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Abstract
Few comparative studies of spatial patterns at different scales have examined several
species in the same habitat or the same species over a range of habitats. Therefore,
variability in patterns among species or among habitats has seldom been documented.
This study quantifies spatial patterns of a suite of intertidal snails and a species
of barnacle using a range of statistical techniques. Variability in densities was
quantified from the scale of adjacent quadrats (over a distance of centimeters) to
tens of kilometers. Significant differences in abundances occurred primarily at two
spatial scales. Small-scale differences were found at the scales of centimeters or
1-2 m and, for many species on many shores, these accounted for most of the variability
in abundances from place to place. These are likely to be determined by behavioural
responses to small-scale patches of microhabitat. Large-scale differences in abundance
were also found in most species at the scale of hundreds of meters alongshore. These
are likely to be due to variation in recruitment (and/or mortality) because of limited
dispersal by adults of these species. There was little or no additional variation
among shores, separated by tens of kilometers, than was shown among patches of shore
separated by hundreds of meters. Identification of the scale(s) at which significant
differences in abundance are found focus attention on the processes (and the scales
at which these processes operate) that influence patterns of distribution and abundance.
Some of the advantages and disadvantages of various procedures are discussed.