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

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tors are randomly distributed, the individuals will be dispersed as a
normal distribution. This distribution can also be considered the result
of one or more organisms within a sample unit influencing the probability
of other organisms occurring in the same sampleo
In this investigation of the distributional patterns it was necessary
to examine the number of individuals in several quadrats of constant size.
However, there is a major disadvantage in quadrat analysis in that changes
in frequency distribution occur when the quadrat size is altered. When
the quadrat size is increased it is more likely to contain many individuals
and less likely to contain no individuals. Preston (1948) has indicated
that in order for the Poisson distribution to be valid the quadrat must contain more space than is actually utilized by the organisms. As the quadrat size is increased, the environmental factors become more variable
and it becomes more difficult to discriminate between patterns of microdispersion, i. e. within a large quadrat highly populated areas are pooled
with sparsely populated areas. The sampling area of the hand coring
device in the short-term study area contained more space than was utilized by the macrobenthic invertebrates but was sufficiently small to
measure adequately the microdistribution of the organisms.
Replicated random sampling was selected as one method of data
collection because it not only obtains an estimate of the mean but also
an estimate of the variability of the mean. Because the mean is independent of the variance in the normal distribution and equal to the variance