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adiated extensively there in many endemic families. They had readily
adapted to the deep sea, their only habitat. On the other hand, isopods of
the suborder Flabellifera, which were not typical deep-sea forms but were in
the process of invading the deep sea and had no endemic higher taxa, had
arrived there only recently. They had apparently invaded the South Atlantic
first, from the Indo-Pacific, and had since spread into the North Atlantic.
When these two groups were added together, they demonstrated not just a
decline in diversity in the North Atlantic but actually a pole-to-pole decline
across the whole Atlantic, again showing an historical build up of these
patterns over a long period, one that was not just ecologically controlled.
Other data, showing a decline in diversity of one group of molluscs
in relation to latitude in the North Atlantic, highlighted the point that an
important interaction of processes on various scales governed these largescale
patterns. According to one current concept, local diversity was often
governed by regional enrichment. Put another way, local diversity
represented a balance in an open system, particularly such as the ocean,
between factors that caused local extinction – biological reactions such as
competition, predation and so forth – and dispersal from a regional pool.
The regional pool was developed over a long period through speciation and
adaptive radiation. If that were true, and if local communities were fairly
open, non-structured systems, then local and regional diversity should be
positively correlated over a broad range of values, as local diversity evolved
to reflect the amount of diversity available regionally to participate in local
communities.
On the other hand, according to more traditional thinking -- a sort of
ecological determinism -- local ecological circumstances controlled the
amount of local diversity irrespective of how many species were around to
participate. In that case, local diversity and regional diversity would be
statistically independent or would level off as a kind of local saturation.
This issue had been investigated in a statistical analysis of a group
of molluscs, both gastropods and bivalves, throughout the Atlantic Ocean,
north and south. It showed a good positive relationship between regional
and local species diversity, the implication being that the regional species
pool over broad areas of the ocean had an important effect on local
diversity -- the kind of diversity that would be affected by activities such as
mining, petroleum exploration or dumping.
The idea that regional processes were important in governing local
diversity had been tested by doing a multiple regression. In this calculation
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