of the burrowing amphipod, Pontoporeia affinis, in Lake Michigan / by Wayne Paul Alley.

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of its variance, then the population is normally distributed. If the mean
is proportional to the variance and the mean-variance regression has an
intercept of zero and a regression coefficient of 1, then the population
conforms to the Poisson distribution, which implies that the population
is randomly distributed within the sampling area.
The mean and variance of the 15 sets of triplicate samples from
the short-term study area 2 were plotted against each other for the
small, large, and total Pontoporeia (Figs. 16-18). The resulting
correlation coefficients indicate that the mean is independent of the
variance for small and total Pontoporeia (r =. 226 and.415, d. f. = 13)
and that these two groups conform to the normal distribution. On the
other hand, both the mean-variance regression coefficient and the intercept are approximately one for large Pontoporeia, suggesting a Poisson
distribution.
The occurrence frequency for the numbers of individuals per
quadrat was determined for each of the three categories from the combined 88 samples of study areas 1 and 2. Small and total Pontoporeia
were treated in such a fashion that 3 to 7 individuals per interval were
combined and called 5, 8 to 12 were combined and designated 10, and so
forth.
An examination of the occurrence frequency histograms (Figs. 19 -21) indicated that the distribution of small and total Pontoporeia tended
toward the normal while large Pontoporeia followed the Poisson distri