(^) In benthic ecology, the term community analysis is applied to several rather specific
approaches to evaluation of faunal assemblages, that is, to interpretation of the
combinations of animals found together in samples. One notion of a community,
somewhat “Clementsian” in tone, is that they are sets of species that tend to recur
wherever conditions are suitable. This notion of recurring assemblages (Fager 1963)
has been widely applied, despite the general conclusion that most communities are
“Gleasonian”. This contradiction will appear in the following examples.
Community Analysis: a Quantitative Approach
(^) In many ecological investigations of particular regions or habitats, there is very little
information about the actual life and times of the organisms. All that is available, or
even possible to obtain, is a suite of samples representing the fauna in different parts
of the region, i.e. samples of dead animals preserved in formaldehyde or ethanol and
convertible to lists of identified species. The problem is to use those samples to
provide information about the character of the habitat. There are important, though
limited, ways. A basic assumption is that a spot where an organism is found is a more-
or-less suitable habitat for it. Thus, the changes of species composition across a region
define differentiable habitats. Once the boundaries of the habitats are defined, they
can be examined to determine their characteristic physical, chemical, geological and
biological features. It is often possible to hypothesize which features are critical for
the well-being of the defining species. As an example, we will examine an old but
excellent study by Bilyard and Carey (1979). It has the advantage that questions about
the fauna were approached in an ascending order of complexity with useful
conclusions emerging at each step. At the final step, they succeeded in showing that
species groupings can distinguish habitats that are in some sense more universal than
those that might be defined by the presence of a single species.
(^) Bilyard and Carey’s problem was to evaluate the number and characteristics of the
distinct habitats on the seafloor off the North Slope of Alaska, in the western Beaufort
Sea. They had a large suite of samples taken from an ice-breaking ship at positions
(Fig. 14.1) ranging from 25 m to 2000 m depth and covering 8° of longitude. Bilyard,
who did the sample work-up and analysis, was interested in polychaetes and confined
his attention to them. This is a common feature of most such studies; they are limited
by the taxonomic expertise of the investigator, and most ecologists can only deal at a
sophisticated level, at the species level, with one or two substantial groups of
organisms. As a first pass at a regional analysis, Bilyard counted the annelids in each
sample and plotted the results on a map of the isobaths (Fig. 14.1). There was a strong
gradient in abundance from west (more) to east (less). That is informative: the
distribution of abundance has the same shape as the tongue of summer current that